35olds

I've recently bought a set of the Coker produced Firestone Wide Oval GR70-14 Radials for my '70 442 and I'm struggling to find any recommended tire pressures for them anywhere (surprisingly nothing on the Coker website that I could find). Just wondering what pressure others are using for these tires - typically unloaded and maybe 2 passengers. Thanks in advance

BangScreech4-4-2

On a GM A-body equipped with radials, I would usually go 33-34 PSI all around.

joe_padavano

It's kind of impossible for a vendor like Coker to know recommended tire pressures for a replacement tire without knowing exactly what it is being used on. As noted, I typically run 33-35 PSI in my radials. Pay attention to the wear pattern and adjust accordingly. Factory recommendations for 1960s and early 70s cars with bias ply tires were focused more on ride comfort than anything else, plus the stiffer sidewalls on bias ply tires can accommodate a lower pressure. When CAFE mileage regulations went into effect, high pressures for reduced rolling resistance were used. Neither of these may be right for your conditions, so it's trial an error to find what you like and what maximizes tire life.

OLDSter Ralph

I will offer my thoughts. Since you didn't mention what width rim you are using, that is a factor.

I think that if you have "Anti-Spin", inflate the rear tires to 30 PSI and do a burnout for 20 feet or so.
Examine the "black marks". Are they uniformly black across the "black marks". If they are lighter in the center, increase pressure 2 PSI and burn out again.
When they are uniformly black across the "black marks, you are done.
You'll likely get lighter black marks on the pavement on the left rear tire.

As far as front tires, I would inflate them 2-4 PSI more than the rear. Don't exceed max tire pressure listed on the sidewalls.
.....Just my two cents worth.

jadatis

I can make you a pressure/loadcapacity list with maximum reserve at wich comfort and gripp is still acceptable.

Then you " ONLY" have to determine the axleloads 99% acurate, the most tricky part, and your responcibility.

I dont know your tires, but you can give me the data. I assume its a radial cartire.

Need next, can be read from sidewall.
1. Maximum load or loadindex
2. Kind if tire to determine the referencepressure.
3. Speedcode, less important, shall be Q or higher.

35olds

Thanks you all for your feedback I really appreciate it. I'm going to start off at 30 PSI and see what the ride & handling is like and will tweak from there. I've replaced my upper ball joints with the UMI tall ball joints so it will be interesting to see how this combination hopefully improves the ride & handling.

jaunty75

Holy crap. This is a hell of thing to do just to figure out a good tire pressure! What do you do to clean the windshield? Fire a nuclear missile at it and examine the pieces to see how clean they are?

But then again, I remember the Olds dealer back in about 1970 or so telling my grandmother, who had asked him about proper tire pressure, to go to an empty parking lot, do a few burnouts, and then come back and tell him the results. She did scratch her head about this, but she did it!

BangScreech4-4-2

It's more of an old drag racer's trick to figure out what PSI is going to give you the best bite off the line with any given tire. As noted, sort of overkill for a street-only vehicle and leaves you guessing as to what pressure is best for the fronts. Unless you have AWD.

jaunty75

Not to mention the damage you're doing to the tires!

oldcutlass

I don't see how doing a burnout helps you figure out tire pressure. Tires grow in diameter during a burnout, so at rest I would think they would be under inflated for the street.

fleming442

The tall ball joints are one of the best things I've done to the 67 to date. That, and dial in as much caster as it will take. The difference is night and day at cruise altitude.
As far as tire pressure goes, 30 psi is a safe bet, then adjust for personal preference.

BangScreech4-4-2

Which is why that method is an old drag racers' trick!

OLDSter Ralph

I probably clean the windshield the same as you do.

And we know that a large uniform tire contact footprint will increase traction.

Damage ? You'll have plenty of rubber left over. You really only need to do a few short burnouts to see if the tread is making uniform contact.

Tires grow in diameter from centrifugal force as they are rotated at higher speeds. You don't need to spin them exceedingly fast. You are trying to create a "witness mark" to gauge under or over inflation. You also don't need to create clouds of billowing tire smoke to accomplish this.
Many, many years ago there was an article written in Hot Rod magazine about "Tire footprints". It could have been written by Roger Huntington or some other well versed person. I am sure it included pictures and diagrams to illustrate things. Perhaps Professor Joe P remembers it.

Technically its not even a "trick".

35olds

Yes thats what I've read on other GM forums too - huge improvement. I've only changed the top ball joints at this stage and will see what level of improvement it gives. Did you change both upper & lower on your '67 or just 1 ??

fleming442

i did both because I wanted to lower it a little.

35olds

Thanks, good to know. I'm taking my '70 to the Oldsmobile Club of Australia National Meet next weekend but on return I think I'll be doing the lower ball joints too. My car has the stock ride height but it's a tad too high at the front so changing the lower ball joints will give the bonus of dropping it almost a 3/4" win - win.

Bfg

Make sure your tire gauge is properly calibrated also, most gauges are off a couple of pounds.

71 OLDS

Don't forget to shave the rear tires down for better launches!!