I am buying new tires for my 1971 Oldsmobile 98 4 door Hardtop. I have found some good options but, as a 16 year old who is still learning about cars, I don't quite know the proper load index to buy. I don't quite understand what a load index is supposed to mean either. Is that the maximum weight that can be individually put on that tire, meaning using 4 of the same tire would distribute the weight? Or is it that the load index is the maximum weight of the car you put the tires on for them to function properly and safely? Sorry if these are total noob questions, but I figured I'd ask people who would most likely know. Thanks guys!

 

The original tires on your car were J78-15 on 15x6 wheels. J78-15s were 28.8" outside diameter with a section width of about 8.7" when mounted on a 6" rim. Curb weight on your car was about 4700 lbs; with a full load of passengers and luggage the gross weight was a little under 6000 lbs. Assume about a 60-40 front/back weight bias and that gets you about 1800 lbs on each front tire. The currently available reproduction J78-15 tires sold by Coker have a load rating of 1860 lbs, so that's exactly what you need. Unfortunately, those reproduction tires are about $240 each.

I'm guessing you're looking for a more affordable option. 235/75-15 is the closest commonly available tire size. It's almost exactly the same outside diameter as your original J78-15, but is about 1/2" wider in section. That likely won't be noticeable on your car. Hankook sells a couple of different tire styles in this size for about $80 each, both blackwall and whitewall. I actually have their Optimo H724 235/75-15 whitewall tires on one of my cars. There are no issues, but these tires have pretty poor traction in the rain. Load rating on these tires is somewhere north of 2200 lbs, so they are fine for your application. Good luck.