[2001 ZTS]

There is some tips below. You don't see the reference to concrete/asphalt mentioned in some but they can react with eachother.

It is mostly related to moisture. The tires heat and cool much faster than more solid things like asphalt and concrete which take longer to heat and cool. Anytime one is warmer or cooler than the other moisture will form:

http://www.1010tires.com/tiretech.asp#storage

http://www.yokohamatire.com/pdf/tsb-112102.pdf

http://member.rivernet.com.au/btaylor/BMWT...oringTires.html

http://www.coopertire.com/us/en/safety/tir...ions.asp#item14

I keep my tires laid like panckakes in an unheated detached garage. Since they are stacked 8 high I store them fully inflated and never had a problem with deformation. The floor is concrete and they sit on a piece of particle board that is raised with 1" high "legs" (just scrap bits of wood).

Tip: since I have a kid running around I have dropped a long stick down the centre of all eight to make the 'tower' more stable