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Old 12-17-07, 08:08 PM   #1
JeffC
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Why Tires Lose Pressure At Different Rates

Each weekend I top off my tires for the coming week of commuting. For the past few months my floor pump always registers the front tires around 55 psi and the rear around 40. I then fill them to about 65.

Has anyone else noticed that their tires are not at the same pressure after a few days? Is there some reason that rear tires in general may lose more air than front tires, perhaps the added weight? Obviously my rear tube may leak ever more slightly than the front but assuming the tubes are in equal condition is there some other reason why a rear tire may lose more pressure than a front tire?
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Old 12-17-07, 08:40 PM   #2
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Valve core possibly leaking abit more and rubber tubes are not all equal. Rubber is porous and some more so than others even in the same brand.
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Old 12-17-07, 09:08 PM   #3
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My front leaks faster.
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Old 12-17-07, 09:14 PM   #4
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Loosing 10 to 25 psi in a week from what are apparently large volume low pressure tires is quite a lot. What type of valves do you have? If Presta, be sure the valve nut is snugged down after filling the tires. If Schrader, be sure the valve core is tight.

Also, you may be loosing a fair bit of pressure if you use a tire gage. Every pressure reading lets air escape and bike tires don't have much volume to spare.
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Old 12-17-07, 09:43 PM   #5
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The weight on a tire won't appreciably change the pressure, it mainly changes the contact area. I would think any differences in leakage rates would be coincidence as to whether the front or back was faster.

Car tires do this too. But they're a lot thicker, have a lot more volume for a given surface area, and operate at lower pressures than most bike tires, so it's not nearly as noticeable.
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Old 12-17-07, 10:10 PM   #6
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Every time I've found one tube loosing that much air that quickly I've always found a leak somewhere. I may have to pump up the tube quite a bit but the leak has always been there.
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