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Old 10-18-07, 09:00 AM   #1
save_alkaline
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how to measure tire pressure without a gauge

hmm.. my tires say no more than 110 psi. my mini pump says it's good for pumping up to 140 psi. any way of knowing when i'm close to my 110 psi max on my tires?
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Old 10-18-07, 09:56 AM   #2
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Hate to say it, but use a gauge. Sure, you probably don't have one that goes that high--but if you're going to ride, you need one. Not that expensive to purchase.

Otherwise, you're stuck doing the thumb test: push down on the tire with your thumb, and see how much it deflects. If it feels stiff enough, good. Or you can do the weight test: site on the bike, see how much the tire squats down. But both are just a bit subjective. Good enough for wide tires; as long as you don't get flats, then you had enough air.
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Old 10-18-07, 10:10 AM   #3
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You want to get decent at the thumb (or feel) test anyway for on-the-road flat repairs. But simple floor pumps with pressure gauges are totally worth the money for home/garage repairs and pre-ride checks.
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Old 10-18-07, 10:51 AM   #4
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Calibrate your thumb.
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Old 10-18-07, 10:54 AM   #5
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i'll look into a gauge or a nice floor pump for the house.

in the meantime, how much should i be able to squeeze it with my thumb? i don't have any reference as to how it should feel. i kind of did what you guys were mentioning, feeling with my thumb and checking compression when i put weight on it, etc. but it doesn't feel all that reassuring, haha.
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Old 10-18-07, 11:17 AM   #6
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Measure the load in pounds on each wheel with a bathroom scale. Apply ink or other marking substance to the tires. Set the tires down on a smooth flat surface without rotating them. Remove tires from surface. Measure the area of each tire print in square inches. Load divided by area equals pressure.

Much easier and more accurate to get a gauge!
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Old 10-18-07, 11:19 AM   #7
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I use a thumb gauge too.
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Old 10-18-07, 11:30 AM   #8
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presumably you are only changing one flat on the road at a time.

just compare it to the other tire, which should be properly inflated from the beginning of the ride.

that should get you close enough to at least get home. if it feels soft then stop and pump it some more.
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Old 10-18-07, 11:32 AM   #9
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My thumb gauge works ok upto 80# or so but above that it flattens out.
80# for me is pinch flat range, especially on the rear.
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Old 10-18-07, 12:13 PM   #10
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just sit on the bike then and look at the tire deflection. i can tell by looking at it.
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Old 10-18-07, 09:27 PM   #11
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If you are using a mini-pump I am sure you wont get more than 80 psi, which will be enough to get you home after fixing a flat. You need a floor pump with guage at home, or a Topeak Morph.
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Old 10-18-07, 10:55 PM   #12
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I use my floor pump at home, and my thumb on the road. Usually you can calibrate your thumb on the good wheel and compare with the repaired wheel, unless of course you double flat.
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Old 10-19-07, 12:41 AM   #13
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If your concern is blowing the tire up, its not gonna happen b/c of 30 extra lbs. For liability reasons, the stamped pressure rating is about half of its true upper limit.
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Old 10-19-07, 07:51 AM   #14
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You need to get a floor pump. When you do, you will kick yourself for using your hand pump all these years. And you will replace fewer tubes with holes around the valve stem.
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Old 10-19-07, 11:07 AM   #15
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I agree with the advice for a floor pump for normal use when you are at home.

I do carry a mini-pump when I ride. To figure out how much air I pump into the tire with the non-gauged mini pump I try it out at home. I begin with a completely flat tire and use the mini pump, counting the strokes that I use and then test it with a guage to see how much air I get into the tire with a given number of strokes. Not precisely accurate but I have found it reasonably so, and good enough to let you finish your ride and get home.
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Old 10-19-07, 01:39 PM   #16
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Your life will be a lot easier if you just get a CO2 inflator for on-the-road. Mini pumps are a real drag compared to a CO2 unit.
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Old 10-19-07, 05:50 PM   #17
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Also floor-pump will result in fewer busted valve-stems and leaks as well. The repetitive flexing and pushing motion of the hand-pump will quickly weaken the stem and cause it to snap or leak.
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Old 10-19-07, 05:56 PM   #18
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I purchased a Topeak digital gauge for about $15 one of the best bike related investments I have ever made. My floor pump has a gauge but it is off by a few pounds and found I had too much air in my tires. It is also handy for using on my car tires. I have checked other riders floor pumps with gauges (they often bring them to the lot before riding) and some are off as much as 10 lbs.
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Old 10-20-07, 07:12 AM   #19
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Originally Posted by geraldatwork View Post
I purchased a Topeak digital gauge for about $15 one of the best bike related investments I have ever made. My floor pump has a gauge but it is off by a few pounds and found I had too much air in my tires. It is also handy for using on my car tires. I have checked other riders floor pumps with gauges (they often bring them to the lot before riding) and some are off as much as 10 lbs.
By what means are you ascribing the discrepancies in tire pressure readings to pumps and not the Topeak digital gauge? I am not familiar with that gauge, but, as with most things digital, I wonder how precise its readings are (had a scale once that was purposely set up to display only odd decimal read outs . . . it would read 10.7 lbs, 11.3lbs, etc. but did not have the capability to display 10.0 lbs . . . the read out was just a gimmick to make a cheap instrument appear more precise than it was). I'm not saying your Topeak is a bad piece of equipment . . . just saying that, unless you compare it (and any of the pumps you mentioned) with some instrument that has been properly calibrated (don't even know where you'd go to find one of those), it's only a guess that your Topeak is the more accurate among the various pump gauges to which you have compared it.

The good thing is that tire pressure on a bike isn't very critical at all. You mentioned that, before obtaining the Topeak, you had "too much pressure in your tires." What made you draw that conclusion? It is almost impossible to put too much pressure in your tires. You might make them more firm than you prefer, but, other than that, more pressure will not adversely affect your tires or your riding.

This was not always the case. 35 years ago (when my first road bike was new) if you put too much pressure in the tires, it would push the tire bead off the rim and the tube would blow out. Today's tires are designed to retain the bead so that, unless the bead is damaged, you can put tremendously high pressure in your tires without causing a problem.

My tires are rated for no more than 115 psi. I never ride without at least 140 psi in them, and have, on occasion, pumped them to 160 without a problem.

How much difference that extra pressure makes is anyone's guess, but I definitely notice the mushiness if the pressure drops to 115 or below. Even that isn't bad - I just don't prefer it.

I would feel lost without a pump that has a gauge, however . . . and I abhor having to pump a tire using my small hand pump. What a drag (second only to walking or calling for a ride when you have a flat and you are 20 miles from home).

. . . not knocking your post at all, just pointing out that your experience is only relative to the equipment you have at hand. The Topeak is probably not much more or less accurate than the other gauges you have used.

Caruso
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Old 10-20-07, 02:48 PM   #20
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most of those gauges, whether digital, on the pump, dial type, whatever are going to be inaccurate and likely "off" by some amount. How much you never know.

I had a friend who was a national champion autocross driver and he had a collection of tire gauges. He had three different gauges he would use, and he'd measure with all three and take an average to obtain something truly close to "accurate"... He had thrown out a couple of different manufacturer's digital gauges because he tested the same tire with several of the same gauge and there was like up to 5 lb between two identical gauges when measuring the same tire! when hundredths of a second count it makes a difference but for bicycles, just pump it until it feels right and go ride
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Old 10-21-07, 11:06 AM   #21
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When I fix a flat on the road, I just pump 200 strokes with my mini-pump. I measured the pressure with a gauge once, and it was about 110 psi.
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Old 10-21-07, 11:09 AM   #22
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It is almost impossible to put too much pressure in your tires. You might make them more firm than you prefer, but, other than that, more pressure will not adversely affect your tires or your riding.
1000% wrong. You must be riding on glass roads for 140psi to feel normal. The small decrease in rolling resistance (if at all) you get for going to ridiculous tire pressures is not worth it for the considerable decrease in ride comfort. Especially in the cases where higher pressure does NOT result in lower rolling resistance. It would be irresponsible to recommend this to everyone.

What tires and what size are you running?

http://www.sheldonbrown.com/tires.html "Width and Pressure" section
http://www.legslarry.beerdrinkers.co.uk/tech/JL.htm

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Old 10-21-07, 10:23 PM   #23
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"My tires are rated for no more than 115 psi. I never ride without at least 140 psi in them, and have, on occasion, pumped them to 160 without a problem"

I believe rolling resistance actually increases past 115-120
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Old 10-22-07, 06:19 AM   #24
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More important than absolute accuracy is repeatability for the readings. As Sheldon pointed out, everyone has a different ideal pressure, regardless of what number the lawyers put on the sidewall. Once you find the pressure that works for you, it doesn't matter what the gauge reads, as long as it reads the same for the same pressure every time.
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Old 10-22-07, 08:54 AM   #25
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Quote:
Originally Posted by Carusoswi View Post
By what means are you ascribing the discrepancies in tire pressure readings to pumps and not the Topeak digital gauge? I am not familiar with that gauge, but, as with most things digital, I wonder how precise its readings are (had a scale once that was purposely set up to display only odd decimal read outs . . . it would read 10.7 lbs, 11.3lbs, etc. but did not have the capability to display 10.0 lbs . . . the read out was just a gimmick to make a cheap instrument appear more precise than it was). I'm not saying your Topeak is a bad piece of equipment . . . just saying that, unless you compare it (and any of the pumps you mentioned) with some instrument that has been properly calibrated (don't even know where you'd go to find one of those), it's only a guess that your Topeak is the more accurate among the various pump gauges to which you have compared it.

The good thing is that tire pressure on a bike isn't very critical at all. You mentioned that, before obtaining the Topeak, you had "too much pressure in your tires." What made you draw that conclusion? It is almost impossible to put too much pressure in your tires. You might make them more firm than you prefer, but, other than that, more pressure will not adversely affect your tires or your riding.

This was not always the case. 35 years ago (when my first road bike was new) if you put too much pressure in the tires, it would push the tire bead off the rim and the tube would blow out. Today's tires are designed to retain the bead so that, unless the bead is damaged, you can put tremendously high pressure in your tires without causing a problem.

My tires are rated for no more than 115 psi. I never ride without at least 140 psi in them, and have, on occasion, pumped them to 160 without a problem.

How much difference that extra pressure makes is anyone's guess, but I definitely notice the mushiness if the pressure drops to 115 or below. Even that isn't bad - I just don't prefer it.

I would feel lost without a pump that has a gauge, however . . . and I abhor having to pump a tire using my small hand pump. What a drag (second only to walking or calling for a ride when you have a flat and you are 20 miles from home).

. . . not knocking your post at all, just pointing out that your experience is only relative to the equipment you have at hand. The Topeak is probably not much more or less accurate than the other gauges you have used.

Caruso
I have had some serious neck issues related to arthritis and degenative disks for about 10 years. It is very slowly over time getting worse. I am scheduled for my 3rd MRI in the last 8 years to monitor the deterioration.At some point cervical surgery may be needed.Tire pressure is very critical to my comfort when riding. I am 59 and generally go on decent paced 50-60 mile rides with my local club. I can feel the difference of 1-2 pounds of pressure. It can mean the difference between riding 60 miles with no problem (other than my usual 3 advils) or turning off the ride after 20-30 miles. In fact I have to be carefull when it is very hot as it will raise the pressure a pound or two. I know my Topeak is accurate I'm guessing to half a pound. Whatever guaue you are using I can't speak for. This isn't rocket science here. Just a stupid gauge.
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