Originally Posted by
mconlonx
I've always assumed an undersized tube would be stretched more and puncture easier, but I got nothing to back that up.
700 is also 29r size, so you might try shopping around for 29 x 1.75-(whatever) or 29 x 1.9-(whatever) size tubes.
But I'd not hesitate to go with the 700x37-43 tubes if that's all you can find.
I agree on all points, except that I have personal experience that backs up the first assumption. A too-small tube can fail very suddenly, like a balloon landing in freshly cut grass. They are also harder to patch.