Some random thoughts: I’ve tried the two wheelsets thing and while it sounds great in theory, it ends up being more trouble than its worth. Swapping between disc brake rotors for each wheelset is always a little fiddly and time-consuming, and multiple cassettes aren’t cheap. Especially for mullet setups where a 10-52 X01 goes for $415 MSRP and doesn’t get discounted much below $325. So you spend a bunch of money on a wheelset you’ll end up swapping once or twice a year.
I’m also a bit of an edge case in that any bike I ride needs to be able to handle a mile of (sometimes very) chunky gravel in either direction before I hit pavement, and I have no interest in owning a bike I can’t ride out my front door. I’ve tried up to 650Bx50 and up to 700x50c, and the larger wheels do ride noticeably better over the heavy washboard we get, particularly in the early spring when it feels like you’re riding over a huge succession of speed bumps.
I’m currently on 700x48c Thunderos, which I’m really happy with, but would still like a little more width. I’ll try 29x2.1 Thunder Burts at some point and I’m constantly resisting the urge for something like a Lauf Seigla where I could put 2.2s on it and call it done. Basically, there are always, always trade-offs and you’re going to feel lacking somewhere. The extra comfort and traction are well worth the tiny trade-off in speed for me, especially considering I probably spend less than 30% of my time on pavement.
All that said, I would love a quiver-killer and there are a few bikes out there that are close. Show me something like the Lauf Seigla Rigid with a lower BB (65mm on the Lauf vs 77mm on the Ari Shafer or 81mm on the Giant Revolt) that doesn’t cost an absurd amount of money and I’ll start throwing money at you. The ones that are closest for me are the Giant Revolt (which I currently own) with a little more tire clearance and slightly slacker geometry, the Ari Shafer with more tire clearance, or the Lauf Seigla with a lower BB. I’m sure there are others I’m missing, too.
Several reasons this won’t work… First off, by shortening the a-c length by a full 77mm, you’re steepening the head tube angle to 73 degrees(seat tube to ~78d). You’re also dropping the bottom bracket by a huge amount(~30mm, putting your pedal about 90mm above the ground assuming 165mm cranks and 2.25" tires). You’re also then mixing boost and non boost spacing for your wheels, which is a major pita. And lastly, the fork you mentioned doesn’t even clear a 2.35" tire(I have this fork). So, while there are options for boost spaced shorter forks(Curve Seek 430mm), there is a lot more to think about(see the Drop Bar MTB thread for my short fork Epic build).
Separately, I know not everyone is concerned with Q-factor, but to gain tire clearance, something has to give. So while MTB’s have been able to progress forward on adding tire clearance, you reach a point where the chain stays/yoke can only get so thin due to brake hoses and cable routing(or ditch one of those, see Siegla). There’s no cheat code where a 57mm tire, with 4mm clearance on each side, plus 10mm chain stay on each side can suddenly mate up to a crankset/bb with a 73mm width and not run into issues with chainrings. So sure, I suppose you could just go the way of the fat-bike and increase the spindle length and slap two chainrings on, but that certainly won’t be ideal. The other option is to widen chainline up front, still using a standard spindle, but then you’re talking about going super-boost out back to maintain any semblance of chainline.
In terms of geometry, yes the HTA is the only thing I’d be skeptical of, but I don’t think the BB drop or STA would really be an issue. A setback seatpost should be more than enough for most people looking for this type of build in my opinion.
Keep in mind that with this type of bike, the point is to run bigger tires so the overall BB height isn’t going to be super low with a 2.4" tire. As mentioned earlier, the Revolt has 81mm of BB drop and that’s acceptable when running 40mm tires. I’d be curious to see what the BB height would be for this build.
Regarding the chainline, this is something Salsa is already doing, so I don’t imagine there are any issues there. They ship with a Boost 46/30.
It also drops to BB height to 268ish. That’s low, to me. It puts the bottom of the pedal around 70mm from the ground. Low enough to be a problem on gravel roads with embedded rocks and some washboard - to say nothing of riding singletrack with roots, rocks, and grade reversals.
The trail gets relatively low as well, drops to the mid-50s. Stock is mid-80s.
As I said earlier with dropbar hardtail conversion, I don’t think decreasing fork length by 77mm and all the changes can just be hand-waved away. Either geometry matters or it doesn’t.
Maybe the Adventure fork isn’t the right option, it’s just the first one I looked at.
I do think a slightly shorter A2C fork on a Cutthroat could work really well (maybe in the 460 range).
I’m not building one up, but the problems around tire clearance and gearing is pretty much solved with that bike in my opinion. If the stack & BB was a little lower I think it would be great for gravel racing in some cases rather than riding like a tourer.
That sounds like a chicken-and-egg problem. Gravel bikes are taking over and if more came with 650b wheels, then bike shops would stock the appropriate gear.
What do you mean? Are you talking about mountain bikes?
(I’m not trying to argue, I honestly have no idea who you are referring to.)
But is that something they have heard or actual truth? Not too long ago, roadies thought 25 mm tires pumped up to 80+ psi are faster and now TdF winners are riding 30+ mm tires on stages.
I reckon Salsa has more leeway here as the Cutthroat is markedly more relaxed than e. g. the 3T Exploro Ultra or the Exploro Italia. To my understanding, if you shorten the wheelbase, you cram everything in the back closer together, which leads to tire width limitations.
This is not a ding against the Cutthroat, just saying that these bikes will likely ride very differently. (I have only ever ridden the first-gen 3T Exploro, in the wrong size and only for around 15 minutes.) On the spectrum of bikes with road bikes on one end and XC mountain bikes on the other, issues of tire clearance are solved much more easily if you start closer to the XC MTB side of the gravel bike spectrum.
Regarding the cassette… if you are in the U.S. keep an eye on Bike Closet. They have the XO1 cassette for $279. I picked up a XX1 rainbow cassette (10-50) last year for $220. Still not cheap but better than MSRP for sure.
And can you clarify why you mean by swapping between disc brake rotors? Why not have dedicated rotors for each set?
Oh, I have rotors on both sets. It just never lines up quite perfectly enough after a wheel swap, so it takes a little bit of fiddling for squeal-free braking. I could probably figure it out with spacers and such but haven’t been sufficiently motivated.
650b and gravel have been close before even the beginning of the named market segment. The OPEN UP came out in 2015 with an emphasis on 650b compatibility (with one of the leading options for speed and racing being the Thunder Burt based off BRR testing - wow how times change!), Cannondale had the 650b Slate, Diamondback had the 650b Haanjo EXP. When Road Plus came out in 2016 there was a big push to get the wheelsize on OEM machines but it didn’t create a large enough foothold in the LBS market or the general enthusiast base.
Years later the situation has improved but overall 650b is still niche and almost always a compensation and not a positive choice.
Jan Heine was biggest advocate of 650b and his general sentiment until recently has lacked embrace of the modern gravel market. Most of his current promotion is around 700c or 26" wheels, with 650b left without much exposure.
Rollover is both. What people have heard, and the truth. The energy lost to bumps and obstacles increases significantly as the wheelsize becomes smaller. Even more if the tire size stays the same. This was effectively hashed out during the years long change in the MTB world from 26" to 29ers with a short step back to 27.5" that faded away quickly.
Remember, not too long ago, there essentially weren’t any 30mm+ tires that were as fast as the 25mm tires of the time. They thought what they thought because that’s what their testing showed because larger tires were made differently than narrower tires. What contemporaneous 28-30mm tire would you give Vincenzo Nibali in 2014 that were as fast as the modern 2024 versions of the GP5K TR or the Vittoria Corsa Pro? There weren’t any, the 28-30mm tires in 2014 were all significantly slower relative to how they are now.
The manufacturers had to develop and implement R&D that was happening. World Tour road racing stepped into bigger tires slowly. 23-25 then 25-28 and now 28-30+. It took tubeless and a completely different way of constructing tires for wider tires to overtake narrower tubulars.
I think most people are effectively able to judge if 650b with XC tires is a cost or benefit to their style of gravel riding. If a popular personality were to get behind 650b as a means to increase compatibility with XC tires and road gearing that may boost the popularity beyond the previous highwater mark and provide better segmentation to the market.
The difference between the two bikes is way more significant than between my aero road bike and the endurance road bike it replaced.
Salsa had more leeway to create a frame that accepts wide tires than if you insisted the gravel bike rides similarly to a road bike. Again, not dinging Salsa, I just think it is a bike for a very different audience.
I’m a huge fan of the work of Gerard Vroomen. The 3T Exploro is literally the sportier brother of the Open UP (he designed both bikes). His bikes are very future-looking and he has a good track record. (FWIW, I own a 3T Strada after lusting after it ever since I saw the initial reviews and especially after I had a loaner. Love that bike to bits.)
Notably, the design brief of both bikes is a bit different, namely you should have one do-it-all frame where you swap wheels to adapt to different riding conditions. The clearance seems to match wheel diameters so that the bike geometry and handling characteristics are roughly the same. Maybe this isn’t as desirable a feature in the eyes of customers, I don’t know.
For mountain bikes, yes, you are correct. But how much does that matter for gravel bikes that see less challenging terrain? I may be wrong, although I’m not convinced that this is an issue for gravel bikes on most terrain.
Bigger wheels also have trade-offs, e. g. you have to increase the wheelbase and/or slacken the head angle to reduce/eliminate toe overlap. This, in turn, makes the bike feel less nimble.
Improvements of rubber compounds and other design features apply to all tire sizes equally. Ten years ago, most road bikes came with disc brakes and they wouldn’t even accept anything wider than 28 mm.
How? How many are able to ride comparable bikes with different wheel sizes back-to-back? (I’d like to do that just to educate myself.)
That’s the question, if the course is such that rollover doesn’t matter, then it’s likely that the additional tire clearance benefit of 650b doesn’t matter either. I think rollover, and rotational inertia; are important considerations, even on smooth pavement and have found smaller wheels are slower, but with significant overlap. We don’t need to reconstruct the same arguments from 20 years ago from the ground up, I’ll see if I can find the math and models from back then.
The improvements in tire construction and design haven’t been applied equally. There are major manufacturers who are still using single compound rubber, for example. The main issue is that gravel tires are not generally built around speed, or to put it another way, there are not enough gravel tires built around speed.
Everyone looks at the Thunder Burt and Race King as really fast XC tires, they both prioritize low rolling resistance over other characteristics. Durability is lacking, grip is less than other tires that test slower - every tire needn’t follow their design, but it’s important to have options. Maybe due to the gravel tire being born out of the Midwest where durability was more important has colored the design even today.
It’s entirely possible in 5 years there would be (a few) ~42mm gravel tires that test at 10-12w at BRR and this whole discussion is overtaken by events. The tire that was the go-to road racing tire 10 years ago - the GP4000 S II is now ranked around 70th out of 147 tires on BRR. The current model, the GP5000 TL - in the same size - has 30% crr.
Right now the trend is that a bigger tire has no tradeoffs, but that’s not true. If there’s a course that’s relatively smooth with 30-40% pavement I don’t want to ride XC tires, they’re not a benefit, and they wouldn’t be a benefit to most riders. A back-to-back comparison isn’t helpful anyway, most riders cannot effectively perform statistical trials and are left with what “feels better” which is what is under discussion anyway. If we go with what feels better, people have chosen against 650b/27.5 multiple times because it doesn’t feel as good as 700c/29".
So now we can see clearly that changing wheelsize from 700c to 650b requires at least 7% more power to achieve the same speed. Of course, the marginal power required when changing from 650b to 26" is almost 0 - which would probably require a reevaluation of the test model, or the conditions during the test.
Let’s see this again:
700c wheels require an additional 56 watts to ride over the rumble strips at speed, compared to smooth pavement.
650b wheels require an additional 68 watts to ride over the rumble strips at speed, compared to smooth pavement.
So we do know one thing now, the “myth” was not busted. If anything, this article confirms that 700c is faster than 650b, when power-tested riding over rumble strips compared to the same over smooth pavement.
650b is actually the worst performer, which would seem to track the reality of the situation given that the author of the article appears to prefer 26" for his gravel racing, and individual time-trial events held over gravel.
That’s very selective reading of the data: on smooth pavement the graphs that you posted show that you need 10 W less on the 650b wheels (229 W vs. 239 W). On whatever a “rumble strip” is, 650b wheels need 2 W more (297 W vs. 295 W). The difference you focus on is larger, because 650b wheels are more efficient on pavement. The data you posted at least does not seem as clear cut as people make it out to be. I’d also point out that a 2 W difference might be within the margin of error whereas 10 W is likely not. (If we assume 1 %, the error would be about 3 W for the rumble strip and a little over 2 W for the smooth pavement. Scientifically speaking, the two figures for the rumble strip would then be identical within the margin of error.)
Taking the data at face value, it seems that 650b wheels are faster on smoother surfaces and about as fast (within the margin of error) on rougher surfaces. That’d suggest 650b wheels should be faster in a variety of situations.
It is kinda easy to cherry pick data to support your narrative and then work backwards.
That’s jumping to conclusions in my mind. In my experience, rollover is particularly important for roots and other obstacles that you need to navigate on a mountain bike. I’m not sure the same demands are placed on most gravel bikes — or at least, the expectation of performance on trails is lower. There are plenty of reasons to go for larger volume tires, e. g. increased comfort over some terrain. Where I live we have some cobbles that shake me up real good on my road bike, unless I give it the beans and “glide” over them.
The data you posted does not seem to support this, the 650b wheel was more efficient on smooth pavement.
Just to emphasize: I’m not arguing the opposite, I’m saying that I haven’t seen data that clearly shows this for gravel bikes specifically. It just seems apocryphal at the moment.
I’d say that for gravel tires (and offroad tires in general), speed is not the only concern. Increased puncture protection frequently comes at the cost of added weight, less suppleness and increased rolling resistance. Balancing all important criteria is important in most situations, and rolling resistance is not the only variable to consider.
Even for road bike tires this is true to some extent. Some tires have less puncture protection than others, which comes at a price. The price may be acceptable for a race, but not when you are out and about in the boonies.
The whole issue is that the experimental trial is not robust. If the difference between wheels (actually tires in this case) is so great for the control, the test is not constructed to isolate the actual variable under discussion - wheelsize. This is not a robust test, as my data manipulation has shown.
The control needs to be done with tires that require the same wattage at the same speed on the control surface. Only then can the experimental surface be tested.
If the trial was robust, a much more relevant headline would be the 10w savings using 650b wheels over 700c - which would be a shocking result. But it’s not, and such wheel size based savings don’t exist.
Yes! This is the problem with the article.
We do not know anything about the wheelsize differences, because the tires are shown to test different in the control. Laboratory roller testing (at BRR) has shown that small differences in tire construction will overrule everything else, which is also shown here in outside, real world testing.
There’s no explanation that the different tires were confirmed to share the same construction, only that they were the same model. It’s not reliable to assume each wheelsize’s tire is constructed the same way or had the same rubber compound. Especially in light of the BRR tire comparison tests that often show results contradictory to assumption.
It’s also important not to look at this test in isolation. Of all the tire testing Bicycle Quarterly has performed over the years I don’t think they’ve ever had a result where their fastest 650b tires - EL Baby Shoe Pass, Switch Back Hill - tested 4-5% faster than comparable 700c tires. Even the 700c EL Snoqualmie Pass tested about the same as the 650b EL Baby Shoe Pass, and IIRC the dual purpose knobbies were the same way. (All on pavement)
So if this test shows the 650b Schwalbe Marathon testing 5% faster than the 700c version on pavement, the tire construction differences or other issue is not accounted for correctly.
