Fuselage C-Body Wagon Tire Pressure help

tfrogh

tfrogh

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Hi. I am looking for a consensus on the proper tire pressure for my 72 Custom Suburban 6pass/360. I have 235/75R15 tires on the car. The owners manual lists bias ply tire sizes and Load Ranges. It calls for 22F/32R with Bias-Ply.

I know it is just shy of a Nimitz class carrier and not meant to corner. Still, when I go slow...I get squeal. This car gets it all. Run around town, winding country roads, high speed interstate (well, 70 in the right lane).

I appreciate any pearls of wisdom.
 
No equal all the way around.
 
I run 37 all around, but the real answer is. It's your car, run whatever pressure you want.
 
If you're getting tire squeal on a low speed turn you may want to have your front end alignment checked.
 
The Station Wagon tire pressure specs have been lopsidedly-low on the fronts since at least 1966, that I know of. Station wagons, are closer to a 50/50 weight distribution f/r as the sedans are right at 55/45 f/r. The front tire pressure are always lower as the rear of the car is where the weight is carried, in the "factory specs" orientation.

On my '66 Newport CL42, I ran the tires at the specified pressures as that was what the factory recommended for 4 passenger loads. Later, when I took it to college, I had changed a few things. I'd become more educated on "understeer" and what caused it AND found a tire pressure/load chart in CAR LIFE magazine (one of their GREAT tech articles back then!).

Chryslers were more-neutral handling than Fords or GMs, back then, with the factory pressures. So, with the load charts for particular tire pressures (increments of 2psi between 24 and 32psi), I determined that "neutral handling" (i.e., front and rear slide at nearly the same time in max cornering mode) if the front tires saw the same relative load as the rear tires, in cornering. With the '66 Newport Town Sedan, the tire pressure needed for that was 30f/28rr, just the opposite of the factory sedan recommendation!

Basically, the "soft ride" spec was 24psi. If speeds above 75mph would happen, then "add 4psi". So, using 28psi as the starting spec for the rear tires, putting the fronts at 30psi would make the relative loads balanced, front to rear.

What this did was stiffen the front tires a little, increase handling response, and make the tires wear "flat" and extend tire life. Plus keeping the bias ply tread "more open" in wet conditions, wet traction was improved.

In the case of the wagon, the P235/75R-15 tires should have enough capacity at 32psi for most anything you wanted to do, much less 35psi (Load Range "B"). Upping the front inflation pressure will help steering response, but 32psi up front will increase ride harshness and steering "feel of the road". A lot of how things feel can relate to the brand of tires and how much tread depth is on them. So, play around and see what works best for you, using the rear tires as the base pressure you deal with.

OEM manufacturers like for "consumer" vehicles to have more "understeer" as when the tires squeal, the driver usually slows down in the corner. Too much speed in an understeering car means the car slides off the road "front first". In an "oversteering car", same speed in the same corner, it goes off "rear first" (spins out). Yet a car with a hint of understeer (whether by design, weight distribution bias toward the front, or tire pressure manipulation) is more fun to drive and somewhat safer in the correct "hands".

Whatever works best for what you seek to do.

CBODY67
 
Look for any placard on the vehicle resembling the attached image.

Most passenger vehicles since the 1980s have mandated one, so I don't know how to go about finding out such info.

Googling "1967 New Yorker GAWR" or "gross axle" netted me goose eggs.

But I digress.

What you would do, using the attached from a 2007 Mopar, is to take the heavier of the two gross axle GAWR numbers, and divide it by two, to get the max load per wheel.

Then, source a tire load & inflation table, look up the size of the tire on your vehicle, and read across until you reach a cold pressure that will support 110 to 120% of the GAWR/2.

So GAWR/2 = 2,810/2 = 1,405lbs.

You would want a pressure that supports 1,500 to 1,600lbs, or a safety margin of 1.1 to 1.2 over gross(maximum) load the car would ever handle (5 passengers plus gas plus luggage, etc), using the example 2007 I provided.

I suppose you could go to a truck weigh station in your slab-side or fuselage era Chrysler, with 4-5 of your best buddies and a full tank of gas, and have them weigh each axle separately.

The point is, the optimal cold tire pressure for these vintage vehicles is not "whatever works for you" or "personal preference".

There is a science, a technique, to finding pressures at least close to ideal for your older ride. The rewards for your diligence: a combination of good handling, ride comfort, and relatively even tire wear.
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There IS a place to easily find C-body wagon tire pressure recommendations. www.mymopar.com , then click on the closest-match model year and model of your C-body wagon Factory Service Manual. OEM recommended tire pressures will be in that document! Same things which were in the Owner's Manual, plus wheel sizes and specifications and lug nut torques.

All C-body wagons were on the 122" wheelbase, so whether Plymouth, Dodge, DeSoto, or Chrysler does not matter as their weights would be very similar. With only equipment levels being a bit different between the brands (as in Gen I Hemi, Poly A, LA, B/RB motors and related transmissions).

Tire pressure stickers/decals started in about 1968. Minimum tire size, for the model, and minimum air pressure specs. Initially, some were on the glove box door (as Camaros) with the later ones being in the lh frt/driver's door door frame area.

Enjoy!
CBODY67
 
CBODY67 said:
Tire pressure stickers/decals started in about 1968. Minimum tire size, for the model, and minimum air pressure specs. Initially, some were on the glove box door (as Camaros) with the later ones being in the lh frt/driver's door door frame area.
Click to expand...

The reason I bring up the certification decal/label is that, as some here have stated, the tire & load sticker was either illegible, damaged, or missing altogether from their vehicle frames.

The cert label still contains info that by deduction and calculation, can lead you to tire pressures very close to the info on the damaged or missing vehicle tire placard.
 
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