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Back in the day it was keystone's policy to derate axles to a GAWR value they wanted to use. They normally used a 5200# axle when derating to 5080#. The derated value becomes certified at 5080. In later years Keystone would use ST225/75R15 LRD tires to satisfy the 5080# vehicle certified axles.
The LT235/85R16 LRE @ 80 PSI has an official load capacity of 3042#. The ST235/85R16 LRE has a load capacity of 3640# @ 80 PSI.
Load range letters are the official method for determining load capacities for all ST & LT tires according to a NHTSA 2007 ruling. The prefix letters LT & ST also became a part of all ST/LT tire "designated sizes".
The only reason for tire load index numbers on ST/LT tires is to officially display a tire speed letter. (Thank President Trump for that).
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