I always carry a Fix a Flat with me on the road. This is a small, orange, pressurized canister especially made for bike tires that fills the tire with air and some kind of sealant. You can get 'em for $5.95 at K-mart. Fix a Flat has saved my butt more than once. It only fills the tire to about 40 pounds, but then you can use your hand pump to blow it up harder. This sure beats having to take the tire off and find the leak.