Disclaimer: If you don't like bikegeekery, this post is not for you. Even if you do, it probably is still not for you, it is pretty tragic.
So. Tyre width. Everyone knows that sometimes tyres aren't the size they say they should be, and most people know that this is because tyre manufacturers are pisstakers. But sometimes, out come the excuses, and one of them is "Different sized rims will make tyres different sizes". And obviously they will, but I'd never really paid any attention to how much, other than having a gut feeling it's less than people think.
So, I got a new Conti Baron, and found that it's very close- 2.3 claimed, 2.28 actual, measured at the widest point. This was on a DT540, pretty typical of the sort of rim that these tyres will be fitted to (slightly wider internally than a Mavic 721).
But how much difference would a smaller rim actually make? On my commuter is a 1990s Weinmann/Bontrager BCX3. It's just 17.1mm wide internally, compared to the DT's 22mm, so realistically you're not going to stick a 2.3 tyre on it normally. It's also 1mm deeper in section which will pinch the tyre further.
And at the same 40psi, it comes up (drumroll) at 56.31mm wide, or 2.21 inches. So, despite the exaggerated difference in rim size, the difference in width is just 1.6mm.
That's practically science, that.
