At this point I'm sure most of you knowledgeable riders enjoy answering this tire size/tube size question. Some day this will all make sense to me, hopefuly today!!
My bike is a Giant OCR2 road bike, ridden on pavement 99.9% of the time with minimal bumps/ruts in the road or on the paved paths I ride.
Anyways, I encountered a rapidly flattening tube last night. The hole is big enough that I don't want to repair it and besides I have the Philly tri later this month so why not put a new tube in. My question is, my tire is a 700X26C, and the tube that was in there was a 700X28/35. I bought a replacement (Specialized) tube that is 700X20/28 (27 3/4 - 1 1/8) tube. Now I'm pretty sure that the new tube is acceptable as a replacement (although let me know if not), but just wondering why my bike shop would have put the 700x28/35 on when they fixed my last flat? Isnt that size a little big? Is there a reason a tube slightly bigger than the tire would be better.
Also, I'm a big guy (250 pounds). Is there an advantage to using one of these (28/35 vs. 20/28) tires for someone my size? Does one have a higher/lower risk of damage at high air pressures with someone of my size on it?
The closer a tube is to the tire size, the less it stretches to fill the tire volume, and therefore is more puncture resistant. Granted, the difference is minimal, and you can flat with nearly anything, but that's the theory anyway. The thorns/glass/bits of metal don't seem to care what your tube size is.
As a racer I used to run a size smaller to reduce rolling weight. Seems a bit silly now as a flat will lose you more time than a weight advantage gains you.