OK but now you are conflating two different issues……the claim was that XC tires were the “best” or “fastest” toe for gravel, not whether “wider” tires are faster. I think ther is general consensus at this point that wider is better, but at what point is it “too wide”. Again, you need to look at how a tire may perform across an entire course, not just some sections.
Meh…anecdotal evidence. The fast guys are gonna be fast, regardless. Heck, Keegan won Unbiund in some ridiculously slow Maxxis tires (forget the model name….Reavers?)….his win didn’t mean they were fast, just that they didn’t slow him down enough to cause him to lose. I would argue that the results from Unbound this year only underline my point that there is a trend towards XC tires and people are jumping on it…without really knowing if they actually are faster.
How many different types of MTBs are there? I think it’s okay for there to be several different types of gravel bikes as well… Each one can have a unique purpose, and people will use them slightly differently.
Part of this discussion is sort of like stating that there is only one MTB that’s “the best” when each one might be the best at something in particular.
No, not all gravel bikes need to fit 2.4"s, but some might work well set up that way.
I have a hardtail with 2.4"s and prefer flat bars for terrain that requires that type of tire, but others might prefer drop bars…
Before long I have a feeling that there will be a bike for all of us!
I think the Baum is the inevitable “next phase” for rowdier gravel bikes. It mates a MTB rear end with a gravel front, so the geometry isn’t all wonky and you have to resort to weird stem / HB setups.
Whether that idea becomes the standard for gravel remains to be seen, though. The CR size may continue to be a limiter. 44t is sufficient for many, but not for the top tier guys.
On relatively smooth surfaces, at some speed the aero penalty of fat tires outweighs any crr benefit. You can only make a big toroidal thing like a tire so aero by adding material to the rim, and of course that brings a weight penalty. I’d speculate that even a magical “zero crr” 2.2” tire would not be faster than a modern 28mm at WT race speeds.
I think the point of the move to fatter tires for gravel is that testing crr in real-world conditions is hard, and eveyrone underestimated how much drag comes from rollover vs. factors like aerodynamics and weight. But at some combo of speed and roughness those lines cross. Trackies still run tiny, crazy-high pressure tires.
Tire compound seems to affect measured rolling resistance the most of all the factors (casing, compound, tread, sidewall protection).
The two fastest-rolling compounds for non-road tires (I.e., larger than 35mm and not slick tread) seem to be Continental’s Black Chili and Schwalbe’s Super Ground Addix Speed.
Those compounds are only available on certain sized MTB tires (Schwalbe is 27.5 x 2.1, 29 x 2.1, and maybe 29 x 2.35? Continental is 27.5 x 2.2 and 29 x 2.2 I think?)
So right now, the fastest tires for gravel are XC tires, not because of XC tires, but of the products the tire manufacturers choose to produce.
Separately, note that Challenge’s Pro HTLR seems to roll pretty fast too. But they only have the getaway up to a 45 or 45, and the slick Strada Bianca up to either 40 or 45 as well.
All I wanted to add was that some of this has to do with what the manufacturers are choosing to make right now.
The wind tunnel testing DJ did with Josh Poertner shows this is not true in all cases. The 2.2 Race Kings with 60mm deep rims were faster than every other combination, and had the same aero drag as the 45mm tires. Except the Race Kings have less crr.
So in this test case the larger tire had both a crr and aerodynamic benefit. Which produced another test result in that DJ had his best finish at Unbound 200. Not in placing terms (he got 9th in 2018 0:55 back) but in both overall time and relative time to the winner - 10th 0:05 back.
Ignoring that you originally offered evidence of someone else’s anecdote (DJ didn’t prefer his 2.2 Race Kings at BWR because he was dropped on the pavement), the fact that many racers are riding faster on MTB tires isn’t anecdotal evidence. I’m not saying I’m faster on MTB tires. We can look at race results and see if X racers are on XC tires and their overall times are faster than when they were on gravel tires, this is strong evidence to indicate those XC tires are faster than gravel tires, at this time.
This would be a review of the available data from professional racing, not an anecdote. There were 4 racers in the top 10 and unbound on XC tires. 3 out of the 4 had raced Unbound previously and each had a significantly better time, and relative result, than they had in the past - when they were riding gravel tires.
As I mentioned earlier, the body of evidence that certain XC tires are faster than most, if not all, gravel tires, is as large and robust as the body of evidence that certain 28-32mm road tires are faster than most if not all 23-25mm tires. We can pick and choose what we believe and what we feel is applicable but there is enough evidence to make a decision.
Torsten Frank’s model and testing provides stronger evidence than anything I’ve ever seen for the current road tire understanding. Of course, Bicycle Rolling Resistance is an accepted laboratory testing suite as well.
The term is hysteresis. (You can see it here starting at 5:04, inside a car tire)
The model that supports wider tires on rougher surfaces cannot have an arbitrary limit. A 2.2 Race King may be significantly slower than a 28 GP5000 on smooth pavement, but that’s not the comparison. The comparison is the 2.2 Race King v. the above average gravel tire. In this comparison it’s not clear, and much data seems to indicate the Race King will be at least as fast on pavement and much faster on gravel and unpaved surfaces.
Exactly, this really comes down to market segmentation. I’ve got a Giant Revolt that’s one of my favorite bikes ever. It fits me perfectly, takes up to 2.1" tires, and is just an amazingly all around capable bike. Easily the most versatile bike I’ve ever owned.
That said, I still want something that’ll take a big-ass mountain bike tire for some of the rowdier, chunkier gravel rides where I live in Vermont. There’s a lot of really fun Class IV riding (basically 90’s mountain biking), that you can connect with nice stretches of gravel. I can do something like a 40-50 mile ride with as many miles of Class IV as I want right out of my front door, and I wouldn’t want to do it on a hardtail MTB because the vast majority of it is still on gravel and dirt roads, with the occasional stretch of pavement.
So there are clearly two different market segments here: one that’s more of an all-road style that could max out at 45-50c tires with closer to conventional road geometry that could be fast on pretty much any road you want throw it, be it paved, dirt, or fire road, and the other than can take even fatter tires (2.2 - 2.4 XC tires) and slacker geometry, that’s fast enough on pavement but also totally capable on some real off-road riding.
I think Trek tried to do this with their new Checkpoint and Checkmate, but things are moving so quickly they’re both under-tired for their targeted purpose. If the Checkpoint could take 2.25" or bigger, and the Checkmate could take 50c, they’d be perfect. Although it really does seem like over the long haul even pure race bikes will need to be able to take up to 2.2" tires, so maybe it’ll be big tires more with road geometry or huge with slacker geo? I’m glad I’m not the one who has to design these things.
I’d just push the industry to make bigger Boost chanrings or to make them all compatible with each other. You’re gaining space where it’s most important this way – at the BB.
You can only do that if you isolate the result from all other factors except the tires. At best, you currently have correlation, not causation. Which goes back to my original point - we don’t really have any hard testing data. We have some flawed conclusions through extrapolation of limited data.
And just to be clear - I am not arguing against wider tires. I’m simply disputing the notion that it is now a given conclusion that XC tires are the fastest option. They may well be, but saying “oh, these guys ride them so they are therefore the fastest option” is not conclusive proof.
Addix Speed is the rubber compound, Super Race/Super Ground/Etc are the construction types.
Otherwise, this model doesn’t seem to be true. Super Race and Super Ground tires use the same rubber compound but different casing construction and the Super Race tires consistently test 10-20% slower than Super Ground.
The comparison tests BRR has performed seem to indicate each part of the tire type and construction is important with perhaps overall thickness the most important. Most likely because constructing a very thin tire requires high TPI with thin threads.
The Gravel King test where the thicker tire tests relatively slower than the thinner tires seems to be a good contrast to the GP5000 test where the tires are much closer in thickness and test much closer in crr.
I’ll be honest and say I don’t know enough about Boost spacing to have a take on it. It came about after my time in the industry and well after I stopped riding MTB’s. Living in the Chicago area will do that.
The biggest challenge would simply be getting the industry to move gravel bikes to another frame spec “standard”. Or maybe Boost is just used for rowdier frame designs…probably a lot of ways to peel that onion.
We do have hard data; there are R Chung tests in the thread I linked, there are laboratory grade tests from BRR, there is real life data from professional racers. There is wind tunnel data from Silca. Torsten Frank has created a comprehensive model that can be applied to tires and courses to help determine where an XC tire would probably be a faster choice, or not.
I say again: On relatively smooth surfaces, at some speed the aero penalty of fat tires outweighs any crr benefit. The test they did didn’t find that speed (32kph is pretty slow relative to WT-level racing, and they didn’t test a real road setup.)
Nothing against fatter tires for gravel, but you seem to be suggesting the world tour would benefit from running 2.2” tires, and I don’t think that’s correct.
This assumption is not supported by available evidence. The fluid model of aerodynamics would not indicate a wider body would create more aerodynamic drag relative to it’s drag at lower speeds, purely because of it’s width. If anything, the Silca wind tunnel test would indicate that the Race King + 60mm rim combo would be faster at any bicycle-capable speed. We know that crr increases as speed increases and increases relative to the initial crr. So the above average gravel tire would have a higher increase in crr, as well as higher relative aerodynamic drag compared to the fastest XC tires.
I am not making this claim either, as I addressed below:
