Probably a silly question. I want to stick some 700×42 tyres on a tourer which has 700×37 tyres. I’m slightly concerned that they may catch on stays or guards given that I’ve gone from 26 x 2.2 to 26 x 2.4 and found the increase in tyre size has been huge.
Is there a rough guide for working out what the change in actual size will be ?

Isn’t there a clue in the numbers?

Plus the fact the marked width is pretty nominal. Different manufacturers and even different models from the same manufacturer can vary quite a lot.

The only way is to try it, or if you’re very lucky find someone who has tried the same combo already.

Tinribz,
You’d think there’d be a 0.2 inch increase in width from a 2.2 to 2.4 but it’s way more on the contis I have. I think SundayJ is right that tyre is fairly arbitrary. I’ll probably buy and hope. The tyres I have at the minute are shot so if I’m unlucky I’ll have the bike off the road for a while experimenting

Look at the gap found the tyre at moment.

Caliper as well as frame.

If it looks tight, be careful.