CHOOSING GRAVEL BIKE TIRES
For some, choosing the right gravel bike tires can seem nearly as daunting as Neo battling to free humanity from the Matrix or time-crunched roadies trying to free ourselves from Zwift.
It doesn’t have to be. After researching the surfaces of 25 popular gravel events in the US, I found each would be best suited by riding one of three types and widths of gravel tires.
In this post, I’ll give you a shortlist of gravel bike tires for each of those events that will also work well for other gravel rides and training workouts you do on similar surfaces. I’ll also suggest some width options based on your wheels, riding goals, and unpaved road riding experience.
WHAT YOU NEED TO KNOW ABOUT GRAVEL BIKE TIRES
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THE MATRIX OF CONSIDERATIONS
As a roadie gone groadie, my first long rides on my new gravel bike got me evaluating all manner of things. I liked rolling on dirt roads, felt slow on paved ones, and my confidence riding different combinations of dirt, gravel, rocks, sand, mud, and trail varied as wildly as the surface I came upon.
The 40mm tires that came with my bike had a lot of good-sized, spaced-out, differently-shaped knobs along the center and shoulder of the tire. I got why they might not roll well on paved roads but had no idea whether they were the right tires for the type of dirt and gravel I was riding.
As you might expect, I read a bunch of gravel tire reviews, asked some friends, went into a few bike shops, and looked at the web sites of the better-known brands of cyclocross and gravel tires.
There was a lot of advice, recommendations, claims, etc. about the tires in general but little about how to decide which were the best gravel tires for the events and routes I was planning to do or for my wheels or skills or performance preferences or most anything else unique to my situation.
Can you get one set of gravel tires that is great for most surfaces or do you need different tires for different types of surfaces? Do you pick gravel tires for the most challenging, gnarly part of a ride or for the kind of roads or trails you’ll be on most of the course? What gravel tires are best when 20-30% or more of your ride will be on paved roads getting to and between the gravel sections?
How do you choose the right width of a tire that’s offered in several widths? Does the rim width of your wheels affect the tire size you should buy? Does your skill riding on dirt and gravel affect the tire or width you need? How about if you want to race vs. do a fast group ride vs. go at your own pace??
What tire weight is reasonable? What are the tradeoffs between lower rolling resistance and better traction? Does aero performance matter? Speed? How well you climb? How well you descend? What kind of handling or comfort you want? What level of puncture resistance you need?
While these are all good questions, what I’ve come to understand is that you need to start by picking a gravel tire tread type that works best for the mix of surfaces you’ll ride during an event you are targeting or for the mix you train on.
The bad news is that there aren’t “all-around” gravel bike tires that do well in all situations the way all-around road bike wheelsets do. The good news is that one of three primary types of gravel tires, what I’ll oversimplify as semi-slick, small knob, and big knob gravel tires, will work well with the most popular gravel events and with local rides you do on similar surface combinations when those events and rides are mostly dry. So, you can fill your gravel bike tire “quiver” with three pairs of tires and perhaps a fourth for wet and muddy riding.
You can deal with many of the questions I posed above by modifying the tire width you choose for a given type of tire. More on that later.
CLASSES OF GRAVEL
As anyone who has ever ridden unpaved roads and trails knows, “gravel” is a loosely grounded term (pun intended). When you go out for a gravel ride, you may find yourself traversing surfaces ranging from smooth, compacted dirt roads to what might otherwise pass for a rock garden.
Before the current wave of UCI road racers became gravel “privateers”, former US professional road cyclist and mixed-surface pioneer Neil Shirley put a stake in the gravel when he published his descriptions of four categories of gravel. This helped early gravel riders decide what bike and size tires to ride well before there were the many, many gravel bike and tire options we have today.
While not acknowledging or perhaps even aware of Shirley’s contribution, CyclingTips came up with its five grades of gravel a couple of years later. CyclingTips inserted badly paved roads as its first grade but the other grades were similar to Shirley’s.
Jerry Chabot of wheelmaker NEXT wrote an excellent piece about the unpaved roads he grew up riding in New Hampshire and Vermont. His father’s experience operating a gravel pit and building dirt roads for a living gives him a refined regional perspective for the right tire and wheel choices when doing one of seven types of rides of different speeds, lengths, and surfaces he outlines in his blog post.
I’ve not searched for them but I imagine there are other region-specific perspectives like Jerry’s worth considering.
Like it or not, you will ride some amount of paved roads at every gravel event. These are often at the start and finish, at feed zones, and linking unpaved segments. A few of the popular events are mostly paved rides but have dirt and gravel sectors where the selection between the best riders and the rest of us is made.
I have quantified the paved/unpaved breakdown for each event but am not considering paved roads in my gravel classes.
Chapeau to Neil for the work he and others have done to help us sort through the different types of gravel. After researching the unpaved surfaces at each of 25 popular gravel events, I’ve tried to build on what Neil started by being a bit more inclusive of the range of surfaces you’ll ride at the increasing number of events and give them simple, perhaps more relatable names.
Class 1 aka “Dirt” – maintained, consistent hardpacked dirt with small-sized or no gravel
Class 2 aka “Gravel” – loose, small and medium-sized gravel spread over the road or in the crown or along the shoulder on top of hardpack or softer/uneven dirt; some washboard and occasional 1-2’ diameter potholes; sand and/or clay sections without gravel
Class 3 aka “Rocks” – unevenly sized, larger/sharper gravel and rocks, partly exposed/buried rocks, truck tire trenches and rain grooves
Class 4 aka “Technical” – big rocks/rock gardens, deep loose gravel, deep ruts, path-, lane- or road-width potholes or single- or double track paths/roads with rocks, roots, fallen trees or other large obstacles
As the descriptions and pictures make clear, the one-word class names Dirt, Gravel, Rocks, and Technical aren’t inclusive of the surface elements you’ll see in each class. They are, at least for me, the first word that jumps to mind (other than “yeah!” or in some cases, “sh*t” and four-letter words) when I enter a new section of unpaved road.
Another way to think about these four classes is by considering the kind of bike that would give you the most speed and confidence riding each surface.
Here’s how I would associate them.
- Class 1/Dirt = Road bike
- Class 2/Gravel = CX bike
- Class 3/Rocks = Gravel bike
- Class 4/Technical = Mountain bike
GRAVEL SURFACES AT POPULAR EVENTS
Of course, most gravel events and rides don’t have the same class or type of surface across the entire route. That would make choosing gravel tires easy.
Instead, the challenge is picking tires that, along with your wheels, goals, skills, and other unique characteristics give you enough tire for the toughest surface class and not too much for the others.
To figure this out, I first came up with the surface mix between paved and unpaved surfaces at the popular events. I then did my best to determine what percent of the unpaved surface at each event was Class 1, 2, 3 and 4 or dirt, gravel, rocks, and technical.
Most event sites will describe their surfaces to varying degrees. Some will tell you how many miles of paved surface you’ll find. Others will describe and show you photos or even videos of the course. Still others will suggest sizes or specific tires they recommend you ride (be aware of tire sponsorships that may sway their recommendations).
Unfortunately, some events reveal little either because they are so new, or the course has changed, or the promoters want to create some mystery to enhance the image of the challenge you’ll face or just want you to chill out.
So how did I come up with the surface mix between paved and unpaved and across the unpaved classes that you’ll see below? It wasn’t easy and I’ll be the first to say there may be a good-sized margin of error in some of the numbers.
Basically, I read a lot of race reports and watched hours and hours of video footage from most of the events. My thanks and admiration goes to those of you who have shared your experience in enough detail to give those of us who haven’t ridden these course a good sense of what we’ll likely see. Special thanks to the videographers including Gravel Cyclist JOM and so many amateur groadies who took and posted hours of GoPro video from their events.
After breaking down the mix of surfaces at each event and reviewing what gravel tires event promoters, outside experts, and serious riders were using and recommending for them, it became pretty clear what type and size of tire would be best for those of us road cycling enthusiasts who are becoming gravel cycling enthusiasts.
As enthusiasts, our goals are to take each ride seriously, train for them, and go fast. We don’t just show up at a ride and hope to finish. Because of that, I’ve evaluated the surface for the longest course option for these events.
With our roadie gone groadie journey, I’m also assuming that most of us come from the road world with not a lot of recent off-road or mountain bike experience, skills or DNA to fall back on.
To make it a bit easier to come up with recommendations, I’ve also focused on 700c, tubeless tires going on disc brake wheels that have a 19mm to 21mm inside rim width on a gravel or cross bike with something near or better than a 1:1 gearing ratio for climbs.
If you do have a lot of off-road skills, wider rims, are on the lighter or heavier ends of the weight bell curve or prioritize confidence and comfort over speed, you’ll see some tweeks to the size or tire pressure I recommend a couple of sections below this one.
And to repeat what I said earlier, if a course is very wet or muddy, you need mud tires. My surface mixes and tire type recommendations are for when these events are run in dry conditions.
Yes, 650b is a real option but I’ve not considered those size tires here (Too many tires, too little time). And yes, some of you may not be comfortable with tubeless or are using narrower wheels or rim brakes and have a tighter gear range on the bikes you want to try out on gravel. That’s all well and good but it’s going to put you at a disadvantage on these gravel courses and in a dwindling group of riders who are serious about riding mixed surfaces. For that reason, I haven’t put together any recommendations for those set-ups.
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SHORTLIST OF SUGGESTED GRAVEL BIKE TIRES
While each gravel tire’s combination of tread pattern, casing, compound, weight, and other design factors are unique, the performance goals are somewhat similar. For a given type of rolling surface, gravel tires aim to give you superior grip, handling, rolling resistance, puncture resistance, comfort, acceleration and climbing traction, braking and wear.
As you can see from the range of paved and unpaved rolling surfaces at most of the popular gravel rides I’ve charted above, a gravel bike tire’s versatility or ability to do well on different surfaces is also a key performance and selection criteria.
With the performance goals and versatility required of each tire in mind, I’ve come up with three shortlists of gravel bike tires for the mix of surfaces you’ll see at these popular events and on other rides with similar surface mixes. I’ve read enough reviews about each of these tires to suggest them to you. My fellow In The Know Cycling testers and I will be riding and sharing our comparative reviews of these tires during the season.
Semi-Slick 30-34 mm gravel tires
Even though they are called “gravel”, there are several events and many rides where you are on a paved surface more than 30% of the time (e.g. Tour of Battenkill, Belgian Waffle Ride) or where Class 1 or hard-packed dirt is the primary unpaved surface (Peacham Fall Fondo, Croatan Buck Fifty, and Barry Roubaix on an infrequent dry day).
On these types of rides, a 30-34 mm slick or semi-slick tire will provide you relatively low rolling resistance and good handling with plenty of comfort on a route where knobs down the center would slow you down and not add any grip or traction benefit when rolling straight.
Some enthusiasts and racers will ride these events or courses on a road, cross or gravel bike with 28mm or 32mm tubeless road bike tires on their road disc wheels. No need for a special gravel tire.
But, when these rides also have a fair amount of turning or sections of Class 2 soft dirt or sand or short Class 3 sections then semi-slick tires – slick down the center with knobs on the shoulders – will give you better handling and confidence than totally slick road tires.
There are three models of semi-slick “gravel” 700C tires I suggest you consider:
Small Knob, 35-38mm gravel tires
Most of the popular gravel events are ridden on courses that are 80% or more unpaved roads where half or more of those surfaces are a combination of Class 2, 3 and 4 or gravel, rocks or technical. This is truly the image of a gravel ride or, at least where there is a lot of gravel on hard or soft pack dirt roads. It may also include sand, clay, and other soft surfaces that make grip and traction imperative.
Except for rides where 40% or more of the route is made up of Class 3 and 4 mileage, or that have roughly half that percentage of Class 4 alone, most enthusiasts will get the best combination of performance from what I call “small knob” gravel tires labeled with 35-38mm widths.
In my attempt to simply your tire selection, I’ll readily admit that “small knob” captures just one aspect, although I think the dominant one, of what are otherwise some very complex tread and tire designs.
Gravel tires with smaller, shorter knobs running down the tire’s center placed relatively close together with often progressively bigger and more dispersed ones moving out to the shoulders tend to provide better grip, handling, braking, etc. on the kind of smaller, loosely spread gravel and softer surfaces you get with Class 2 gravel surfaces than do “big knob” tires.
On larger, sometimes deeper gravel, rocky, trenched, and rooty Class 3 or rocks and Class 4 or technical surfaces, tires with big knobs that are taller and placed further apart will usually perform better in all the ways that matter (grip, handling, acceleration, and deceleration, “floating above” rolling resistance, comfort) compared to smaller knob ones.
While some of the “small knob” tires I suggest come in sizes wider than I’ve listed, I note there is a tendency of roadies gone groadies to “over-tire” this category of tires. Some of us will get small knob tires 3-8mm wider or get “big knob” tires to compensate for their lack of off-road riding skills and confidence or when faced with concerns of how to get through some of the short Class 3 or Class 4 sections, especially the climbs and descents.
Line and technique are usually as or more important than getting a wider or bigger knobbed tire in these situations. And, a wider tire and especially one with bigger knobs than are best for 80% of the unpaved surfaces that would be best on a small knob and narrower tire can really make for a less enjoyable experience for most of your ride.
With that bit of explanation and caution, here are the 700C small knob tires and sizes I suggest you consider:
Bontrager GR1 Team Issue 35mm, also comes in 40mm. Available at Trek
Kenda Alluvium Pro 35mm, also comes in 40mm. Available at Know’s Shop
Specialized Trigger Pro 2Bliss Ready 38mm. Available at Know’s Shop
Big Knob, 38-42mm gravel tires
Above, I outlined when you’d want to get small knob vs. big knob tires and provided a simple definition of what their primary design and performance characteristics are. Events and rides requiring big knob tires usually demand the greatest off-road technical abilities and top fitness levels.
As a road cycling enthusiast, you likely know how to get in shape for these ridiculously long rides. If not, start with doubling your weekend training rides.
For the technical skill building part, find someone with mountain bike DNA or a groadie whose been at it for a while and learn from them.
What I’m getting around to the long way is that while these 700C big knob tires I suggest you consider below will certainly help, they won’t fill the gaps in your skills or training.
Bontrager GR2 Team Issue 40mm. Available at Trek
OPTIONS FOR YOUR SITUATION
While much of the attention around gravel bike tires focuses on tire width, I hope the above sections have convinced you that getting the right type of tire for the mix of surfaces you are riding is the most important consideration.
Once you’ve picked a semi-slick, small knob or big knob tire and model, that’s when size comes into play. The sizes I’ve recommended for each tire type above are based on you riding 19-21C rims, having built your gravel riding experience starting with roadie rather than mountain biker skills, and having the enthusiast goal to ride these events and surfaces fast rather than leisurely.
Let’s look at some options if your personal situation is a bit different.
Rim Width: As with a new road bike, your gravel bike is likely to have heavy, underperforming stock wheels that you’ll want to replace. If you have already upgraded your road disc bike wheels, you may want to simply move them over to your gravel bike and put your new gravel tires on them. Totally reasonable.
While the difference between the label width and actual width of gravel bike tires aren’t any more reliable than what you find on road bike tires, what I’ve seen is that gravel tire label width appears to associate best with 19-21C rims. And, your upgrade road disc wheels are likely to be in the 19C to 21C width range as are most stock wheels that come on gravel bikes.
If you get a better set of alloy or carbon gravel bike wheels, they are likely to be in the 22C-25C range, far wider than your road wheels. There are good reasons to get dedicated gravel wheels including saving your road wheels from potential gravel damage, getting better grip, handling and puncture resistance, and avoiding the time and hassle of moving your wheels and re-mounting tires each time you change between road and gravel bikes.
My testing with several tires and rims shows that the mounted and inflated tire width will increase 2mm when you go from 19C to 25C rims whether at 50psi or 35psi. This was the case for both 40mm big knob gravel tires and 38mm small knob ones. So your actual width will increase roughly 1mm for every 3mm of rim width above 19C.
Gravel Skills and Ride Goals: If you have a mountain bike background, you likely have a range of handling, descending, line choice and other skills and the confidence level doing things on dirt and gravel that most roadies gone groadie lack. Where it’s offered, you would likely be fine with a size narrower rim width.
If you are a roadie looking to ride gravel as a nice change of pace rather than as hard as you ride on the road, go a size wider. This can give you more confidence and comfort in the same way a 28C road tire might over a 25C even though it won’t be as fast.
Either way, stay with the type of tire that’s right for the surface you are riding and just change the width. If the event or ride calls for a small knob type gravel tire, don’t go to a semi-slick if you’ve got good dirt and gravel riding experience or to a big knob one if you want to take it easy.
Rider Weight and Tire Pressure: Just like with road bike tires, the best gravel tires will not perform great if you don’t get your air pressure right. A guide like the tire pressure chart from ENVE here can help you get started.
Personally, I’ve found that trial and error is key to finding the pressure that gives you the right tradeoff between performance and comfort for a specific tire, wheelset and surface combination. You can be comfortable with lower pressures but it will affect your speed and handling when it’s too low. If it’s too high, your rolling resistance may increase and slow you down if you are riding on surfaces that aren’t mostly Class 1 dirt. Likewise, if you are doing a 100 mile or longer ride, you may want to ride a lower pressure to trade-off some speed for more comfort.
There may be a temptation to go with a wider tire if you are a heavier rider and a narrower one if you are lighter. Unless your skills and goals drive you to a wider or narrower tire, I’d work first on dialing in your tire pressure rather than choosing a different tire width.
Components: Recognize that tire type and width can’t make up for the wrong combination of components. A big knob tire isn’t going to get you up a 15% dirt or gravel pitch a whole lot better than a small knob one will if you have a 34-28 gear ratio. And if your brake rotors are undersized for your weight or the kind of pitch you are going down, the size or tread of your tires isn’t likely to help you control your speed any better.
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In upcoming posts, we’ll review the semi-slick, small knob, and big knob tires on the shortlists above. We’ll also provide you our reviews of carbon and alloy gravel wheels.
As always, I welcome your comments below. I also invite you to keep up with new posts and stay connected by filling out the e-mail pop up form or clicking on the Facebook, Twitter, Instagram and RSS buttons on the right at the top of the post.
Enjoy your rides safely, both on the road and gravel!
First published: February 15, 2020
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