Given the stresses put on tires in normal use, it's hard to imagine stacking them 8 high is going to make any difference. It's like racing cyclists used to hang their bikes on the wall when not in use so the wheels would stay round. If sitting them on concrete is bad, imagine the harm being done to tires by underground and other concrete parking garages.
Good to know we should take your common sense advice and ignore the storage recommendations of numerous tire manufacturers and retailers.
I mean, what do engineers know? Stack 'em high.
Numerous experts but you don't provide a single citation?
So I did a search. Most tire storage advice doesn't even mention stacking height. That by itself doesn't support that it's a huge concern.
http://www.tirebusiness.com/article/20070521/NEWS/305219993/tire-storage-dos-donts-dont-just-stack-em-up-and-forget-about-them- commmercial truck tires: stack'em as high as you can lift them
http://www.tirebuyer.com/education/storing-tires-for-longer-life- if the stack is too high the stack can fall over and the tires may thus be damaged (!)
Ah, at last. From eBay advice:
http://www.ebay.com/gds/How-to-Store-Winter-Tires-/10000000177404749/g.html"The most common practice is to lay the tires flat, stacked up to four high. This keeps the tower from becoming too tall and unstable, and allows for even pressure to be exerted on all parts of the tire."
Sounds like nonsense. "Even pressure on all parts of the tire"? How is that possible?
Here's the official Michelin advice, which describes an even higher degree of care:
http://www.michelin.co.uk/tyres/learn-share/care-guide/the-storage-story"Do not stack tyres in piles over long periods. Try to avoid crushing your tyres under heavy objects. When handling tyres, it is recommend that you use protective gloves and clothing. Tyres may be stacked on top of each other in piles no higher than 1.2 metres (4ft), preferably on pallets. Reverse the order of the tyres every four weeks. When tyres are mounted on rims, store them inflated in a vertical position or in a single row on shelves. For longer-term storage, place tyres vertically on racks raised at least 10cm (4") above floor level. Slightly rotate them once a month to avoid distortion. If a fitted tyre is not used for a longer period of time, check the pressure regularly and maintain it at level recommended by the manufacturer."
It's difficult to see car tires as fragile when you see how well ones improperly disposed of, last in the environment. Lots of sites list storage on bare concrete as a moisture concern. Tires that wash ashore from the ocean don't seem to have been harmed by moisture. I suppose in Vancouver the damage to mounted tires from moisture must be balanced by the lack of sun exposure.
As to forming flat spots, a tire's own weight is about 1/25th of the weight it would bear holding up a typical car. Since modern tires flat-spot little or at all, it's hard to imagine a tire will flat-spot under its own weight.
