rustmyrtle

How can you tell if a frame should use 700c or 27 x 1/4 wheels?

thanks,
Kristin

Jeff Wills

Generally by its age. The change happened in the '80's- before 1980 most road bikes were 27", after 1990 most were 700C. In the '80's things were all over the lot.

It usually doesn't matter unless you have a frame for 700C wheels and very short reach brakes and you want to put 27" wheels on it. Then you'll run out of room for the tire.

garage sale GT

For 27", the larger of the two, (630mm/2)+32mm should equal at least 347mm from the center of the axle to either the fork crown or the underside of the middle of the brake caliper, whichever is less.

For the back, you have to measure to the brake bridge or the caliper whichever is less.

You should also measure to make sure the fork and chainstays have enough room to allow a 32mm wide tire at a point about 10-15mm above the edge of the rim, which will be 315mm from the center of the axle. If you have a bike with horizontal dropouts in back, the axle should normally be located roughly where the chainstays and seatstays would meet.

I am not sure but I think some 27" bikes may be made for a 27x1-1/8 or 28mm tire.

I had an '85 PXN10 frame which did not allow the use of 27x1-1/4 tires.

garage sale GT

The tire could also hit the seat tube but I have found that most older bikes typically have longer stays. I can't think of a simple way to find the point at which the seat tube is closest to the rear axle other than to place one end of a tape measure in between the drops where the axle would go and swing the other end in an arc where the tire would be, and make sure it doesn't get any closer than 347mm. It's actually not a problem for me because I ride a 58 but smaller bikes might come with shorter chainstays.

rustmyrtle

thanks, guys. this is really helpful.

ironwood

A lot of older European (and perhaps Japanese?) bicycles were sold in the US and the UK with 27" wheels and in Europe with 700C wheels, so for many bikes there is no real difference in the frame. It is only a 4mm difference in the rim radius. But some short reach brakes might not reach a 700C rim.

If you use fenders and wider tires, a little more clearance is nice, as is the greater choice in 700cC tires.