How can I tell which replacement Inner Tube to buy?

look on the side of your tire. it should give the diameter of the wheel and the thickness of the tire.

most likely the diameter will be it will be 26"

and then it will give you a thickness.

I ride a mountain bike (2")

example= http://3.bp.blogspot.com/_G4IFi9T97mU/Snj0a19VRNI/AAAAAAAAEdM/E2bfAXFfoRo/s400/IMG_2397.jpg

(look at the area next to the name. you will see small letters. sometimes, these letters are not printed, but are made of rubber (i guess "cast out of rubber" is the right phrase)

http://3.bp.blogspot.com/_G4IFi9T97mU/Snj0a19VRNI/AAAAAAAAEdM/E2bfAXFfoRo/s400/IMG_2397.jpg

tadlos
October 2009

The cycle shop will be able to tell you - diameter and width are important - often moulded onto the side wall of the tyre when I were a lad... however... You may wish to consider a puncture repair kit and mend the tube with a patch...

http://www.youtube.com/watch?v=ntYIITLp90k

Good luck...

Peccavi
September 2009