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  • Wheels / Tires: which tire size?

    My '55 Commander is riding on old G78 15 bias tires. That crosses over to P 215/ 75 R 15 or P 225/70 R 15 radials. Any recommendations?

  • #2
    It all depend on the width of your rim. The later Lark wheels are narrower than the early rims. After 67 years, the rims should be inspected for stress cracks. If you have a spare tire that is past it's prime, take the tire off and measure the rim width. As I recall, Larks are 4.5 inches but I don't remember the early cars 15 inch width but I know it is wider.

    My first Studebaker was a 55 K and the first set of tires I bought new were Firestone 500's and the tire were 775X15! I will let the other gurus weigh in but you don't want to have too wide a tire on an old Studebaker Rim

    Bob Miles
    As soon as you know, get those old G78 changed

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    • #3
      I just put 4 215 70x15 on one of the Speedsters. They fit well and seem to be close to the original height of the 7.10 15.
      78 Avanti RQB 2792
      64 Avanti R1 R5408
      63 Avanti R1 R4551
      63 Avanti R1 R2281
      62 GT Hawk V15949
      56 GH 6032504
      56 GH 6032588
      55 Speedster 7160047
      55 Speedster 7165279

      Comment


      • #4
        Since this popped up, I was going to ask what tools do you like for installing your hub caps, both full size and dog dish? Thank you

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        • #5
          Originally posted by 64studeavanti View Post
          I just put 4 215 70x15 on one of the Speedsters. They fit well and seem to be close to the original height of the 7.10 15.
          That is my thought after doing some further research. 205 75 or 70 is the max I used on the Larks when I had one. I do have 215-70x15 on my 1957 Golden Hawk.

          Bob Miles
          The size is still available, whitewalls may need to be ordered from a tire companies warehouse.

          Comment


          • #6
            215-70-15 fit PERFECT on 6.5" wheels on both my '62 GT and my dads '53 Coupe.

            For putting wheel covers or hub caps on I use only my hands, and a little finesse.

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            • #7
              I also install wheel covers using only my hands. I have to sit on the ground to do it. I remove them using a small, flat crowbar that is fairly sharp on the end. NO screwdrivers!
              --Dwight

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              • #8
                Originally posted by 64studeavanti View Post
                I just put 4 215 70x15 on one of the Speedsters. They fit well and seem to be close to the original height of the 7.10 15.
                That tire is just about the same as the 205-75-15

                Comment


                • #9
                  Originally posted by Edsel Face View Post
                  My '55 Commander is riding on old G78 15 bias tires. That crosses over to P 215/ 75 R 15 or P 225/70 R 15 radials. Any recommendations?
                  215/75/r15. The original 7.10-15 tires were around 83 aspect ratio. The "G" tires on your car are 78 aspect ratio. 75 is the skinniest/tallest ratio in modern tires and 215 brings them to the proper outside diameter. 225/70 tires will have similar diameter, but will be wider and more likely to rub on suspension components.

                  Make sure to check your rims for cracks.
                  RadioRoy, specializing in AM/FM conversions with auxiliary inputs for iPod/satellite/CD player. In the old car radio business since 1985.


                  10G-C1 - 51 Champion starlight coupe
                  4H-K5 - 53 Commander starliner hardtop
                  5H-D5 - 54 Commander Conestoga wagon

                  Comment


                  • #10
                    According to the math,
                    7.10x.83=5.893
                    205x.75÷25.4=6.053
                    215x.70÷25.4=5.925
                    ​​225x.70÷25.4=6.200

                    Avanti tires are 6.70x15
                    6.70x.83=5.561

                    FWIW, the tire guy said the Speedster rims are 5.5" wide according to his measurement.
                    78 Avanti RQB 2792
                    64 Avanti R1 R5408
                    63 Avanti R1 R4551
                    63 Avanti R1 R2281
                    62 GT Hawk V15949
                    56 GH 6032504
                    56 GH 6032588
                    55 Speedster 7160047
                    55 Speedster 7165279

                    Comment


                    • #11
                      Did some research and I believe that the aspect ratio for bias ply tires is closer to .90.
                      that would make 6.70 x .90 = 6.03 and 7.10 x .90 = 6.39.
                      78 Avanti RQB 2792
                      64 Avanti R1 R5408
                      63 Avanti R1 R4551
                      63 Avanti R1 R2281
                      62 GT Hawk V15949
                      56 GH 6032504
                      56 GH 6032588
                      55 Speedster 7160047
                      55 Speedster 7165279

                      Comment


                      • #12
                        Originally posted by 64studeavanti View Post
                        According to the math,
                        7.10x.83=5.893
                        205x.75÷25.4=6.053
                        215x.70÷25.4=5.925
                        ​​225x.70÷25.4=6.200

                        Avanti tires are 6.70x15
                        6.70x.83=5.561

                        FWIW, the tire guy said the Speedster rims are 5.5" wide according to his measurement.
                        What you are calculating is the sidewall height in inches. It's part of the calculation to determine overall wheel/tire diameter.

                        The first number (205 for example) is the width of the tire in MM. 205mm = 8.07 inches wide

                        The second number is the aspect ratio....the ratio of the width of the tire to the sidewall height. 205/75 for example, means the sidewall is 75% of the 205mm width of the tire or 153.75mm or 6.05".

                        If you want to calculate the overall diameter of the tire, you would need 2 x 6.05"= 12.1" + the diameter of the wheel (15") or 27.1" total.

                        An original 7.1/83/15 would be ((7.1" x .83) x 2) + 15 = 26.8"

                        This calculator is an easier way to do it...

                        https://tiresize.com/calculator/
                        Dick Steinkamp
                        Bellingham, WA

                        Comment


                        • #13
                          Dick, I know I was computing the height of the side wall and would need to double and add to wheel diameter. What I was questioning is that the aspect ratio of bias ply tires is .83. My research indicates that the correct ratio is .90 for tire sizes ending is 0. This works since the accepted diameter for a 6.70 tire is about 27" and for a 7.10 it is about 27.8".
                          78 Avanti RQB 2792
                          64 Avanti R1 R5408
                          63 Avanti R1 R4551
                          63 Avanti R1 R2281
                          62 GT Hawk V15949
                          56 GH 6032504
                          56 GH 6032588
                          55 Speedster 7160047
                          55 Speedster 7165279

                          Comment


                          • #14
                            Instead of straining my brain by calculating, I used the numbers/dimensions in the Coker catalog.
                            RadioRoy, specializing in AM/FM conversions with auxiliary inputs for iPod/satellite/CD player. In the old car radio business since 1985.


                            10G-C1 - 51 Champion starlight coupe
                            4H-K5 - 53 Commander starliner hardtop
                            5H-D5 - 54 Commander Conestoga wagon

                            Comment


                            • #15
                              Did speedsters get special wheels? (Why don't I follow my own oft given advice and look it up?)

                              Regular/stock 1955 Studebaker car wheels are 5" wide.

                              OK, I looked it up. All 55 car wheels are 5" wide. So if the ones on your Speedster are really 5.5" then they have been replaced at some point in time.
                              Last edited by RadioRoy; 10-06-2022, 10:24 AM.
                              RadioRoy, specializing in AM/FM conversions with auxiliary inputs for iPod/satellite/CD player. In the old car radio business since 1985.


                              10G-C1 - 51 Champion starlight coupe
                              4H-K5 - 53 Commander starliner hardtop
                              5H-D5 - 54 Commander Conestoga wagon

                              Comment

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