Would a frame designed for 27" x 1 1/4" wheels fit 700c wheels?

Question

And vice versa? Will the arms of the brake calipers reach?

Answer 1

Not usually.

As you are probably aware, 27" wheels are larger than their 700C bretheren, so the hole in the fork crown and the height of the brake bridge is too far up for 700C.

That being said, SOME people (not me) have filed the slots longer in the brake calipers to allow the brake pads to reach far enough to hit 700C rims. In my opinion this is a dangerous proposition.

Depending on the brand of brakes you may be able to locate drop bolts which replace the center bolts on the calipers and "drop" the calipers down sufficiently. These are quite rare but I am confident you can find a few in those old dark London and Manchester shops. These were common in the era that 27" wheels were being phased out in favor of 700C.

One other thing. Because of the glorious weather in the UK, some companies adopted the construction of frames that use short reach brakes and also have mudguard clearance. If by chance you have one of these bikes you merely need to swap the short reach brakes with long reach versions.

Answer 2

The diameter of a 27" rim is 630mm, while a 700 rim is 622mm.  Thus, your brakes need only 4mm, or so, of adjustment.  Should be no problem unless the pads are already as far down as they'll go.

Hope this helps.

Answer 3

Maybe.  700c is just over 1/2 inch larger 27 inches.  You have identified the issue: brake reach.  Most modern 700c frames use short reach brakes, and while the brakes on a 27 have some adjustability, it may not be enough.  Typically there will not be an issue of fork or rear triangle clearance.  Of course you can buy fairly inexpensive generic short-reach brakes from one of the big online retailers.  One example linked below.

The quick way to determine this is to borrow a 700c wheel from a friend and check out the dimensions.

I hope this helps.  Keep on riding.

Ben