Correct tire pressure

[Finally Mine]

I just purchased a set of tires from the Treadwright corporation. These are retreads on BFG AT casings. So far I am very pleased with the look and workmenship of these tires. I just had them balanced yesterday and installed them on my 1978 FJ40. My question to all is what is the correct tire pressure? The tire itself says max psi 50, but the vehicle plate says psi of 32. That seems like a drastic decrease. I did call the Treadwright company and they said to go by the vehicle plate. Just want to be safe, and not wear the tires down because of incorrect tire pressure. Your thoughts? Thanks, Steve

 

[steffan]

The psi on the sidewall is the maximum cold pressure the tire can be inflated. That being said, since it is a retread, it might be different. This rating has nothing to do with what psi you should run with your particular vehicle - every tire and every vehicle is different so you just have to play with it until you find a good pressure to run. There are dozens of threads on this subject

 

[bmorrison83]

The best way to make sure you have the right pressure in your tires is to use chalk on the tires. Get some chalk turn it on its side and color an area across your tread about 2 to 3 inches wide. Then drive it so your tire does a couple of revs then look at the chalk markings. If the edges are worn and not the middle then add more air and if the middle is worn and not the edges then remove air. You want the chalk to be evenly worn across the tread. After you find that magic number write it down so you don't have to do this again until you buy new tires.

 

[fj4068]

https://forum.ih8mud.com/80-series-tech/111671-tire-inflation-ultimate-answer.html

 

[agaisin]

a thread i started when i got confused on the topic: https://forum.ih8mud.com/100-series-cruisers/399681-correct-tire-pressure-very-confused.html

and here was an interesting approach (mystery author) that seems to make sense and to work from what I've seen:
"
I worked for Michelin Tire Corporation for 7 years and Yokohama Tire Corporation for 11 years. I have given numerous tire seminars on tire maintenance and especially how to determine the correct tire pressures. So here goes.
The pressure on the sidewall of the tire is the maximum pressure at the published load at approximately 55 mph. (The speed can vary somewhat but it is not important for our discussion).
The air pressure is required to support the load that the tire must carry in such a manner that the tire flexes at the designed place on the sidewall of the tire.
If the load on the tire changes then the air pressure should change accordingly to keep the tire flexing at the proper place.
The reason for correct air pressure is to prevent the tire from overheating. It was put together with heat and it will come apart the same way. An under inflated tire will eventually self destruct due to excessive heat build up. An over inflated tire will ride harshly and be more likely to burst upon impact. Sorry for the long explanation but here is the bottom line.
To determine the correct air pressure, check the pressure when the tire is cold. Run the tire for several miles at highway speed. Stop and immediately check the air pressue in the tire. It should be higher than when cold but no more than 10% higher.
Now here is the hard to believe part. If the pressure is more than 10% higher you must ADD AIR and test again. For example if you start with 50 psi cold. If the pressure is 60 when hot, you have exceeded the (10%) in this case, 55 psi maximum safe heat build up pressure. You must ADD AIR. In this case I would add 5 psi which would take the tire to 65 psi when hot. After you run the tire again you will find the pressure to actually drop because the tire will run cooler. The heat build up causes the tire pressure to increase when under inflated.
On the other hand, if the 50 psi cold pressure does not change when hot. You have more air than needed. You can remove 5 psi or so and test again when they return to cold. Like the next trip you take.
So a fully loaded rig will require more air in the tires than one with empty tanks and a light load on board. Always error on the side of over inflation. Thus the maximum sidewall pressure indicated on the tire is usually used. It usually is more than needed. Each axle has its own requirement based upon the load on that axle.
"

Sent from my iPhone using IH8MUD

 

[Rubiconcruiser]

Now this is an explanation, thanks...It makes sense.