Originally Posted by bellweatherman
You guys with the sloping top tube frames and the different size wheels. These bikes rock! But, do you carry two different size tubes when you go riding in case of a flat on either wheel?
You'd have to. Stretching a 700c tube onto a 27" rim is easy (and standard practice), but you're asking for trouble if you try to stretch your 650 or smaller tube around a 700 wheel.
However, in the mountain biking realm, where fatter tires are the norm, there is a new breed of bikes that have a 29'er front wheel (700c diameter) and a 26" rear wheel. Some people will just use 26" tubes for those, and because they are wider and have more material, will be able to stretch them in case they flat the big front wheel too.
Or, you could just go tubeless or tubular.