WHAT TUBE DO YOU NEED?
To replace your tube, you'll need to know three details to get started: tire size, valve type, and valve length.
TIRE SIZE
Wheel diameter and width should be on your tire sidewall, and also on your old inner tube. It will look something like this: 26" x 1.75". Our butyl rubber inner tubes stretch, so they will fit a range of up to a quarter inch with no issues.
We do not recommend using a tube with a width far smaller than noted your tire. You will be more likely to flat, and you may feel unevenness in ride quality. A tube that is too wide for the tire will be difficult to mount, and more likely to pinch between the rim and tire during inflation.
VALVE TYPE
Check which type of valve you have. Most likely it is either Presta (skinnier, pointy one) or Schrader (like on a car). Our standard Presta valves are 48mm long. If you have standard rims, they won't look silly-long, and they will work well unless your rim section is more than 35mm deep.
VALVE LENGTH
Unless your rims have a very deep V shape, our valve length will work fine. If your rims are deeper than 35mm, we offer a 60mm Presta valve. If you have deep section 700c aero rims and are looking to save weight, we offer an 80mm long aluminum (not brass) valve stem. If you need to go longer, Topeak's valve extender can be used on our tubes with no need to remove the valve core.
ATTEMPTING TO "MAKE IT WORK"
If your rim is drilled for Schrader, the hole in the rim is about 8mm in diameter. That's big enough to also fit a Presta valve and can probably get you home in a pinch. However, this is not an optimal setup and could eventually compromise the tube.
The hole drilling for Presta is about 6mm. Rim makers often use a Presta size hole because the rim is too narrow to use Schrader. Drilling a Presta hole to fit Schrader could compromise your rim to the point of being dangerous.
A tube that is sized just a few millimeters bigger or smaller than the rim diameter can usually work OK. There is enough stretch in the tubes to accommodate the difference.