Chombi

Aside from the fatter tire possibilities, wouldn't the smaller diameter wheel result in quicker handling. This was the case when sportbike motorcycles in the early 80's started using smaller 16 inch diameter wheels. It was more of a novelty as after a few years, riders ended up demanding the manufacturers to bring back bigger 17 inch diameter wheels because the smaller wheels felt too nervous/skittish on the road for many riders.......quicker handling could be an advantage for bicycles used in races like Criteriums though......just my thoughts....

Chombi

ColonelJLloyd 

Not if the overall circumference is comparable, right? Add to that that a bigger, lower pressure tire would be "less quick". This is just conjecture on my part. I'm not a physicist or an engineer.

Grand Bois

A fatter 650B tire also has a larger diameter, so there should be no significant change in handling.

GrayJay

I remember a few full size road race bikes available with dual 24" wheels. QuintanaRoo had one I am pretty sure. Not just a triathalete/TT frame but a bike intended for a full size rider to road race on. Pros: Lighter, stiffer, more aero wheels, cons: sketchy handleling, higher rolling resistance, odd frame geometry. The fact that they were tried and never really caught on would seem to indicate that it was not a good tradeoff.

nerobro

That's not actually how that went. Motorcycles went from 19" wheels to 16" wheels. They didn't go "back" to 17.

They really went from 19f/18r" wheels to 16f/18r" wheels. Then settled on 17f/17r" wheels.

Chombi

Regardless of the exact wheel dimension history/sequence, My real point was, the smaller the overall diameter you wheel is, the quicker, some would say, more "nervous" your handling will be. Thus the u-turn away from the 16 inch wheel that motorcycling did.

Chombi

noglider 

OK, I do see the point for some people (bikes) but very few. I took a quick test ride on the bike I just fixed up. It's an old Trek 830. I pumped the tires to 80 in front and 90 in back. It felt very quick. Best mountain bike I ever rode, but that's because I don't care for mountain bikes much. The tires are pretty light, too.

nerobro

I should get picky and point out, that with the weight, and speeds involved in bicycles, wheel diameter isn't going to limit the transition speed of the bike. On a motorcycle, with a 30-40lb wheel, with a 30-50-100mph rim speed, sure, diameter is going to seriously affect stability. But on a bicycle, even at 40mph, with only 2-3lbs of mass on the rim, you shouldn't be seeing any effect that even moderate muscle can't overcome.

bobbycorno

An MTB w/80-90 psi? That's gotta ride like a truck! My 650b conversion is a light steel (True Temper OX Platinum) frame w/38mm tires at 50 psi. RIdes like a big BMW - way fast, way smooth.

SP
Bend, OR

Mike Mills

Tom, did the mountain bike have knobbies or slicks?

WNG

^ those psi's must be for a narrow 1.25 or 1.50" slick.

I'm running 1.95" gumwall near slick tires on a rigid MTB. 65 psi max. @ 60, it's fast but bordline harsh. Some of that is on account of the quality of the tire too. But playing with tire pressure will get you your sweet spot.

cs1

Honestly, I don't think there's any logical reason. Everyone will say it's to get a cush ride on racing bike but that's BS. IMO, it's just something to do for those of us, me included, that want something nobody else has. With that said, I want to do one myself, just to be different.

dbarnblatt@usa.

Why is it BS? I'm building a 650B for complete fun but also because tooling around the ripped up streets of Venice, CA is a hell of a lot nicer on a 40mm tire then on a 25mm tire! I'm essentially making a city bike. I look at it as a road bike mixed with a beach cruiser. Functional and different.

noglider 

Slicks!

I can't wait to hear from the customer.

cs1

That's the essence of what I just said. There really isn't any reason to do it except to be different and to have fun. So, have fun.

Grand Bois

I think cs1's got it right.