Tire Pressure Issues - FYI

[johncarron]

While trying to figure out what size and load range to get for my LC, I ran across this interesting (for me anyway) article re: LT tire pressure requirements. Food for thought...

http://www.nittotire.com/assets/safety/Replacing Tires on Light Trucks.pdf

 

[hoser]

Interesting. Thanks for posting.

Also found a little bit more info (same company):
http://www.toyojapan.com/tires/pdf/Inflation_pressure.pdf

 

[cary]

While trying to figure out what size and load range to get for my LC, I ran across this interesting (for me anyway) article re: LT tire pressure requirements. Food for thought...

http://www.nittotire.com/assets/safety/Replacing Tires on Light Trucks.pdf

We have also covered the subject on the 80's board pretty heavily with links. Check my inflation thread there and the Tire FAQ.

 

[100 TD]

When I purchased my LT tires, I wrote to the manufacturer and asked the maximum load for the tire at different pressures. They wrote back with X lbs at 35 PSI, Y lbs at 40 PSI, Z lbs at 45 PSI etc etc up to 65 PSI. This way I was sure what pressure I could run at varying loads without overheating my tires. ( I don't have the chart with me at the moment)

 

[cary]

When I purchased my LT tires, I wrote to the manufacturer and asked the maximum load for the tire at different pressures. They wrote back with X lbs at 35 PSI, Y lbs at 40 PSI, Z lbs at 45 PSI etc etc up to 65 PSI. This way I was sure what pressure I could run at varying loads without overheating my tires. ( I don't have the chart with me at the moment)

The problem with this is that if you figure out the load on a per tire basis you would end up running about 20 psi. You want to start with the factory recommendation pressure and the load capacity of the factory tire at that pressure (its about 2300 pounds per tire (after factoring the P metric 91% factor) for the 100 series) and then see what the required PSI is for your new tire for it to carry 2300 pounds. Then you may want to adjust up slightly if you are carrying heavy loads or have armor, etc on the truck that increase its base weight. Also, taller tires are going to require less pressure.

 

[100 TD]

The minimum allowable pressure for the tire (Kelly Safari AWR LT265/75/16 Load range D) was 35 PSI @ Xlbs and the maximumum allowable load at 65PSI is 3000 lbs, these figures are at the rated maximum speed of the tire.

Having this information ensures that I am not overloading my tires.

The whole point of the exercise is to make sure I am not underinflating my tires! That is, load the vehicle up and drive off without making sure I have sufficient air in them and not just putting the vehicle nameplate pressure of 29/32 PSI in them. They also get an extra margin for highway speed versus around town travel!

The problem with this is that if you figure out the load on a per tire basis you would end up running about 20 psi. You want to start with the factory recommendation pressure and the load capacity of the factory tire at that pressure (its about 2300 pounds per tire (after factoring the P metric 91% factor) for the 100 series) and then see what the required PSI is for your new tire for it to carry 2300 pounds. Then you may want to adjust up slightly if you are carrying heavy loads or have armor, etc on the truck that increase its base weight. Also, taller tires are going to require less pressure.

When I purchased my LT tires, I wrote to the manufacturer and asked the maximum load for the tire at different pressures. They wrote back with X lbs at 35 PSI, Y lbs at 40 PSI, Z lbs at 45 PSI etc etc up to 65 PSI. This way I was sure what pressure I could run at varying loads without overheating my tires. ( I don't have the chart with me at the moment)

 

[mtycruiser]

I got this info from a Good Year site, it is for a LT285-75-16 tire, used on the highway at 65 MPH:
PSI - Load (pounds)
35 - 2130
40 - 2340
45 - 2540
50 - 2755
60 - 3110
65 - 3305

I usually run my 98' UZJ100 between 35psi and 40psi, depending on how heavy I'm traveling on the highway. Usually closer to 35 for comfort, no issues so far and tires (BFG AT/KO) are wearing evenly during their 40K miles.

 

[CrusrDug]

With all of this talk about PSI I checked mine today and it was way off. Probably because of the cold weather we're having, but I also recently got a nice pressure gauge. I was wondering why it felt a little loose in the corners!!

 

[SWUtah]

With all of this talk about PSI I checked mine today and it was way off. Probably because of the cold weather we're having, but I also recently got a nice pressure gauge. I was wondering why it felt a little loose in the corners!!

I read some where that you lose 1 lb for every 10 degree drop in temp.

 

[cary]

I read some where that you lose 1 lb for every 10 degree drop in temp.

That is about right. That is why you are supposed to check tires when they are "cold", as checking them after driving them more than a mile you can get artificially high readings. The usual wisdom is if you check them hot (driven more than a few miles) add 4 psi to the cold inflation to get the right pressure.

 

[cary]

I got this info from a Good Year site, it is for a LT285-75-16 tire, used on the highway at 65 MPH:
PSI - Load (pounds)
35 - 2130
40 - 2340
45 - 2540
50 - 2755
60 - 3110
65 - 3305

I usually run my 98' UZJ100 between 35psi and 40psi, depending on how heavy I'm traveling on the highway. Usually closer to 35 for comfort, no issues so far and tires (BFG AT/KO) are wearing evenly during their 40K miles.

Thanks for the chart. If you compare the chart for the stock sized p-metric tires, you will see that to get the same load capacity (remember to multiply by .91 to adjust the P-metric to LT) you should be setting the pressure right about 40-42 psi.

 

[SWUtah]

That is about right. That is why you are supposed to check tires when they are "cold", as checking them after driving them more than a mile you can get artificially high readings. The usual wisdom is if you check them hot (driven more than a few miles) add 4 psi to the cold inflation to get the right pressure.

I always check mine cold then drive to the gas station. take another reading that tells me how much the pressure has increased and air up from that point. I also air up at 40-50 degree weather and add a couple of extra lbs to compensate for the 20 degree weather that way you stay in range.