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  • Wheels / Tires: Radial to bias converter

    I’ve always used this excellent site when fitting tires to my classics. Wanted to share it so others can keep it as reference.

    It’s basically a page comprising a wide range of bias to radial tire conversions, metric to “letter series”, etc.:

    https://www.turbinecar.com/tires.htm

    The OEM chassis manual states that the standard size for my 59S-F4 was a 5.90-15, with an optional size being 6.40-15. At some point, the spare rim was fitted with a Firestone 6.50-15, which replaced the 6.40-15 (so it says in the sidewall).

    The PO fitted new 205/75R15 narrow ww tires, which work out to be ~6.40-15 so right on the money. However, I’m thinking about going to a 5.90 to lighten the steering effort a bit and keep with the ultra-basic options mine left the factory with. Coker always sales on this very popular size every now and then.

  • #2
    A handy chart, but 6.40 x 15 would equate to 165/90x15, if such a thing existed. The closest one could get today would be 185/75R15 -- a size that used to be available, but mostly not any any more. The chart can't account for the changes in aspect ratio, which occurred a couple of times in the 1960s, plus again when the letter sizes appeared.
    Skip Lackie

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    • #3
      Originally posted by Skip Lackie View Post
      A handy chart, but 6.40 x 15 would equate to 165/90x15, if such a thing existed. The closest one could get today would be 185/75R15 -- a size that used to be available, but mostly not any any more. The chart can't account for the changes in aspect ratio, which occurred a couple of times in the 1960s, plus again when the letter sizes appeared.
      Keep scrolling down the site page, there’s several correlations between the aspect ratios.

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      • #4
        And always a revelation to me - how the folks at Coker still make these faithful reproductions by hand here in the USA. What a neat process.

        https://youtu.be/P-xn44WZG2k

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        • #5
          I enjoyed the Coker video. Didn't realize that they were still hand made. They are the exact tire that I put on my 60 Hawk. They balanced out nicely, and run smooth.

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          • #6
            Originally posted by Skip Lackie View Post
            A handy chart, but 6.40 x 15 would equate to 165/90x15, if such a thing existed.
            Ah, the VW Beetle tire for YEARS was a 165R15 with abut an 80 or 84 aspect ratio. 165/80R15 is still available from multiple sources.

            Frank DuVal

            50 Commander 4 door

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            • #7
              After seeing the craft required to make those tires, I won't complain of their cost anymore. IIRC, our Studebakers involved more "hand working" than more modern factories in later years.

              In 1985, I wanted to match the original spare in my low-mileage '62 GT (optioned with Firestones). Our local tire shop ordered a set of Cokers that. The car sees few miles these days, but still rides, very carefully, on those tires. Dangerous, I know, especially at Mid-Ohio last year.

              Looks like Santa's delivering some Cokers this year!
              Andy
              62 GT

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              • #8
                Originally posted by Andy R. View Post
                After seeing the craft required to make those tires, I won't complain of their cost anymore. IIRC, our Studebakers involved more "hand working" than more modern factories in later years.

                In 1985, I wanted to match the original spare in my low-mileage '62 GT (optioned with Firestones). Our local tire shop ordered a set of Cokers that. The car sees few miles these days, but still rides, very carefully, on those tires. Dangerous, I know, especially at Mid-Ohio last year.

                Looks like Santa's delivering some Cokers this year!
                Not as dangerous if they do match the original, meaning that they are bias ply. If they are steel belted radials, they are way too old.
                Gary L.
                Wappinger, NY

                SDC member since 1968
                Studebaker enthusiast much longer

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