650c front wheel rules?

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Anonymous's picture

Can anybody tell me how riding a bike with a smaller front wheel (650c) feels relative to a standard 700c x 700c bike?

Is it less comfortable? Harder to steer?

Are there rules against racing such a bike?

Anonymous's picture
Christian Edstrom (not verified)

Are you considering a bike with a 650C (571mm ISO) front wheel because you're time-trialing/triathloning or because you need a top tube shorter than 52cm and a sensible seat tube angle and front center?

That would help in answering your questions.

- Christian

Anonymous's picture
ben (not verified)

Hi Christian,

I just won it on eBay. I was shopping for a fixed gear bike for around the city. This is a cheap '80s Bianchi Tri bike (funny-bike). I won't convert it to a fixed gear bike, but I am dumping the Biopace chainrings for circular ones.

I don't do Triathlons, but I do race the Central Park biathlons by NYTC. Does the 650 front wheel really make much a difference? Is it just aerodynamics or is there something else going on?

Anonymous's picture
Christian Edstrom (not verified)

Cool! Eighties funny bikes are really neat.

The idea behind building those bikes around 650c wheels was, as you suspect, to improve the aerodynamics.

As it's a time trial bike, it's likely to handle a little differently than your road bike, but I would anticipate that any discernable differences will be due to different weight distribution and head angle/rake/trail more than the difference in wheel size. Also, since a 650c (571mm) wheel is smaller, the trail for that type of bike should be decreased.

I don't think that it's possible to make any qualitative judgements on the handling without knowing the headtube angle, the rake of the fork, and the resulting trail. For what it's worth, since a 650c (571mm) wheel is smaller than a 700c (622mm), the trail for that type of bike should be decreased from the standard 55-59mm. I'd guess that a 650c bike might handle most neutrally at around 50mm of trail. Since your bike is a dedicated timetrial frame, where straight-line stability is prized, it might even have lower trail than that. This might mean that it'd be easier to ride no hands than a standard bike and more willing to track a straight line at low speeds. Or (alas) it might not.

Trail is a pretty fascinating concept. If you're interested, the best place to look is the framebuilders forum on bikelist. You'll find very good posts by Bill Boston, Freddy Parr, Mark Stonich, Kirk Pacenti, and NYC native Tony Rentschler.

Enjoy the bike!

- Christian

Anonymous's picture
Tony Rentschler (not verified)
Wheel size and trail

Christian said:
>>> For what it's worth, since a 650c (571mm) wheel is smaller than a 700c (622mm), the trail for that type of bike should be decreased from the standard 55-59mm. I'd guess that a 650c bike might handle most neutrally at around 50mm of trail. <<<

Based on my very limited experience with 26-inch (559) road bikes, I think the TRAIL should be a bit MORE for smaller wheels (though the fork OFFSET would be a bit LESS), i.e., 56 mm or greater. I think this article is a good starting point:


Anonymous's picture
Christian Edstrom (not verified)

Tony is, as usual, right.

I muddled it up, because if you install a smaller wheel on the same frame/fork with a constant OS and head angle, you will reduce the trail.

- Christian

Anonymous's picture
Basil (not verified)
650 vs 700

"Some reasons that come to mind (definitely not exhaustive) for 650 wheels:
- Better acceleleration
- More efficient aerodynamics

I ride a 700 (Trek 5200) road bike and a 650 (Kestrel KM40) tri bike - both carbon frames.
No real scientific evidence but I feel (and to a degree can confirm this by my limited ""time-trialling"" efforts in CP) the 650 is significantly faster around a couple of loops. (Admittedly this may have a lot to do with the wheels also - the tri bike has Spinergy ""bladed"" wheels).
It also feels significantly LESS stable (but that's probably due more to the geometry than the size of the wheels).
Hawaii Ironman survey showed significant 650's for some years but in recent years trend has been moving back to 700's - except (as in Carols' case) where size of frame/rider gives other reasons for 650 preference.

Anonymous's picture
Carol (not verified)

I ride a bike with 650 wheels both front and rear because I have a small frame. In that set-up, it's very comfortable with normal steering. I don't know what it would feel like to have the smaller wheels on a larger frame - might make it a bit squirrelly.

Anonymous's picture
anon (not verified)
650 cc wheel

I took a very long ride on a Terry, which is the 650 upfront 700 back. I found the riding quite odd and felt really unstable (like, not surprisingly, I had two different length legs). This set up may not be that applicable as the two different wheels on the Terry are to compensate for the smaller woman's size frame.

Anonymous's picture
Christian Edstrom (not verified)

"The Terry's with different sized wheels have 24"" (520mm) front wheels and 700c (622mm) rear wheels. Terry's with 650c (571mm) wheels have the same size rims front and rear.

(And because someone is bound to point it out -- _very_ early Terry's used 600A (540mm) front wheels.)

- Christian"

Anonymous's picture
anon (not verified)

regardless, the point i was making -- and still holds true regardless -- is that the terry has two different sized wheels and it felt quite odd.

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