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Old 03-04-10, 11:17 PM   #1
johnr783
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Tire pressure question

I havent been able to ride my commuter for the past couple of weeks. I have been riding though so please be gentle. . .

My question is: Before I was able to inflate to 80 psi, and today I was inflating the tires and was only able to get it to 60. The tire specs are 26x1.5 and the tube is 26x1.25-1.75. As stated, I have gotten up to 80 before, no problem, but today I wasnt able to on either the front or the back. One tube is the same, the other tube is new.

I did take the tubes out of the tires, I had to replace a liner, and they stuck to the tire. Could that be why? Maybe they have to be run for a few miles before I can get them up to 80 again?

Its not a huge problem, as long as the tires are firm, I was just wondering why the change.

Thanks
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Old 03-05-10, 01:10 AM   #2
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I'm not sure what you mean by "couldn't get it up to 80." Would the air not go in at all, or did you keep pumping, hear the hiss as air went through the valve, but the pressure didn't rise, or what?
It's not likely both tires developed a problem simultaneously, so I suspect the pump or gauge. Many gauges are junk--they work inaccurately for awhile, then quit, or die, or read wrong.
as for the pump, if there's an obvious way to open yours (unscrew an end plug?), do that and pull the guts out. There will be a shaft and a leather or plastic washer-looking thing on the end that seals against the inside of the pump. Make sure that's not folded or dirty or worn out, put a LIGHT coating of grease on the part that contacts the pump cylinder and reinstall carefully, so it doesn't wrinkle.
Check the "chuck," too, the part that clamps or slides onto the valve. They have soft gaskets inside that can wear out, and sometimes the cam goes. May be repairable, may not--your bike shop or the manufacturer's web site can probably tell you (generally, cheap pumps are throwaways; you can order repair kits for more expensive ones. A few companies have sent me free parts when I've asked about buying them, or you can sometimes find hardware and hoses at places like Home Depot). In any case, pumps are pretty simple. I've made or substituted parts several times with materials from hardware stores.
If it's a tire leak, fix it, but find the cause so it doesn't happen again. A sticking rim strip or liner isn't likely to cause a flat, in my experience, but it can. You can avoid stickage by dusting the inside of the tire with talc or baby powder when you reinstall everything.
To check for leaks, pull the tubes out of the tires, inflate them a little, and if you don't see or hear anything obvious, dunk them in a bucket of water and watch for bubbles. Try to keep track of where the holes are in relation to the tire and rim, and check those areas carefully for thorns, protruding spoke ends or whatever so you don't have the same problem again tomorrow.
if they don't work right when you put them on the rim, they won't work right after any number of miles. They don't have to "seat" or anything.
One last tip: when you install a tire and tube, rotate the tire so its label is at the valve and facing to the right side of the bike. Then when you do get a puncture, you can tell by the location of the hole in the tube where the sharp thing came through the tire and be sure it's not still in there. Saves a few seconds to several minutes looking for a little tiny thorn.

Last edited by Velo Dog; 03-05-10 at 01:17 AM.
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Old 03-05-10, 07:17 AM   #3
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My wild guess is that you're using a frame pump, in which case the solution is to get a real floor pump for your routinetire top-orffs and save the frame pump for what it's designed for - emergency use on the road.

It's normal for the tube to stick to the liner or tire casing. If this bothers you, you can apply baby powder to the inside of the tire before installing the tube.
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Old 03-05-10, 09:53 AM   #4
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Presta valve or schrader?

The most common cause for the situation you are reporting is a sticking poppet valve on a presta valve tube. The easy solution is to "burp" the valve by pushing it into the inner tube and releasing a tiny amount of air pressure before attempting to inflate the tire.
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Old 03-05-10, 09:55 AM   #5
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you're gonna need a stronger pump I think. you should be able to pump the heck out of a tire/tube combo until they burst which should be well above the MAX rating on the sidewall
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Old 03-06-10, 02:21 AM   #6
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I was using a floor pump and I have never had a problem pumping to 80 psi before. It was weird though, the air pump would inflate and once I hit 60 the air would shoot outside the valve instead. I tried taking it out and reattaching many times but nothing worked.

Oh well, its not a big deal. I was just curious. Thanks for the time and responses everyone.
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Old 03-06-10, 05:31 AM   #7
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Even 60 psi sounds pretty high for a tire that wide. How much do you weigh?
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Old 03-06-10, 08:12 AM   #8
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Even 60 psi sounds pretty high for a tire that wide. How much do you weigh?
Quite a few 100psi 26x1.5 tires on the market. Which isn't to say that they need to be inflated to 100 for most of us.
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Old 03-06-10, 08:27 AM   #9
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i ran into a similar problem... seemed that was how much pressure the hose was withstanding. when you're pumping. is any air going into the tube? With mine, it wasnt, upon inspection, I found that the pump wasnt pressing the valve, hence the air was never leaving the house. i wrote the pump off as junk & used another one.
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Old 03-06-10, 12:59 PM   #10
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Quite a few 100psi 26x1.5 tires on the market. Which isn't to say that they need to be inflated to 100 for most of us.
Right. There is "max" pressure a tire can handle and then there is "proper" inflation for the weight of the individual. FWIW, I run my 28mm tires at 80psi, my 32mm tires at 50psi. A 1.5" tire is even wider so I'd run them even lower.
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Old 03-06-10, 01:12 PM   #11
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Originally Posted by pacificaslim View Post
Right. There is "max" pressure a tire can handle and then there is "proper" inflation for the weight of the individual. FWIW, I run my 28mm tires at 80psi, my 32mm tires at 50psi. A 1.5" tire is even wider so I'd run them even lower.
Generally your rolling resistance will increase as you drop pressure.
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Old 03-06-10, 06:11 PM   #12
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Let's not go through that whole discussion again!
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Old 03-06-10, 07:15 PM   #13
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Air pressure question

hypothetical situation. If you had a recomended tire pressure between 50-80lbs. I know your rolling resistance would be different, but would your rim be more likely to bend with 80lbs than with 50lbs?
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Old 03-06-10, 07:59 PM   #14
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Why would the rim bend?
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Old 03-06-10, 10:34 PM   #15
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More pressure

Seems like 80lbs of pressure would make your wheel stronger.
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