Spare tire is cracking. Sidewall cracking

Tire Dry Rot: How it Happens and How to Protect Your Tires Car Storage

Neat little page on what causes tire dry rot.

In my own experience, I've seen this on cars traded in at the dealership several times. Now I can't prove this, but generally when that spare was in crappy shape, there was also a plug in the bottom of the trunk that was either missing, or rotted to the point it no longer sealed the area. Coincidence? I don't know, but it generally seemed to coincide.

 

Read the article in the link.
HEAT speeds up all of the factors listed too.

"Donut spares" are not made as well as "real" tires and often deteriorate quicker.
IE cheaper tires fail faster.
Sorry no warranty.

 

mine is almost 6 years old and pristine, but it is probably cooler here than oakland on average.
still, i would look for the manufacturers warranty in the paperwork that comes with the car.

 

Depending on who you agree with tires are good for 6 or 10 years from the date of manufacture, I never heard miles mentioned. Rubber products start breaking down right after they are manufactured, if used and exposed to sunlight the process speeds up.