Tires and Air Pressure

CanAmMick

New member
About 6 weeks ago we purchased our first Jeep, a 2018 JL Jeep Wrangler Unlimited. The dealership already had a lift and larger tires installed on it. Tires are BF Goodrich All-Terrain T/A KO2 35x12.5R18LT Load Range E. They had the air pressure set at 42.

When driving the Jeep on the highway/interstate it wandered all over the road. I figured it had to be because of the air pressure, but didn’t have a clue of how much lower I should go. I talked with a few people and everyone that had the same tires was using different air pressure, from 30-32, 34-36, and 40-42. I finally sent wayoflife a PM, and he was able to provide me with a good starting point.

I started with 30, went to 32, then 34, and back down to 28. I ended up going back to 30. So far we have 2600 miles on our Jeep. It rides much better than it did when we purchased it, and no longer wanders all over the road. I think it would be a great help to others if a lot of us posted what tires were on our Jeep, and what air pressure we were using.

Also purchased a TazerJL so I could change the settings for TPMS, along with some of the other features. Great device, well worth the money.

Thanks again Eddie for your help!
 

BillArnett

New member
On my way home from Colorado a couple weeks ago, I did a little experiment with my tire pressures. I'm running Cooper STT Pro 37x13.5R17 (load range E). On I-80 west of Salt Lake City the road is absolutely flat for 100 miles and the speed limit is 80 (Bonneville Salt Flats is nearby). So ran at various speeds at two different tire pressures and recorded the mpg numbers from the EVIC (first column is mph, second is 25psi, third is 35psi):


80 14.6 14.6
75 16.8 17.6
70 19.2 18.9


As you can see at 80 and 70 there was essentially no difference at all with the two pressures. (I think something went wrong with my trial at 75.) This is somewhat counter-intuitive. Perhaps a more careful experiment would show a slight improvement at higher pressures? I don't know. But I suspect the effect would be small.

I can't say much about the handling from this experiment as the road was absolutely straight but it maybe felt a little more precise at 35psi. The ride is a bit rougher at 35psi but not much. I'm sticking with 25 psi for normal driving.

OTOH, there's a HUGE difference with speed, as expected.
 

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