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A place to ask bicycle repair questions, and for bike shop monkeys to share advanced non commercial wrenching resources (no YouTube self promotion). This is only for repair related topics.

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Tire pressure odyssey, what am I doing wrong? (self.bikewrench)

submitted 9 months ago by Natal to c/bikewrench

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Hello everyone.

I recently got myself a mountain bike from Canyon. It all works, got myself all the gear, pumps and all. And the pressure gage give me a reading of 10 PSI, which is odd because the tires are firm. 10 PSI should be nearly flat.

I have other pumps, including one that works for my car too, which I trust because I cross checked its values with my mechanic.

Here's the odd thing. I got the bike out and plugged it to the car tire pressure device and it also gave me a reading of 10 PSI. I also have a Topeak Shuttle Gage, 10 PSI.

How is that possible? I can't really believe all three readings come from faulty devices so I'm thinking I'm the one doing something especially stupid, or maybe a defect somewhere on the valve/tire but it's brand new, so I think I'm the one to blame. Any ideas where I've been an idiot?

I did open the nut on the presta valve prior to taking measurements.

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[–] [email protected] 4 points 9 months ago (1 children)

Since you've got multiple, previously checked instruments indicating the same, I think it's reasonable to believe the value it's telling you.

For a mountain bike at rest, 10 PSI (0.7 bar) wouldn't necessarily be flat, but might still be a bit low. If you sit on the bike, I would expect to see the tires bulging out at the bottom. What does the tire sidewall recommend for the pressure range?

[–] Natal 2 points 9 months ago

The range on the side is 20 to 50 PSI. To the touch, the tire is very firm. Not rock hard, but very little softness/squishiness to it. When I sit on it and ride the bike, there's a little bulging at the point of contact with the ground, I think it looks normal but my partner thinks it looks like flat. Still, it feels like a firm bike while riding.

Thank you for your answer :)