by J. B. Griffin III.

Dear JB,

What makes tires wear and does tire rotation help with this problem? It seems to me that they would wear out at the same rate whether rotated

or not. Another question is where all the rubber goes that wears off tires? It seems that the roads would be rubber-coated or something like that by now with all those worn out tires.

signed,
All Tired Out

Dear All Tired Out,

You pose some interesting questions. First, as you may know the only thing that holds your car to the pavement is the friction between the road and the tire. The fact that there is sometimes a scrubbing action as a tire slips across the surface of the road and breaks this friction is

one thing that induces tire wear. You can usually hear this type of wear as it occurs like in the instance of a tire-squealing take-off or stop, or even as you take a turn a little too fast. This accounts for some tire wear, but not much unless you happen to be known to your friends as "Junior." For most of us, though, the majority of tire wear is due to the effects of heat. Heat can be introduced externally, such as the sun

heating up a stretch of interstate road to 160 degrees or so, or it can be created internally in the tire by high speed driving or loading the tire with heavy cargo. Years ago, when these types of things mattered to trucking companies, I remember a large trucking firm that put an absolute speed limit of 55 miles per hour on all their truck drivers. There were a number of reasons for this, among them safety, fuel economy and longer drivetrain life. But the number one factor was tire wear. At 55 mph the tires lasted exactly twice as long

as they did at 70 mph! A third thing that produces ultra-fast tire wear is an out of line suspension system. I have seen brand new tires worn down to the steel tread in 30 miles! This is, of course, an uncommon event, but does remind us of the importance of having the alignment checked on our cars from time to time.

As for the rotation question, here is my opinion. Yes, the same amount of tire wear takes place with each mile driven no matter which tire is on the front end. Just because a fresh tire is put on front doesn't slow the wearing effect, it just begins wearing that tire. The reason most people rotate tires is for the convenience of having all four wear out at about the same time. It is an old southern tradition and one rich in heritage to replace all the tires at once. The only people I know who go into a tire store and only buy two tires are penny-pinching yankees. Another good reason to rotate tires is that it is usually free. And why is it free? It gives the tire store an extra opportunity to sell you brakes and shocks while they have your car on the lift.

Now as to where all that rubber goes from all the tires? Your guess is as good as mine. Maybe is dissipates as microscopic dust. Maybe it leeches into the soil where it contaminates the ground water and is consumed by unsuspecting school-aged children. Maybe it is carried into the ionosphere where it reinforces the Van Allen Belt (Van Allen Steel Belt?) One thing is for certain. Neither tire wear, $3 gas nor dark of night will ever deter the American public from our (largely self-) appointed rounds.

JB Griffin owns and operates JB's Auto Sales and Service in Evensville, Tennessee. You may see him weekly on the WDEF-TV News 12 Morning Show every Tuesday at 7:10 a.m. where he will answer your car care questions live and on air. Visit him on the web at:  www.500overcost.com
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