PSI cold warm vs Tread Depth

I've used the search function but didn't find an answer.... JKU leveling kit 33" MT ATZ, no after market bumpers or excessive weight...daily highway driver 120km per day. Cold I have 30 PSI all tires. Once I get to work I'm 32.5PSI Tires have 10,000km and have been rotated every 5,000 km (twice thus far) When I rotate I use a depth gauge and measure each tire cross section at three points... Outer / Middle / Inside All four tires are measuring 16.75 / 16 / 16.75 32nds of an inch To me this means the centre is wearing more then the in or outside.

Would the right thing to do is lower my cold pressure to 29 or 28PSI to "offset" the increase in pressure as the tires warm up?

Thanks

Simply, yes.


Sent from a a few tin cans and some string.

On a side note, I've seen a 5~6 psi difference here in TX from a morning "cold" psi to "hot" psi after driving non-stop in 100 degree temp.


Sent from a a few tin cans and some string.

Thanks, I'm learning as I go, never had 'oversized' tires before...just stock, so like everyone else want to make sure I'm running these right to make them last.

Good point on ambient temp! Wow, that's hot! Things are cooling down here, I suspect to your point I will see greater variations in the summer months when its 30 deg C hot and humid.

:beer:

Do the chalk test to find the perfect PSI so that all if your tread is contacting the road.

What load range are your tires?

My personal experience and also others that I've read about find the greater the load range, the less psi required.

i.e. Stock tires with load range 'C' seems to be just fine at a more "traditional" ~32psi.

My current tires are a load range 'E' and are much happier at ~26-28. Appears this is due to a much stiffer sidewall that is capable of supporting my rigs weight at the lower psi.

I second the poster's advice above to do the "chalk test." Essentially you steal your kid's chalk or a neighbor kid's chalk and completely color about a 4" wide band, HEAVILY chalked up, from one side of the tire to the other. Start your Jeep, place in drive/reverse, and drive slowly forward/backward one complete revolution.

Get out, look at the ground where the chalk transfer is left on the ground. If your psi is set perfectly/acceptably, you will see pretty much an exact transfer of chalk from the tire to the ground. You can also look at the tire and see where chalk is/isn't.

Examining chalk on the ground: if it lighter or missing on the edges, you have too much psi/air. Let some out and repeat test.

Examining chalk on the tire itself: One would interpret the results conversely from examining the ground. If chalk is heavier on the sides and lighter/missing in the middle, you have too much.


The converse of the above tests and subsequent examination would mean the opposite. Chalk on the ground heavier on the edges of the transfer would mean too little air.


Sent from a a few tin cans and some string.

You may have to drive where your tire(s) complete several revolutions. I found a few photos to help illustrate above post:

Band of chalk heavily colored on the tire:


After a few complete revolutions you can see the middle is worn off the most meaning over-inflation:


Sent from a a few tin cans and some string.

CerOf said:

You may have to drive where your tire(s) complete several revolutions. I found a few photos to help illustrate above post:

Band of chalk heavily colored on the tire:
View attachment 52386

After a few complete revolutions you can see the middle is worn off the most meaning under-inflation: View attachment 52387


Sent from a a few tin cans and some string.

Click to expand...

My tires are Load Range D, and I'm now running 27.5 psi cold...30 warm

Thanks for the chalk test tip...I have kids they have chalk...now I piece less

In the last above photo were the chalk is left only on the sides I thought that would mean over inflation

Cheers

webejeepin said:

In the last above photo were the chalk is left only on the sides I thought that would mean over inflation

Click to expand...

I think that's what he meant. Over inflation means the middle portion of the thread balloons out so it creates more contact with the ground. Under inflation would leave no chalk on the outsides I believe.

Don't follow me, I'm lost too! O|||||||O

GuillaumeC91 said:

I think that's what he meant. Over inflation means the middle portion of the thread balloons out so it creates more contact with the ground. Under inflation would leave no chalk on the outsides I believe.

Don't follow me, I'm lost too! O|||||||O

Click to expand...

Ayup, made a typo.

I went and fixed my post so it is correct. Unfortunately what my brain tells my thumbs to type often doesn't come out right.


Sent from a a few tin cans and some string.