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?
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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

Originally posted by 64studeavanti View PostI 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.
Bob Miles
The size is still available, whitewalls may need to be ordered from a tire companies warehouse.
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Originally posted by Edsel Face View PostMy '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?
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.
10GC1  51 Champion starlight coupe
4HK5  53 Commander starliner hardtop
5HD5  54 Commander Conestoga wagon
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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
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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

Originally posted by 64studeavanti View PostAccording 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.
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
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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

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.
10GC1  51 Champion starlight coupe
4HK5  53 Commander starliner hardtop
5HD5  54 Commander Conestoga wagon
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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; 10062022, 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.
10GC1  51 Champion starlight coupe
4HK5  53 Commander starliner hardtop
5HD5  54 Commander Conestoga wagon
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