Commuting - Tubes Losing Pressure?
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07-28-10, 03:32 AM
My KHS Urban-X (awesome & cost effective, BTW) came equipped stock with Kenda Kwest tires, and tubes of an unknown make. The Kwests are rated at something like 40-85 PSI, and I've been filling them to about 60 PSI. I've noticed that no matter what, they lose air. Slowly...maybe 10 PSI a week.
I thought I might have some slow leaks, but they seem to stabilize around 30-40 PSI. I've let them go pretty long without filling just to see if they'd go flat, but they never get out of range.
Is the slow loss of air a normal part of riding, or should I maybe look into replacing the tubes? I've ridden the bike for a year and ~1000 miles, and to the best of my knowledge this has been cropping up since early on.
07-28-10, 04:29 AM
I wouldn't be worried about that unless you're annoyed by having to re-pump the tubes once a week. Maybe the valve isn't completely airtight. Running the tubes with low pressure isn't a good idea though imo.
10psi a week isn't anything to worry about. Just top them off once a week. All tubes leak a bit. The higher the pressure the faster the tubes will leak, then the leak gets slower. If it gets worse, say you have to top off every 2 days, then yeah replace the tubes. Or, if you're still in any doubt, then just replace the tubes and stop worrying :D
Yep tubes are cheap, replace them if they worry you. I fill mine up every about 150 miles or two weeks (just less than 90 lbs). I ride on real bumpy roads and (I might be wrong) but I think that effects the pressure too.
EKW in DC
07-28-10, 08:53 AM
Like others have noted, not a major cause for concern. It's pretty normal. I try to keep my tires between 90 and 100 PSI and make a regular practice of topping off the air once a week or before longer rides. When I top off, I find that the tires have normally fallen to between 75 and 85 PSI - so down 10-15 PSI/week. That's been standard w/ whatever tubes I have in there for the 8 months I've had my tires. This includes numerous tube replacements for a variety of reasons.
So, I'd say, top off the air and ride! Nothing to worry about.
BTW, unless there's a ton of glass and other dangerous debris, if you're riding on paved roads and trails, I might suggest going towards the higher end of the range for inflation on your tires... just an extra unsolicited thought.
rubber leaks air, just like a balloon.
07-28-10, 01:50 PM
My 700x25's lose about 2psi per day, and I pump them back up (to 120psi) each and every morning. It takes less than 60 seconds, maintains consistency, and helps avoid flats.
Higher quality tubes retain air pressure better than cheap tubes, but as sm1960 points out, rubber is porous and inner tubes will leak small amounts of air pressure over time.
Conti, Michelin and Schwalbe all make higher quality tubes than what is commonly available at the LBS. You can expect to pay roughly $7-$10 retail for these tubes.
Worth it? Depends on how many times one has had a tube fail, or how averse to airing up one's tires a person is.
I have the same tires/tubes on my Urban Express. I haven't had any trouble with them but I do pump them once a week to top them off. I run them at about 80psi and it works pretty well for me.
No cause for concern.
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