Originally Posted by
spectastic
2 extra mm on a 23 wide tire means 18% more air volume. that's not trivial.
15c as in 15mm inner rim width.
While I recognize air volume is a factor I'm just not sure how much it is compared to the % that is above the rim's outer edge.
I come from riding slightly wider sew ups (23/24mm usually) the common for close to 30 years. During this period the clinchers I rode were 30mm+ wide. I noticed that the sew ups had better pinch flat resistance even with their narrower spec. But the amount of air above the rim's edge is greater with the narrower sew up then with the wider clinchers. (The thinner casing and tube helped the smoothness too)
So, back to this thread's topic, I view this discussion through the amount of added air that's above the rim, not the total volume. Call me two dimensional (and making bad puns) but I think the height of the tire has a large factor to real life, everything else being the same. IIRC the 2mm of width is usually about 1mm in height, difference wise. So I see 4% of difference between a 23 and a 25mm tire on the same rim. Not too much.
Having said that I would choose the 25mm tire every time, over the 23mm one. Andy.