'83 K20 Tire Pressure Recommendation

[MARKDTN]

I have an '83 K20 with stock wheels. I am looking for the recommended tire pressure. I thought it would be easy to find, but it's not. I do not have a door sticker and from what I can see it would be for the original 215/85/16s anyway. I am running 245/75/16 Bridgestone Revo ATs. I have had this truck since '91 and have always run this tire combo, but as I get older I am getting more cautious about tire pressure. I have not really driven it in about a year, and this morning they were all around 40 psi. In the past, I have been putting them around 60 psi, but looking for some validation. Anybody have any thoughts on this?

[donut]

What does the sidewall of the tire say?

When I owned the K-20, tire pressures would depend on load. Winter with the plow 60psi.
Summer driving 40-45 psi, whatever was comfortable. Keep and eye on the wear pattern of the tires, they can tell you what they like.

Edit-- the tires were rated for those pressures.

[rich weyand]

I think those pressures are high. Draw a chalk line across the tread of the tire, then drive about a hundred feet and look at them The chalk line will wear evenly across the tread if the pressure is right. If the chalk line is gone in the center and still there on the outside, the pressure is too high; if the chalk line is gone on the sides and still there in the center, the pressure is too low.

BTW, the tire pressure times the area of the contact patch has to hold up the vehicle. If you underinflate, the tires will flatten until the contact patch times the pressure equals the load, and if you overinflate, the tire will stand up on the center of the tread until the contact patch times the pressure equals the load. So the pressures should go up if you are carrying a load, and down if you are running fatter tires with more tread width.

On my 78 K10, I run 35 in the front and 30 in the back unloaded on BFG 31x10.5R15, because the fronts have more load on them than the backs. I run 35 all around when I am loaded in the back.

[MARKDTN]

Originally Posted by donut

What does the sidewall of the tire say?

When I owned the K-20, tire pressures would depend on load. Winter with the plow 60psi.
Summer driving 40-45 psi, whatever was comfortable. Keep and eye on the wear pattern of the tires, they can tell you what they like.

Edit-- the tires were rated for those pressures.

Sidewall says 80 max, but I have found out that this is not what you should inflate to.

[Liberty]

What does your Driver door say?

[gramps77]

Originally Posted by Liberty

What does your Driver door say?

Sir,
He stated he DOES NOT have the sticker there.

[Bigstevex4]

The door sticker is the correct way some one should have one but there going to have them as if loaded. 40 is about right 35 rear un loaded

[Liberty]

Originally Posted by gramps77

Sir,
He stated he DOES NOT have the sticker there.

D'oh! That's what I get for not reading it close enough.

[KQQL IT]

My ck2500 is at 40 up front and 30 psi out back. Unless it's actually working...

[rich weyand]

Tire inflations and load limits are covered in section 3E of the Light Truck Service manual.

The 1983 manual only covers P215 and P235 tires, for which the load limit at 36 psi is 1532 and 1742 pounds per tire respectively.

Note how the load limit goes up as the tread width increases, because there is more tire patch. For a 245 tire at 36 psi, the load limit should be around 1847 pounds per tire.

At 44 psi, P215 and P235 tires have a load limit of 1742 and 1984 pounds respectively. P245 should be around 2105 pounds per tire.

You can scale these pressures, such as the load limit for 40 psi should be halfway between the load limit for 36 and 44.

You should be able to get your weight per axle pretty easy at some local outfit with a scale, like a grain elevator.

[1976gmc20]

I've always run about 50-55 in mine, but then I haul loads sometimes, and run a lot on gravel roads.

[tucsonjwt]

I have an 83 C20 with 235/85R16 tires. I am attaching the stickers on my door. I drive at slow speeds around town and keep them at 44 lbs. front and rear. If hauling a heavy load, I inflate to 60 lbs. My tires are well worn, and if I inflate them to 60 lbs. with no load, and then stop abruptly, the rear wheels will lock up. Ride is much better at 40 lbs. and the tires seem to wear evenly.

[imjeff]

As was mentioned earlier, chalk them. Then if you have a load on you can air up the rears.