TT wheel diameter?

[jb1883us]

Looking at a few photos of TT bikes in the tour (and Cadel's outlandishly low handlebar position...), I wondered why riders don't use two 650c wheels instead of 700c?

Maybe I'm missing a UCI rule, as I know you can't use different diameter wheels, but it seems to me you could significantly reduce frontal area by using 650's. Are there other drawbacks/factors I'm omitting?

(Punt to salon)


p.s. On a completely unrelated issue - a tri guy called my bike a "road toad" the other day. Too bad I averaged a full 2 mph faster than that guy (on a P4) in the one and only tri I did two weeks ago. Ok rant over.

[caleb]

You can't use 650c wheels in UCI events - against the rules.

Although some argue that a smaller wheel increases rolling resistance, I haven't seen any compelling evidence for that case. In my mind, they're still a good idea for triathletes under about 5'8" using bikes with integrated headsets (5'10" with a standard headset). Also a good idea for short women's road bikes.

Economies of scale killed the 650c wheel, not inadequate function.

[jb1883us]

You can't use 650c wheels in UCI events - against the rules.

Ahh...question answered!

[jscott]

You can't use 650c wheels in UCI events - against the rules.

Really? Rule 1.3.018 specifies maximum wheel diameter of 70cm and minimum of 55cm. 650C is ETRTO 571mm, so it should qualify.

I agree with the economy of scale argument, though.

[suhacycles]

Several years ago, I recall seeing Ulrich use a TT bike in the Tour with a 650C front wheel. During the Indurain years I heard Rominger had a special Colnago made for him with 650's to use in the mountains but I've never seen photos of it.

From personal experience I used 650's for about a decade. The first 4 yrs were on a custom Hujsak which got me a collegiate RR win in NY. It always looked funny compared to regular road bikes as I'm 5' 10" but felt I got pretty good acceleration and climbing out of them. Went back to 700s two years ago as I was getting tired of having limited tire choices and missed the smoother ride. Plus my tires would wear out faster and I never really felt faster on flats or downhill so overall I don't feel like I'm missing much.

[jb1883us]

Really? Rule 1.3.018 specifies maximum wheel diameter of 70cm and minimum of 55cm. 650C is ETRTO 571mm, so it should qualify.

That's what I had read, but I wasn't sure if it was out of date or not applicable. Weight (but maybe not rotational weight...) seems to be a non-factor now days, with bikes as light as they are. I was only thinking of this in terms of frontal profile. And if the back has to match, so be it.

[Saab2000]

Several years ago, I recall seeing Ulrich use a TT bike in the Tour with a 650C front wheel. During the Indurain years I heard Rominger had a special Colnago made for him with 650's to use in the mountains but I've never seen photos of it.

I saw this. It was fugly. I'll try to find pictures.