biker jk wrote:
That's because the Zipp rim is 28.5mm wide so the 23mm tyre on it measures a lot more than 23mm wide when on the rim. In essence, drag is reduced because the tyre's side profile is not like a light bulb (think 23mm tyre on a standard 19mm rim). So if you have 19mm rims then yes the lower rolling resistance of moving to a 25mm wide tyre could be more than offset by increased drag. The equation changes with the new wider rims.
The zipp is a new wider rim and they are saying 23mm is faster on it
In any case it's not much just as the change in comfort is not much.
I haven't tried wide clincher rims though I don't see how such a small percentage increase in size can be such a revelation in terms of ride comfort and grip.
It was more than offset by the less snappy feel on my narrower rims.
Maybe one day I'll be as rich as you blokes and be able to try wide rims out. I reckon by then they'll be back to marketing narrow rims as lighter and a revelation in speed.