Originally Posted by
msu2001la
Inner tube sizing has always seemed unnecessarily specific to me. Inner tubes are very stretchy. A standard "road" tube is usually labeled as 20-25c, but with just a few lbs of pressure it will balloon out to several inches if not inside a tire. When installed, the tube is contained by the tire (and rim bed), so it's not going to stretch out. A standard 20-25c road tube has zero problems filling out 28-32mm tires.
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I think the only issue is that smaller road tubes become thinner when filling out larger tires. This may make a difference when it comes to flats. A road tube for larger diameter tires will maybe be thicker at the specified size.