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Tires on 2500HD calculation HELP

Discussion in 'Chevy Trucks' started by letmeplowu, Oct 5, 2009.

  1. letmeplowu

    letmeplowu Junior Member
    Messages: 15

    I am planning to buy new tires and wheels and hopefully try to upsize.
    I have found many tire calculators out there but they seem to negate each other.
    1st site:
    2nd site:

    If I input my current tire of 245/75/16 going to 265/75/16
    One calculator says my speedo will go faster while the other says the opposite.

    I found 2 other online calculator with the same results.

    So does anyone here know which is correct?
  2. RichG53

    RichG53 PlowSite.com Addict
    Messages: 1,135

  3. letmeplowu

    letmeplowu Junior Member
    Messages: 15

    thanks the same as the Miata calculator.

    So i guess the question is: Which of these tools are correct? They all contradict each other.
  4. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    As you increase tire diameter you're speedo with show SLOWER than your actual speed.
  5. jeff52984

    jeff52984 Member
    Messages: 99

    Well might might be off but I have that exact tire size on my truck and mine according to my gps is slower than what im actually doing. Say my spedo says 68 my gps says 71 something like that
  6. haejinjoe

    haejinjoe Junior Member
    Messages: 28

    B & B is correct (as always!) as is jeff52984 regarding the speed of the truck being faster than the speedo shows with oversize tires.
    I am not sure of this, but I think www.tirerack.com may have a tire calculator on their site. They also have a lot of real world info and testing results of different tire combinations. You may want to check it out.

  7. aeronutt

    aeronutt Senior Member
    Messages: 262

    Why worry about the speedo error being one way or the other? Just reprogram the truck computer to compensate if you find it to be off too much after the tire swap and the speedo will read correct again.

    FWIW: I have 265/75/16 Blizzaks on my 2500HD and the speedo reads within 1 MPH of the GPS without reprogramming. It read slightly high before the tire upgrade.
  8. haejinjoe

    haejinjoe Junior Member
    Messages: 28

  9. sechracer

    sechracer Senior Member
    Messages: 478

    I know my truck actually matches the gps when I run my 285's vs the factory 265's