Wheels / Tires: which tire size?

[Edsel Face]

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?

[6hk71400]

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

[64studeavanti]

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.

[solar]

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

[6hk71400]

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.

[bensherb]

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.

[Dwight FitzSimons]

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

[Hawklover]

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

[RadioRoy]

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.

[64studeavanti]

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.

[64studeavanti]

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.

[Dick Steinkamp]

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/

[64studeavanti]

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".

[RadioRoy]

Instead of straining my brain by calculating, I used the numbers/dimensions in the Coker catalog.

[RadioRoy]

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.