Winter tires flat after sitting for over a year? How concerned should I be?

So, I just picked up a set of extra wheels and snow tires (Nokian Hakkapeliitta's) from a buddy of mine. The tires have about ~500 miles on them- tread-wear looks just about brand new. When I checked the pressure on them, 2 of the 4 of them were damn near flat. They've been sitting outside (mounted to wheels) in tire storage bags for about a year now. I always stored my extra wheels/tires in my garage or basement, but, to each their own... at least he put decent tire storage bags over them I suppose.

I inspected them pretty well and didn't see anything that looked like dry rot on the sidewalls. I also didn't see any punctures or nails/screws ect anywhere on either of them. I aired them back up in my garage and didn't hear any audible leaks either. I'm going to check them in the morning to see if the pressure drops overnight. Assuming the pressure stays the same overnight, how concerned should I be?

Maybe they just went flat from sitting outside through seasonal changes? Or is there something else I should be concerned about?

Thoughts?

Thanks in advance!

I wouldn't be … most tire/wheel combinations will loss pressure over time … (especially is left sitting ..for some reason)

if you have a large tube, air them up and push them down in the tub … slowly rotate them and look carefully for any tiny bubbles … if you don't see any .. use um … if you're worried, check the pressure once a week … but we should be doing that as a matter of course... LOL

I was astounded that my tires held full pressure over the last 9 months. I wouldn't worry, just check them frequently and repair if needed down the line.

Likely the valve stems. Remove the valve core and replace with a new core. The rubber on the core tends to go bad. You can get a core tool and new cores at wally world for about 12 bucks.