kuan

I went to my LBS in search of tubes for a 32-507 tire. This is a Kenda SB8 also marked 24 x 1.125. The guys couldn't figure it out. The closest I can find on the Schwalbe site is the SV 9. It fits the following:

47-507
28-540
37-540
28-541
37-541

24 x 1.75
24 x 1 1/8
24 x 1 3/8

Can anyone help me?

ThermionicScott 

If it were my bike, I'd be tempted to see if an AV8/SV8 would stretch enough on the inside circumference to work. Since all of the 507 options are "big", make sure you put some air into the tube before installing the second bead.

kuan

Is there a downside to stretching the tube? The kid is maybe 60lbs. Maybe. So lower psi.

ThermionicScott 

Not really, provided it's not too extreme. Consider that it stretches plenty in the "outward" direction.

kuan

Ah good point.

speedy25

Stretching a tube a bit is better than folding a tube into a space. I have pulled out tubes that were too big that had abraded on themselves and lost air.

-SP

FBinNY 

As a rule it's better to stretch an undersized tube, than try to stuff in a fat one. But when the wheel diameter (not width) is under it can make mounting a pain, because the tube will pull down below the unmounted part of the tire increasing the chances of pinching it.

Also consider that tube sizing is a very approximate thing, and there's little close correlation between what's written on the box, and the tube inside.

One place you might try is Terry Precision bicycles. They use (used to use?) a high performance narrow 24" wheel on some of their bikes. I believe it's something fairly close to a 25-520 (aka 24x1), and the tube could be a very good fit for you. Going slightly long on the wheel diameter, won't make it hard to stuff, and can even help because with a bit of air it'll position itself deeper into the tire and stay away from the bead, lessening the chance of pinching.

Bill Kapaun

https://sheldonbrown.com/harris/tires...tml#lesscommon
Your tire would be a 24X1.25. (1.125 would be 28MM, not 32MM)

24X fractional number such as 1-1/2, 13/8 etc. is WAY TOO big.
The decimal size BSD is 507MM
The fractional size BSD is 520 to 547MM

FBinNY 

You might phone Kenda in Ohio. They keep a decent stock of odd size tires and tubes, and if they sold the size OEM for bikes destined for the USA, might have the exact tube available. They may sell you directly, or refer you to a source that stocks it. Another good source ofr odd (and normal size) tires and tubes is Yellow Jersey, in Madison], Wisc. They're good in that if they don't have it they're willing to try to find it, instead of just saying tough.

kuan

I'll be darned! The markings are wrong on the tire! I measured it. It's a hair under 32mm. So it's not 1.125 inches wide, it's 1.25.

prathmann

The SV9 is shown as fitting a range of tire sizes that includes the one you have (i.e. it's ok to use with a diameter in the range 507 - 541mm and a range of widths of 28 - 47mm, so it should fit a 507 - 32 tire) - so go ahead and use it.

As others have mentioned, tubes can stretch alot so it's not too critical to use the 'right' size. I've used a 700c (622mm) tube in tires as small as 12" (trailer tire) and it worked fine - just had to fold it up some. And when my daughter had a flat on her mountain bike at college (559mm tire) the only spare tube handy was also a 622mm. She rode on it every day for a semester without any issues before I finally changed it out with one of the correct size. With significant mismatches the main problem is making sure that none of the tube is pinched between the tire bead and the rim.