Bicycle Mechanics - tires keep losing air?

I ump up my tires religiously before I ride, like 3 or so times (at least) a week. they're always losing air. the thing is, they're brand new tubes. and it will alternate, front and back. I'm kind of new to presta valves, but I've never had this problem before. I'm using a Presta to Schrader adaptor to inflate, if that means anything. I'm so confused; I've never had such a slow, peristent leak. Any ideas?

Are you closing the valve after using the adapter? If not, on bumpy roads at speed the presta valve can open causing you to lose air.

The procedure goes: open the presta valve by unscrewing the top nut, screw on the adapter, inflate, remove the adapter, then close the presta nut. At this point you can either replace the adapter or not, your choice. You may also want to look at your pump to see if it adapts to presta valves. If so, you won't need an adapter other than for using a compressor. Most of them unscrew, you flip the internal parts around, replace them and screw it back together.

Hope that helps you.

Are you closing the valve after using the adapter? If not, on bumpy roads at speed the presta valve can open causing you to lose air.

The procedure goes: open the presta valve by unscrewing the top nut, screw on the adapter, inflate, remove the adapter, then close the presta nut. At this point you can either replace the adapter or not, your choice. You may also want to look at your pump to see if it adapts to presta valves. If so, you won't need an adapter other than for using a compressor. Most of them unscrew, you flip the internal parts around, replace them and screw it back together.

Hope that helps you.

But don't forget when you put air into a presta valve you need to burp the valve after you've unscrewed it, then put your adapter on and pump away. When done pumping remove the adapter and screw down the valve but not real tight just till it stops, then you can put the adapter back on the valve to store it on the valve if you choose too.

BUT I have a feeling you already know all of this that Wordbiker and I have mentioned; therefore the next question is what brand tubes are you using, and which ones as well as to their weight in grams? Because if your using tubes that are considered ultralight or racing tubes, they are thinner thus will bleed air out naturally at a rate of between 5 to 15 pounds a day depending on how ultralight they are. I use Specialized Turbo tubes that weigh 65 grams and these lose about 10 to 15 pounds a day. The only way to get around this is buy thorn resistent tubes that are quite a bit thicker, or cheap thick Walmart tubes, and those will probably lose about 5 pounds every other week.

Yeah, how much are you losing? 5 to 15 pounds per day is normal for high pressure road tires.

Al

I'm running 28's at only about 85-90 psi. the tubes are nothing special, I think they're branded as schwinn 28-32s. I may not be screwing the valve all the way in, or it may be working its way loose; I ride on brick streets all the time (one of the reasons for low pressure and wider tires), and sometimes it's pretty brutal.

10-15 lbs a day? I never Knew.

Thanks for the help.

Those Schwinn tubes are fairly thick, but could still lose 5 psi a day especially on hot days, banging down on brick roads don't help either.

10-15 lbs a day? I never Knew.
Yep. All pneumatic tires are permeable and lose some air. The rate of loss is proportional to the pressure differential. Car tires have thicker carcasses, a much lower pressure differential (~35 psi vs. 80-160 psi), and much more air to lose so they lose pressure much more slowly.

My 120 psi 23s lose about 10 psi/day.

You should look seriously at a floor pump, btw. They aren't expensive.

Well, I took the tube out, because it wouldn't hold air at all. (the rear tube is magically ok for some reason), and the whole valve had ripped out of the tube. I beleive this was Operator error when I installed the tubes, cranking the valve stem retaining nut all the way down before I initially inflated the tires.

Thanks for everybody's help.