40 Coopers STT tire pressure

[ehackler77]

so I have been trying to figure out what tire pressure to run in my 40's. had them installed a few days ago and the shop had them set at 30 psi. I told them not to worry about tire pressure because I always chalk test my tires. With that being said, this is the first set of coopers that I have run and no matter how far I air down I can't seem to get the outer lugs to wear. Could it be that they are mounted on a 9 inch wide wheel and it's keeping the tire crowned a bit? Anyone else have experience with these tires? Any recommendations on PSI? My setup is fairly basic so I don't think my truck is on the heavy side.

2021 Rubicon JT
17X9 KMC Grenade Bead lock Wheels
40 inch Coopers
Metal cloak Gamechanger with EVO springs
Steer smarts steering flip
Falcon Shocks and Stabilizer

Thanks again for the input.

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[JD101]

All I can add is I ran 37x12.50 stt pro on 17x9 and they seemed to do well at 28 psi cold . Contact was pretty even , stability and ride were really good also . By that knowledge you should be lower with a 40 since it has more volume. Currently running 38x13.50 trail graps at 27 ( but still dialing them in ) . This is all with no added static load in the vehicle .

 

[ehackler77]

Thanks for the input. Ive chalk tested down to 22 PSI and can't really tell that big of a difference between 28 and 22. Do you think I should keep going? To me, 22 psi seems a bit low for street driving.

 

[JD101]

I would say if chalking , once you hit the max psi with proper contact patch for your tire any lower would yield diminishing returns . And on a light loaded glad 1 psi in a 40x13.50 is more like several in a 33/35 due to volume . Personally I would think 22 cold is low . 24-26 maybe in range tho . I have noticed that my tires become pretty bouncy once I get too low, despite the patch still looking acceptable. Other than time , it's pretty much free to experiment , so test on !

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