box vs aero wheels

Aero trumps weight even for hilly courses. You will be faster on the Velocity wheels. How much faster? Can't really say. The number I always hear/read is ~1.5 minutes faster for 40K going from 32-spoke box section wheels to deep section (60mm) aero rims. Since the Velocitys are 30mm deep you won't see all of that improvement. But I think you will see more than 5 seconds.

In the mid-80s, I built a pair of aero-wheels. The rims weren't very deep - only ~20mm. But I seemed to be noticably faster on them.

I'm going to offer a friendly counterpoint.

The aerodynamic-benefit-to-rim-depth ratio isn't a direct one. There's a break point. It depends on the informtation source, but generally, you'll see a cutoff somewhere between 30mm and 35mm, below which it's generally agreed that the aero principle is completely negligible at the speeds nearly all cyclists travel.

In other words, I don't think the data can support even a subtle efficiency increase between a 24mm rim and a 30mm rim, whether it's billed as aero or not. The soundest arguments I've heard maintain that you simply can't expect the tradeoffs to amount to anything unless you're springing for a true deep rim aero rim, like Zipps, Mavic Carbones, Heds, Boras or the like -- something pushing the mid-30's mm range, or well-beyond.

Given that, I'd base your decision on weight, price, and any sense you've got about quality, style, the retail source, and so on. Good luck.

lokstah said:

I'm going to offer a friendly counterpoint.

The aerodynamic-benefit-to-rim-depth ratio isn't a direct one. There's a break point. It depends on the informtation source, but generally, you'll see a cutoff somewhere between 30mm and 35mm, below which it's generally agreed that the aero principle is completely negligible at the speeds nearly all cyclists travel.

In other words, I don't think the data can support even a subtle efficiency increase between a 24mm rim and a 30mm rim, whether it's billed as aero or not. The soundest arguments I've heard maintain that you simply can't expect the tradeoffs to amount to anything unless you're springing for a true deep rim aero rim, like Zipps, Mavic Carbones, Heds, Boras or the like -- something pushing the mid-30's mm range, or well-beyond.

Given that, I'd base your decision on weight, price, and any sense you've got about quality, style, the retail source, and so on. Good luck.

To echo Lokstah, I've read the best deep aero rims are good for 30 seconds over a 40K TT. This would apply to a perfect, no-wind day. In sidewinds which result in a relative wind from 15-20 degrees off center, the aero rims actually have more drag due to the larger sail cross-section they present. Also, the handling is a handful in gusty winds. Explains why not many people bother with them except for TTs.

dhk said:

To echo Lokstah, I've read the best deep aero rims are good for 30 seconds over a 40K TT. This would apply to a perfect, no-wind day. In sidewinds which result in a relative wind from 15-20 degrees off center, the aero rims actually have more drag due to the larger sail cross-section they present.

This is true but misleading. The drag on aero rims increases with increasing angle of attack but so does the drag on conventional box rim wheels. In fact, as angle of attack increases, the rate of increase is less for the aero wheels than the standard ones, so the benefit from aero wheels is greater as side wind increases. See fore example: http://www.bsn.com/cycling/WheelAerodynamics.html