Tire pressure?

[notsosan]

Sidewall pressure is the pressure required for the tire to carry its maximum rated load, not the recommended pressure which is specific to each model. That said, most of the pressures given in the manuals for these vehicles would be for bias ply tires. Radials are likely different. I start with 32 PSI in the 225/75R15's on my car and adjust pressure according to how they wear. The only time I have ever used sidewall pressure is on trailers and the rears of my truck when towing a 5th wheel. 80 PSI in the rears of an empty 1T is not very comfortable.

 

[Rusty Muffler]

These guys complaining about a hard ride, what is the condition of your shocks? Don't make the tire do the work of the shocks.

Shocks are brand new KYB's.

 

[413]

Check this thread, they are no afraid to raise pressure to suit.

Tire pressure for a 1962 Valiant with 14" tires

 

[Darter6]

80 PSI in the rears of an empty 1T is not very comfortable.

Agreed. Rides like a wooden wheel buckboard wagon.

 

[Top Cat]

My 57 Belvedere has new Hankook Optimo tires and KYB shocks. When driving it drives straight and firm except on coarse or weathered asphalt. I can really feel it in the steering wheel. It's great on smooth asphalt. Is that tire pressure or the nature of torsion bar suspension? The original recommendation for pressure is like 24 psi cold. But that was in 57. What should I be running these radials at? They're at 30 now.

What you're feeling on rough pavement may be "lack of structural rigidity". Auto testers including Consumer Reports noted this characteristic on all of the new Forward Look '57 Mopars.

If you lower your tire pressure, the car will ride less harshly. I'm in the mid-20s on radials on my '60 Dodge Dart and I do just fine. If your Plymouth has manual steering it will steer easier with more pressure in the front tires. (I have power steering.)

Here's what Consumer Reports had to say, April 1957:

 

[Rusty Muffler]

Very interesting, thanks!

 

[ynst]

Very interesting, thanks!

I’m surprised that nobody has raised the issue of drastic front suspension changes when manufacturers switched over to radial tires.

The old bias ply tires did not sit flat on the pavement when cornering like radial tires do.

There was, also, very little flex in the sidewall on bias ply tires.

Radial tires are supposed to lay flat on the pavement and one of the ways this is accomplished is to soften the sidewall. The other way is to drastically modify the front suspension.

Bias ply tires tend to break into a skid quite gradually whereas radial tires suddenly break loose when the over-stressed sidewall snaps the tread back under the center of the rim, thus suddenly breaking traction.

I’ve been running radial tires on a bunch of bias ply vehicles since radials first came out.

My hemi powered 34 Ford has them and I DRIVE that car from the Boston area to Louisville, KY every year.

I put radials on Tex Smith’s old ‘48 Chrysler in Rawlings, Wyoming in ‘86 when I bought it and drove it home to eastern Mass from Tex’s place in Driggs,ID.

My ‘72 Dart Swinger has had them since I got it in the early eighties. It's a drum brake car and was set up for bias ply tires. It was my daily driver until I hurt my back at work and couldn’t comfortably sit in the bench seat and my 47 year old daughter got it as her first car when she got her license in high school.

My bought- it-new ‘68 GTX got switched over to radials nearly twenty years ago when I restored it

I run all of these vehicles between 32 and 35 psi.tire pressure (just like I do with my three Dodge Magnums)

Also, ANY gas filled shock is going to give you a harder ride. That’s to keep the radial tire firmly planted on the pavement. If you’re unsatisfied with the ride, put the original type shocks back on it.

On the oil topic, I run Valvoline VR-1 20-50 in the ‘34 and GTX and the rest of the fleet gets Shell Rotella with a bottle of ZDDP. Rotella used to have lots of zinc but not anymore.