dry rotted tires

the other day on my way to work i had a flat on my 15" si rims so i changed it with my original 13 i had in my trunk cause i didnt want to have to rely on my donut. about 3 days after (i was waiting on my falken zeix's to arrive via shipping) my 13" caught a flat so i rimmed it to the tire shop seeing i didnt replace that spare the guy told me the tire was dry rotted(before i put on my si's the tires had about 1000miles on them if so much) i cant under stand how this happened can anyone add any insight or tips on how to store tires so they wont dry rot

How long have your thirteens been in your trunk?

frequent changes in temperatures and dry air will cause tires to dry rot

I Had It In The Trunk Since The End Of Summer

there are two factor affect on the tire and the motor oil too

1- how old of the tire and of course it is the same year of the car model and in my opinion if the tire live more than 8 year they will start failer even if you did not use them ( note that is my opinion )

2- second factor is the millage and it depend on the material which made from and the temp and weather you live at. and the way which you use (in case of the tire not oil )

Do you live in an area where the weather changes a lot or where the temps between summer and winter are a big jump (like 90 avg to 10-02 avg.) If so that could be the culprit. If not then the only other option would be the age of the tire, even if it's only got 1000 miles on it, if its been on the wheel over 10 months then that could be the problem. It could be a combination of both.