I'm currently working on a bike where the clearance on the rear brake bridge is so tight I can't even get a 23c tyre on there without it being too tight, so I've had to go and buy some 20c tyres. Just shows how once 20c was pretty much standard, whereas 23c was relatively wide, I guess...when talking about real 'race' frames, I mean.Properly nice! Clearances are even tighter than on my fixed. I cannot fit tyres larger than 700 X 23 on that as they won't fit under the fork crown.