Dear Ole Mechanic:

Tire SeparationFor a while I have noticed a vibration in my 2004 Jeep Grand Cherokee when I get out on the highway and am going to town.  The other day it got noticeably worse, so I started checking the tires.  What I found was one rear tire with a chunk of the rubber tread missing, and then I found another one with a big bump on it. 

I am very diligent about keeping the correct air pressure in my tires.  It saves gas dollars.  I took the Jeep into town--very slowly-to my cousin who works in a tire store.  He said it was a “tread separation.” and that it could have been caused by “any number of things.”  Even the one with a chunk of rubber missing was only about one half worn down.  To be safe, I had four new tires put on.

My questions are what are the “any number of things” that could cause tread separation, and is there anything that I can do to keep this from happening again?



Dear Re-Tired;

Actually, the “any number of things” means that your cousin couldn’t tell exactly what caused the separation.  There are several possible causes, such as a tire being manufactured incorrectly, old age, heat, impact and speed. 

Incorrect manufacture can be due to several things. The tire carcass might not be clean when the tread rubber is molded to the carcass.  If the tread is vulcanized to the carcass at the wrong temperature, this can cause separation.  A change in the rubber composition or the type of rubber can also cause the problem.

Old age has become a problem as longer tread-life tires have been developed.  This has shown up mostly in recreational vehicles like travel trailers and motor homes.  I believe the RV industry recommends replacing tires every six or seven years--no matter how much or how little the tread is worn.  I have had personal experience with that, as a tire on my travel trailer had about 90 per cent of the tread left but was eight years old when it threw its tread.  It caused about $500 worth of damage to the trailer and stranded me about 40 miles East of Kingman, Arizona.  That is one of those places in the "middle of nowhere.The carcass still had the correct air pressure, but the tread was buried in the trailer fiberglass and scattered back down the highway.

Tire SeparationOverheating due to overloading or low air pressure from neglect or a puncture is one of the causes of tread separation.  It is most easily explained as something that is bonded together with heat (the tread to the carcass) will be unbonded by too much heat.  Truckers refer to the slabs of tire tread that are scattered along our highways as "gators" or "road gators."  Semi-truck tires carry enough weight that they can be punctured and go flat easily.  You say that you keep your tire pressures checked?  Try keeping up with eighyteen tires.  The outside temperature is something that we have to deal with during our Texas summers and probably has a direct effect on the tire age recommendation of the RV industry.

Impact is something that we all can understand, because if you hit something hard enough, you will break it--namely, the bonding between the tire tread and it's carcass.

Speed can also rip the tread right off of a tire's carcass.  Most people don't realize that tires have speed ratings in addition to load-rating limits and air-pressure maximums.  Normally, the speed rating is not something most people need to be concerned about unless they drive a race car, a Corvette or a Viper.

I suspect that your Jeep may have run into an age, impact or manufacturing problem.  Unfortunately, the latter is all too common a problem, now that most tires are imported from overseas.

Herr Professor Nuzanbolts