dsouthard

Hello, I've been looking for info on tire size on a 70 442. I've searched but can't find anything pertaining to a 17 inch wheel with stock suspension. Most have lowered their car but my oil pan hangs below the crossmember and I don't really want to change it. I have 235/60/15 on the car now all the way around with no issues. A company selling wheels has recommended 225/50/17 for the front on a 17x8 and 255/50/17 on a 17x9 for the rear. Any suggestions on this size or something that might work better?

svnt442

The 225/50/17 will be shorter. If you do a 235/50/17 it would be closer to what you have now. The 255/50/17 should be a little taller and wider, but with the MASSIVE wheel wells on that car you shouldn't have any issues unless you do something stupid with the offset.

VC455

Be careful of load range when you select tires. Don't go below the factory recommended load capacity.

If your door decal is still intact, you will see that the factory used load range G tires on your car. In current 50-section, 17-inch terms that equals a 265/50-17.

The 225/50-17 that was recommended equals load range B. That is the load range used on a 6-cylinder 1964 Mustang that has a third less weight than your car.

That would be a dangerous tire on a 442--especially on the front.

Your minimum should be 265/50, 245/60, 235/65, or 225/70.

joe_padavano

I don't know where you got this, but even the cheapest BFG Advantage T/A tires in the tiny 225/50-17 size have max load rating of 1,477 lbs. That's nearly 3,000 lbs capability on the front wheels, which is more than adequate for a 442 with a BBO motor.

As for the actual sizes, these cars look best with a tire diameter in the 26.5" to 27.5" range. The recommended 255/50-17s are a measly 25.8" diameter and would look better on a Honda. I'd go with something more like a 245/50-17 on the front, if you can find them. You should only need a 7" wide wheel for these.

At the back, the 255/50s are fine (though again, a wheel in the 7" to 8" range is more than adequate). You could easily fit a 275 or wider tire if you wanted. If you can get a 275/50, that would look great. Unfortunately, most of these larger 17" tires are truck/SUV tires, not performance car tires.

VC455

Hi Joe.

I used the load range for the factory-recommended tires and showed the equivalent in various aspect ratios of 17-inch tires.

You are right to infer that a pair of those factory-recommended tires could probably support nearly the entire weight of the car.

However, to ensure a safe application, I did not question the factory's judgement on this topic as they were not noted for wasting money on anything that exceeded requirements.

joe_padavano

I'm having trouble with this because the load range on the tires on my Crewcab Dually is only "D". I've never even heard of a Load Range G tire - even the tires on my 10,000 lb equipment trailer are only Load Range F. When I look at the PIM, the tire application charts show mainly 4 ply rating with some 8 ply rating tires for HD applications like police use. 4 ply rating is Load Range B and 8 ply rating is Load Range D. Neither of those is the actual max load the tire can carry, since that depends on both the tire size and the Load Range.

This page provides more detail.

VC455

Joe, I'm using the wrong term. I apologize for the confusion.

The standard tire on a Cutlass of that era was a G series, such as G70-14. At that time, the G denoted a specific tire capacity. A G70 had the same capacity as a G78 or a G60.

I took the capacity (in pounds of load) of that G series tire and used that to find equivalents in today's tire terminology.

oldcutlass

You are somewhat correct based on mechanical engineering and air chamber size of a tire. However the letter designations were really more about size than load capacity. The letter designations were A-N (although the article says A-L) really more about diameter and aspect ratio than load rating.

This is a good explanation.
http://automotivemileposts.com/tires101.html

VC455

Eric, that was a good, comprehensive article that you referenced.

One of the statements it made in regard to the alpha-numeric system of the era was, "the letter at the beginning denotes the load range rating or load carrying capacity of a tire."

That corresponds with my recollection. The letter indicated the load the tire could take. Designators starting with the same letter had the same load capacity.

oldcutlass

Yes, and no... It really did not play into the decision process in the larger sizes, say from F - L. The letter designation as it was when I was a youngster was related to diameter, the higher the letter the bigger the diameter. The numerical number or aspect ratio, was related to width. So a 78 series had the most sidewall height but was a narrow tire. As you got into the wider 70, 60, and 50 series tires. The sidewall height got shorter and the
width grew wider. So here's the caveat as the tire sidewall shrank and the tire got wider the load rating went down while still using the the same letter designation. Tire letter sizes went from an A78-13 all the way to an N50-15.

There was a panel printed on the side of the tire back then and load rating was based on tire pressure and plies. The more plies and pressure, the higher the load rating. The physical size of the tire was based on the size of the car they went on, but really more of a look than anything else.

So as you can see it gets complicated.