I’ve got a question on the areo benefits or lack thereof with the movement to running 50-54mm MTB tires on my gravel bike with wheelsets that violate the rule of 105.
I’m considering upgrading my 31mm OD wheelset to a 40mm OD for running 50-54mm MTB tires on my gravel bike. Since both violate the 105% rule, are there any aerodynamic benefits to the wider rim?
My current wheelset is the Enve 4.5AR- 49mm deep front and 55mm rear with a 25mm internal width and 31mm external width. The wider wheelset I’m looking at is 45mm deep front & back, 40mm outside width and 29mm internal width.
In general, and I’m too lazy at the moment to think through what evidence I want to pull up to strengthen this though, the answer is yes, even in those scenarios.
I upgraded from heavy 2000g 25mm deep stock alu wheels to 1450g 40mm Light Bicycle Falcon Pro on my gravel bike, I can definitely feel the difference in ride feel and a slight bump in speed, but it’s hard to give actual numbers. Strong sidewinds have more effect on the bike, but as I live in a very flat and windy area I’m satisfied with the depth. Another bonus of the upgrade is that these wheels have no spoke holes and are really easy to set up tubeless, even for a first timer like me. Right now I’m running 40mm tires, will go up to 45mm soon.
John Karrasch (@flexfitbyjohn) • Instagram-Fotos und -Videos tested this too and posted the results somewhere here in the forum. As I don’t have instagram, I can’t look for it on his profile but it’s there somewhere. He compared 40mm wide tires and I believe the 2.1 thunder burts on shallow and mid-deep wheels and both tires were faster on the deep wheel in the realm of 4-7W if I remeber correctly.
If that applies to your scenario I can’t tell. If I had to guess I’d say it won’t affect aero drag as much as moving from shallow to deep wheels so it’s probably not worth it.
Dylan Johnson did some aero tests, I seem to recall. It’s on his YT channel or in a Silca video. The number of watts saved was really small and I seem to recall that the specific tire had a lot of influence.
There’s a benefit per Specialized. This video is a few years old, but they showed there was still an advantage in using deep wheels with 42mm tires which clearly violated the “105 rule”. I’d imagine these benefits scale up to today’s wider tires and rims.
Whether that upgrade is worth spending the money is up to you. I’m 100% for wide tires and wheels!!
You didn’t say what your intended use case is but a 50mm tire is going to be much wider than the 40mm of the rims you’re considering, coming in much less than 105%. So max aero will not be achievable. That said I would not be overly concerned unless you are worried about max speed in long flat fire roads in a race scenario where you are worried about a podium spot. A 50mm or wider tire is going to have many benefits in most other aspects of a gravel ride that it’s worth it even if max aero takes a hit.
The “proof” is all over the place. Hunt has a report. Swiss Side has a report. Zipp has a report. Dylan Johnson has a video.
Ren Herse says there’s no aero benefit.
The lowest benefit was from Zipp. “At average race speeds (about 29-36kph), Zipp internal testing found 2-watt savings from aero efficiency gains compared with a peer wheel. The advantage grew to 10 watts or more when speeds exceeded 53kph on descents and other fast sections.”
I’m pretty sure this was on 40mm ish tires.
The biggest benefit is fat internal width for lower tire pressure.
It would seem that as pros racing something like Unbound and the need for an aero edge has bled over into what lesser competitive riders “think” is important. Gravel is not road the dynamics have little in common and what works on pavement (many would argue that aero is not really that necessary for most) definitely isn’t what anybody but the top pros need. Mount the fat tires and go have a great time with all the benefits fat tires give you on dirt.
I’m 100% for wide tires and wheels!!
