Fast gravel build: do 45mm wheels make sense for aero + climbing?

[Ada]

Yes, that's the one. How did you get it for such a low price? Did you use some hidden coupon?

[Leo.D]

the rough rule of thumb that's held up across a few wind tunnel tests: for a given rim, the aero benefit starts evaporating once your mounted tire measures more than ~105% of the rim's external width. So a 38mm external rim with a 40mm tire (105% match) will perform noticeably better than that same rim with a 45mm tire (118% — the airflow detaches at the tire-rim junction).

[hubba]

The rule of 105 was that the rim needed to be about 105% of the tire for it to re-attach the airflow. Not the other way around. But with modern rim profiles it's not so true anymore but still a good starting point. And if a rim is deep enough even if it's a lot narrower than tire it will still help even with wide gravel tires.

[Alancik123]

S,o what you're guys saying, I need a rim with 50mm external to ride 55mm tyres at maximum aero efficency?? 

[lidation]

I just think that the 105% rule is just marketing BS for average amateurs who don't race.  Look at our bodies, even the fittest person have a much larger cross-section than the wheel/tire. Plus, with any hills, the climb speed won't matter in terms of aerodynamics.  On the downhill, gravity is helping so aero is playing a secondary factor anyway.

[hubba]

Yeah the savings are tiny but still there. Having a tire few mm wider than the rim vs few mm more narrow is only a few watts. Aero socks might save you more watts than that. But it's also a wheel stability thing, a well matching rim and tire behaves better in the crosswinds.