Difference between 22x635 and 40x635 wheels/inner tubes? Today I had my first encounter with the wildly variegated world of inner tubes / tires / wheels sizes. My wheel shows this, no info readable on the tire:



I already discovered that 28x1.5 and 28x1 1/2 are two completely different sizes, as I bought the former inner tube and I couldn't manage to fit it in (it was too large). Now my question is: 

I found a shop that sell 40-635 (28x1 1/2) inner tubes. Are they the same as this 22x635 (28x1 1/2)? Can I buy it safely or the tire itself may play a role?

If they are, why does the first number change so much? I thought it was the width expressed in millimeters!
The 22x635 is the rim telling you its own ISO designation, which is internal rim width x bead seat diameter in millimeters. The 28x1-1/2 in parentheses is an attempt to help make it a little bit clearer what tire goes on it, or maybe help out in the case of a tire, presumably an old one, that only has that size printed on it. (28x1-1/2 and similar numbers are nominal sizes, and they make tire sizing confusing in a number of ways.) 

Presuming your tire has an inflated width of around 40mm (say 37-43mm), and also presuming the valve type is correct, the tube you are looking at is the right one. I'm pretty sure virtually all 635mm tires are around that width.