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Bias-Ply tire dimensions

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  • Bias-Ply tire dimensions

    For anyone considering the purchase of bias-ply tires, not all listed tire sizes are dimensionally the same.

    The Squarebird standard tire was 8.00x14, optional 8.50x14. 430 w/air were standard 8.50x14.

    I've compared Cokers (BF Goodrich) with Universal (Goodyear)

    Coker 8.00x14 - 27.58"OD x 4.58"W
    Coker 8.50x14 - 28.10"OD x 4.75"W
    Universal 8.00x14 - 28.67"OD x 4.95"W

    There are more tires available, the Universal Brand and Lester, these sizes vary also with the above.

    Depending on your preference, tall or short, price, choose accordingly.

    I talked to Coker, the tires are from the original molds, what you get today is the same as 50 years ago, tire sizes back in the day weren't as exacting as today's standards.
    1959 J Convertible
    1960 J Hardtop

  • #2
    Any idea of what Coker radials translate to the 8.00 x 14 and 8.50 x 14 bias ply?
    1960 Hard Top/430
    Thunderbird Registry Number 1231


    • #3
      Originally posted by GTE427 View Post
      Coker 8.00x14 - 27.58"OD x 4.58"W
      Coker 8.50x14 - 28.10"OD x 4.75"W
      Universal 8.00x14 - 28.67"OD x 4.95"W
      Those width numbers are the tread width, the more important number is the section width. The Coker 800x14 are 8.1 wide, the 850-14 are 8.35 wide.

      For modern sized, the section width is the first number of the tire, but it's in millimeters, not inches. 25.4mm = 1in.

      I could go into a dissertation on tire sizes, but I've done that before (do a search here on tire sizes, you'll find it. ). The bottom line is that most folks go with either 215/75R14 or 225/75R14. The former is supposed to be close to the 800's, the later the 850's. In reality, they are each a little too short and a little too wide, but they are the best match. I believe that's what Coker recommends as well. They have a handy conversion chart here.

      Discount Tire has a neat tire size calculator that can help too.
      DGS (aka salguod)
      1960 Convertible - Raven Black, Red leather


      • #4
        Here is another GREAT tire sizing calculator I have saved over the years:

        It ran these facts on these 2 tire sizes.

        225/75R14: VS. 215/75R14:

        Sidewall 6.6" ~~~~~~~ 6.3"
        Radius 13.6" ~~~~~~~ 13.3"
        Diameter 27.3" ~~~~~ 26.7"
        Circumference 85.7" ~~ 83.9"
        Revs/mile 739.0" ~~~ 755.0"
        MPH 60MPH ~~~~~~ 58.7MPH

        The speedometer on a car running the 215/75R14 tires (compared to a stock 225/75R14 tire) would be reading 2.2% too fast....
        Last edited by tbird430; April 22, 2008, 11:24 AM.
        The 1960 Ford Thunderbird. The WORLD'S most wanted car....

        VTCI Member#6287.