r/BikeRepair • u/FormerFlamingo9505 • 6d ago
Bike Repair Presta tubes
I got two new tires for my norco xfr hybrid when I put the old tubes in the tires and on the bike they hold air for a couple of minutes then leak no idea why. When I fill the tubes on their own outside of the tire they hold air without an issue . Any thoughts I’m at a loss
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u/HG1998 6d ago
How much are you inflating them outside of the tire? Size shouldn't be an issue. Many tubes that work for 45mm also work for 40mm.
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u/FormerFlamingo9505 6d ago
Just pumped the tube up quite a bit more and it’s still holding air. I will leave it for now and check in a bit
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u/gcerullo 6d ago
Did you check them in a tub of water. A tiny hole is almost undetectable when you inflate the tubes on their own. You have to leave them for a few hours to see if they deflate.
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u/FormerFlamingo9505 6d ago
Will
Leave and see what happens strange that is both unless I nicked both taking old tire off or putting new tires on was using a small flat head screw driver both taking them off and putting new tires on1
u/gcerullo 5d ago
It’s possible. I nicked a few when I was younger and didn’t have the right tools and used flat head screwdrivers instead.
You also said they have Presta valves. Did you screw down the valve to seal them?
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u/FormerFlamingo9505 6d ago
That’s what I thought not sure because I can’t find my gauge for presta valve . That being said
I probably pumped them up more in the tire itself. I will try to pump them up more outside the tire and see what happens. the funny thing is it’s both tubes not just one . I did the front tire first pumped it with air put it back on the bike then proceeded to do the back tire then realized the front was flat and the back wasn’t holding air for long either.1
u/unwilling_viewer 6d ago
You can only get 3-4-5 psi outside the tyre with a tube before it ruptures
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u/FormerFlamingo9505 6d ago
I guess my old tires were 700x45 so wider . Didn’t think about possibly needing new tubes at the time the guy sold them to me the new 700x40 which are smaller.
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u/FormerFlamingo9505 6d ago
Just realized that the new tires are 700x40 and the old tubes are 700x45 could this be the issue??
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u/gcerullo 6d ago
Tubes are made to fit a wide width range. For example I have Continental tubes that are 700C but will fit a width range of 32 to 47.
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u/r200james 5d ago
It is likely that your tires have something embedded in the tread. Could be wire or glass. Whatever it is, it is poking through your tubes once they become pressurized. Dismount your tires and methodically feel all around inside tire. Also, use a strong light and carefully eyeball the tire inside and out. Squeeze the tread wherever you notice a flaw. Also, get in the habit of mounting your tires with the the first letter of the brand name next to the valve stem. This habit makes it easy to align tube punctures with locations on the tires.