I pumped the tires on my new bike up to 45 PSI a few weeks ago, and noticed they're both down to 36 PSI now. I tried the water bath test on the front tube and it was fine.
Do tires just leak air naturally, the way balloons leak helium?
Check the valve too. They can slowly lose pressure. I run trails with 25 pounds in my tires--29x2.25. Otherwise they would be bouncy and lose traction. Smaller diameter or road oriented tires could go with 45psi.
Tubes do leak over time. I've never paid much attention to how fast mine go down, but nine psi over several weeks is probably not something I'd worry about.
Yes the only question is how fast....if a bathtube test is negative for air bubbles my guess would be about 6 weeks, to go from 45 to 36 with a say 2.25 x 26 tire
If you are running tubless they will almost be flat within a month, and lose quite a bit of pressure in a couple weeks.
If you are running tubes, you will lose maybe 10psi a month, and be completely flat over the period of a season, say if you put you bike up for the fall, they will be flat by the spring.
It is always good to check you pressure before every ride, even if that's the old fashion thumb and finger squeeze to make sure its at least close.
If you are running tubless they will almost be flat within a month, and lose quite a bit of pressure in a couple weeks.Not in my experience
If you are running tubes, you will lose maybe 10psi a month, and be completely flat over the period of a season, say if you put you bike up for the fall, they will be flat by the spring.
It is always good to check you pressure before every ride, even if that's the old fashion thumb and finger squeeze to make sure its at least close.
^^ Both above are accurate in my experience. True UST 3-4 weeks. Ghetto tubeless every few days.
Also, drastic temperature swings, like those in the desert southwest where I am (40F in the morning and 100F in the afternoon) play a role in tire pressure.
I have 2 mtn bikes, 1 with Schrader valves, the other with Presta. The former will hold the same pressure for weeks without needing air; the latter loses pressure halfway thru a ride and needs more. These are brand-new tubes with no holes in them. I just really hate Presta valves.
There is no reason to run presta on a mtn bike. I have always been baffled why people even bother with them. In a race, a presta change just takes more time to change.
Sealant will also seal leaky schraeders if they ever happen to leak.
IME, regular tires with sealant (Conti Mtn King) go flat in a few days.
My UST version of the same tire seems to lose pressure at close to the same rate as a tubed tire, which seems pretty consistent with what the OP is dealing with, and is totally normal.
I have not used any tubeless ready tires to compare. but the casing definitely makes a difference. and also of course the rim seal makes a difference.
It's two weeks later, Friday, Sept 7th 11pm, the bike has been in storage the whole time and both tires are down to 43.7 psi front, 45.0 psi rear. So losing about 0.7 psi/day.
This is either a)normal, b)bad tubes, c)bad tires.
I haven't had a chance to take it on any trails yet, and forget doing any downhill on this cheap BSO. Just riding around the neighborhood for now, mostly plaved, I hear a higher PSI is better for that. First bike I've ever bought myself, legs not in biking shape, etc etc...
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