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Old 07-26-04, 10:49 AM   #1
nopain
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Tube Questions - small tubes/large tires

Anyone know where I can find extended presta valve tubes in a 1.25" size (specialized Fatboys) for 559. Standard prestas work with an "extender" however this renders my zefal guage unusable. And to insure the stem doesn't leak I have to remove the valve extender and tighten the top of the valve then reinstall the extender. In short annoying. An alternative would be to use a 650 tube, however I'm not sure it would expand enough to properly fill the somewhat larger tires. As a final alternative I could go with 1" 650 tires, but they don't seem to have as low a rolling resistance as the fatboys. Please advise if you know of a source or have tried smaller tubes inside larger tires. thanks
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Old 07-27-04, 07:54 AM   #2
sch
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The smaller diameter tube would easily expand to fill the tire, but the greater expansion means that any small defect in the rubber would be rapidly magnified
by the expansion and thus a tube that is designed for a 1" tire inflated enough
for a 1.5" tire would be more likely to fail. If it does fail, it will fail fairly early. The
problem is micro cuts on the surface of the rubber propagating to the ripping point.
Depends on whether you get a "good" or "bad" tube. Note that patches on a
tube expand very little and patching an undersized tube and inflating results in
a definite constriction and hourglassing of the tube.

On the other hand, if the tube is under sized for the wheel diameter, say 650c into a 700c wheel, it will be almost impossible to mount, it won't stay up in the tire, even with inflating the tube lightly. Steve

Last edited by sch; 07-27-04 at 01:07 PM.
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Old 07-27-04, 01:11 PM   #3
nopain
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Quote:
Originally Posted by sch
The smaller diameter tube would easily expand to fill the tire, but the greater expansion means that any small defect in the rubber would be rapidly magnified
by the expansion and thus a tube that is designed for a 1" tire inflated enough
for a 1.5" tire would be more likely to fail. If it does it will be fairly early. The
problem is micro cuts on the surface of the rubber propagating to the ripping point.
Depends on whether you get a "good" or "bad" tube. Note that patches on a
tube expand very little and patching an undersized tube and inflating results in
a definite constriction and hourglassing of the tube. If the tube is under diameter, say 650c into a 700c wheel, it will be almost impossible to mount, it won't stay up in the tire, even with inflating the tube lightly. Steve

Thanks. I went to my local bike shop and they showed me a continental 650 tube w/extended presta valve. Supposedly the valve dissasembles so you can add slime to the tube as well (I didn't). But I do run slime on my mountain bike tires (lots of thorns and debris on the roads). It would be a nice option as I have yet to find a presta valve tube you could put slime in. Anyways. I had them install the tube and so far it seems to work. I guess I'll find out if it's going to fail in the next couple of weeks. I also contacted my bicycles manufacturer and he said Kenda has come out with new tubes that are of the correct size and should be available in a month. I didn't find any information on the Kenda Website, maybe they are custom fabs or too new to be listed. Finally a correction to my above post it should have said 559 1" tires not 650 1" tires. Steve, again thanks for you're advise. If I encounter a problem with the conti tube I'll post it here.
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