Direction of gravel bikes

[crandallGA]

@Teddy_Focaccia

On relatively smooth surfaces, at some speed the aero penalty of fat tires outweighs any crr benefit.

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.

@Power13

@crandallGA

Sure, but he was back to trumpeting Thunder Burts and Race Kings in the next episode or the one after. And anyway, prior to his adoption of MTB tires he repeatedly said he’d never run anything smaller than 47mm pathfinder pros on any course including BWR

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.

@crandallGA

One could also take the stance that we are seeing significant real life iterating and testing by racers this year, at events. There were a lot of XC tires in the top 25 at Unbound this year, for example.

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.

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.

This thread, which you have many posts in as well, contains many tests which show results in favor of specific XC tires: Is a MTB tire the fastest and best tire for Gravel racing?

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.

@Teddy_Focaccia

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.

The term is hysteresis. (You can see it here starting at 5:04, inside a car tire)

Roughness is commonly known as impedance: https://silca.cc/blogs/silca/part-4b-rolling-resistance-and-impedance

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.