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.
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?
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 :)
Close the presta valve and see how high you can get the pressure reading, and if it maintains pressure or leaks immediately, even a small amount. A badly matched seal due to the valve stem could be a commonality. Is this a problem with both tires? What about other bikes you may have, can you test it on them?
Thank you for your answer! Appreciated. I only have that one bike, but it happens on both tires and, actually, one is tubed and one is tubeless. What I did is trying to get them to feel as close as possible in terms of firmness without actual data and then checked pressure. Both read the same PSI, give or take a couple points, which I attribute to the vagueness of pumping "to the touch".
I did what you asked and what happens is the following: I can get to 24.5 PSI before the pump resists very hard. I probably could force it a little more but I'm afraid to break something? The pressure stays there until I release the pump handle which was resisting, when I stop holding it, it goes back up somewhat and I lose a bit of PSI, but not all.
What kind of pump are you using floor or hand?
It's a floor pump. This one: https://www.action.com/fr-fr/p/2561081/pompe-a-velo/ I also have a hand pump but I guess it's not particularly useful right now?
This is my floor pump against a typical presta valve easily holding ~175psi. You should be able to get well over 100psi on any floor pump against a closed valve.
Take the bike/pump to a local bike shop to compare readings and pressures against a known good source or at least just take your pump(s) and verify against a known good pump.
There's no risk to using force? Maybe I just didn't push hard enough because I was scared to put too much pressure on the presta and bend it. They look weak.
No risk. Road can go well over 100 psi in road stuff all the time.