I had my first flat this morning--the first one since my bike was overhauled last summer and the first one I've fixed myself--on the rear wheel of my bike. When I put together a repair kit to carry I bought a spare tube the same size as my tires: 27" x 1-1/4". However, when I took out the old tube (tires and tubes were replaced in the overhaul) I noticed it was clearly stamped 27" x 1-1/8". Shouldn't the tube size and the tire size match, or is such a small difference not that critical? It seems to me that a tube that is too small for the tire would be stretched thinner when it is inflated and thus be more prone to puncture. ??

I haven't checked, but I'm assuming my front wheel has an identical tube in it; should I assume it's a flat waiting to happen, too, and go ahead and replace it? Is the old tube worth patching to use for a spare, or should I toss it and only use tubes that are the correct size?