Tire pressure

JLsport19

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New tires on yesterday. Cooper STT pro 255/75/17 on my sport. Dealer put 40lb in. Seems too much. What y'all think pressure wise? Don't do too much off road mostly around town and some highways here in there. 35lb?
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TRJeff

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I would think too much, 35 psi would be a good guess, start cold and try 10% rise hot pressure rise,and or chalk test, chalk line across tire short drive hot tire and check even loss of chalk line
 

Rhinebeck01

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@JLsport19

"The 255/75R17 Cooper Discoverer STT PRO has a diameter of 31.89", a width of 10.3", mounts on a 17" rim and has 652 revolutions per mile. It weighs 51 lbs, has a max load of 2405 lbs, a maximum air pressure of 50 psi, a tread depth of 19/32" and should be used on a rim width of 6.5-8.5"."

I'd say you would best run them at between 32psi and 35 psi (Cold inflation psi) but do encourage you to do a chalk test.

Can tell you at 40# psi, you will find that 2 dr. wandering all over the place.

Do read here in regard to chalk testing:
https://www.jlwranglerforums.com/fo...ould-i-run-do-a-chalk-test-to-determine.4622/

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JLsport19

JLsport19

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Thanks! I'll try that. It does wander I noticed. I've only put 10 miles on them so far. Gonna lower pressure tomorrow and try the chalk test
 

Rhinebeck01

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Thanks! I'll try that. It does wander I noticed. I've only put 10 miles on them so far. Gonna lower pressure tomorrow and try the chalk test
@JLsport19

Adjust cold, in the morning before you drive or Sun heats up the tires.

IF you don't have time to chalk test right away, DO just get them down to 35psi, as soon as possible..

Use a decent tire gauge. Do not adjust by looking at the evic display. Evic display is nice but adjust with a gauge.

You will notice less wandering. Also.. your steering wheel telescopes.. be sure it is adjusted so you have some bend on your arms. IF you are reaching for the steering wheel, this can cause wandering.... especially as your arms get tired.

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RCH

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Wow. I have a new Wrangler and just posted about my high speed wandering yesterday in the General section. I received the same advice. I am currently running the Factory 33's at 41 PSI. I will drop them this morning to 35. I have to go buy chalk to do a chalk test.

This may be a great (and easy) fix. thanks to all.

v/r rch
 
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JLsport19

JLsport19

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im going to try it this weekend when i get a chance. its not my daily driver so i did not do it this morning due to not driving it. thanks for the advice and information from everyone! its appreciated!
 

Rhinebeck01

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Wow. I have a new Wrangler and just posted about my high speed wandering yesterday in the General section. I received the same advice. I am currently running the Factory 33's at 41 PSI. I will drop them this morning to 35. I have to go buy chalk to do a chalk test.

This may be a great (and easy) fix. thanks to all.

v/r rch
@RCH

I don't think it is a "a great (and easy) fix" I know it is ...

....if you set your Cold tire pressures to 34 or 35# psi and adjust your telescoping steering wheel so you have a bend in your arms ... so you are not reaching for the steering wheel.... you will see wandering is not going to be an issue.

Do your psi adjustment, now. Your tires are overinflated.. Worry about the Chalk for as soon as you can do it.

IF your tires are brand new / mileage under say 100 miles, you may need to get say, a hundred more miles on them, before you really see them track well.

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RCH

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Rhinebeck01: I have 1250 miles on them. All at 39 - 41 PSI (41 is due to spring finally arriving). Can't wait to go try this.

Thanks to all who make this forum great. v/r rch
 

OldGuyNewJeep

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35psi is the sweet spot on my (stock) 2dr Rubi. I use a Tazer to lower TPMS warning threshold.
 

Rhinebeck01

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35psi is the sweet spot on my (stock) 2dr Rubi. I use a Tazer to lower TPMS warning threshold.
@OldGuyNewJeep

Yup, Cold Pressure adjusted 35# , is what I run with. Though I have a Tazer JL Mini, I have never adjusted the TPMS warning threshold. I never have had a TPMS warning on my JL, running as low as 32# psi.

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RCH

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I set mine to 35 this morning (stock Rubi 33 tires with stock rims). I didn't get to the highway, but, already feel the difference when running my errands today. Much more stable.
My gauge says 35, but, my TPS says 38. Go figure. Rechecked with my gauge (digital) 3 times. I am at 35.

v/r rch
 

Rhinebeck01

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I set mine to 35 this morning (stock Rubi 33 tires with stock rims). I didn't get to the highway, but, already feel the difference when running my errands today. Much more stable.
My gauge says 35, but, my TPS says 38. Go figure. Rechecked with my gauge (digital) 3 times. I am at 35.

v/r rch
@RCH

When you cold set psi as you should, you will see the TPMS reflect change in psi, due to environmental temperature, your actual driving the vehicle, etc..

With that said, your TPMS in the morning will report say 35 but after you drive the vehicle a bit, the Sun hits the tires, it warms up outside, your TPMS will read, say 37, 38 or a tad more possibly.


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