hansen65

What's a Procal?

What's the Chalk Line test? Wow the dealer did something without charging??? Thats amazing in itself.

cpobr

The pillar sticker on my 07 Unlimited w/ stock 17" wheels calls for 30# front & 35# rear, cold. Specs much have changed since early 07.

redrunner

I personally would not choose on-road (high) speed tire pressure simply based on ride alone. See the following for additional considerations:

http://home.comcast.net/~kingslea1/J...bstitution.pdf

spinlock

This is excellent advice!

Aside from physical hazards, heat is tires #1 enemy, and heat is generated very rapdily when a tire is underinflated for the load that it is carrying and varies significantly depending on the sidewall design.

The reason many of us "get away" with running lower pressures is that most JKs are not heavily loaded (Curb weight of ~4200 lbs for 4WD unlimited and 1000 lb
payload), so the load on each tire can be ~1500 lbs which some LT tires can readily handle at 28-30 psi.

This type of problem is quite simple to detect by running the tires on the road at the recommended pressure for a few miles and feel the tire temperature to the touch, then lower it to the target pressure and do the same.

I have seen claims that chalk test results in pressures in the 25 psi range on these tires which lowers the load capacity signficantly.

Widewing

Chalk testing is recommended by many... Except tire engineers. They use a pyrometer to check for even heating across the tread.

The chalk test is flawed. Why? Because the shape of the tire (as well as its diameter) change at highway speed. Most do the chalk test by rolling forward a few revolutions going very slowly.

Years ago, I bought a tire pyrometer (probe type, not infrared) to check my race tires. I used it on my street tires as well. I still do.

For street use, I currently run 37 psi in my 255/75-17 tires, with uniform temperatures and wear.


My regards,

Widewing

pastorsteve

Check your spare.

Hitch Buddy

Well it's winter in chicago I am running my stock KM'S AT 24 psi and it seems to help a LOT with traction.

Lorrel

You're probably right about chalking the tires, having a bit of a flaw, however it's a very good baseline for seeing how much tread is actually touching the surface of the road. I'll also agree once the tire heats up on the highway it will become a little more pressurized, however once you get that baseline and check the pressure, you know the pressure, that is right for your tires, and can adjust accordingly. I doubt most do not know how to properly use a pyrometer, let alone own one. I'll take a 5 cent peice of chalk and be on my way, as it has worked for me.

Hiball

I've been running 35lbs in mine, not bad on the highway.

goldtr8

I run my stock Rubi Tires at 45 psi to get better gas mileage. If I run at sticker pressure 37 I lose 1 MPG. Wear is not an issue with a 5 tire rotation for my rig.

I prefer better mileage than a soft ride.