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I recently got an xtech pressure gauge that reads up to 160psi. My bike is a road bike that uses presta valves on the inner tubes.

Here's the gauge (the one at the bottom): http://www.moruyabicycles.com.au/contents/en-uk/d377.html

When I pop it on the valve the reading only seems to go up to about 40 psi. I feel if I inflate my tires much more they might explode (they are pretty much rock solid and I was expecting a reading of something more like 100) - they seem to have the same level of inflation as I bought them.

So my question is, is there a special way in which I should be hooking this up? At the moment I'm just unscrewing the metal release thing on the presta valve and pushing the gauge on firmly. The gauge holds its reading even after you remove it, and I've tried resetting it by pressing it's release valve button but that doesn't seem to make any difference.

I'm guesssing it's busted but maybe I'm doing something silly.

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You can't really judge pressure with your fingers/thumbs past maybe 30 psi. Instead, try leaning all your weight onto the saddle and/or handlebars and see how much the tire squishes out. If you think about the physics, your thumb's contact area is about one square inch: how different does it feel lifting 40lbs vs 100 lbs with just that part of your thumb? –  freiheit Apr 30 '11 at 0:57
    
Put it this way, at a reading of about 40 psi the tire feels like it's solid rather than filled with air. I'm pretty sure from the shop it was around this kind of inflation and it's been good for riding on. Perhaps I am just crazy, should I try pumping them up to 90 psi according to my gauge and if I do that am I risking breaking my pump/inner tube/tire/face? –  John Hunt Apr 30 '11 at 1:13
    
Just FYI at the current pressure, using all my effort I can pinch the sides in about 2mm on each side, hopefully that gives you an impression of how inflated they might be? –  John Hunt May 5 '11 at 11:20
    
Just spoken to my friend, he reckons at 85psi on his bike he can only manage about 1mm - 2mm...maybe I'm just broken? Anyway, I'll probably just take it to the bike shop this weekend. –  John Hunt May 5 '11 at 11:28
    
Ok, riding at a suposed 60psi was actually alright, not too hard/bouncy a ride.. maybe I am just being paranoid! –  John Hunt May 5 '11 at 22:45
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3 Answers

I suggest borrowing a pump with a pressure gauge and pumping up your tyres with that. Then try your gauge once you know the tyre pressure. Bike shops and a lot of cyclists have a floor pump because they work better than the little portable pumps than most cyclists carry. And those have a gauge on them that's usually fairly accurate.

You say the pressure release button on the gauge "doesn't seem to make any difference". What do you mean - does the gauge drop back to zero? If not it's definitely busted.

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Yeah it goes back to 0 when I release the pressure on the gauge. –  John Hunt Apr 30 '11 at 8:47
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Presta valves can be a little tricky as well. An old practice is to unscrew the lock-ring all the way and then push it in to break the seal before applying the pump. Sometimes the valve will stick and you'll get false readings.

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Thanks, will look into that and get back to this! –  John Hunt May 4 '11 at 5:56
    
Ok well I don't think I can do that with my gauge, but anyway I've pumped my tires up to (apparently) 60psi which makes the sides of the tires very hard to push in. I'm going to ride into work tomorrow so I'll soon figure out if that is insanely high or not. My tires recommend between 85 - 110psi, is that even attainable by a regular bike pump (albiet a good lezyne one)? –  John Hunt May 5 '11 at 11:06
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up vote 1 down vote accepted

Just went on a ride with some friends, one of which has his tires inflated to 90psi. 90psi is way higher than I thought.. there is no give on his tires when you squeeze them. Looks like I need to pump mine way higher!

Also, considering getting a floor pump as 90psi might be a pain with my hand pump.

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Try looking at this. –  ChrisW May 8 '11 at 13:38
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