59Rocket

My 1959 Super 88 weight is 4090#.

The inter webs tell me the radial replacement should be P235/75R 14 with Maximum Load Capacity: 1930 pounds at 35 PSI

I believe an acceptable alternate would be P225/75R 14 Max Load Capacity: 1797@35PSI

The car is driven @ highway speeds.

Additional Human & luggage weight max 400#

QUESTIONS:

Do I really need the higher load capacity?

Will there be any significant difference in ride?

Gas Millage?

I appreciate the help/advice as there is about a $300 price difference.

oldcutlass

The load capacity is really not an issue. Can you live with a smaller diameter tire?

59Rocket

The diameter difference is 27.9 vs 27.3 and the food print width is 9.3 vs. 8.9. So not much difference.

I believe the idea is Gross vehicle wt divided by 4. so 1022#s per tire. Of course the front end would need to handle a heavy load due to the engine.

MDchanic

That is a 2.1% difference, so your engine run 2.1% faster, and you will get 2.1% lower gas mileage.
In most cases, this will not be noticeable.


Are you seriously asking about the load capacity of regular passenger car tires when installed on a regular passenger car?

- Eric

joe_padavano

Only if your car has a perfect 50-50 weight distribution, and you never accelerate, decelerate, or corner...

MDchanic

... But load ratings on tires are not based on instantaneous load, like certain engineering specifications, but rather on safe use while bearing a certain physical weight... No?

- Eric

59Rocket

Yes, the front is substantially heavier in this car. At 18' long the mid point is about the drivers seat. Which is why I was a concerned about the smaller size.

Knowing the speed/mpg is not significant enough to be a concern. I'm more concerned about safety.

D. Yaros

P235/75R 14 is what are on my 62 Dynamic 88 convertible.

I seriously doubt there would be a noticeable gas mileage difference with a change to the P225/75R 14 tire.

oldcutlass

They are basically the same load rating, your over thinking the safety thing. Your driving a 52 year old car in Chicago and your worried about safety....

59Rocket

Actually, I'm trying to figure out the REAL value in spending the extra $300.

oldcutlass

Is a 1/2ish inch worth the difference?

MDchanic

I'm still trying to wrap my brain around this.

According to you, the "recommended" tire has a weight rating of 1,930 pounds, while the next smaller tire has a rating of 1,797 pounds, and your car weight 4,090 pounds.

The original specified tire for your car is the 8.50x14. At the time these tires were made, load ratings were not customarily assigned to tires, but "ply numbers" were - the greater the number of layers when the tire was constructed, the higher the rating, so a 5-ply tire carried more weight than a 4-ply tire. In general, though, bias ply tires had lower weight ratings for a given size than radial ply tires do today, so any modern tire that is the same size as your original tire should automatically be able to carry more weight than the originals.

Getting back to your car, it weighs 4,090 pounds, which, when divided by four wheels is 1,023 pounds per wheel.
In general, when sizing tires for passenger cars, we do not get into weight distribution - that's for trucks which may carry a lot more in back when loaded than they do in front. With cars, you just divide the weight equally.
But let's just speculate and assume a widely disparate weight ratio of 60/40 front to back - If 60% of your car's weight were on the front axle, each front tire would carry 1,227 pounds.
Even if we went wild and decided that the weight ratio was 75/25, the front tire load would be 1,533 pounds each.

The tires you are considering are rated to carry 1,930 pounds and 1,797 pounds.

For a concrete example using modern tire designations:
1976 Lincoln Continental Mark IV: Curb weight 5,265 pounds, used 230/70x15 tires.
The closest modern equivalent, 225/70x15, have a load rating of 1,753 pounds

So, again, I am trying to wrap my brain around what, exactly, is the problem here.

Go buy some tires and stop trying to outthink yourself.

- Eric

59Rocket

MDchanic - This is just a few questions in an attempt to make a sound decision not trying to "out-think" anything what-ever than means?

The problem is my lack of understanding. That's why I started the thread…to learn.

I joined this forum to learn a little bit more about Oldsmobiles not to get in pissin' matches. I hope I made a good choice doing that?

MDchanic

I'm just laying out the mathematical facts, so that we can all see them, in order to clarify the question and the answer.

Sometimes when you lay out all of the facts, rather than trying to intuit them, the answer becomes obvious.

If you are concerned about whether you are getting your money's worth out of a tire, you should consider such things as wet and dry traction and sidewall stiffness and lateral stability, all in relation to the specific suspension of your car, including shock absorber choice.

Since the only people who can do this are the people who drive car models which are identical to millions of others on the road (ahem - "A-body"), where you may be able to find others with your exact configuration, except for one detail, folks with older fullsize cars such as yours, and who aren't made of money, are out of luck, and need to essentially take a shot in the dark and see how it works out.
The one thing you do not have to worry about when making these decisions is load capacity.

I may be snarky, sometimes even cranky, but I very seldom get into pissing contests.

- Eric

59Rocket

"If you are concerned about whether you are getting your money's worth out of a tire, you should consider such things as wet and dry traction and sidewall stiffness and lateral stability, all in relation to the specific suspension of your car, including shock absorber choice."

Good points.

Wet traction really a non-issue, this car won't be seeing wet conditions of any significance.

stiffness and lateral stability, here one would think the larger tire would be a plus. The suspension is sound and I've installed NOS Delco Remy shocks.

MDchanic

The thing to remember is that bias ply tires behave very differently on turns and over bumps than radial ply tires do, and your suspension was designed to use bias-ply tires.

Bias ply tires have much stiffer sidewalls, but it is much easier to peel their treads off of the road with lateral forces.

The question may be what exact tire will provide performance closest to the original design of your car, but it is most likely that the question really is, which tire will provide a ride and handling that you personally like the best (and these two are not likely the same things).

If I could recommend one thing, it would be to see whether you can contact other people who own and drive full size Oldsmobiles in your year range, find out what parts and tires they have installed, and see whether you can take a spin in their cars, and then use what you have learned to make the most educated decision possible.

My gut feeling is that you will be happiest with the larger tires and with a set of newer high-quality shocks (like Bilsteins), if they are available, but I have no actual experience with your year range.

- Eric

59Rocket

Thanks Eric

59Rocket

Got the wheels back from the local powder coat shop and put on the Coker WW 235/75R-14.

unnamed_zpsvceom5qz.jpg

Decided the bigger tires would give me the ride
i am after.


Thanks everyone for the advice.

BangScreech4-4-2

Lookin' good. Let us know how you like them.