1976gmc20

Jeep: P225/70r15 1753 lbs @ 35 psi


Burb: LT235/75r15 1984 lbs @ 50 psi


When I do the math, the passenger tire supports 50 lbs psi, but the larger heavier duty light truck tire only supports 39.7 lbs psi. This makes no sense to me at all


Theoretically, if I upgrade the XJ to the bigger LT tires, I should be able to run less pressure than the 30F/35R as recommended by the owners manual, but if you do the math I would have to run 44 psi on the rear to match the current load rating !!!!


I run about 45 psi in the Burb, BTW - that thing is heavy.


Anyway, how can a passenger car tire be rated so high compared to a larger and higher load range light truck tire? Are the passenger tire ratings just blowing smoke or are the light truck ratings vastly conservative?


This is all academic as I am not buying tires right away, but I'm just sitting around thinking. The LT tires look to be about 1.5" taller than the current tires on the jeep. We live out on crappy gravel/dirt roads so overkill on tires is a good thing IMO (I run 10ply on the two pickups with 16" wheels). The jeep is stock, no lift.

jbsjunk

I ran 10 ply LT's on my XJ. Huge mistake. Rode like a lumber wagon at 30psi. Put nice C's on it and it rode well.

1976gmc20

Where did you find 15" tires in 10 ply (E) ???????


I've no intention to go to E on the jeep, but figured I could run less than 30/35 psi if I went to LT C.

jbsjunk

These are 16" Moabs.

1976gmc20

So just out of curiosity, what street pressure would you run in LT235/75r15(C) under an XJ ???


(and how do you come up with that value?)

cruiser54

30.

sycoglitch

What is up with making physics and crap out of tire pressure. For stock tires, run what the door says. My 01 says to run 32 but using the dirt method i run 32 up front and 30-31 in the rear since i run light. When i get my 32s next weekend, fingers crossed, ill start with 28-29 front and rear but itll depend on the dirt test once again

sycoglitch

I loved my 10ply destination ATs. They do ride
Rough but damn they can take a beating and hold up. Plug up easy too

1976gmc20

I was asking about a non-stock tire size

1976gmc20

Both front and rear ???


If going five psi under stock tires, seems like it would be 25/30 F/R.

cruiser54

"Every tire is different. There are too many variables to give a "one size fits all" answer. The only way to verify proper inflation is to use the chalk test. See the link below".

http://www.jeepfan.com/tech/checking...rect-pressure/

cruiser54

30/30 on 235s.

sycoglitch

But why Are you doing 25/30. Are you running that much gear in the rear. Do the chalk test. Too many variables. Numbers have no place there. For example, you need shock sizes on a lifted jeep, you go flex and measure. Need tire pressure, go chalk and drive

1976gmc20

Thanks, I will use that as a starting point when I get new tires.

1976gmc20

Never did. The factory recommendation is 30/35 so I was subtracting five psi to get 25/30 for a bigger tire. I'm sorry if all this math is too much for you


Does the "chalk test" work on gravel? Seems like I would have to drive to town, mark the tires, and then drive around a while and check them before coming home.