sjt78

Just checking to see if I will experience any problems running two different size rims on my road bike? The bike came with a front 27" wheel and a rear 700c. Besides having to buy two different sized tires, will there be any problems with this arrangement? Thanks.
-Steve

Michel Gagnon

No problem, except for spare parts.

700c rims are only 4 mm smaller (in radius) than 27" rims, so it doesn't change the geometry of the bike. The same tubes fit both tires, so it's only the tires that differ.

Because of that, I wouldn't use such a bike to tour in far-away places, where it's safe practice to carry a spare tire around. But I would use it without problems for commuting, day rides, etc.

BTW, my commuter bike has been set up that way for about 2 years. It originally came with 27" wheels, but there wasn't enough room in front for a knobby or studded tire (useful in Winter). So I bought a 700c wheel for the front and continued to use the 27" wheel in the rear. I eventually replaced the rear wheel two years later as I broke a spoke when I fell through it (while on foot) and discovered most spokes were rusted in place.

John E

Been there ... done that. Things like this happen when you assemble bikes out of whatever parts you have available! In any given application, you will get a bit more braking leverage with a 27" wheel than with a 700C, because the latter demands 4mm longer brake reach.

froze

Though I have never done that there should be no problems as long as the brake calipers reach both rims. One thing though, wouldn't it be better to put the 27 on the rear?

sjt78

Thanks for the advice everyone. The brakes line up well on both wheels because of the long reach brakes. It is impossible to use the 27" on the rear because it is laced up to a front hub. I wanted to make sure this wouldn't be a problem to use. The bike will be set up as a snow/rain bike. I don't mind buying different sized tires for this purpose. It's not my race bike Thanks again.

froze

Not impossible, but you would have to respoke both rims to switch them around, just a hassle and an expense maybe not worth doing. Though if you do get a hair up your armpit to respoke, that would be a good time to lighten the wheels a bit by using double butted spokes and alloy nipples.

spindle

Maybe this is a stupid question, but why do companies bother making two different sized tires if there's only a 4mm difference between them?

Michel Gagnon

Back until 1983-1985, 27" was the road standard for bikes sold in North America. France and many continental Europan countries were using 700c (with many 650 in France), and U.K. had mostly 26" and some larger (either 27" or 700c, I don't remember).

Then came globalisation, and North America moved down to 700c. Except for the transition, I think it is a good thing to use the same tires in many parts of the world. I wish we would use the same sizes in Asia and Africa too, as it would make world touring easier.

Now, the 4-mm difference in radius is not too much for tubes, which expand a lot. But for tires, it's just enough that 27" tires (630 mm rim) would fit just a tad outside of the bead of a 700c rim.