So, while rubber is not nearly as volatile as milk (blew your mind there, huh?), it's still important to know how old your tires are. Again, most tire manufacturers advise replacing a tire after it's around five years old. You might not be able to tell the age by glancing at it, but if you notice cracks along the carcass of the tire, it needs to be replaced immediately. Too bad the ole sniff test doesn't work here as it does with that carton of milk.