I'd normally search to find this out but I'm not even sure what to search for. Been riding road for a few years and am used to the road terminology. Just bought a Giant Talon 29er 1 yesterday and I'm looking at wheels for it.
What are the sizes all about. Example: looking into Crank Bros Cobalt 2's. Have choice of 9mm or 15mm by 135mm. What does that refer to?