Tire Pressure (33's)

[cjaama]

I just bought a set of lightly used Nitto Terra Grapplers in 305/70/16 (33x12) and will be putting them on my LJ.


My questions is, what air pressure do you run on similar sized tires for the street? Particularly helpful would be with LJ’s, due to the increased weight.


I am aware of the chalk test and tried it, but I didn’t have confidence in the results.


Thanks in advance!

 

[CodaMan]

What load range are those tires, 'C' or 'E'?

 

[cjaama]

E load

 

[CodaMan]

You'll be in the 24-26 psi range

 

[bobthetj03]

Chalk tests are inconclusive. 26 psi is pretty common. Adjust from there based on your load.

 

[derekmac]

26 psi would be a good starting point.

 

[Starrs]

I run 28 psi, but I don't have an LJ either. Yea 26-28 psi should be the ticket.

 

[JamesAndTheSahara]

27-28 here on a TJ with load C MTs. E load would be lower.

 

[CodaMan]

Most with load range 'E tires run a couple PSI lower than those with the same size tire in a load range 'C'. The stiffer sidewall of the 'E' tire can be punishing to our light weight TJ's.

 

[cjaama]

Thanks for all the advice guys. I honestly can't even remember what I'm currently running my current tires at, but I believe it's closer to 30.
Still open to any and all advice.

 

[Rory O'Brien]

I run it a little higher this time of year, 29-31, but i'm usually in the 28-29 range with 33x12.5

 

[Chris]

You'll be in the 24-26 psi range

X2. Don't go higher than that, the TJ isn't that heavy of a vehicle compared to something like a F-350, where then you would want the higher tire pressure.

 

[Shwane]

27psi 33 x 12.5 grabbers

 

[JMT]

26psi 33x12.5 Load C. I’d run 24psi on a Load E. Sidewalls are much stiffer. Try it and see if it doesn’t improve your ride. TJ’s can knock you around if your psi is too high.

 

[Starrs]

If your in the 30 degree weather I wouldn’t be dropping tire pressure too much his time of year. The cold air will suck a couple psi out anyway.

 

[JMT]

When you drive the tires warm up due to friction, so the pressure will increase. If you’re measuring 24 psi cold, once your driving they’ll warm up to 30 or so. So you’re not really driving much on 24 psi, unless they are very short trips. The only way to know what psi they warm up to exactly, without tire pressure sensors, is to get out after you’ve been driving for awhile and check the pressures.

 

[Starrs]

When you drive the tires warm up due to friction, so the pressure will increase. If you’re measuring 24 psi cold, once your driving they’ll warm up to 30 or so. So you’re not really driving much on 24 psi, unless they are very short trips. The only way to know what psi they warm up to exactly, without tire pressure sensors, is to get out after you’ve been driving for awhile and check the pressures.

Correct tires do inflate more when driving. Now if you drop PSI to say 24 and you have your car parked outside and you live in the Midwest and a week or so goes by, your cold psi may be less than the cold 24 psi you thought you had. The colder temperatures are going to pull air from your tires is what I meant. Unless they are nitrogen filled.

 

[Serbonze]

I'm running my 33x12.5 load range e tires at 21psi cold.

 

[JMT]

Correct tires do inflate more when driving. Now if you drop PSI to say 24 and you have your car parked outside and you live in the Midwest and a week or so goes by, your cold psi may be less than the cold 24 psi you thought you had. The colder temperatures are going to pull air from your tires is what I meant. Unless they are nitrogen filled.

Yes, tires do lose air naturally especially if there are small punctures in the tire that are not detectable by tire shops. However, the bulk of the air pressure that is lost is due to temperature drops which cause the molecules in the air within the tire to move slower. Same thing will happen with a balloon in a much more noticeable way as an experiment. All things being equal, and if there were no punctures in the tire, pressure will still decrease as temperature decreases, about one psi per 10°. Then, if the temperature increased to the original the pressure would increase to the original pressure. This means the actual psi in our tires is fluctuating throughout the day due to temperature changes. I think the moral of the story is to choose a temperature and pressure at that temperature and keep a good watch on your pressure, say every couple weeks.

Edit: of course, the tire itself provides a barrier between air outside and inside the tire, so the change of temp within will be more gradual and less noticeable until equilibrium is reached

 

[jeepndogs]

The way the OEM’s come up with the PSI rating on the doors is by using a formula. Max weight of tire listed x 4= x. X / curb weight = x. Max PSI listed on tire / x= suggested PSI

So sidewall max weight = 2250 x 4 = 9000
9000 / 4000 ( weight of Jeep) = 2.5
Max psi listed 55psi / 2.5= 22 psi recommend for Jeep.

Is you call most if not all tire companies and ask them how much psi to run they will ask weight of vehicle and use this formula. If I can find it I will actually post a file Cooper sent me on SST pros.