If you've ever changed a tire, then you know that many bicycles and some vehicles use an inner tube inside the tire. Similar to a tire, a tube has a measurement on it to tell the correct size. It doesn't come with instructions, however, on how to interpret the notations, which can cause some confusion for the user.
Size Measurement Methods
To compound the tube size problem a bit further is a fact that there are five types of inner tube measurement systems used by the tire industry. These include a standard inch distance, the European metric system, an alpha system, and the low-profile versions of standard and metric tubes. Depending what rim and tire you are using along with the tube, there can be some mixing of types, but not every tube will fit every rim and tire in its size range.
Why Care About the Size Being Off a Bit?
What difference does the tube size make if off slightly? A lot. A wrong size tube can create all sorts of problems when riding or driving. Too small a tube, and it can get offset and cause a tear at the valve; too big of a tube, and you will get folding that fails to distribute the air properly. Both will eventually cause a wear or tear, and eventual tube failure. At a minimum, the tube needs to match the size of the rim or it will not fit at all.
Reading the Tube Size
You will find the tube size reading on the side of the inner tube either painted or stamped on the rubber. The measurements typically begin with the first number being the correct wheel diameter the tube will fit. Then will come the width measurement of the tube, or how wide it can expand. For a bike tire, the measurement 26 x 2 will mean it fits a 26" tire and will expand to fit a maximum 2" width. Any bigger will pinch and any smaller will be too loose in width.
As noted earlier, not all tubes follow the same reading. A metric measurement would read something like 700 x 23-25c. Again, the first figure is the tire diameter in millimetres; the second is the range after expanded with air.
Does a Tube Work for Any Tire?
In a word, no. Tubes are made to match different types of tires. You could have tubes for a small trailer tire or riding lawnmower, and you can have tubes for an earthmoving dump truck. Clearly the sizing is going to be different for each. Sizing gets put into six general categories:
Bikes: Bike tubes are for bike tires, and come in the obvious thin range.
Motorcycles/ccooters: Thicker than bike tires, these tubes are still meant specifically for thin rims and would never work on a car rim.
Car/truck/van: Considered small tubes in the vehicle world, tire tubes for cars that still use them are sturdy enough to be used in a car for thousands of miles, and are commonly used for water play as well.
Tractor and semi: These are large tubes to fit very large wheels, many times larger than a grown person.