Storing tyres

I've had a search but can't find the answer to this. I have just had 4 new tyres fitted. Wanted a matching set. The back 2 still have quite a lot of tread left so I have kept them in case I have a puncture or something with one of the other tyres and want a temporary fix whilst waiting for new tyres to arrive (or until I can afford one!). In the mean time, I want them out of the way. What's the best way to store them? Ideally, I can put them behind the shed. They wil be of out of direct sunlight but they will be open to the elements. Should I lie them flat, or stand them on their treads? Should they be on some bricks? Can I stack one on the other? Lots of questions. Any advice would be welcome.

Thanks, Mark

Should be laid flat with a cover to stop water collecting in/ on them and raised off the ground . If you stand them up you'll end up with a flat point on the tread.

I stored some tyres in a neat pile, flat to the ground, four high, and then couldn't get a decent bead on the bottom 2 when fitted, so my advice would be flat but individually and covered/ wrapped OR try and knock up a simple rack to store them upright ( it works for tyre fitters) and covered - it should be dead simple in Dexion or similar

Great advice. Thanks guys. Given that I've only got two and behind the shed is completely unusable for anything else, flat and covered it is!