Originally Posted by h2o_polo_boi
Inner Tube Sizing For many years the bicycle industry labeled tube boxes with the exact diameter and width of a known tire size, which obligated stores to inventory tubes boxed and labeled for every known tire size, even if the same model of tube was used in several differently labeled boxes. In the 1980's some bike store owners and some importer/distributors became more savvy to the concept that the same tube was being packaged in boxes labeled differently only in the "size" listed on it. Tubes started to come boxed with a size "range" printed on it. The box would state a wheel diameter then give a width "range" that the tube would accommodate. An example would be 26 x 1.95-2.125", this tube is intended to fit a 26" tire whose nominal width is between 1.95" and 2.125". The truth about tube sizing is more simple still. It will work, provided the diameter is at least close, for mountain tires if the width is within 3/4", or for road tires if the width is within 3/8" of the nominal tire size. Remember, the nominal tire width is almost always somewhat bigger than the actual width, and rubber itself is an elastic substance that stretches considerably under pressure without failure. As an example, to take the tire product images (photographs) used in the tire article, we used a 26 x 1.6" tube for all tires that had a nominal width greater than 26 x 1.25. We used a 26 x 1.0" tube for the 26 x 1.1" and 26 x 1.25" tires. The same tube elasticity permits you to use a smaller diameter tube in a nominally larger diameter tire, which is why 700c and 27 " tubes are used interchangeably. In a pinch, if you find yourself with only an obviously larger diameter tube, say a 700c/27" diameter though you need it for a narrow 26" tire, some expert riders will fold the tube back on itself, install it in the tire and inflate it normally (usually without any performance loss). Serious riders as a rule, for weight reduction purposes, will choose the proper diameter tube with the smallest acceptable width for their inner tube. - Bikepro.com
Can anybody confirm this? I have a 26 x 1.5 tire on a 26 x 1.95-2.125 tube at 70 psi. It shouldn't go limp on me all of a sudden right? Thanks
The quoted material is correct. Tubes are stretchy rubber balloons, don't need to fit exactly.
Using an excessively wide tube may lead to wrinkles, which could be a problem. Also it is difficult to install the tire if the tube is seriously oversized.
Using an excessively skinny tube will cause it to be stretched thin, so you may need to top off the air more frequently.
By the way, 70 psi is AWFULLY high pressure for a 1.5" tire, unless you're using it on a tandem.
See:
http://sheldonbrown.com/pressure
Pressure has nothing to do with the inner tube, only the tire.
Sheldon "Psssssss" Brown
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