BONTRAGER RSL 37 – LIGHT AND NIMBLE CLIMBER

The Bontrager Aeolus RSL 37 disc wheelset is a lot of fun to ride. Scooting around with it on my bike brings me back to how I remember riding as a kid. You go left, right, up, down, and straight ahead without giving it much thought. You just go where you want without holding back.

These wheels are very light and yet stiff enough without being overly so. That’s probably the combination that made me feel so agile and free riding the RSL 37 in almost every situation. I climbed my most challenging steep, long “hill repeats” with comparative ease and did a few 50-mile, rolling rides on days after my hardest interval training of the week and felt totally relaxed and unfatigued during and at the end of those rides.

I’ll admit, I felt as though something was out of whack when I rode the RSL the first time. It was early spring with a lot of crosswinds and I was coming off too many stay-at-home-mandated Zwift rides. Early season legs, wind in my face or from the side, and bib tights can make me feel a bit slow.

With the Bontrager RSL 37 disc, I cut through all of that. I immediately felt light, almost too light and I worried I’d get pushed around in the winds. Didn’t happen. The freehub engaged on command and the wheels accelerated as quickly as I wanted and far faster than expected to the point where I had to shift down the cassette sooner than I normally do to keep up my speed.

At 37mm, the RSL rims are deeper than climbing wheels have traditionally been but about the same as the benchmark for that category set by the ENVE SES 3.4 (38mm front, 42mm rear) a few years ago. They’re nearly as deep as where carbon all-arounders have historically started (40mm) but no longer where they currently range (45-50mm).

For me, the Bontrager Aeolus RSL 37 disc is a climbing wheel. It climbs as well as any I’ve reviewed from any brand. Bontrager must think so too are they are retiring the 28mm deep Aeolus XXX 2 disc wheelset in its lineup.

Bontrager Aeolus RSL 37 disc

At the same time, Bontrager will continue to make the 47mm deep all-around Aeolus XXX 4. Makes sense as I found the RSL 37 doesn’t sustain your momentum the way I’ve experienced with a deeper and slightly wider 45mm-50mm all-around wheelset.

The tires I rode these wheels with – 25C Bontrager R3 Hard-Case Lite and Continental Grand Prix 5000 tube-type tires and the tubeless Continental Grand Prix 5000 TL – measured within a half mm of the RSL’s 27.5mm outside width. That’s a smaller difference than the Rule of 105 calls for (rim at least 5% wider than the tire so the air to re-attaches as it moves between tire and rim) though Bontrager (and others) don’t strictly adhere to that rule of thumb in their rim design for aero optimization.

As far as wheelset weight goes, I normally don’t make much mention of it because most of us can’t tell the difference between wheels weighing within 100-150 grams of each other that is typical of what you find from wheels in the same category. But since I’m reviewing a climbing wheelset and there may be a few of you weight weenies reading along, and principally because Bontrager gives you a few options that do make a difference, I’ll go through it here.

If you want to use tube-type tires, Bontrager provides you a cloth-like rim strap along with the wheels that you can easily install by stretching it over the rim wall and snapping into the rim bed. Per my scale, these weigh 22 grams per wheel.

If you prefer tubeless tires, the cloth strips won’t hold the air or sealant. Instead, Bontrager provides you plastic rim strip inserts to go into the rim bed. Those need a bit of experience to install without cracking or breaking or getting them just enough off-center to mess up the bead lock alignment. These add 62 grams to each rim, an unwarranted penalty if you care about climbing wheel weight.

The best solution is one they don’t provide with the wheels but have approved and I found works well. Good old 25mm rim tape. One wrap or two. I tried both and each sealed up successfully. The tape weighs 5-10 grams per wheel depending on the kind you use and the number of wraps.

It seems odd that Bontrager wouldn’t include the lightest weight solution with their lightest weight wheels but, no matter how you set it up, these wheels are still going to be light. I set them up initially for tubed-tire riding with the cloth-like rim straps (1376g) and later pulled them out and taped the rims (1352g not including the valves) and mounted tubeless tires. With the 62g per wheel tubeless inserts, they’d weigh-in around 1450 grams.

At 1352g for tubed or tubeless tires, it’s an easy choice.

Enough about climbing weight already! Going downhill and cornering at speed on the RSL 37 is a confident blast. And you don’t have to worry about crosswinds riding exposed roads. Simple. Fun and done.

As to comfort, these Bontragers aren’t any more or less so than most set up with tubes and the added pressure they require even with the RSL’s 21mm inside width. As with any other wheelset this wide, you could safely lower your 25C tire pressure 5psi below the suggested level, use tubeless tires and drop it 10psi or mount up 28C tires. Wider tires would add a good deal more weight and further diminish your aero performance when riding above 18-20mph/29-32kph.

DT Swiss 240 EXP hubs on the Bontrager Aeolus RSL 37These wheels get an attractive glossy finish with black stealth logos. Also contributing to a skinny look and the low weight are the new DT Swiss 240 EXP hubs used on this wheelset. They roll a bit smoother than the last generation DT 240s but their freehubs are a bit louder even after I regreased them. They’re not nearly as loud as Chris King, Industry Nine or other hubs seeking attention and DT Swiss hubs with a very similar design to the EXP have historically required next to no maintenance.

All in, the Bontrager RSL 37 does a joyful job of its main purpose in life – climbing – and is a wheelset you can feel quite spry riding any day on rolling routes. Priced at $2400, you can order them direct from Bontrager using this link to the Aeolus RSL 37 disc wheelset page on their parent Trek’s website.

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You can compare my performance evaluation of the Bontrager RSL 37 with other lightweight road disc wheelsets in this review.

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18 comments

  • Are these specifically designed to be placed on trek bicycles or will they function well on other carbon arrow type frames? Are there any sizing or dimensional issues associated with fitting these wheels to a non-trek bike?

  • Thanks for the review. Really interesting insight into the new wheels. Have been looking for a climbing disc wheel and wanted to get your view on the RLS 37 vs the DT Swiss mon chasseral. Would you recommend any other better climbing wheels

    • Tariq, Haven’t ridden the new Mon Chasseral. It’s relatively narrow and shallow compared to the RSL 37. I’ve also reviewed and would put the ENVE 3.4 disc and 3.4 AR disc on par with the RSL. They each offer something different that may align with what you are looking for. Steve

      • Thanks Steve. I have a set of Enve 4.5AR and was looking for a set of climbing wheels as I venture more into climbing in the Alps with a few sportives with long alpine climbs.

        I wondered whether the Enve 3.4 would be too similar to the 4.5 (albeit slightly lighter and shallower).

        So ideally a lighter, stiff, lower profile, tubeless, disc wheel which I can use on the long climbs. Hence why I was thinking of the RSL 37, DT Swiss or even the Lightweight (most likely outside of my budget).

        Would appreciate your thoughts

        • Tariq, Would choose between the 3.4 disc an RSL 37. They ride very similarly and both are quite different than the 4.5 AR. The primary differences are in the hubs – Enve offering several options including Chris King and their own Mavic-made, DT 240 like hub and RSL having the new DT 240 EXP hub. the RSL is about 75 grams lighter but the rim weights on the two are very similar. If you want a little variety, perhaps go with the Bontrager RSL 37 which has a very nice glossy rim finish vs. the matt finish of the ENVE that you are used to. 1st world problem! Steve

  • Super easy to mount tubeless Schwalbe Pro Ones on the RLS 37. Just managed to do it by hand in about 2 minutes per wheel, a personal record by far for tubeless. 4.5 AR are way at the other end of that spectrum — have required lubrication, levers, bead jacks, and hours of struggling. My fingers do not like them at all. My speculation is that this is in part because the ARs are hookless so the fit needs to be a lot tighter.

  • Steve, in your article you mention that using Rim tape for tubeless set is an approved method from Bontrager. Is this documented anywhere? Or did you have direct chat with Bontrager?

    • Tariq, Yes, I exchanged messages with Bontrager tech about this. Taping takes some skill (not much IMO) and that’s why they don’t promote it. On other wheelsets (e.g. ENVE) it’s the only way to go. An enthusiast should know (or learn) how to do it. Steve

  • Steve, which 25 mm tape did you use to tape the rims for tubeless operation? Stans/DT Swiss/something else? Also, with a taped rim, did you use the tubeless valves that came with the wheels or did you use different valves? Appreciate your reply.

    • Sid, Yes, I used the Stans (available here) valves that came with the wheels but, installed well, I’d think any good 25mm tape and appropriate length valves would do. Steve

  • Hello Steve,
    which wheelset is stiffer, the RSL 37 or XXX 4? Asking because I wonder if stiffness has been sacrificed in the pursuit for low weight and I as a sprinter need stiffness more than anything. Bontrager claims the wheelset performs comparably in the aero department, so if I could get a wheelset that is just as stiff as the XXX 4 whilst weighing less, than that would be great. However I don’t think that’s the case, is it?

    • Mike, I wouldn’t say I noticed a big stiffness difference between the two. The power transfer is very good in both. With the right tires, I’d say the XXX 4 is more aero though. That will help you more in sprints. If you haven’t read it, here’s my review of the XXX 4. Steve

  • i have the RSL 37 on my Mason Resolution and set up tubeless with DT swiss tape and Continental GP5000 TL 28mm and I can say its was the easiest race tire tubed or tubeless i ever mount. bigger volume gravel and MTB is always easy. last year i put some ordinary GP5000 on Bontrager XXX6 and it was a pain!

    best Wheels i have Ride, using them on brevet full serie and a 1200K brevet this summer, fast smooth and no problem with side winds, imortant when riding very long distance

  • I have the XXX2s on my 2019 Madone. I’m 5’ 3 1/2”, 115lbs. I don’t get as much speed advantage from the XXX 2s as I would like and they seem slow to spin up. I’m considering the RSL 37s. It sounds like cross winds would not be an issue but you mentioned they don’t sustain momentum as much well as a deeper wheel set. Any thoughts on how they would compare to the shallower XXX 2s?
    Thanks!

    • AJ, I found them more responsive and a better climber than the XXX 2s. Apparently Bontrager did as well as the RSL 37 has now replaced the XXX 2. Bontrager has also introduced a 25C R3 tire to replace the 26C R3. We haven’t finished testing it yet but I did measure it narrower than the 26C (duh) but also narrower than the other 25Cs I’ve measured and reviewed. That would help the aero speed of the RSL 37 a bit but it’s still shallower than most wheels you’d look for if you want to go fast on the flats. But, it’s a climbing wheel and as such, one of the best I’ve tested. Steve

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