Tire pressure? (1 Viewer)

[flagstaff]

I've got a questions about tire pressure. I have a '94 LC80 with aftermarket wheels and I'm not sure what my tire pressure should be.

The door says 32 psi for stock tires, 275/70R16.

I'm running 305/50R20 tires and it calls a max load of 3086 lbs and a max pressure of 50 psi.

I noticed my tires were beginning to wear unevenly on the inside and outside of the tread of both front tires. The wear tells me that my tires were under pressure because the wear on the center of the tire is even.

Sooo, I checked my pressure and it read 28 to 29 psi. Too low, but is that enough of a difference to cause uneven wear or should my pressure be higher, say 36 psi or more. Definitely on 50 psi, but what?

 

[Ebag333]

I run 35 PSI in my 315 Grabbers.

You'll probably need to play around with different PSI's to find the balance between comfort, ride, and wear.

 

[IdahoDoug]

Couple things. One you don't want to hear is that you've created a wear pattern due to perhaps incorrect offset on the wheels, perhaps low pressure, perhaps something bent, or perhaps alignment issues. Increasing the pressure after there's uneven wear across the tire face can then result in squirrely handling as the pressure across the contact patch now changes and must wear the tire 'flat' again. So, you'll be fighting a losing battle.

Putting wider tires on the truck and keeping stock pressures means the contact patch square inches is the same but it changes shape - elongating across the tread face instead of in the direction of travel. This actually reduces stopping and starting traction despite a whole bunch of popular misconception to the contrary where people generally believe larger tire > more traction. Reducing your inflation pressure will help somewhat but then you've got uneven pressure in the contact patch, sidewall roll, etc.

One of the best ways to find ideal pressures is using chalk lines across the tread when the tires are new. This won't work with worn tires like in your situation. As to whether the tire pressures caused the uneven wear, it is unlikely. Some tread patterns will simply wear unevenly, some mfrs make poor tires that wear unevenly, and unrotated tires wear unevenly. In your difficult scenario, I'd go to stock pressures (32/32) and run the tires until you start to get sick of them.

DougM

 

['74 UA FJ]

Run 35-40psi.

 

[CreeperSleeper]

I run 32psi... But that's in a 37x14.50 tire on an 8" wide wheel.

 

[BirfMark]

I do the chalk-test to see what tire pressure my vehicle needs. Here's the best explanation I found:

"Another school of thought is that you should inflate the tire such that it has uniform tread contact with the road. This can be determined in a number of ways. The easiest is to try to slide a thin card under the edge of the tread. Inflate the tire until you can just get the card under the edge a little bit. A more involved check is to place a chalk line across the tread face, drive a short distance straight ahead on a smooth surface and then observe the chalk line. You are looking for it to be evenly worn off the tread. Another variation is to measure the length of the contact patch and make it even front and rear. This works well on vehicle where the rear load can vary, such as a pickup and especially if a recommended pressure is known for the front end. Slip a paper sheet under the tire to stop at the leading and trailing edge of the contact patch, measuse the separation of the two sheets (making sure they are parallel). Then set the rear pressure such that the length of its contact patch is the same as the front."

From here: LINK

 

[Cruisin']

FWIW I run about 40-45 on my Toyo A/Ts (smaller though at 256/75-16). I figure a little on the high side makes for a little better milage. with 30,000mi on them they seem to be wearing very evenly. I do run about 5 psi less in the winter.

The door sticker usually gives a pressure assuming no load (sometimes a loaded pressure is also given), and they assume you want maximum ride comfort. I'll sacrifice a small amount of comfort in exchange for a small gain in MPG.

my $.02

 

[-Spike-]

The door sticker assumes stock tires. Size, brand, model. Put anything other than stock tires on the vehicle and you can toss the sticker out the window.

 

[Tapage]

for my kind of driving and roads down here .. 32PSI as max ..

 

[flagstaff]

Thanks for all of your input. Since my tires are different than the stock size, I'm going to try the chalk or card trick (most likely both) for checking tread contact...on my next set of tires. Trying now may be like applying Bondo over duct tape.

For now, I'm going to try 35-40 and see how the difference effects ride quality.