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  1. Tire Size Vs RPMs

    Wheels & Tires
    What is the relation between the tire sizes and RPMs? Will there be any noticeable different in RPMs if I go from 285/75R16s to 265/75R16s? I'm currently running 2K RPMs at 70MPH with the 285/75R16s. I know there will be some change, but how much? Thanks for any input.
  2. Are my RPMs normal? Newbie

    01-04.5 LB7 Duramax Powertrain
    Hey guys, I have a 2003 GMC Sierra 2500HD with the LB7, of course. Anyway I had a 7.3L back in the day, but I have been out of the diesel seen for awhile and just bought this truck. I have been driving it for about a week and noticed my RPMs seem to be high. At least it makes me a little...