Old tubes AND new tubes appear to be too big!

[Deeelightfully]

Hey guys, I need to help as I am very confused! One of my tubes went flat on my bike and I went to go replace it. I bought new tubes in the specified size, but when I went to put them on the tires they were too big. I thought that maybe I had just gotten the wrong size but both my old tubes and new ones are the same. The old tubes were the ones which came withe the bike, so I'm very confused. Does anyone know what might be going on here? I tried putting them on the rims but obviously they are too large, and if I were to try putting the tires over them they would not properly inflate. So what's that all about? I'm baffled.

[AL_BUNDY]

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

[DaveM]

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?

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(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

[nfmisso]

My technique for installing tires on bike wheels. I have tried many over the years before settling on this one.

note: the primary purpose of my bikes is commuting, so not having flats is of paramount importance to me.

Place the tire flat on a table.
Install the tire liner inside the tire.
Partially inflate the tube (less than 5 psi is plenty).
Locate the valve stem opposite the overlap area of the liner.
Completely install the tube inside the tire; let some air out if needed so that the tube fits inside the tire with no buckling or twisting.
Lift the tire off the table, and place the wheel on the table.
Line up the valve stem with the hole in the tube, and push the valve stem through the hole, seating one side of the tire against the rim.
By hand - NO TOOLS - seat the one side of the tire inside the rim all the way around, starting at the valve stem and working in both directions approximately equally - this is to avoid un-due stress on the valve stem.
*** make sure that the valve stem stays straight; if not back up. ****
Next, starting at the valve stem, seat the other side of the tire inside the rim.
Again working both directions more less equally from the valve stem, seat the other side of the tire in the rim; again NO TOOLS.
Let a little air out of the tube as required.