Saturday, July 07, 2012

Automotive Tire Rotation And Why It's Wrong.

Back in the old days tire rotation in an X pattern was the industry standard, it was also a time of blowouts by the thousands. Back before there were super highways driving speeds were not as high as they are these days and the period of high speed driving was less. Most cars were driven shorter distances to work and back and moms made grocery store runs, if the family was a two car household, during the day and picked up we little brats after school. Automobiles equipped with bias ply tires and really were not the best design for extended hi speed driving and handling not to mention the added weight of the car itself plus, the extra stress loads on the turning/steering tires. So in theory tire rotation and proper tire air pressure was a good thing to balance out tire wear. Any tire, Bias Ply or radial, run with low air pressure is going to build more heat and accelerate damage to the tires structural integrity.

Later on we have steel belted radials that run cooler, grip better, run longer and handle better that those old Bias-ply tires. You can have steel belted radials and fiberglass belted radials or a combination of the two. And you can still have a blow out or tread separation. A blow out does not give much if any warning at all like a balloon filled to over capacity it will burst all of a sudden. Tread separation on the other hand will usually give you a fair amount of warning. You will begin to feel a vibration, shimmy sometimes for several days as if you have lost a wheel weight. If you stop to inspect the tires more often than not you won't see anything wrong. What is happening is the inner belts are disconnected from each other causing the belts to move around forwards and backwards and side to side. Pretty much what happens in an earthquake with the earths plates. Soon the only thing holding the outer tread to the tire carcass is the outer layer of rubber and when it wears through enough the tread will completely separate from the rest of the tire like a peeled orange. The inner carcass may still be holding air while the tread simply folds away revealing the tires cords and belts. Under inflated tires will generate much more heat in the side walls area and damage the cords there and where the tread cores meet with the side wall cords

I have had this happen more than once in years past, I've had it happen with retreads which is why you only run retreads on the rear. Retreads are basically new tread that is adhered by heat to a used tire in effect glued on. You never ever want to rotate a retread from left of the car to the right of the car once it has been run. I also caution against retreads on any passenger vehicle that is run at sustained highway speeds. Retreads are great for city driving and cars used only for short trips. I've actually had a retread tire come apart and the tread wrapped around my differential taking a brake line with it after it had beat on my inner fender well. I was on a back road in the heat of July running around eighty when it gave way. It was the same as tread separation from a regular tire. I had been feeling a little slight movement as if on a section of road where you can see the asphalt seams or like hitting a small patch of black ice in winter. When it went the rear of the car began a swishing motion and I held tight to the steering wheel and never touched the brake pedal, eased off the gas until the swishing stopped then coasted down to almost a stop before applying the brake. It was pretty hairy.

Now tire rotation should only be done with the tires of the same side of the vehicle. The left front goes to the left rear the left rear goes to the front left. The right front goes to the right rear and the right rear goes to the right front. The standard X pattern of tire rotation - In My honest opinion - should never be done. Why you ask. Because belts in a tire will tend to wear in at one direction when running a tire. When you take that tire and put it on the other side of the car you are asking for a blow out or tread separation. Because if you take a tire from the left front and put it to the right rear, that tire now is running in a reversed rotation and the belts will try to realign themselves to the new rotation and this is when small breaks will occur in the steel belts of the tires core and the steel cords will begin to separate inside the tire.

Take a piece of stranded wire or a cable from a bicycles brake or shifter cable and bend it over one way, now try to bend it the other way. You will see that there is now a kink in the cable and the strands are not tight any longer at that point, you will also see that the strands are moving away from each other. This is what happens inside your tire when you take it off one side of the car and put it on the other side. Take a coat hanger and do the same thing but keep bending it back and forth, you will see it has kinked and will have a slight hump to it. Keep bending the coat hanger back and forth and then feel the wire at the bend, it's getting hot. See where I'm going. By bending the cable or coat hanger, each time it gets weaker and weaker until it finally breaks. When this happens with a car tire a blow out will happen or the tread will separate.

One of my brothers had a Corvette and the tires for this hi-performance car were uni-directional. You could rotate front to back or back to front on the same side but never from one side of the car to the other. Race cars also run in there tires, scuffs, and mark the axle location of each tire. They mark them as LF for left front, LR for left rear, RF for right front and RR for right rear. These tires go back on only at those axle locations. This also aids in tire temperature readings.
Don't include your spare tire in the rotation process if it is a full sized spare but do keep a check on it's air pressure. If you have a donut spare and it has been used then it should be replaced with a new one. Front wheel drive cars are even harder on front tires so do not run a tire that has been on the left and put it on the right and vice verse.   
So when doing a "tire rotation" keep the tires on the same side, Left front to left rear and left rear to the left front. On the right side, right front to the right rear and the right rear to the right front.


Billy Jones said...

Excellent advice.

WooleyBugger said...

Yep, but some people will not listen until to late I'm afraid. It makes me wonder if this is what contributed to all those Explorer rollovers with the exhaust pipe excelerating the process,