Just wondering what PSI I should be running for daily/highway use? I have 33x12.5 Mickey Thompson MTZ's. When I got it from the dealer, they had them up to full capacity (50 PSI!!!) I dropped them to 38 but would love some input from you more experienced JK owners. 1st time Jeep owner here, so take it easy

Also, what about off-road??? (mud,sand,snow)

 

I run my 35a @ 30 psi on road, and 15 psi off road. I would never run them @ the pressure listed on the side of the tires, it is WAY too high !!

On the driver's side door frame, or owners manual, the recommended tire pressures should be listed for your jeep. That is the pressure you should run if your stuck on doing things the "text book" way.

Congrats on the new jeep !!!

 

Cool - I was having some traction control issues - I'll drop em down to 30 and see how it rides

 

Do a search for the chalk test. It tells you the correct pressure to use for the weight the tire is carrying. I'm guessing 28-30#s

 

24psi or so would give me the perfect patch. I run 36psi because I prefer less rolling resistance..

 

My jk is my dd and I drive between 45 and 90 miles everyday. I'm running my "D" load 33s that are about 11.5" wide at 35 psi. When I first got them the guys had them at 65 psi and it was like driving on rocks, and darting all over the road. At 35 psi the tires are wearing great and it's a good ride. I may bring it up to 40 psi and see if it will help a little more with mpgs only because I drive so much. Experiment with yours and you'll find your "sweet spot".

 

I run mine at 35psi also. When I check mine it is in the morning when the tires are cool and the vehicle is still in the shade.

 

I run mine at 30 psi onroad. offroad i go between 13-15 psi.

 

i usually run mine (35s) around 28-30 psi on-road/higway. offroad i run around 10 psi stock rims. everybody running 15psi or more offroading needs to drop it down and see the difference.

 

Actually the text book way would be to use the door placard data along with the Service Description of the OEM tire. The Service Description is a 3 number code as to how much weight a tire can support at a given inflation rate, generally often followed by a letter for the tires speed rating.

Using an ETRTO chart you can cross reference the supported weight of the OEM tires and find a corresponding inflation rate for the service description of your new tires. It's pretty simple, the worksheets and charts are on just about every tire manufacturers website and ETRTO charts are readily available if you want to download them.

While I don't believe this cross referencing is the end all, at least you know where the vehicle and tire manufacturer recommend that you are to match stock spring rates and promote your safety. It's also important to note in the case you have any warranty issues with your tires.

I use the ETRTO charts to find my initial inflation rates and then move on to the chalk test that is the favored way to determine inflation rates by so many on this forum. Generally this will tend to be lower than the ETRTO charts suggest and I use the difference as the window of where I want my tires to be, promoting ride quality and handling.

Some description on what the chalk test entails. Use a piece children's sidewalk to draw a line across the tread width. Move your vehicle far enough to get a few rotations of the tire and inspect where any chalk remains. Chalk remaining on the outside of the tread suggests you should reduce your inflation rate while chalk remaining towards the center suggests you should increase your inflation pressure.

As for off road use, this is mostly a matter of personal preference but most will find a comfort level with between 12 to 20 psi, often lower with bead locks. Different tires will respond differently and for example on my former Toyos I would drop them to around 12 psi because of the extra sidewall support and my Goodyear MTRs with Kevlar I run at 16 psi.

Hope that helps!