I upgraded to LT 275/65/R18 Cooper A/T tires a while back. I was getting ready for a long road trip and realized I didn't know the proper tire pressure for these beasts.

So do I use the formula on the door placard which is for a different size tire or do I inflate to another value. The interwebs are all over the place with recommendations.

 

I'd do a chalk test. Every upgraded/modified 4x4 will be different and the sticker in the door is totally meaningless unless it's the OEM tire size. I ran 26PSI for example in both my 05 Jeep Wrangler Rubicon's with 33inch M/T's, which was nothing like the door sticker had listed for the stock 31inch tires.

 

Got it. I will do that tomorrow. Thanks!

 

I would think 26-28 psi would be plenty.

 

No problem, yeah I took a lot of heat for running under 30PSI on my Jeep's from so called fellow Jeepers. I also got close to 50K out of a set of M/T's so I'm not complaining. I told all those Jeep owners how a chalk test works, and they just looked at me. Once you get a nice even amount of chalk across the tire = you have the proper PSI for your vehicles weight/config for on road travel/use. Off road of coarse = air down if needed for maximum flotation/traction.

 

Can you explain the chalk test? I’m about to put a different sized tire in my D2 (245/75-16) and am interested what to run.

 

YouTube videos out there explain it pretty well. You use chalk on your tires and drive it for a bit to see where the chalk rubs off. By inspecting the chalk you can see whether to increase or decrease pressure.

@Best4x4 should this be done when the tires are warm or cold? Finding conflicting info on the interwebs.

 

I would say warm. I've always done it after I get a set of tires mounted for example after the drive home. Those darn tire shops put like 45PSI in those suckers making for an awful ride home!

 

Yeah that is what they did to mine. I didn’t even think to check them until I started playing around with my tire deflators. Did the chalk test warm this evening. Looks like 30 seems to work pretty good.

thanks again for the help! Heading to the mountains tomorrow!

 

I think I just realized my tires are way over-inflated. No wonder I am not enjoying the ride! Im going to air down for sure.