Has anyone ever thaught of stretching a 20" tube to fit a 24" wheel? Its highly common to size a 29er tube to a 36er wheel. Does anyone have some sort of guide on stretching tubes? My MUni is a beast and I figured ti was time to put him on a very strict diet
Clichée came to me at 12:13 am on X-mas eve. So I typed it up on my Ipod so I dont forget.
Happy Holidays!
.
Unikid2
I have never tried stretching tubes. To stretch a 20" tube to fit a rim for a 24" tire you are only asking for an additional 20%. To stretch the 29" tube to fit a rim for a 36" tire you are asking for an additional 24%. If anything, it should be easier to do. It certainly is a cheap experiment. I question the weight savings. A Coker tube is very heavy so the weight savings are substantial.If you are using one of the thick, downhill tubes in your 24", just going to a standard 24" tube might save you enough in weight already.
I think it’s gonna be a tough fit. There is quite a bit more rubber to stretch in a 29" tube than there is in a 24". If your goal is to drop the weight a little I think a lightweight tube in the right diameter would be better. You could try a cheap 25x1.5-1.75 tube. It should only cost three bucks, and it would be lighter than a tube made for a 2.5-3.0 tire.
From my experience, stretching a 26" tube to fit a 27" wheel(bicycle) was quite difficult. Later I remembered that for every inch of diameter, you have pi inches of circumference. That means that my 26" tube was 3.14 inches shorter in circumference than a 27" tube.
That also means that with a 20" tube, you will have over 12" less tube to work with then if you used a 24" tube. I wouldn’t even try, but maybe it is possible.
Oops. Sorry. You’re asking for an additional 25% in this case so it’s about the same as the 29er stretch. I still agree with jtrops that a lightweight 24" tube would probably be effective enough.
I’ve stretched a 20"x2" tube over a 24" muni rim in order to tubelessify my muni; it was a bit of a tight fit, and I must confess to half expecting it to go BANG as I inflated it to seat it properly. It wasn’t too difficult to get on but even at low pressure it looked strained and a bit thin in places; I don’t think I’d have liked to ride on it (assuming it could have been inflated to riding pressure in the first place!)
Get some sealant and go tubeless instead, it’s awesome - no more punctures, lighter, and much better bump-absorbing properties… 
Phil
This sounds like a diet for a flat tire. I recommend trying the tubeless route, or shopping for lighter tubes. Regular 24" tubes don’t weigh that much in the first place so it’s not a great place for savings. You could save a lot more rotating weight by choosing a lighter tire and/or rim.
I don’t know that it scales. I tried using an 18" on a 20" freestyle rim once–only ~11%. Everything seemed okay, but then it exploded while I was getting ready to go ride.