Last weekend I replaced my folder with a pair of new Schwalbe tyres (28-406) and tubes (SV6A). The tube are Presta valve and lightweight. I pumped them up to 60psi but they both leaked in 24 hour and before I had a ride yet. The front dropped to 45 and the rear to 30. Then (2 days ago) I pumped again but to 90psi just above the min. tyre pressure 85psi. They both seem okay to keep the air pressure. It really puzzled me. Would it be 60psi not enough to shut the valve completely and thus cause the leak? Does a tube have a recommended pressure range? I have already tightened the valve lock nuts properly and replaced the dust covers. I even had a under-water check of the front tube and no leaking was found. Thanks
Franky

You may have let some air out when you first checked connecting your pump.

No. I always hand check by squeezing on the tires first. I found the rear tire much softer the first time I realized a possible leak (60->30psi).

You probably lost some air when you put the pump on to check the PSI.

i wouldn't worry about it. just check before riding

As long as you don't have a problem to actually remedy, chalk it up to one of those great mysteries of life. It's working fine now, so thank the gods of butyl and enjoy the bike.

Tubes do not have pressure ratings -- the tires do. The tube should work at any pressure that the tire is rated at.

Neither presta nor schraeder valves need a certain amount of pressure to stop them from leaking either.

Dust covers just keep dust out -- they won't stop a leak in most cases.

If you didn't let the air out yourself accidentally, it is possible that there's a slow leak, though I know you said you checked. Tires do lose air over time -- high pressure skinny tires tend to need airing up every other day or so, but fatter lower pressure tires should last a week or two. But losing half the pressure overnight? Not normal.

I had a tire once that leaked when I put air in it. I let all the air out, and it didn't leak anymore.

Are you screwing down the stem lock nut after putting in air? Sounds like leaky valves.

If the presta valve with a removable core, remove it, clean it, then re-install it.

If it's a schraeder valve, like a standard car tire, sometimes the valve core can become loose. The remedy is to get a valve core tool and tighten it a bit. I normally remove it completely, inspect the core (sometimes the spring gets hung up or the rubber gasket is split) then reinstall it. Even on new tubes. And dust can work its way in the valve core and wedge it open. I've seen this happen all the time in the Nevada desert. Who knew that a valve cap has some utility?

Perhaps some of the excess powder they use to avoid the butly sticking together was in the valve seat and just needed to be blown clear with some extra pumping. I can't say I've noticed anything similar but then I've never just pumped up to part pressure. And by the time I put enough strokes worth of air into the tire to fill it so I can actually ride it I've pushed enough air through the valve to blow it clean.

You don't have latex tubes, do you? Those leak slowly in the garage.

Thanks for all your opinions. I've been busy for a few days. Almost four days ago, I pumped up the tires to 100psi and the bike has been just sat there. I checked pressure today and both were just below 85psi. I think I can confirm that both tubes are in normal condition (though still out of my expectation) and lose a 4-5 psi each day. btw, there was quite a lot of power on the tubes when they were installed. Just not sure whether that was the cause at the beginning. Next time when pumping up a brand new tube, it may probably be good to push the valve core a couple of times to blow away any powder around the valve and allow valve to close properly. Then pump it to the disired pressure. Just a guess and no harm doing that, I think.

Both my new tubes are schwalbe SV6A. I think they are butyl rubber instead of latex. Please correct me if it's not true. Anyway, just dont know the difference.