Why do my tires always deflate between rides?

Question

I realize this is a topic that’s been posted about a few times, but please forgive me for adding a new thread anyway just to make sure I’m not missing something. I don’t know much at all about bicycle maintenance or modern mountain bike tires.

Every time I want to go for a ride, I have to inflate my tires. It’s been that way since I bought the bike brand new (Giant Talon 2) and continued even after confirming there were no leaks.

The same problem, albeit to a much lesser degree, occurs with my 2nd bike that uses the older style standard valves (the main bike uses the Schrader-style valves). The only variable I can think of is the temperature of my garage, which can get mighty warm here in Phoenix with air temperatures hitting 40-45 degrees C (104-113 degrees F) The bikes are hanging from a hook on the wall with no weight on the tires.

Can the extreme heat in my garage actually change the shape of the tubes/tires, thereby permanently changing the seals, causing a slow leak? If the answer is yes, is there any kind of solution?

It is a gigantic pain in the butt to have to pump up the tires before every ride, even if only 24 hours apart. I’ve never had the tires get low during a long ride, so however it’s leaking, it’s very slow.

Thanks in advance for any advice you might be able to provide.

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Thanks so much for all of the thoughtful replies! I actually rode down to the bike shop yesterday with the intention of having them check my tubes, but they'd gone out of business! The leak is still happening even when I don't hang the bike, and seems to be worse in the front than the rear. The really odd part? The more I ride it, the slower the leak seems to be. That makes no sense whatsoever so I'll assume I have that wrong somehow, but that's what seems to be the case. As a short term solution I bought a portable pump to carry on the bike, but the leak is slow enough to where I don't think that's too much of a concern (getting stuck on a ride). I think I'll just try a different shop & maybe just spend a few extra bucks on some higher quality tubes.

Answer 1

First of all, do your tyres (tires) lose air at the same rate or are there noticeable differences, one going down faster? If this is the case the last paragraph may explain things.

All tyres lose air over time. However the bigger the tyre the longer it will take to notice the loss. And also the higher the pressure the faster the loss. Your car wheels have the same drop of pressure but because of the bigger volume and the comparatively lower pressure the drop is less noticeable. Still you're always advised to check air pressure each other month.

Pressure drop is mainly due to permeability of the rubber, let's call it like that, of tyre and inner tube which are constants for a specific type of compound. In the late 80s latex inner tubes came to use because they were very light and more resistant to perforation. The disadvantage however was that the pump came into daily use.

The quality of the seal of the valve plays another part. It is quite normal to top up a 25mm racebike tyre @100psi at least once a week. All Schrader (car type) valves have a removable core. For many newer Presta / Sclaverand valves it's the same. To do this you'll need a special, inexpensive tool. For some factory fresh valves the core isn't properly screwed in and may leak. It's always a good idea to check the tightness of the core, it could be a reason for leaks.

Answer 2

Inner tubes are made of a compound of rubber and other materials, that rubber is "visco-elastic", and when the tube is inflated, it expands the surface of that tube and therefore very tiny spaces where air can leak naturally.

So my first question would be, are you using good quality tubes? What is the brand/model? If your tubes are of low quality, the high temperatures may somehow affect the rubber. For example my bike came with Maxxis tubes, and they were the best I've ever used, I noticed a huge difference, almost no deflation overtime, and it took a real hard hit on the back wheel from a mistake of mine to make it puncture.

But when I did first puncture, I mostly started using Michelin's Butyl tubes and they're also great (butyl is known to have very good air/pressure retention properties), they did deflate a little overtime when I didn't use my bike for over a month, but it was nothing dramatic (and during summer with lots of temperature variations), just a couple PSI less.

Another thing that comes to my mind are valves, their quality may also play a role, similarly, if your valves are a bit loose or damaged, air might leak, sometimes air also leaks at the junction of the valve and the tube, I've had that issue countless times before I start using better quality tubes.

All in all, it's normal that tubes would deflate over time, but from what you're describing, the very short time windows between your rides are definitely not normal. So I'd double check the tubes' quality and also the valve junctions, try pushing aside your valves and inspect if there is a micro-fissure or hole next to the seal. As for the valve core, that would be the last thing I'd check, they're usually another reason for leaks but less common of a culprit.

Try checking if those tubes aren't already micro-punctured (especially if your tubes are made of two parts "glued" together, sometimes the join of these two parts can deteriorate), drop them in a basin of water, and see if bubbles appear, very tiny tiny fissures in the rubber can be there if the tubes are old.

Hope that helps.

Answer 3

I had the case twice when the tire gets flat overnight without any visible damage for the tire or the tube. I replaced multiple tubes in both cases, but for both cases the problem was with the tire, not with the tube, and went away after the tire replacement. I managed to find the puncture on the tube once, it was very subtle and looked like a tiny cut on the outer side. It was only detectable after inflating the tube outside the tire.

I still do not know what was wrong. It was a rear tire in both cases, and not new, while did not look completely worn. In both cases it initially served well for some time.

Answer 4

If the outside temp is 40C/104F then I bet its easily much hotter in your garage, up high where the bike is hanging.

As a simple test, try not hanging the bike, and leave it right way up on the floor. See if that makes a significant difference, by doing careful pressure tests before and after.

The orientation of the rubber shouldn't have any effect at all, ie which way around the valve is pointing.

Answer 5

When I was a kid in the 90s, I remember experiencing the same deflation for the bikes in my Grand-Parents house, but we are talking about weeks if not month between rides.

What my Grand-Pa told me then is that the material used is not pure rubber (anymore), and you should expect porosity from the inner tube. One would think they are perfectly sealed, but it's a fact that they let air loose overtime. Temperature may be an aggravating factor for porosity.

You can find some more discussion about inner tube leakage here https://www.quora.com/Why-is-it-hard-to-make-bicycle-inner-tubes-that-dont-leak-air

Now since you mention big temperatures in your garage, you may want to try not inflating your tires to the max, as the compressed air getting out from the pump will be noticeably colder than outside temperature. Instead, give a bit of time for the air from the air in the tube to heat up, and therefore expand. Check pressure and adjust afterwards.