HOW WIDE WHEELS AND WIDE TIRES CAN MAKE YOU FASTER
What You Need To Know About Wide Wheels and Wide Tires
Wide wheels and wide tires can help you ride faster when you choose and set them up in the right combination knowing how and what your ride.
The term rolling resistance as commonly used is incomplete. Reducing the rolling resistance that comes from vibration losses can improve your speed more that by picking between the top scoring tires in drum roller tests that measure tire compound and casing losses.
Wide wheels and wide tires have made the rule of 105 an anachronism (mea culpa). Today’s wide wheels and tires have made for combinations that are faster than those that strictly adhere to a relative rim-tire width guideline.
Wide wheels and wide tires are the new normal. The cycling industry pitches this to us as the way to a more comfortable and faster ride.
To make your ride more comfortable, you can reduce the tire pressure on any width of wheels and tires. Reducing the pressure on wider tires or getting more compliant wheels and tires can make for an even more comfortable ride.
But using wide wheels and wide tires to ride faster isn’t so straightforward. You need to make a lot of the right choices. And not just about selecting the fastest wheels and the fastest tires.
Instead, you need to choose which are the best fast wheels and tires to use together at the right sizes and inflation pressures. And those choices depend on your own, unique riding profile – what kind of surfaces and the terrain you ride, how fast you go, how much you weigh, and a few other things.
The right combination of choices will make you faster, or slower, on wide wheels and wide tires largely because of aerodynamic drag, sidewind stability, tire losses, vibration losses, road feel (comfort, handling, grip), and the interplay of those and a few other factors.
It can look like a complex set of trade-offs to consider with insufficient information to make the right choices. That’s because it is.
In this post, I try to make it simpler and give you enough information to make the right choices for your riding.
To do that, I unpack and answer four questions:
To come up with answers to these questions, I gathered and evaluated a lot of input.
That input came from answers to questions I put to and data I reviewed from product and engineering people at wheelmakers (in alphabetical order Bontrager, Campagnolo, ENVE, and Zipp), published research from other companies (wheelmaker Hunt, tire supplier Rene Herse), and published research from third-party tire testers (e.g. Tom Anhalt, Bicycle Rolling Resistance, Josh Poertner, RennRad, TOUR, Wheel Energy) and wheelset testers (TOUR, Hambini).
I’ve also revisited some of our own In The Know Cycling tire and wheelset road tests and done some new analyses of rim and tire combinations.
I’ll warn you that this is a long post that might take a bit of time to fully read and digest. You can shorten the process by clicking on the questions above that you are most interested in reading about.
You can also start by reading the WYNTK (an abbreviation for What You Need To Know, my version of tl;dr) at the top of each long section and decide whether you want to read more about that topic or skip to the next one.
Before jumping in, let me just remind you this post is about how the right choices of wide wheels and wide tires for road cycling can help you go faster. I’ve written about 10 ways to ride faster on your bike, most that cost you far less than new wheels or nothing at all, and many that can improve your speed more than what I’ve written about in this post.
But, if you already have those things dialed in (e.g. fitness, technique, positioning, nutrition, well-maintained gear, etc.) or kitted-up (aero road helmet, form-fitting clothes, shoe covers, etc.) or you’re looking to make decisions about your next wheels and tires and want them to help you ride faster, then this post is for you.
I. What Makes Wide Wheels Faster?
WYNTK: Wide wheels currently measure 21-25mm wide inside the rim (between the bead hooks) and 27-32mm outside of it. Faster wheels have superior aerodynamic drag, sidewind stability, stiffness, compliance, and weight properties when set up with the right tires at the right inflation pressure.
The terms wide and faster are relative and require some definition.
What is a “wide” wheel?
With modern road cycling wheels, both the inside and outside widths need to be considered to describe how wide the wheels are. On wheels that use rims with hooks that tire beads lock into, the inside width is the distance between the hooks. On those with hookless rims, the inside width is the distance between the walls that the tire’s beads press against.
Since most modern wheels use rims that have curved profiles, compared to the box-shaped rims of old, you can measure the outside width at various points. The minimum outside width is at the edge of the rim where it comes in contact with the tire. For those rims that bulbous or toroid profile, the maximum width is often found about halfway up the height or depth of the rim.
With narrower wheels, both of those outside width measurements were important when considering how the air flowed between the tires and rims. But as wheels have become wider both inside and out, the difference in those outside width dimensions has become smaller – typically less than a millimeter and often no different – and less significant to their aero performance as I’ll detail with data later on.
The conventional published measurement of outside width, and the one I use to measure rims, is the distance across the brake tracks on a rim brake wheel or where it would be if you were to superimpose a brake track on a disc brake wheel rim.
On most wheels currently being made, that outside width starting a few millimeters up from the tire edge doesn’t change much or at all across the depth of the rim until you approach the opposite or spoke edge. Rims with a U-shape profile quickly get narrower as come to the spoke edge while those that narrow more gradually make for more of a VU shape profile.
How have rim widths have changed?
Rims widths have increased significantly since the early 2000s. Most road wheels had box-shape or v-shape profiles with 13-15mm inside and 19-21mm outside widths. Wind tunnel testing showed 18-20mm tires mounted to those size wheels created the least amount of aerodynamic drag.
From wind tunnel testing done in 2001, Josh Poertner at Zipp formulated what he called a rule of thumb and later, the rule of 105 which said “the rim must be at least 105% the width of the tire if you have any chance of re-capturing airflow from the tire and controlling it or smoothing it.” Without re-capturing the air so it could continue along the rim, the airflow coming off the tire stalled and aerodynamic drag increased.
For a 21mm wide rim, that meant a 20mm tire was the widest racers should use for optimal aero performance. (21/20 = 1.05). Yet some pros preferred the road feel, specifically the comfort, handling, and grip of the 21mm tires they were given to test around that time. So wheel makers set about to produce wider rims so the air coming off the wider tires the racers preferred would still be recaptured to prevent stalling and aero increases.
A slow and uneven back and forth of wider tires and wider wheels has played out over the last 20 years and continues today. But because wheel and tire makers are probably some of the most independent and competitive cycling companies, very little of these width increases have been coordinated and until recently, haven’t been guided by updated standards.
And of course, these wider wheels and tires need to fit within brake calipers and bike frames whose product development cycle is usually much longer.
Complicating matters, there have been other wheelset and tire developments – most notably a shift from alloy to carbon rims, deeper and deeper rims on climbing and all-around wheels, changes in rim profiles, the emergence of disc brake wheels and tubeless tires, a significant updating of wheel and tire standards – that companies have devoted their development attention to and that figure into their product designs and sizes.
Now (circa 2022), most modern road wheels have internal rim widths of 19-21mm while the widest are 23-25mm. External rim widths measure in the 26-28mm or 30-32mm ranges.
However, wider inside and outside rim widths don’t always align. For example, you’ll find some wheels with 21mm inside and 31mm or wider outside widths while others have a 23mm inside width while only a 28mm outside one.
And while there are still more rim brake and disc brake bikes on the road, nearly all new enthusiast-level road bikes being made are disc brake ones. That means new rim brake wheels, to the extent they are still being introduced, will not get any wider than those with 19-21mm inside, 27mm or so outside widths available now. There just isn’t room for wider ones or even some of the widest ones now in most rim brake frames.
It’s hard to predict how much wider disc brake wheels will get. Clearance on the latest road disc bikes has increased to allow 30 or 32mm tires. As rims spin further inbound and between still wider areas of the fork, chain, and seat stays, you could certainly fit the mid-30mm wide depth rims available now in most new road disc bikes.
We’re also seeing more “all-road” bikes designed to ride on both paved roads and dirt and gravel off-road surfaces. They make room for 40-45mm tires. However, most gravel bike wheels currently aren’t any wider than the widest road bike ones.
As I’ll get into later, the widths of your rims are important in choosing the tire widths and pressures you want that will make you faster.
What makes one wheelset “faster” than another?
WYNTK: Broadly speaking, a wheelset’s 1) aerodynamic drag, 2) sidewind stability, 3) stiffness, 4) compliance, and 5) weight with the right tires and inflation pressure for that wheelset will determine how fast you can go on it vs. another wheelset.
While I’ve laid those out roughly in order of the relative contribution to going faster, their relative importance will vary depending on your specific speed, skillset, and riding profile.
1) Aerodynamic Drag
The faster you go, the more aerodynamics will matter. That’s because aerodynamic drag increases exponentially with speed. In other words, it becomes exponentially more important for you to reduce drag as you go faster.
To make this more tangible and actionable for us real-world enthusiasts or even those super-human amateur racers among us, I asked and researched how much difference the aero performance is between:
a. wheelsets of similar depths
b. wheelsets of different depths
Here’s what I found.
a. Similar Depths
WYNTK: Between current generation wheelsets of similar depths (within 5 mm) from brands developing their own wheelset designs, I found there’s little aero drag difference (0 to 3 watts) between them even at racer or wind tunnel test speeds of 50kph/31mph. Between those wheels and ones sold by those that don’t design their wheels, there could be as much as a 6 watt difference, a more significant amount.
Despite very different test protocols (e.g. wheel only vs. wheel in bike with a live rider, weighted average yaw angle, tire model and width, etc.) published tests from TOUR Magazin, Hunt, and Hambini show this to be the case.
TOUR’s 1-2022 review (subscription required) of six 57mm to 62mm deep current models of aero wheels from well-established brands showed a 217-watt average aero drag and 0-2 watt range tested at 45kph/28mph.
Aerodynamic drag tests run by Hunt comparing 45mm-50mm deep wheels showed a 0-3 watt range around a 74-watt average at 45kph/28mph. Further tests beyond those shown below comparing these and additional wheels of the same depths with 25mm and 28mm Continental Grand Prix 5000 tubed tires and Schwalbe Pro One tubeless tires produced the same 0-3 watt range of aero drag.
Hambini tests use a protocol significantly different from most cycling industry wind tunnel testing. A live rider on a bike holds an aero position in a tunnel with winds blowing at a wide array of yaw angles he feels better match what cyclists experience on the road than the 0-20 degree weighted yaw angle distribution used in traditional cycling aero tests.
He’s also compared what looks to be close to 100 wheels from different generations (2013 to 2022), of different depths and widths, and with both rim and disc brake profiles. He tests both at the slow end of enthusiast cyclist speeds (30kph/18mph) and at fast, pro racer pace (50kph/31mph).
In all of Hambini’s tests, he uses a 23mm wide tire. He states upfront that “bicycle wheels are particularly sensitive to tire size and having a wheel and tire combination that bulges will cause a significant increase in drag. Ideally, the tire and the rim should be of the same width.”
Seen by some as a truth-teller, independent of the cycling industry and by others as an out-of-his-element, attention-seeking crank, his testing protocol and results have been hotly debated on cycling forums by industry representatives, unaffiliated engineers, and curious cyclists.
As you might expect from the protocol he uses and the mix of wheels he’s tested, the results show far wider absolute wattage differences than the Tour and Hunt tests. Yet Hambini provides what he labels as a “warning” ahead of the display of his test results that essentially says anything below a 15-watt difference wouldn’t be noticeable to a rider.
All but one of the 60mm or so deep wheels tested at 50kph/31mph show a drag between 587 to 595 watts which is inside his 15-watt, unnoticeable difference warning zone. Among the wheels tested in the more all-around rider depth of 50mm or so and at rider speeds of 30kph/18mph (below), his results show less aero drag but a similarly tight 182 to 190-watt range for all but one wheelset.
I’d certainly notice a 5 or 8-watt difference on a long, spirited ride between wheelsets and I’d expect most enthusiasts would as well. Yet, given the protocol he’s using that’s more open to variation, the wheels he’s tested that come from designs spanning almost 10 years, and his use of a constant tire width that may not always deliver the wheels’ best aero performance, his tests do suggest remarkably close aero drag for similar depth wheels. This is consistent with the TOUR and Hunt results, each that also used unique protocols but with wheels introduced within a couple of years of each other.
I got very little pushback from the engineers and product managers I contacted at wheelset companies who design the wheels sold under their brand name when I suggested that the drag differences between rims of similar depth sold by them and those that don’t design their wheels could be 3-4 watts or less.
Some pointed out that it’s quite easy for competitors that do little or no aero design, computer modeling, or wind tunnel testing, including those selling rims sourced to multiple brands from catalogs and open molds, and still make aerodynamically competitive wheels. Instead, they merely cut a section of whatever rim appears to be the most aero and use that profile in their next wheelset. There’s up to a couple of year lag associated with these efforts to get similar designs in the marketplace.
To demonstrate the improvement that can be made from one generation to the next, one company that designs their own wheels shared data from their testing that showed a roughly 7-watt reduction in the power required at 45 kph/28mph both for their 50 and 60mm depth wheels from the prior generation. Notably, the new wheels are 2mm wider. I’ve not been able to confirm these results with independent testers.
The prior generation of each of their wheels was ranked in the top quartile of Hambini tests against wheels of similar depths. Test protocols used by this company and Hambini are different so it’s hard to quantify how many watts of improvement would be found in Hambini’s testing.
A time lag may help explain the wider variance between the wheels of the same depth that Hambini tested from those introduced around the same time that Tour has tested. Tour’s 4-2019 review (subscription required) of eleven 45-50mm deep wheels from leading and smaller brands whose designs may have been based on older designs (my conjecture) showed a wider 6-watt range (223-229 watts) than the six current 57-62mm wheels from brands that design their own wheels whose 2-watt range I wrote about above.
b. Different Depths
WYNTK: In current generation wheelsets of different depths from brands developing their own wheelset designs, aero drag reduction is small (1-3 watts) but notable as rim depth increases from 45-50mm to 60mm and again to 75-80mm at top end racer speeds. At lower speeds more typical of group rider enthusiasts, the gains are typically less than 1 watt for each step up in rim depth.
The data published by independent 3rd parties and shared by wheelset makers with me does show wheelsets of different depths do have distinct aero drag performance results. Simply stated, deeper wheels create less aero drag and will be faster than shallower ones.
But unless you are riding at the high end of the speed range (45-50kph/28-31mph), the differences between wheels of different depths are in the same range as the differences between current generation wheels of similar depths from the brands developing their own wheels that I reviewed above.
Specifically, the wheelset company data I reviewed shows that across a given company’s wheelset line, drag is reduced 1-3 watts as you go from 45-50mm to 60mm deep wheels and another 1-2 watts as you go from 60mm to 75mm ones.
When riding at 30-32kph/18-20mph, there’s less than a watt’s decrease in aero drag for each step up in depth in the company wheelset line. The same goes as you move up from a 35-40mm modern climbing wheelset to 50mm all-around.
But in tests comparing wheelsets of 45-50mm in early 2019 vs. 60mm ones in late 2021, TOUR’s tests suggest a bigger gap of 6-10 watts. It’s hard to know how much of this can be attributed to wheelset depth vs. newer designs.
In my review comparing all-around road disc wheels, I described how the key characteristics of carbon disc brake wheels have evolved over what I see as 4 generations from 2014 to 2022. Each next generation of wheels has been both wider and deeper for the same or less weight than the prior one.
In the latest generational shift, the 45mm deep, 19-21mm inside, 28-30mm outside width all-around wheelset has been succeeded by a 50mm deep, 23-25mm inside, 30+mm outside width wheelset that often weighs 100-200g less.
While I suspect but have not found conclusive, independently verified data that the latest generation of wide wheels has less aero drag than the prior one, the data on today’s wide wheels and wide tires used together that I’ll share later shows that the combination is indeed faster. That wouldn’t be possible with wide tires on narrow wheels.
2) Sidewind Stability
WYNTK: Variances in sidewind performance are far greater than the differences in aero drag when comparing wheelsets of the same depths, of different depths, and sold by different brands. The way suppliers and independent testers describe the quantifiable differences (Newtonmeters of steering torque) isn’t one that most cyclists can easily relate to. However, we certainly do feel how some winds can blow our wheels and us off our line and cause us to slow down while others remain stable and allow us to continue apace despite the wind.
If you’ve ever ridden with a steady wind coming at you from the side or been hit by a gust, you know how unsettling it can be. People who ride along the coasts, across the plains, down an exposed mountain road, or generally anywhere where the wind blows have experienced it.
Even along many of the tree-lined routes in the northeast US where I and my fellow testers ride, I often think I’d have more control if I were on a sailboat than a bike on some of those early spring and late fall days when the winds can be particularly strong.
A 10mph or greater crosswind or sidewind coming at you from a sharp angle can push you off your line and cause you to steer to get back on it. You may ease up on your pedals when a gust comes through or find yourself backing off your pace and aggressiveness if it’s blowing steady or you are regularly getting hit by gusts.
Or, knowing how the wind can affect your wheels, you may decide to not even leave the house to get on your bike.
As the returns from working to further reduce aero drag seem to be diminishing, some of the leading companies are trying to set their wheelsets apart by making them more stable in side winds. It’s not a new emphasis; it does appear to be one they are putting more engineering and marketing effort behind lately.
Directionally, 3rd party and company test results I’ve seen show that differences in sidewind stability for wheels of various depths and brands is similar to their aero performance and probably what you’d expect. Deeper wheels are generally affected more than shallower ones and some brands of wheels do better than others.
But, the variances in sidewind performance are far greater and often noticeably so within and between depths and brands. That’s consistent with what I and my fellow testers have experienced testing wheels out on the road.
TOUR has done the best independent laboratory testing I’ve seen. Across 11 brands of 45-50mm deep wheels, the best was 2x better than the worst with half scoring nearly as badly as the worst in their measurement of Newtonmeters of steering torque. They translated these to an 8-point scale for easier understanding and described the effect of that range as the difference between merely feeling the wind and actively fighting it.
Their test of six leading brands of 57-62mm deep aero wheels show remarkably similar values for all but two of them. Within 10 degrees of side wind or yaw, the four best scored nearly as well as a 50mm deep benchmark they rated 3 on their 1-8 scale. Between 10 and 15 degrees, those four experienced 2x the steering torque of the 50mm wheel. Beyond 15 degrees, the differences with the shallower benchmark lessened but each to a different degree.
This inability to predict sidewind effects by depth or brand is consistent with our anecdotal, seat of the pants (chamois on the saddle?) road testing. Many, but not all of the leading brands – those that develop their own wheels – seemed to have tamed the side winds with their latest wheels at both the all-around, 45-50mm and aero, 55-65mm depths. You don’t feel enough sidewind effect to push you off your line or back off on your pace no matter how deep the wheels are.
With others, you’ll get blown around even in the low 40mm range enough to make for a more cautious and slower ride.
There’s still a lot to work on here. There are clear tradeoffs and a whole lot of CFD (computational fluid dynamics) variables to modify and iterate to come up with a wheelset that gives you the desired combination of low aerodynamic drag and high side wind stability.
Also, we enthusiasts need better ways to more meaningfully get our heads around the current measures of sidewind effects. I took college physics twice but Newtonmeters or grams/degree of steering torque doesn’t really do it for me (but then, neither did physics).
Perhaps a green, yellow or red traffic light color scheme for different wind speeds would work better or a warning label that says “you’ll be fine” or “you’re going to die” riding these wheels in gusty winds would be clearer than the steering torque measure.
Needless to say, riding green or “you’ll be fine” wheels on a windy day will allow you to go just as fast as on a calm one. Riding yellow or red wheels in the winds, you’ll likely be slowing down or getting kicked out of the paceline because of your sketchy handling.
3) Stiffness, 4) Compliance, 5) Weight
WYNTK: Stiffness, compliance, and weight in combination will determine how well a wheelset responds and handles, both key to using tactics that will make you faster in many situations.
While it certainly feels like a laterally stiff wheelset translates the power your legs are putting out more efficiently than a noodly one, I’ve not seen any data to support that.
If you do a lot of crits or road racing or just like to ride hard and fast on your solo and group rides, a wheelset’s stiffness will be key to how responsive the wheels are as you start or follow moves away from the pack, maneuver through the field, and handle through turns.
Likewise, a more vertically compliant wheelset will make you more comfortable, expend less of your energy and allow you to put more of that energy into going faster. Yes, most of the comfort you feel depends on your tire pressure but there’s only so much you can do by lowering it to cover up a wheelset’s or bike’s lack of compliance without making performance trade-offs elsewhere.
And while a lighter wheelset is always marketed as a faster one, comprehensive testing has shown that weight matters most and more than aerodynamics only on long, steep alpine roads. If you are riding on a course with more than 1,000 feet of vertical every 10 miles (roughly 300 meters every 15 kilometers) then lighter wheels will be faster.
For the rest of us, aerodynamics is exponentially more important than weight once you start riding faster than 19kph/12mph. And, I sure hope most enthusiasts ride considerably higher speeds than that.
A lighter weight wheelset will help you accelerate faster and, along with wheelset stiffness contributes to how responsive your wheels feel. My experience testing different wheels suggests you won’t notice the acceleration difference of similarly stiff wheelsets until there’s at least a 100-150 gram difference in their weight.
Do wider wheels lead to better stiffness, comfort, and weight characteristics and therefore make you faster? It’s debatable but likely only a small effect.
Theoretically, added width gives the designer more material to build stiffness into their rims. But wouldn’t more material lead to heavier rims?
My understanding is that while rim width can or does play a part, there are more effective ways to control stiffness and weight than width. I don’t notice riding them or have seen any data showing that wider wheels are stiffer than narrower ones.
And many of the new, wider wheels are actually lighter than the narrow models they replace. Perhaps engineers have innovated to find new ways to reduce weight in wider wheels to deal with the added material that would bring added weight if they didn’t.
While wide wheels can make you more comfortable because you have better suspension from the larger air chamber in your tires. However, you have to adjust your inflation pressure and have a sufficiently supple pair of wide tires to take full advantage of the comfort wide wheels can enable.
Some of you may be asking, what about spokes and hubs? Don’t bladed spokes or wider diameter hub flanges or ceramic bearings make wheels faster? I asked these same questions to the engineers at the wheel companies I contacted.
The answer was a resounding meh. Or at least, I’m told there’s little difference between what is used on current generation wheels and what research has shown could be improved upon to add up to even a 1-watt difference.
Most carbon wheels that focus on delivering performance (vs. low prices) already use bladed spokes. Hub flange diameter is just one of several ways to get the desired stiffness. Ceramic bearings may wear better than steel ones and hubs that have them may roll longer in a stand than others. But, there’s less than a 1-watt benefit from ceramic bearings, and the hundreds of dollars, pounds, or euros added to the wheelset price is unacceptable to all but a few cyclists paying for their own wheels.
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What wide wheels should I buy for my wide tires?
WYNTK: Buy your wheels first, then buy tires for your wheels.
Well-meaning readers periodically ask me “What wheels are best for 28mm tires?” For an enthusiast to choose a $1000 to $2500 wheelset based on a $50 to $100 tire demonstrates the power of the cycling industry hype machine.
I even once got the question “What bikes are best for 28mm tires?”
While I get where these questions are coming from, they are bass-ackwards and, quite frankly, can drive me up the wall.
If you have a bike you are planning to keep, find out how wide a tire you can put on it. Most modern road disc bike frames will have clearance in the fork and stays to fit at least a modern 28mm tire plus the 3-4mm of added clearance you want on either side of the tire for deflection in high-speed cornering.
Even if it fits, a 28mm tire may not be best for you if aerodynamics are most important to the type of riding you do. Most wheels with a 21mm or narrower inside rim width and a 28mm or even 29mm outside width will not be aerodynamically optimized with a 28mm tire.
That’s because most tires once installed and inflated measure wider than the width labeled on the tire or packaging and a tire that’s wider than the rim isn’t as aerodynamic as one that is narrower.
If aerodynamics is less important than comfort or the road surface you ride will give you fewer rolling losses with a wider tire (more on this later), then put that 28mm or wider tire on whatever wheelset you buy as long as there’s enough clearance for it in your bike.
But please, buy the wheelset that has the best aero, sidewind, stiffness, compliance, and other performance characteristics you can find within your budget to go your fastest. Then pick the best tire for that wheelset.
That’s what I’ll get to in the following sections.
II. What Makes Wide Tires Faster?
As with the section above about wide wheels, I’ll start this one with some definitions and explanations about wide tires.
What is a “wide” tire?
Leading the evolution of ever-wider wheels since the early 2000s, the most popular road bike tires have increased in width from 21mm to 23mm to 25mm and now 28mm in 2022. Each next increase in size seems to have been popular for a shorter time period than the former one.
On some of the latest road bikes, we also see clearance for and tires coming on stock wheels of 30mm and 32mm.
These are the size designations you see labeled on the sidewall of the tire or marked on the package it comes in. A tire’s actual measured width once installed on your rims depends on the inside width of those rims and your inflation pressure. It’s rarely the same as what’s labeled on the tire or package.
Until recently, the labeled size was close to what you’d get if you put the tire on a rim with an ETRTO (European Tire and Rim Technical Organization) standard 15mm inside width, a size we moved on from years ago. Installed on wheels with 17mm, 19mm, or wider inside rim widths, most of the 23mm labeled tires I’ve mounted measure closer to 25mm and 25mm labeled tires measure closer to 28mm.
By 2020, ETRTO and ISO (International Organization for Standardization) formally increased the rim size used as the standard for road bike tire width marking. Most of the road tire size designations introduced shortly before or since then more closely match the actual installed width measurements on 19 and 21mm rims.
But, because of the distinct materials and properties of tires, the same tire with a 25mm or 28mm labeled width from a handful of leading tire makers can still measure a millimeter or two differently on the same rim and at the same pressure. And, as you’ll see below, the actual width and how it relates to the rim is key to how fast you go.
Tubeless, tubed clincher, and tubular tires have all gotten wider. However, they haven’t done so at the same rate due to different popularity, benefits, and rim beds.
What makes one tire “faster” than another?
WYNTK: For tires of the same type, labeled size, and inflation pressure, a tire’s 1) compound and casing losses, 2) road feel, 3) aerodynamic drag, and 4) actual width will determine how relatively fast or slow they are.
My caveat about comparing tires of the “same type, labeled size, and inflation pressure,” is important in setting a baseline to compare tire speed. Admittedly, it does take away some choices that are more important to your speed than the tires themselves.
I’ll dive into tire size and inflation pressure choices in the next section of this post called What makes the combination of wide wheels and wide tires faster? If you want to go there immediately, just click on that link.
As to tire type, I’m referring to speed differences between:
a) tires for racing, training, and more recreational or commuter riding which, due to their construction, generally get slower as you progress through that order.
b) tubeless, tubed clincher, and tubular tires which, while you can find fast tires of each type, also generally get slower as you progress through that order.
With that caveat established and while it takes some of the fun out of the discussion, at least for now, let me dive into what separates the speed of road tires.
1) Compound and Casing Losses or “Tire Losses”
WYNTK: Compound and casing losses are the energy lost by a tire when it flexes in response to the force from imperfections in the road surface. These “tire losses” are what are commonly measured by drum roller testing and are one of the two sources of rolling resistance.
“Vibration losses” or the losses incurred when your tires come up off the road surface and land back on it is the other contributor to rolling resistance.
You might ask what are compound and casing losses or aren’t they the same thing as rolling resistance, a term we’re already familiar with?
Compound and casing losses are the energy lost by a tire when it flexes in response to the force from imperfections in the road surface. Those losses come in the rubber compound between the time when the force is applied and the tire begins flexing or deflecting and rebounding (aka hysteresis) and, once flexing begins, from the friction or heat generated between the threads in its casing and between the casing and inner tube.
To make the discussion easier going forward, I’ll combine those separate forms of losses into one term – tire losses – since they both happen in the tire.
Independent testers like Bicycle Rolling Resistance and subscription publications TOUR Magazin and RennRad conduct tests of tires rolling against drums with surface patterns designed to emulate road surfaces. Others do similar drum and road testing for tire makers and other cycling publications.
As with wind tunnel testing, each of these testers uses their own protocols to measure the amount of energy lost in watts from the tire’s resistance to the rotating drum. While the general approach is similar, the amount of force applied on the wheel, the speed at which the drum turns the wheel, the width of the rim the tire is mounted on, the lab temperature and pressure at which the test is conducted, and the surface and diameter of the drum is different. They also inflate the tires to different pressures.
Because of all these differences, the absolute values vary between testers. However, the relative rankings of tires if not the absolute or % watt difference between them is generally, though not always the same.
Bicycle Rolling Resistance (BRR) has the most comprehensive and accessible tests. Looking at their results shows there are big wattage differences between tire types. For example, in their tests at 80 psi/5.5 bar,
- The top 5 tires with the lowest tire losses (they call it “rolling resistance”, I’ll explain the difference later) average 9.7 watts for tubeless tires still in production, 11.6 watts for tubed clinchers, and 15.2 for tubulars.
- Four of the five tubeless tires also have lower tire losses than the top tubed clincher tire (10.6 watts) and tubular tire (11.1 watts).
- For those of you who inflate to higher or lower pressures, the relative performance of the three types of tires remains the same tested at 120 psi/8.3 bar, 100 psi/6.9 bar, and 60 psi/4.1 bar.
Those gaps between tire types have grown in recent years as companies have put more development into tubeless tires and less into tubular. I expect the gaps will grow even larger over time.
Yet, there are far smaller differences between the best tubeless tires. For example, in BRR’s tests at 80psi/5.5 bar,
- The three tubeless racing tires (don’t have a puncture belt) still in production with the lowest tire losses have only 0.9 watts of difference between them (8.3 to 9.2 watts).
- The lowest tire loss tubeless training tire (does have a puncture belt) still in production has a tire loss (10.1 watts) only 0.9 watts more than the 3rd ranked tubeless racing tire.
- The next five tubeless training tires still in production are separated by less than a watt of tire losses (12.1 to 12.8 watts).
But because the testing protocols differ slightly as does the production run the test tires come from, there may be almost no real differences between the best tires that would make us choose one of the best over another based on tire losses.
- Bicycle Rolling Resistance found the Continental Grand Prix 5000 TL and Continental Grand Prix 5000 S TR tire that replaces it have tire losses within the margin of error (0.2 watts) but have less tire loss (2.5 watts on average at 80 psi/5.5 bar) than the Schwalbe Pro One TLE.
- TOUR Magazin’s tests found the S TR has a tire loss 1 watt more than the TL in their smooth surface test and 3 watts more in their rough surface one.
- Renn-Rad Magazine’s tests show the Schwalbe Pro One TLE and Continental Grand Prix 5000 TL have similar tire losses (0.2 watts difference).
If all of this suggests to you that it’s a mistake to choose between the top tubeless racing tires or training tires solely based on their watts of tire loss or relative ranking in these tests, then that’s the conclusion I’ve reached as well. You can pick any from the top group of tire loss performers and be confident that there won’t be a tire loss difference that will affect your speed or time.
And that’s the great benefit that BRR, TOUR, Renn-Rad, and other independent testers provide us as cycling enthusiasts. They allow us to see which small group of tires are among the “best” or in the “top” tier rather than which individual one to buy based on an absolute best tire loss rolling resistance number.
I have found and written about other considerations for choosing between the best tubeless tires that are as or more important than the watts or rating of tire losses reported by different respected sources. These include how well a tire performs aerodynamically in combination with your wheels, how its road feel (comfort, handling, grip) allows you to ride faster, and how easy it is to install.
In this discussion of tire losses, you’ll note I haven’t called it “rolling resistance.” Why?
For years, a tire’s compound and casing have been considered essential to the measured resistance as it rolls along a road surface. Everyone called it, and most everyone still calls it rolling resistance.
Tires with a more efficient compound and a more supple casing lose less energy and have less rolling resistance. Those tire material qualities lead to predictable rolling resistance relationships in drum roller testing.
While that’s true, it’s not all of what makes up rolling resistance or the resistance your tires encounter rolling down the road.
In 2009 Tom Anhalt, one of the original independent drum roller testers, and Jan Heine of tire maker Rene Herse, working separately showed that on “real-world” road surfaces, usually rougher than those simulated on a drum roller, the measured rolling resistance increases when you raise the tire pressure beyond a certain point. This was contrary to the experience on drum rollers where rolling resistance decreases when you raise the tire pressure because there is less flexing at higher pressures.
This added resistance to rolling down the road comes as energy is lost when the tires (along with the wheels, bike, and rider) come up off the road and return to it over and over again, essentially vibrating. This is in addition to the tire losses that happen when energy is lost in the tire compound and casing when it deflects and rebounds or flexes to absorb the imperfections in the road.
“Vibration losses,” a term someone gave to this type of rolling resistance (but I don’t know who so I can’t credit them) best communicates what is going on here. Anhalt described them as transmitted losses. Heine called them suspension losses. Poertner calls it impedance, a phrase akin to the resistance you get in an AC electrical circuit. All of these names refer to the same thing.
Vibration losses plus tire losses sum to your rolling resistance. The contribution of each depends on your tire model and width, inflation pressure, and road surface. Poertner’s tests showed examples of this including a key conclusion that vibration losses can be the dominant contributor to overall rolling resistance.
In another Poertner post, he points out that tire losses are relatively efficient – 90% of the energy absorbed in the tire when it deflects is released back when it rebounds. Vibration losses aren’t nearly so. He estimates that only 30-40% of the energy that leaves the road when the tire, wheel, bike, and rider leave the surface during vibration is returned when the tire, etc. lands back on the road. The rest is absorbed in the body tissue of the rider.
Yeah. That’s one of the reasons why we fatigue so much more when we’re riding on rougher surfaces.
You can reduce your tire losses by picking a tire model from the group with the least amount of tire losses. But choosing the right tire size and inflation pressure must be made in concert with the wheelset you ride, the profile of the riding you do, and the road surfaces you ride on to reduce your overall rolling resistance. I’ve saved the discussion of those combined wheelset and tire choices for later.
2) Road Feel
WYNTK: Road feel, the combination of the comfort, handling, and grip provided by your tires, plays a role in how precisely and confidently you ride which, in turn allows you to ride faster.
When I describe a tire’s road feel, I’m talking about how comfortable it is, how well it handles in corners or maneuvers when you’re changing direction, and how much grip it provides in those handling maneuvers and when accelerating or just speeding along straight down the road.
The better the road feel, the more precise you’ll be taking those corners or doing those maneuvers, or generally accelerating on your bike. While it’s hard to measure, the added confidence that comes from tires with a superior road feel will allow you to ride more aggressively without taking on more risk. That will make you faster.
Tire size, compound, casing, and tread all contribute to the road feel as does the inflation pressure and wheel size in combination with the tire.
We’ve all read how a wider tire, inflated to the same pressure, gives you a wider contact patch between the tire and road surface. A wider contact patch can give you better handling. A narrower tire at the same tire pressure as the wider one gives you the same tire patch area but is narrower, running more along the length than the width of the tire and therefore doesn’t handle as well.
However, a wider tire at the same air pressure has a greater volume of air in it. That gives you less suspension and therefore less comfort.
One of the major reasons people use wider tires is to improve comfort. So you lower the air pressure to reduce the air volume and improve the suspension and comfort in a wider tire. (Throw the contact patch argument out the window.)
With a tubeless tire that’s filled with sealant, you can keep lowering it and get more suspension without concern for a pinch flat. More suspension, especially on a rougher road can also give better handling (and lower vibration losses) until you hit a pressure where the handling feels imprecise or mushy when cornering or accelerating.
Tire compound and casing also play a role in how the road feel of tires differ at the same width and inflation pressure. You can often feel the difference with a tire that has a more supple casing or grippier compound. These contributions to better road feel give you the precision and confidence to ride faster.
Most road tires are slick down the center with a limited amount of tread on the sides. It’s hard to know if the tread on a road tire actually improves acceleration and handling the way it does on a gravel or mountain bike tire.
My fellow tester Miles and other serious road racers believe the tread adds grip when they’re ripping through corners. Miles doesn’t like to ride tires without grip. Real or imagined, it adds to his confidence and makes him faster.
Tire companies say the tread is there to channel moisture on wet roads and trip the air to reduce aerodynamic drag. Not wanting to mess with Mother Nature or Father Grime, I religiously mount tires in the direction indicated in hopes that it will help me ride faster or at least, not work against me should I find myself riding out on a wet, oily road.
Cynics, or perhaps those who know more about tire marketing than I do, say the tread is purely cosmetic. Per this reasoning, road bike tires deflect and rebound as their primary way to give you grip and traction, not from a small amount of tread.
But, as this perspective goes, since almost every vehicle tire has tread, consumers expect it and road bike tires sell better with it.
3) Aerodynamic Drag
It’s a commonly held belief, without published data behind it, that the tread on Continental’s Grand Prix 4000 and 5000 road tires aerodynamically outperforms that of others in wind tunnel testing.
A tire supplier I spoke with in my research for this post says the pattern they put on their tires improves aero performance by roughly 1 watt over the Conti Grand Prix tires. I call it a pattern as it’s recessed within the tire than sitting on top. Conti’s is more of a tread or a tread pattern since it sits on top of the tire.
The theory goes that a raised tread or recessed pattern can be designed to trip the airflow coming off a tire to improve its reattachment to the rim and make for a more aerodynamic combination.
I’m not aware of any company or independent tester that has published a comparison of the aerodynamic drag reduction provided by the treads or patterns on modern bike tires. But since all of the best tires have a tread or pattern of some sort, perhaps to channel moisture or for marketing purposes or to improve aero performance or some combination of these reasons, any aerodynamic advantage one tire may have is likely the most incremental of incremental gains in making you faster.
4) Actual Tire Width
As I described earlier, tires with the same width dimension won’t measure the same actual width even on the same rim even with the updated ETRTO and ISO standards that use wheels with modern-day rim widths. In my measurements of current tires and wheels, it can vary by as much as 1.9mm for 25mm tires and 0.9mm for 28mm ones. You can see these differences in the charts I prepared for my review of the best tubeless tires.
Since tire inflation tools give you recommendations based on the width labeled on the tire and box rather than the actual width, you’ll be guided to inflate every 28mm wide tire used on the same size rim, on the same surface, for the same rider and bike weight, etc., to the same pressure. Yet at the same pressure, the measurably wider tire will also have a wider contact patch and provide better handling and grip, though less suspension and comfort and potentially more vibration losses on a rough road surface.
The wider tire may also increase the aero drag of the rim-tire combination.
I know that’s a rather qualitative take on the role that the actual tire width of those with the same labeled size plays in your speed. I don’t know how to quantify these trade-offs.
However, all other variables like inflation pressure being equal and without moving beyond the tipping point that increases your vibration losses or combined rim-tire aero drag, I’d expect the 25mm or 28mm labeled tire that actually measures wider than another with the same labeled size could improve your speed.
III. What Makes the Combination of Wide Wheels and Wide Tires Faster?
WYNTK: The long held beliefs about what rim and tire widths and inflation pressures you need to go faster have been turned on their heads in this era of wide wheels.
With what I’ve laid out earlier, we know what makes wheels faster and what makes tires faster. And we know why wider ones of each are faster than narrower ones.
So why can’t we just go look at the reviews and test data, combine the fastest wide wheels and wide tires, and have that make for the fastest ride?
You can, but only if you also make the right size and inflation choices. And those choices are so important that they can make slower individual wheels and tires combined with the right size and inflation choices faster than the fastest wheels and tires combined with the wrong choices.
There are three primary reasons why those choices are so important.
1) Combined Rim-Tire Aerodynamic Drag
WYNTK: To minimize aero drag, your rim should be wider than your actual tire width but there’s not as big a penalty as there was when rims and tires were far narrower.
I wrote earlier that Poertner formulated his rule of 105 in 2001 based on wind tunnel tests that showed aero performance suffered when the ratio of the rim’s width to the tire’s width fell below 105%.
The physics of rim-tire aerodynamics is rather straightforward. Illustrated by the image in the upper left of the graphic above, when the tire is the leading edge of the wheel spinning down the road and it’s wider than the rim, the airflow comes off your tires and diverts away from your rims no matter how deep they are.
But, when the tire is narrower than the rim as shown in the bottom left image above, the airflow can continue or re-attach to the rim after it leaves the tire and be controlled by the rim. How long it continues and how fast and smooth it flows along the rim depends on the rim’s profile and depth and the angle or yaw of the wind.
When the rim is the leading edge, as shown in the three images on the right, the rim profile, rim depth, and yaw angle determine the aero performance of the rim-tire combination as well as how it flows around the tire more than the width of the tire does.
When the tire is the leading edge, the rim-tire width relationship is key to reducing aero drag. However, when the rim is the leading edge, the rim profile is key to reducing the effects of side winds. A rim profile that’s best for reducing aero drag isn’t always the best for reducing side winds and vice versa.
Poertner and his engineering team led the development of Zipp’s first, toroid-shaped Firecrest rim in 2010. The rim measured 16.5mm wide between the bead hooks, 24.7mm at the brake track, and 26.5mm at the maximum width of the toroid profile rim. With a 23mm Continental Grand Prix 4000S II installed at 7bar or 101psi, the rim to tire width ratios were 1.0 or 100% at the brake track and 107% at the rim’s widest point.
When 25mm sizes of the same tires were installed, the rim at its widest point measured slightly wider than the tire or 102% at 6 bar/87psi, equivalent or 100% at 7bar/101psi, or narrower at 98% at 8bar/116psi.
Compared to the 23mm tire that had the 107% rim to tire ratio at the rim’s widest point, the wind tunnel tests above showed a roughly 1- to 2-watt penalty with the wind coming straight on (0 degrees of yaw) for 25mm tire widths that violated his 105% rule. (10g of drag = 1.3 watts at 30 mph)
But at 15 degrees of yaw, the penalty grew to 3 watts for the 102% rim-tire combination, 9 watts for the 100% combination, and 15 watts for the 98% combination.
As you might expect, the airflow continues longer (or stalls later further in on the rim) at a greater yaw angle for the 107% rim-tire width ratio combination than it does for the ones with a lower ratio.
And after about 1000 km/620 miles of wear per an ongoing endurance test of the Continental Grand Prix 5000 tubed tire done by BRR on a 17mm inside width rim, your tire will increase its width to where you would want a rim to new tire ratio of 108% to get the same results as the 105%. The wind tunnel test above is good for showing that situation.
You can also see from the test labels that for every 1 bar or 15psi increase in pressure above 6 bar/87 psi, your tire width increases 0.4 to 0.5mm. I’ve found a similar width increase going from 4 bar/60psi to 5.5 bar/80psi in my own tire measurements.
Looking at all of this together and depending on the yaw angle distribution you think applies to the winds where you ride, the depth of your rims, your speed, your tire mileage, and tire pressure, per this rule you could be in for a little or a lot of penalty watts.
Ah yes, but wide wheels and wide tires changes things
WYNTK: Today’s wide wheels and wide tires have made the rule of 105 an anachronism; it isn’t part of design considerations at wheelmakers and should no longer be part of your tire width choice (mea culpa).
One of the reasons I decided to do this deep dive about wide wheels and wide tires is that, as wheels and tires have gone wide, I’ve seen what looks like an open disregard for the long-revered rule of 105. Leading wheelset companies started saying cyclists could put 25mm, 28mm, and wider tires on their latest wheels in the last few years when some couldn’t pass the rule with 25mm rubber installed on them and very few could with the increasingly popular 28mm width tires.
We’re these wheelmakers buckling under the pressure of the wide tire hype? Had they given themselves over to the comfort culture warriors who slew the aero is everything ninjas (who overwhelmed the weight weenies crusaders)?
Some cyclists follow technology as if it were fashion and if your product isn’t “on-trend” you could expect its sales to lag. Did that explain this apparent willingness to violate the rules or at least the rule of 105?
Or do they know something about the place of the rule of 105 in today’s wide, wide world they hadn’t shared with the aerodynamically obsessed cyclists among us?
What I found in my exchanges with a handful of wheelset makers that do considerable research on aerodynamics and all the other things that make wide wheels faster was three things:
a. To optimize aero performance with wide wheels and tires, it’s still recommended to use a tire that’s narrower than the rim.
b. Engineers at leading wheelset makers don’t consider the rule of 105 in their product development.
c. Aerodynamic drag losses may be more than made up by reduced vibration losses.
Let’s look at these in more depth…
a. To optimize aero performance with wide wheels and tires, it’s still recommended to use a tire that’s narrower than the rim.
While wheelset companies will often say their road wheels can be used with a range of tire widths including those wider than the rims, more and more road bike wheel specs now include an “aero optimized tire size.” You can see examples in the screengrabs below. Other companies have shared the aero optimized sizes – typically 25mm – for their wheels with me in our discussions.
Companies that do CFD and wind tunnel design typically use a few sizes of a specific tire model in their design and testing. For example, many used the 23mm and 25mm Continental Grand Prix 4000S II in the early and mid-2010s and the 25mm and 28mm Grand Prix 5000 (tubed clincher) and 5000 TL (tubeless) more recently. Others like Bontrager and Zipp used the 25mm and 28mm sizes of their own branded tires when developing their most recent wheelsets.
Per my measurements of the best tubeless tires mounted on the latest model wheels, the rims of these wheels are generally wider than the actual width of the aero-optimized size tires at the pressure ranges we should be riding them.
But the actual rim to tire ratios vary. That’s not unexpected since the width of tires of the same labeled size also varies from brand to brand even on the same rim.
ENVE, a recognized leading carbon wheel maker whose wheels we’ve rated highly in our testing, designed their own branded tires to optimize the speed of their existing wheels. Per their measurements (I don’t have access to all of their wheels and tires so couldn’t measure them myself), the rim to actual tire width ratios varies from 103% (for their 31mm wide rim) to 107% (32mm and 29mm wide rims) to 114% (for another 29mm rim).
My own measurements of two of Bontrager’s latest wheels with the tires they used during the rim design show a 108% rim to tire ratio with their 28mm tires even though the aero-optimized size is 25mm and generates a higher ratio.
So, while a 25mm or 28mm tire will give you varying rim to tire ratios depending on the rim and tire models you chose, how much you inflate them, and how much they’ve expanded from wear, the “aero optimized” size is one where the rim is wider than the tire. That hasn’t changed as we’ve gone to wider wheels and tires.
b. Engineers at leading wheelset makers don’t consider the rule of 105 in their product development.
The rule of 105 was established in 2001. In the 20 years since then, wheels and tires have gotten wider and wider, carbon wheels have supplanted alloy ones, rim shapes have morphed from box to V to toroid to U to VU, and road wheels are now built for disc brakes and tubeless tires.
A lot has changed in the world of wheels and tires.
As deeper carbon wheels have grown in popularity, engineers have continued to focus on reducing aerodynamic drag. But, as I showed in the discussion of wide wheels, it’s become harder for wheel makers to separate the aero performance of their wheels from those of their competitors.
The competitive playing field has broadened at some wheelset companies to include improved side wind stability for 40mm and deeper wheels, becoming an even bigger design priority than before.
And there are still stiffness, compliance, weight, manufacturability, cost, and likely other design goals to meet.
Automotive and aerospace engineers along with computational fluid dynamics (CFD) technology have all come to cycling since 2001 and added new expertise, modeling abilities, and design processes to help address these complex and interdependent design goals. And while rim and tire widths are key inputs to CFD model iterations, things like rim profile, spoke face shape, and many other properties are also included in the mix to meet the desired aero drag, side wind stability, and other goals.
CFD technology allows engineers to do thousands of iterations in search of designs that consider the tradeoffs needed to best meet their goals. Wind tunnel testing now mostly confirms what is seen during CFD modeling.
Before CFD came into and expanded across cycling in the 2010s and certainly well after the rule of 105 was declared, wheel designers depended on their experience, applied available NACA airfoil research, and used CAD programs to develop bike rim designs and prototypes. These were first tested in wind tunnels rather than in any kind of computer simulation. And because wind tunnel testing was (and remains) very expensive, you didn’t get many chances to iterate your design before your budget and development time ran out.
While slowed during the pandemic, road testing of prototypes from designs that best pass the CFD modeling and wind tunnel tests is widely done by pro racers and wheel maker staff to add “real-world” testing and validation of the wheels that will be brought to market.
Recall that Poertner found from wind tunnel testing that 1.05 was the minimum rim to tire width ratio that allowed the air to leave the tire, re-attach to the rim, and then be controlled by the rim. That was made all the more difficult because the narrow tires (19mm to 23mm) and rims (15 and 16mm inside width) used at the time created a “light bulb” shaped tire and a notch at the rim-tire interface that the airflow had to jump to reattach to the rim.
With the right combination of rim, tire, and inflation pressure, this also smoothes the angle of the notch that the airflow needs to cross at the rim-tire intersection.
Rather than needing to control the air across the light bulb-shaped tire by narrowing its width, the wider rim and tire create a tire shape that the air flows between more smoothly.
And with the wider, taller tires, there’s also more tire surface area to attach and stay attached to at bigger yaw angles.
One engineer put a point on all of this when he told me:
“105 came from compensating for narrow rims at the brake track where you could lose attachment of the airflow. Now that everything is considerably wider, you don’t have that loss of attachment. So you have airflow remaining all the way across the tire and all the way across the rim. We’re not seeing stalls in the brake track area where we use to.”
The head wheel engineer at another company said they’ve never been concerned with the rule of 105. Instead, their iterative CFD and wind tunnel development processes determine the right design and the rim-tire ratio is a by-product rather than an input.
The result of all this? Less aero drag penalty as you go to a wider tire.
On the current wheels made by one of the companies I spoke with, you only add somewhere between 1 to 3 watts of drag as you go from the aero optimized, 25mm wide tire to a 30mm one whose installed width would measure wider than the rim.
That’s a big difference to what you see in the Zipp 404 Firecrest chart above where the tire that’s wider than the rim (98% rim-tire ratio) adds 3 watts of aero drag compared to the aero optimized one (107%) at just 5 degrees of yaw and adds up to 6 watts of drag by the time the air flow stalls at 10 degrees of yaw.
Another company for which 25mm tires are the aero optimized width for their current wheels told me that going from a 25mm to a 28mm tubeless tire, adds only 0.4 to 1 watts of drag depending on the inflation pressure. More importantly, they’ve found that for the same labeled tire width, depending on the brand and model of the tires, the shape they get from a tubeless model can reduce drag by up to 3 watts compared to a tubed clincher or tubular.
That same engineer I quoted above summarized this data when he said “Now, there is less aerodynamic sensitivity to different tires with wider rims” because “overall they are shaping the tire sidewall into the rim better.”
2) Vibration Losses
WYNTK: Reducing vibration losses by using wider tires looks promising, if not yet well documented, in making you faster on wide wheels.
Recall the third item I mentioned earlier about what makes the combination of wide wheels and wide tires faster
c) Aerodynamic drag losses may be more than made up by reduced vibration losses.
While I’m not sure when tires and rims got to the widths where the air started coming out of the rule of 105 – pardon the pun but it’s quite literally appropriate here – I’m estimating it happened at least a wheelset generation ago.
Proprietary company data shared with me from tests done in 2018 on the roads where the Kona triathlon happens tells quite a story. Using their 2018 production wheels with an outside width of 27mm, the company tested 23mm, 25mm, and 28m tires at a range of pressures to see how many watts the rider had to put out to maintain a 40kph/25mph speed. The total watts came from the sum of the aero drag (cda) and rolling resistance (crr).
At those sizes and pressures, only the 23mm tire had a rim wider than the tire. The 25mm tire was about the same width, and the 28mm tire was wider than the rim. As they used the same tire model, the compound and casing tire loss portion of the rolling resistance should also have been less for the narrowest tire as it was inflated to a higher pressure than the wider ones.
The results showed that using the 23mm tire inflated at the pressure (105psi) that required the least amount of power to maintain the target speed, the rider put out 1 watt more power than when riding a 25mm tire at its optimum pressure (90 psi) and nearly 4 watts more than the 28mm tire at its optimum (75 psi).
So in this test, the added drag and tire losses using tires as wide or wider than the rims and at lower pressures were more than made up by the reduced vibration losses on a paved highway road surface.
On any road where your ride slower than 40kph/25mph and on rougher roads where you might naturally ride slower and reduce your inflation pressure further, your aerodynamic drag should matter less and vibration losses should matter more. So the reduced vibration losses should matter even more than the aero gains from a wider tire inflated to lower pressure compared with the testing described above.
That naturally leads us to Jan Heine and what he’s been saying about wider tires and lower pressures for years. To quote the most relevant point from his Tire Pressure Take Home article of years ago:
- On rough roads, lower pressures are faster. So if you want to optimize your speed on all roads, including rough ones, go with a relatively low, but safe, pressure.
But then Jan’s company sells tires for rough, off-road, adventure riders that use far wider tires and run at far lower pressures and are ridden or raced at lower speeds than any used in road cycling. And until all-road bikes and tubeless tires came along, there wasn’t clearance for tires as wide as those his company makes in your road bike or tubed tires run that at the low pressures you ride off-road without regular pinch flatting on paved roads.
[While I take Jan’s basic points, his article showed much less sensitivity to the kind of wattage differences we roadies would die for. For example, he concluded that “pressure makes little difference in performance” based on tests that showed 5-10 watts of difference in 25mm CX tires in use at the time inflated between 6 bar/87psi and 8 bar/115psi.]
It’s fair to say that the gap between Jan Heine’s slow, wide, off-road world and Josh Poertner’s fast, narrow, road racing world has narrowed as road wheels and tires have become wider.
Paris-Roubaix has become the pre-eminent race where those worlds have come together and is the ideal test ground for wider wheels and tires.
Most of the race is ridden on quite nicely paved roads that most of us road cycling enthusiasts would enjoy riding or racing using the wheels and tires we regularly ride and at the pressures we normally use. But the more famous cobbled sectors, those that we would likely avoid if we came upon them during a regular ride, are where the race is won and lost and where the wheel, tire, and inflation pressure choices are made that racers live with for the entire race.
While Paris-Roubaix may be on some of our bucket lists, a “gravel” ride that includes sections of paved, dirt, gravel, and single track surfaces is more likely the environment that will challenge our tire width and inflation pressure choices in the near term. This is where you can put those 40mm+ wide tires on wheels with 23mm or 25mm inside widths not too much wider or the same as you ride on nicely paved roads.
If you’ve read articles about Paris-Roubaix technology or ride gravel, cyclocross, or mountain bikes, you know that tire width and pressure are what determine how fast you can go.
Yet some wheelset companies market the aero performance of their gravel wheels and cycling journalists who should know better prattle on about them in adoring reviews when even the best riders aren’t riding at speeds where wheel aerodynamics make much if any difference to how fast you can go.
Back on paved roads, the inverse relationship between aero drag and vibration losses seems qualitatively clear – sacrifice some watts with a little added aero drag to gain a lot more of them from reduced vibration losses. But it’s not easily measured or well quantified yet. I’m not aware of any comprehensive testing like the Kona data I reported earlier done by different groups of testers that’s been published for us to dig into.
As one wheelset company product manager humbly put it, “the effect of surface texture is novel research that has very little precedence and we are still uncovering basic science in the subject.”
One of the leading independent testers of tire rolling resistance had a similar, more practical response to my question about whether he would consider measuring vibration losses. He wrote: “I’ve done experiments with this but it isn’t as simple as just adding bumps to the drum and then measuring the results. The problem is the suspension losses are hard to measure as the machine, when undamped, is insensitive to vibrations, unlike a real person. Doing these kinds of measurements on a drum would require extensive research with all sorts of damping setups that can absorb the vibration energy.”
Tire makers are also running into conflicts optimizing for both the tire loss and vibration loss parts of rolling resistance. One shared with me that materials used in some of the top-rated tires to get those low tire loss scores in drum tests also give those same tires higher vibration losses on rougher roads compared to tires with higher tire loss scores on the drum tests.
Since good drum test scores sell bike tires and vibration loss testing is a rather nascent or at least a proprietary endeavor, this may put sales and engineering people working within tire suppliers at cross purposes when they develop their next generation of road tires.
As the aero drag penalty for going to wider tires has diminished and the potential those wider tires can give you by reducing vibration losses looks promising if not yet publicly documented, the best approach, for now, is to do your own testing with one or two tire widths at different pressures to see which combination is fastest for the kind of riding you do.
3) Road Feel
WYNTK: The right combination of tire width, rim width, and inflation pressure will give us the road feel that makes us confident to go our fastest.
As I’ve written in the wheel and tire sections, compliance/comfort, handling, and grip or “road feel” are key to how aggressively you are willing to ride, where during the ride, and for how long. All of this together adds up to speed.
Putting the right width tire and wheel together at the right pressure can improve the road feel better than putting one that’s too wide or narrow relative to the other.
In our desire for a more comfortable ride, the most common mistake we’ll make is to put a wide tire on a rim that isn’t wide enough to give it the road feel that makes us most confident. If we lower the pressure too much in search of more comfort and lower vibration losses, handling begins to feel mushy or pinch flats can occur if the sidewall folds over against the rim during hard or high-speed cornering.
The opposite can happen too; we can mount a narrow tire that has great aero properties on a wide rim but the course we’re riding requires more cornering or is on a rougher surface than is ideal for that combination. When this happens, you will feel your wheels skipping or sliding rather than railing a corner.
While some will debate this point (see Jan Heine’s argument here that wide tires don’t need wide rims), those of us who ride a lot will find the right combination of tire width, rim width, and inflation pressure for the speed, courses, and surfaces we ride that will give us the road feel that makes us confident.
With good quality rims and tires that are generally in the right relative width ranges (one not way wider or narrower than the other), you can often improve the road feel or get the feel you want by adjusting the tire pressure. But with the wrong rims (e.g. not stiff enough) or tires (tread too narrow for the casing or stiffer tires than is right for the riding you’re doing) or wrong combination, a less than optimum road feel will make you less willing to ride your hardest when it matters and slow you down.
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IV. What Combination of Wide Wheels and Tires Will Be Fastest for Me?
WYNTK: Find the right tire pressure for whatever you ride now and choose any new tires and wheels based on how and what you ride.
What should you do with all you’ve read above to go faster?
1) Find the Right Tire Pressure
First, find the right tire pressure for whatever combination of wheels and tires, road surfaces, courses, and speed you ride now.
If that sounds rather open-ended, well it is. That’s because there’s no simple, one-size or one-pressure-fits-all answer. You can use some tools to guide you but, because there’s also no one-tire-calculator-fits-all solution either, I suggest you also do some experimentation on your own to come up with the best pressure for your unique riding profile.
Silca (which sells tire pumps) and SRAM (parent of Zipp which sells wheels and tires) each offer online calculators. You enter weight, tire, surface, and other information and they recommend front and rear tire pressures. They ask for slightly different information and can produce results I’ve found that are 5-10 psi different for the same type of inputs, the Silca pressure recommendations typically being higher.
Annoyingly, to get the “Pro Version” of the Silca calculator you need to enter your email address which signs you up for their marketing list though they don’t tell you that this is what you are doing or ask for your permission. Unsubscribe when you get the email that immediately follows your sign-up. You’ll still be able to use the pro version after you’ve unsubscribed.
The Silca calculator is somewhat more specific than the SRAM calculator. The Silca calculator asks for your “measured tire width” yet doesn’t tell you what pressure to measure it at. It also asks you how rough the surface is you’re planning to ride.
SRAM’s calculator asks for the labeled tire width and inner rim width, from which it likely estimates the measured tire width. As to surface properties, it only asks whether it is wet or dry.
You enter your own rider and bike weight into both calculators. If you can’t measure your fully loaded bike weight, I’d suggest adding about 5-10 pounds to the weight listed on your bike spec sheet for your pedals, filled bottle(s), saddlebag contents, shoes, clothes, and whatever you stuff in your pockets.
Both calculators also ask for the tire casing type though neither provides any guidance on the options they list. You can see the ones I chose in the screenshots that are right for the kind of training tires enthusiasts use; pick the next option up on both if you are racing on a tire without a puncture belt and the next one down on the Silca calculator if you are using a tube-type clincher training tire.
The Silca calculator also asks you for your speed group rather than the actual speed while the SRAM calculator asks if you are using tubular, tube-type clincher, or tubeless tires, the later with hooked or hookless rims.
It’s not surprising that the results from these two can be so different. At least the SRAM calculator puts a disclaimer on the bottom that encourages you to find the right pressure for yourself using their calculator as a starting point.
Before the Silca and SRAM calculators came along, I used the tire pressure chart from ENVE (which sells wheels and tires). As you can see below, it’s simple. You find a recommended pressure on the chart at the intersection of your inner rim width, labeled tire width, and body weight.
Note that all but the first group of columns on the left are for sizes on ENVE wheels that are hookless. That results in a 3-5 watt lower pressure than would hooked rims at the same widths and weights but lower is better than higher until it isn’t (imprecise or mushy handling).
The ENVE chart also points out that their recommendations are a place to start but warns that these are maximum levels and based on tubeless tires. They have similar charts for gravel and mountain bike rim, tire, and weight combinations.
Their suggested pressures are typically lower than those from SRAM, albeit with far less info. As a tubeless tire rider, ENVE’s numbers have been the closest to the pressure my experiments get me to for the best road feel (comfort, handling, grip) without feeling any slower.
That’s not an endorsement, just my experience. Once again, I encourage you to use these tools only as a guide for your own experiments. Start with a number from one of them and drop the pressure 3-5 psi on successive laps over a typical section of road you ride or until the tires start feeling too imprecise or mushy for the speed and handling you do.
Run the front tire a few psi lower than the rear one and see how that feels. Since more of your weight is on the back (maybe 52-55% on a road bike), you may benefit from running it 2-3 psi higher in the back. Silca’s recommendations usually fall in that range while SRAMs calculator typically recommends the rear tire be inflated 4-5 psi higher than the front. ENVE’s only gives you a single pressure guide.
Do your testing on a recovery day. You’ll benefit from it every other day.
2) Choose the Right Tire
Assuming you aren’t planning to buy new wheels anytime soon, the next best thing you can do is to pick the right tire model and size for your current wheels. (Then find the right inflation pressure for the combination of the new tires and your wheels as described in the section above).
As I detailed earlier, tubeless tires are faster than the best clincher or tubular ones. And if you can’t bring yourself to use one of the best tubeless tires because of your resistance to change or the struggles and sealant mess you’ll make the first few times you set up tubeless wheels, use a latex tube in a tubeless tire. You won’t get the benefit of a tubeless tire’s resilience to punctures and pinch flats, but at least the tire losses will be nearly the same as using sealant per BRR’s testing. If you use a butyl tire, you’ll add a couple more watts to your tire loss rolling resistance
Once you’ve chosen the tire model, you need to choose the right size. That will depend on how fast you go, what kind of surfaces you ride, how wide your rims are, and what kind of handling you do.
One way to tell whether you should go with a wider or narrower tire is to plot where you land in answer to each question below.
The faster you go, the more aerodynamic drag matters. Narrower tires will usually have less drag on rims of any size, even though the advantage is much less with today’s wide tires on wide wheels than the narrower ones we’ve used in the past.
The rougher the road, the more vibration losses matter. Wider tires allow you to reduce your pressure more than narrower ones while still providing enough suspension from the additional volume of air in the rim-tire chamber to give you a good road feel (comfort, handling, grip) and reduce your pinch flats.
If wide enough, wider rims can use wider tires without suffering aero drag losses. This is the modern cycling gear equivalent of having your cake – reduced vibration losses and improved road feel of wide tires – and eating it too – reduced aero drag. Narrower rims need narrower tires to minimize aero drag losses.
If you race or ride courses where you’ll be doing a lot of hard, fast handling, a wider tire will allow you to ride more confidently and safely. But, if you are riding where a limited amount of handling is required or you slow considerably to reduce your risk in the turns, getting your inflation pressure right will typically set you up to do all the handling you need even on narrower tires.
These four considerations – speed, surface, rim width, handling – aren’t equally important or need to be in alignment. You could ride fast on rough surfaces with rim widths and handling characteristics that fall in the middle of the range. Depending on how fast and how rough the surface is (and how deep your wheels are), you have to weigh the trade-off between aero drag and vibration losses that appear to weigh in favor of the wider tire with today’s wide wheels and tires.
Also, if you already have a wheelset on the wide end of the range, there’s little to be gained by going with a tire that measures much narrower than the width of the rim vs. one that measures narrower but only by a 1mm or so regardless of the other considerations.
What’s “wider” and “narrower”? In 2022, the widest road tires for the current generation of road disc wheels and bikes are 30-32mm wide while the narrowest ones for earlier generation disc and rim brake wheels and bikes are 23 mm wide. More typically, the choice for enthusiasts who have wheels and bikes they’ve bought within the last 3-4 years will be between 28mm and 25mm tires.
Distilling all that I’ve learned preparing this post, I’d suggest road cycling enthusiasts use a 28mm tubeless tire if you fall left of center for whichever characteristic or characteristics are most important in your riding and 25mm if you fall to the right.
If you are uncertain, a wider tire would be my suggested default. Recreational riders and commuters should go to 30-32mm wide tires if there’s enough clearance for them in your bike frame.
3) Choose the Right Wheel
If you’ve decided you need or want new wheels, there are a lot of considerations that go beyond the scope of this post. I wrote a separate post about how to choose the best wheels for you to help you comprehensively define your goals, rider profile, and budget to come to the right choice with the help of the comparative wheelset reviews we’ve done in a half dozen different categories.
You need to answer three questions that relate to the topics in this post when buying new wheels.
The answer to “how wide?” is straightforward – as wide as your bike has clearance for. Most disc brake road bikes will have clearance for most of the widest road disc wheels made today. As most companies are no longer developing new rim brake bikes or wheels, clearances and widths have maxed out at around 19-21mm inside, 25mm-27mm outside width wheels, and 25-28mm tires. Some rim brake bikes won’t fit tires wider than 25mm.
The biggest challenge is typically having enough clearance between the chainstays and seat stays for wider tires. Most disc brake road bikes will have enough room for at least 28mm tires which, once installed and inflated can measure as much 30-31mm. On top of that, you want to have another 3-4mm on either side of the tire for rim deflection in cornering. A safe clearance is about 40mm.
The newest disc brake and all-road bikes will typically have clearance for 30-32mm wide tires.
The best carbon disc wheels are typically made today in three depths for cyclists focused on speed. “All-around” wheels have rims that measure 45-50mm deep while aero wheels come in around 60mm+/- and time trial/triathlon ones are 75mm and deeper.
Choosing between these for speed matters most if you already ride fast. Reprising the data I shared earlier in the section about what makes wide wheels faster, you can expect a 1-3 watt aero drag reduction in wheels of the same generation made by the same company each time you go to a deeper section wheel if you ride at the highest end of the speed range (45-50 kph/28-31mph).
If you ride in the low 30s kph/low 20s mph range, there’s little aero drag benefit from deeper wheels.
Picking the latest wheelset model from the brands that design their own wheels appears to make a bigger difference in speed than going with a deeper wheelset. The added speed principally comes from the combination of reduced aero drag, improved sidewind stability, a wider rim that enables wider tires, and the associated reduced vibrational losses and improved road feel. Stiffness, compliance, and weight are less important to your wheelset’s speed.
While the differences are hard to verify and easy to debate (that’s where marketing comes in), my read on all of this is that if you ride at the high-speed end of the range (45kph/28mph) you can potentially get on the order of a 5-10 watt or faster wheelset in a new model of a 60mm deep model from a company that does their own engineering vs. a 45-50mm model from a company that doesn’t.
If you ride at the lower end of the speed range or wait a couple of years to buy a lower price wheelset from another brand that has learned from or copied the design of the fastest models, you’ll be at no speed disadvantage with the shallower, all-arounder. At least, that is, until another new model gets introduced from the company that develops a design that’s faster still.
That’s the way innovation works and why some cyclists are willing to buy new wheels more frequently or pay more for the latest wheelsets from design leaders even if it’s hard to determine which is truly faster and knowing that few of us other than racers ride well enough to really benefit.
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Thanks and enjoy your rides safely! Cheers, Steve
First published on March 13, 2022. Date of the most recent major update is shown at the top of the post.