Tire Pressure Based Upon Load - A

[JCStr329]

All tires are designed to give maximum service when inflated to the proper air pressure load they are carrying. By service we mean proper footprint, even wear, ride comfort, and traction. Any more or any less air pressure will result in less total service. Too much air will cause the tread face to crown resulting in accelerated wear in the center, a harsh ride, and less traction than the tire is capable of achieving. Running the air pressure to low will cause the treadface to collapse concave resulting in accelerated wear on the edges of the tread, a spongy ride, and less traction traction than the tire is capable of achieving. Low air pressure also causes more sidewall flex which generates more heat. We can figure the proper air pressure by weighing the vehicle on each axle, and using the information on the sidewall of the tire.

Example:on the sidewall of the tire it states that it will carry a maximum weight of 3100lbs. at 80psi. We are running with 4500lbs. on our front tires, beings that we have 2 tires carying the load we will devide this by 2 and come up with 2250lbs. load. you dually guys keep in mind you will need to devide by 4 when you figure your rear.

2250lbs. load divided by 3100lbs. maximum load = 73%
80psi. max air pressure x 73% max load = 58.4psi.

so the formula goes
(load/max load) x max air pressure = optimum pressure

beings that the load carried on the front will rairely match the rear we can do this formula for each axle. also keep in mind that becuase we are running at optimum pressure there will be less room for error in terms of pressure loss over time so it is a good idea to start a pressure maintantence schedule maybe as often as one to two times a month to be safe. Lastly, when a radial tire is at proper inflation, there will be a small flat spot were the tire is resting on the ground. if we have done the formula properly we will notice this charactaristic.


if any questions please feel free to PM me. I would also like to hear of any experience you may have in trying this out.


thanks JC

[CD in NM]

Thanks for the formula JC. Excellent information. Have to give a look see at the back end of a truck's weight plus maybe the average of 1/2 tank of fuel to calculate the pressure for the rear tires. We could get real anal and weight everything (tool boxes and their load, other stuff we carry too). This could become a real project to measure wear based on the right air pressures. Somewhere I recall seeing the dry weights, I'll check out the manual.

CD

Excellent info , I will hafta look into this with my truck, I run the 19.5 tires with "H" rating of 6400 lbs, I know that if I run them per recommendations the ride is way stiff, I think I have 85psi in them now.

I will get more info and get back with ya

Cheers, Kevin

[ben]

Wow.

I just lay down a line of carpenters chalk, drive over it, and adjust pressure until the line is almost across the entire face of the tire.

Interesting stuff.....

Ben this formula would be a good way to check and see how close you were

OK heres what I came up with

front axle weight = 4890
rear axle weight = 4770

sidewall on tire states 6400 lbs at 120 psi cold

I came up with91% loaded on the front and 89% loaded on the back

So my pressures should be 109 front and 106 back???

This dont sound right to me, I run 85 psi in them so I dont shake my teeth out, I have about 60k on them and the tread is about 50% worn and doing breat for wear pattern.

Can someone better at a calculator check this out for me

[ben]

My tires have always worn great also. This set allbeit a little QUICKLY but even nontheless.

Ok, this is a dumb ?, but where are you guys getting the front and rear weights from.

[JCStr329]

Originally Posted by Whitmore

OK heres what I came up with

front axle weight = 4890
rear axle weight = 4770

sidewall on tire states 6400 lbs at 120 psi cold

I came up with91% loaded on the front and 89% loaded on the back

So my pressures should be 109 front and 106 back???

This dont sound right to me, I run 85 psi in them so I dont shake my teeth out, I have about 60k on them and the tread is about 50% worn and doing breat for wear pattern.

Can someone better at a calculator check this out for me

make sure to devide your axle weight by the number of tires on that axle to figure the load on each individual tire

I came with
45.8psi front
44.7psi rear
beings that your tires probably have a steel sidewall ply(as most 19.5's do)this should soften up your ride a bit and give you a larger footprint as well

I have always rounded up to the nearest 5psi. to give me some room for error in the event that I don't keep up on my monthly air checks.

[JCStr329]

Originally Posted by ben

My tires have always worn great also. This set allbeit a little QUICKLY but even nontheless.

Ok, this is a dumb ?, but where are you guys getting the front and rear weights from.

most of the DOT scales up here are left on even when they aren't open. Many of the recycling centers have scales that ony charge around $5-$10 to run across their scales. I have always gone this route instead of using the the manufactures weight figures beacuse of my body weight, amount of fuel I normally run with, and of course the weight change from accesories I may have added or removed.

[millco]

JCStr329,
I agree with you're figures for Whit!
Thanks for posting this formula for us! Seems too simple.
I want to go to a parking lot and put sidewalk chalk accross the tread and see how your formula holds up...... I noticed when we buy our trucks they come off the lots with about 40 or 45 PSI in the tires to give a soft ride. I even noticed one dealer leaving the rear slider open a little so the doors shut easier.... My local tire dealer said to run at least 70 PSI in the stock Michilins to get max tread life out of them. So I will have to go out and see how that holds up to the chalk marks.
Dan
(It would seem that the very best test would be the chalk mark accross the tread and then seeing how it wears off)