Wheel is doing my head in.

When to get some new tyres on sunday, 26 inch 1 3/8 road tyres, went to fit them, and they didn't god knows how we got it on, but the people at halfords had to cut it off. this baffles me because the tyre that came off is a 26 x 1 1/4, so in theory I had an 8th of an inch to play with. Now I'm no mathmetician but this doesn't make sense to me. The bike is from the 70's so the only possible explanation is the tyre sizing has changed maybe?

Any ideas?


Über Member
Welcome to the wonderful world of tyre sizing!


It makes more sense when you look at the ISO size - the big number is the diameter

26 1 1/4 = 597mm diameter
26 1 3/8 = 590mm diameter

(modern 26" mtb is 559mm)

so your new tyre was 7mm diameter too small for your rim. It's not surprising it didn't fit, though it's quite surprising you got it on in the first place!
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