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Law and Order Tests Police Tires, Part 10 of 10
Tire Wear and Tread Life
For two reasons, this tire test did not involve any aspect of tire wear, tread life. Why not? Wouldn’t the tire wear during this test tell something about tread life? No.
And why weren’t before and after tread depths reported? First, it is completely invalid to compare tread life in a couple dozen laps of EVOC-style, accelerated wear tests to 10,000 miles of patrol use. The side force (g-force) on the tread blocks is totally different, and so is the heating of the tire.
Second, during the handling tests, two tire models were selected as control tires, one for wet and a different one for dry. The control tires were inserted at several points through the test to provide a baseline for subjective ratings and to allow for tracking any potential change in surface, vehicle or driver performance during the test. Any tire that was driven on a second (or even third) time was rotated in an effort to minimize wear in any one wheel position.
Since one tire model features a directional tread pattern, all tires were rotated front to rear, regardless of their tread design. One (non-directional) control tire was rotated in an X pattern for its third and final drive in the wet, again in an effort to balance wear and minimize performance differences due to wear.
No valid test exists for tread wear in a police application. While the tires showed some feathered tread blocks, this must not be considered an indication of tire wear or tread life. The only valid way to test tread wear is to actually mount the tires on your patrol cars driven by a couple of different officers for the entire duration of the tire life. Even still, that resulting tire life will only be valid for your department or a department exactly like yours. Tire life tested by the highway patrol will be different from a heavily urbanized metro PD. Tire life tested by the county sheriff will be different from that of officers patrolling a suburban community.
Tire wear, tread life, is certainly an issue among fleet managers. However, this is only a topic for discussion AFTER the tire has been approved for duty use by some form of performance testing. That is, it must pass a fitness for duty test first. Experience shows higher mileage, longer tread-life tires, give up aspects of braking distances and road holding ability to gain tread life.
Two facts about tread life warranties. First, they do not apply to police use. Second, the long-lasting tire gives up dry and wet performance to gain tread life. In the end, you will get a warranty you can’t claim, put on a slippery-when-wet tire, probably violate the OE speed rating and perhaps endanger the life of the officer driving the vehicle…and you may not get THAT much more tread life.
Published in Law and Order, Aug 2009
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