Originally Posted by
Retro Grouch
Let me add this to what the others have posted:
I think that it's better to use a slightly undersized tube than one that's a little too big. It's hard to cram a big inner tube into a 23mm tire and you're more likely to pinch the tube under the tire bead. Given your preference for one size tube to fit all of your bike tires your bike shop guy served you well.
+1
I initially bought 700x28-32 tubes when I built my commuter on 700x28 tires. The tubes are huge and didn't fit in my seat wedge in addition to being a pain to stuff in the tire. I've now got thousands of miles on 700x19-26 tubes inside my 28's with great results. I can fit 2 tubes in my seat wedge and can also use them in my 23's on my road bike.