WASHINGTON-The U.S. Postal Service is changing the tire specifications on its most common delivery vehicle-a move that should improve both tread life and retreadability for those tires. An eight-ply design for the 195/75R14 radial on the Postal Service's Long Life Vehicles (LLV) could nearly quadruple the longevity of those tires, according to William E. Messitt, vehicle maintenance analyst with the service.
It also should prevent the belt separation that can occur over prolonged use in the currently specified six-ply tire.
LLVs account for 149,000 of the approximately 200,000 vehicles in the Postal Service fleet.
In fiscal 1994, the service bought 158,048 new tires for its LLVs. However, the number of retreads procured is not known because those purchases are not re-corded by size.
While the service has used six-ply Uniroyal Laredos on the LLVs, the tires average only about one year on the vehicles, or approximately 2,800-3,500 miles.
Driving conditions for the LLVs preclude long tread life for their tires, according to Mr. Messitt. Even so, he said the Postal Service found 3,500 miles too low, and its program to maximize retread use was hindered by the poor condition of many of the LLV casings after the tread had worn off.
Tests with a Goodyear six-ply, steel cord 195/75R14 showed those tires could last about 1 1/2 years on an LLV under normal use, he said.
In July 1991, it began testing 400 eight-ply Michelin tires on the LLV; the tires are still in use after 3 1/2 years or some 12,000 miles.
``The feedback on those tires is sufficient for us to decide we will change the specifications to eight-ply tires,'' Mr. Messitt said, adding that the service wants to put the new bid solicitations out by next January. The current contracts expire at the end of October 1996.
U.S. tire makers need time to design and test an eight-ply LLV tire, he said, since no one now makes that tire in this country.
The service has notified 22 new-tire makers, private branders, retreaders and industry associations about the changes. It has also requested that the General Services Administration design a Qualified Products List test specifically for eight-ply LLV tires.