chaadster

Wow, 60tpi, 310g tires are your favorite 25s?!?

Well there you go; that's a pretty good indicator this thread has jumped the shark.

chaadster

Perhaps not a guarantee in the legal sense, but both Zipp and Flo, for example, designed their rims for aerodynamic performance with 23s based on some pretty specific analyses and wind tunnel tests, so when Zipp's Josh Poertner says, "In general, our wheels are optimized around 23mm tires, which means that 21mm tires usually run about equal, maybe a fraction of a watt faster, but don’t change the behavior of the wheel. Moving to a 25mm adds drag, but can also change the stall behavior of the wheel. And by the time you are at 27mm, you have something that behaves quite differently" (Tech FAQ: Again, bigger tires roll faster! - VeloNews.com), I believe him.

But at the same time, there's no guarantee that any given 23 is more aero than any other 23 on any given rim, either. It depends, primarily, on the sidewall design and the rim/tire interface.

Dunbar

From what I've seen in the test data the difference is around 1-2w at 30mph even for wheels optimized for 23mm tires. When you consider how much power it takes to do 30mph 1-2w doesn't seem all that significant. Most manufacturers post drag data at various yaw angles but fail to mention that yaw angles go down as speed goes up. At 30mph 80% of yaw angles encountered are 10 degrees or less.

chaadster

I was addressing achoo's suggestion that a 23 wouldn't be more aero than a 25 on a given rim, which is not true, and I was not addressing the issue of significance of the aero advantage, which is a whole other can of worms. Suggesting aero benefits are insignificant, especially without outlining very specific terms for the evaluation, is pointless.

I say it's pointless first because obviously aero will mean nothing for recreational rider who's content to noodle around well below their maximum output and at speeds in the teens, and so there's no point in having a discussion about aero benefits for that crowd, whereas aggressive riders and racers who give it all they've got and measure their ride results in seconds, or fraction of seconds, will equally obviously care greatly about maximizing their output by taking advantage of aero benefits.

Secondly, aero is everything; it's a fait accompli in the cycling world. The benefits are proven, accepted, and that ship has sailed. From bike manufacturers, to component manufacturers, to tire manufacturers, to clothing manufacturers, and even down to seat bag manufacturers, they're all looking at aero. Racers, riders, engineers and designers are all engaged in evaluating and optimizing aero. So in a situation where you've got significant portions of industries, massive dollars, and thousands of people arrayed in the support of, and development of, a quantifiable performance benefit, it certainly seems that any comment suggesting it's insignificant is misplaced.

The Flo guys have a great blog with a bunch of info about how they design and test their wheels, with some of the best modeling (in terms of understandability; I'm not a mathematician!) I've seen and most complete data revelations, and this this article in particular gives some insight into aero benefits: Flo Cycling Blog: Aerodynamics

Again, I'm not attesting to the veracity of the calculations (it's way over my head), but they seem thorough, serious, honest and legit, but if there are critical flaws, I honestly wouldn't know, but I haven't seen any claim of such yet, so I do consider this benchmark info for the time being.

Dunbar

I've seen the Flo and Zipp data on 23mm vs 25mm tire drag and that's where I got the 1-2W difference at 30mph. Like I mentioned, the drag at higher yaw angles in these graphs can mislead people into believing the difference is greater than it really is. I say this as someone who runs a 23mm wide tire on a wide rim (but will probably go back to a 25 when this tire wears out.)

sijray21

23mm up front, 25mm in the back. Nice and comfy in the back with some additional rubber for wear. Front still has less of a surface area and turn-in is nicer. I took the staggered set-up from the attack/force combo I used to run plus the idea from motorcycle set-ups. So far I like it, but it just means you can't rotate the tires if you tend to do that.