Why do my tires always deflate between rides? 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.
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.