So do I have to replace the stock wheels on my 1956 88 if I go with the P225/75R15 size you suggest?

 

Tricordati, I moved your post to a new thread. Hopefully you get more responses this way. Plus, the thread you posted to was quite dead.

FWIW, if you want to put P225/75R15s on you stock rims I suggest you inquire at a tire shop. You can also do some research on Tire Rack (shameless advertising).

I bought P235/75R15s to go on my 71 98. I found that these were closest to the J78s that were originally on the car. I used General HTS radials. They are good tires without an agressive tread. I think you'll find that radial tires in the sizes we need for our land yachts and luxo barges are generally for light trucks and SUVs. I rejected numerous tires in the right size because they had an agressive off-road style tread.

 

Call Coker Tire in Chattanooga. They also have the correct matching whitewalls in radials.

 

Thanks for the responses. Any experience with Diamondback Tires?

 

I installed diamondback tires on my 57 olds. Replaced the 2 year old Coker tires because of the yellowing of the whitewalls. I have had the diamonback wide 3" whites on the Olds for 3 years now and no yellowing. Their customer service is great.

This is not a slam against Coker Tires as I have used them in the past with no issues. Just decided to try something different.

 

If your car was originally equipped with the standard tires, the rim width should be 5.50". This is what most of them are. Supposedly, the optional larger tires (8.20) had 6" wide rims, though I haven't seen any yet. The Oldsmobile part number for the 5.50" ones was 457705 or 567705 (?). I don't know which is correct. They have a 5" bolt circle. The part number for the 6" wide ones was 557559, but some books show it for only the years 1948 & 1949. There was also supposed to be a heavy duty 15"x5.50" wheel available from 1952-1957 (part number 563976). In 1957 all standard wheels went to 14"x6.00". Pontiac and Oldsmobile used similar wheels back to at least 1940.
Tire manufacturers usually specify the wheel's rim widths required for their tires. A competent dealer should be able to provide this information.