Issue link: http://read.dmtmag.com/i/34501
CASING MANAGEMENT TIRE MANAGEMENT The goal of every truck operator is to achieve the lowest possible operating cost, taking advantage of the performance built into each high tech MICHELIN ® radial truck tire. Tire maintenance, proper air pressures, repairs, vehicle alignment, and retreading, are all keys to help ensure maximized performance and extended casing life. Over the past 10 years, a number of operational and product changes have occurred that should be considered when establishing tire use patterns. The single most important point of any program is “Know Your Customer.” TIRE CHANGES 1. New Tires: Today’s wider treads and deeper tread depths provide more original tread miles. The tire arrives at the retreader with more time in service, more miles, and exposure to road conditions. 2. Retread Changes: Wider treads, new tread designs, and new compounds have increased retread mileages. VEHICLE CHANGES 1. Longer Trailers: There has been a move from 40' to 48' and 53' trailers as standards in the contract and private carriage business. 2. Wider Trailers:Widths have increased from 96" to 102". The combination of longer and wider trailers increases the frequency of the duals being curbed. 3. Setback Front Axles: Moving the steer axle back increases stress on steer tires and load efficiency by allowing better load distribution. The result is higher average axle loads. 4. Electronic Engines: Better engine control and more efficient operation improve the ability of the vehicle to maintain higher cruise speeds.* OPERATIONAL CHANGES 1. Speed limit: The national limit has continually increased in the past decade.* 2. GVW (Gross Vehicle Weight):With the Surface Transportation Assistance Act of 1983, the weight limits went from 73,280 lbs. to 80,000 lbs. With setback axles, you can realistically load to 80,000 lbs. 3. Greater Vehicle Utilization:More loaded miles mean productivity gains. All of these changes lead to the casing arriving at the retread stage with a higher level of fatigue. To utilize these casings to their maximum, casing management should be employed in the selection of the retread. CASING MANAGEMENT TODAY Highway fleets typically employ the casing management pattern below: Tire First Position of First Subsequent Used On Retread Use Position of Retread Use Steer Drive or Trailer Drive or Trailer Drive Drive Trailer Trailer Drive or Trailer Trailer In terms of casing fatigue, the severity of use is as follows: • Drive Axle – most fatigue. New drive tires (lug type) often can accumulate twice as many miles (or more) before retreading than new steer or trailer tires can. The same is true for drive axle lug type retreads. The tires also run hotter (deeper tread) and with more torque. • Steer Axle – moderate fatigue. Steer axle tires operate at higher average loads than drive or trailer tires (20 to 40% higher). However, they wear out sooner than drive tires and are moved to lighter axles in the retread stage. • Trailer Axle – least fatigue. The trailer tire starts life with a shallow (cooler) tread and is usually retreaded with a shallow retread. Annual miles are low. The trailer tire casing usually sees more curb abuse, neglect, and old age problems. Thus, the practice of retreading new drive axle tires back to the drive axle puts the most highly fatigued casing back onto the most highly stressed wheel position. CASING MANAGEMENT FOR THE FUTURE The following guidelines are recommended in sorting casings for their next tread life. Such a sorting would allow the fleet and retreader to make better decisions regarding the handling and utilization of casings recovered from 6x4, 4x2, and trailer applications. Casings that are judged to be more “highly fatigued” should be retreaded in one of two ways: 1. A low rolling resistance/low heat retread rubber in rib and drive (consult your retread supplier). 2. A shallow retread (no more than 15⁄ 32"). These retreads will reduce the operating temperature in the crown of the tire. Determining which tires are “highly fatigued” requires * Exceeding the legal speed limit is neither recommended nor endorsed. a working knowledge of each fleet’s individual operation. The following guidelines can be used: 1. Two or more repairs on the casing. 2. Heavy sidewall abrasion. 122 Section Nine: Appendix