07-05-2012, 07:13 AM
I find the best way to mount tubes is to pump them up enough that they just take their donut shape, put them into the tires first, and then mount tire & tube onto the rim. This lets you get the tube sitting in the tire properly with less chance of twists or pinching. If you're having trouble getting the tube into the tire straight, let a little air out as needed.
Tubes are able to stretch to fit a surprising range. But it is important that they are not twisted, folded over themselves, or pinched between the tire and rim. Some tubes are designed for 27" or 700c tires which are close, but not the same and you sometimes get tubes that seem too big to fit a 700 tire.
What size do your tubes and tires say?
I don't know about 20", but there are several sizes where fractional and decimal are completely different sizes even though both refer to inches. For instance 26 x 1.75 is not the same at 26 x 1 3/4. It's not that the width is different, it is that the diameter of the rim & tire are different even though they are both called "26". The most common issue with this is people trying to put 26 x 1.5 modern mountain bike tires on a bike with 26 x 1 3/8 wheels. They will never fit. In fact, there are two different 26 x 1 3/8 sizes that are not compatible with each other even though they are marked with the exact same size. Bike tire sizing is a mess.
When in doubt, refer to the ISO size which is accurate and consistent:
http://sheldonbrown.com/tire-sizing.html
Tubes are able to stretch to fit a surprising range. But it is important that they are not twisted, folded over themselves, or pinched between the tire and rim. Some tubes are designed for 27" or 700c tires which are close, but not the same and you sometimes get tubes that seem too big to fit a 700 tire.
What size do your tubes and tires say?
(07-04-2012, 08:05 PM)AL_BUNDY Wrote: I had this happen with 20" wheels once. I cant offhand remember the exact size but it was the difference between the lettering being printed in fractions or a decimal point like 3/4 versus .75.
I believe one is inches and the other is Centimeter
I don't know about 20", but there are several sizes where fractional and decimal are completely different sizes even though both refer to inches. For instance 26 x 1.75 is not the same at 26 x 1 3/4. It's not that the width is different, it is that the diameter of the rim & tire are different even though they are both called "26". The most common issue with this is people trying to put 26 x 1.5 modern mountain bike tires on a bike with 26 x 1 3/8 wheels. They will never fit. In fact, there are two different 26 x 1 3/8 sizes that are not compatible with each other even though they are marked with the exact same size. Bike tire sizing is a mess.
When in doubt, refer to the ISO size which is accurate and consistent:
http://sheldonbrown.com/tire-sizing.html
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