The AAR Intermodal Interchange Rules dated January I, 2014 have a significant change regarding slid flat tires.
The AAR rule defining slid flat tires will be modified effective June I, 2015.
The below guidelines replace all former references to slid flat criteria for AAR control tires.
Section F.82.g.(1) Replacement Criteria: "Damage to tires and tubes as a result of being slid flat. Any tire is considered to be "slid flat" if a flat spot occurs and removes tread or rubber to 2/32 inches of remaining tread or less in the affected area (flat spot) while the remaining unaffected tread is more than 4/32 inches. It is not necessary for the tire to have a loss of air. Any tire with more than 2/32 inches of tread remaining at all locations does not require replacement." Section F.82.g.(2)Rotation Criteria: "-Tires on the same wheel set that have a flat spot occur which removes 6/32 inches of tread or rubber (when compared to the remaining tread) and do not meet the slid flat criteria in section 82.g.(1), may be re-matched to position the affected areas from 90 to 180 degrees from each other.
In summary: Flat spots above 2/32 of an inch are DOT and AAR compliant and are considered good tires. They should not be replaced. Tires with a flat spot at or below 2/32 are considered bad and must be replaced. A tire with a slid flat spot at or below 2/32 while the remaining tread is at greater than 4/32 is considered damaged and is a slid flat tire. A tire with a flat spot at or below 2/32 while the remaining tread is at 4/32 or less is considered a worn tire and will be replaced as an owners item (even if slid through the casing). The useful life of the tire has been expended.
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