Originally Posted by
msu2001la
It's more complicated than that, and to be clear I'm not a tech expert, I'm just some random dude on the internet that listens to a bunch of bike tech podcasts, so what I'm saying may not be 100% correct.
Here is Enve's response to this question:
It seems to be an industry wide agreement that gravel specific wheels (rims) should be quite shallow. As the American gravel scene seems to be the main motor in gravel R&D, with popular events like DK and others, why have the industry and ENVE in particular, decided that the aero benefit of a taller rim + a well-fitting tire, is less important on gravel, even when the ride is 200km + long?
Would love to hear your thoughts on this, both for your own company and others. Shout out from Norway! -JD
ENVE: Sure, and a great question. ENVE has been looking at this for many years at this point and we asked ourselves the question of “aerodynamics in gravel” back in 2014 in the development leading up to the launch of the SES AR Series of wheels. What we learned is that basically once the tire exceeds 32mm and gains any side knobs/tread, you lose the majority of aerodynamic benefits. To make an aero rim for a larger tire is possible but it starts to get crazy wide and therefore exceedingly heavy, and again, this is assuming there is little to no tread on your tire.
https://bikerumor.com/2020/02/07/aas...o-dirty-kanza/
Josh Poertner of Silca (former tech director at Zipp) has also talked about this topic on his podcast. I don't have a link handy, but I recall him discussing tests that showed gravel sized tires significantly reduced aero gains compared to road tires on the same wheels, and when considering that gravel riding is usually at a slower speed than road, the aero gains are marginalized to the point where they are barely measurable.
I'm sure there are
some aero gains regardless of tire size, I just wouldn't make this a priority when shopping for a gravel wheelset.
Thanks. It is indeed complicated and requires very specific language to be made clear. For example, Enve say the majority of bennies are lost when tire sizes are in excess of 32c *and gain* side knobs/tread, creating ambiguity around something like a file tread 35c. They go on to say that its possible to make an aero rim for big tires with little-to-no tread, but requires a really wide rim. Given gains are usually incremental ather than all or nothing (which is why we say “optimized”), those comments suggests that there may be intermediate, sub-optimal steps where gains are present but not maximized. Does that describe a 35c file tread on a 25mm IW rim compared to that same tire on a 19mm IW rim? Are they factoring in speed, like Poertner is? They must, right, because aero doesn’t happen in a vacuum, but that Enve comment doesn’t mention speed at all.
I don’t know the answers, of course and agree with your closing point about not prioritizing aero for gravel. For myself, I don’t sweat aero on gravel because I don’t sustain the kinds of speeds where aero gains are typically felt and measured, and because I know I’d see way bigger gains dropping 20lbs of body fat than I would dropping 20g of wheel drag!