Recommended tire pressure - on road

[Sporadic]

Nitto trail grapplers 35x12.5xR18, 2.5" lift.

I had tires set at 37 psi but after last service visit to dealer I found them at 40-41 psi! I noticed more "wandering" on the highway which led me to check the tire pressure.

What psi are you guys ruining on your 35's when on-roading?

 

[paychex.308]

I run my 37" KM2s at 28 psi on the road.

 

[JKNuts]

I have found that 32 psi works for my 09 JKUR with 35 inch BF Goodrich mud terrains. I have more even wear that way. I know some of the guys at Teraflex said they never run over 30 psi on their 37 inch tires. My son runs 37 psi in his 35's and I find it harder to drive.

 

[munstie]

I run 28 psi on the street in my 35" Toyo M/T's. Try chalking the tires and adjust your pressure accordingly.

2011 JKU 3.5 R.E. Longarm lift.

 

[wayoflife]

As mentioned, you really want to be running closer to 28-30 psi.

 

[StrizzyChris]

agree with everyone on here...I am running my 35" Nitto Muds at 29. I had a ton of wondering from the dealerships 35lb...lowered it to 28 and it felt great. On my drive from Ohio to Cali, the air and tires warmed up and mid trip I developed the "sensitive steering" again. It was back to 35lb range. After lowering down to 29 its the perfect feel for me! :yup:

 

[Sola_Christos]

agree with everyone on here...I am running my 35" Nitto Muds at 29. I had a ton of wondering from the dealerships 35lb...lowered it to 28 and it felt great. On my drive from Ohio to Cali, the air and tires warmed up and mid trip I developed the "sensitive steering" again. It was back to 35lb range. After lowering down to 29 its the perfect feel for me! :yup:

Good stuff guys! I was just wondering about that. "Now I know...and knowing is half the battle!!" (for you old heads out there!)

 

[OverlanderJK]

I currently run 28PSI in my mud grapplers but might bump it up to 30 to see how it feels.

 

[rtguy1]

28-30 is good. the km2's are thinner walled so they flex a bit more and you can get away with a bit more psi

 

[The Wandering Jeeper]

I run my MT/R's at 35 psi on road hence forth my good gas mileage. Trails are anywhere from 3-8 psi.

 

[Chairokey]

I wondered about this myself.. So plz allow me to high jack for a moment lol

Discount set my duratrac 33x12.5 15's at about 40 psi. Wonder if that's normal since it sits on a 15 or should I try airing down as well?

also you folks with 35-37's sitting at 28-30 psi, do you have so sacrifice mileage to be that low?

 

[gouacats]

Discount set my duratrac 33x12.5 15's at about 40 psi. Wonder if that's normal since it sits on a 15 or should I try airing down as well?

Discount did the same with my 33x2.5r15 Duratracs. I've found that I like them about 32 psi. That being said, I've not checked gas mileage vs. a higher psi. All I know is that my JK gets WAY better mileage than my TJ used to.

 

[cozdude]

I run my MT/R with kevlar at 38psi going down to 35 tho to see how that feels

 

[Sporadic]

Folks,
Thanks for all the feedback. I'll be airing down the Nitto's today to see if I can find the "sweet spot".

 

[OverlanderJK]

I run my MT/R with kevlar at 38psi going down to 35 tho to see how that feels

I wondered about this myself.. So plz allow me to high jack for a moment lol

Discount set my duratrac 33x12.5 15's at about 40 psi. Wonder if that's normal since it sits on a 15 or should I try airing down as well?

also you folks with 35-37's sitting at 28-30 psi, do you have so sacrifice mileage to be that low?

I asked the guy doing the tires to put them at 28PSI and he said yes. I got home and they were at 35PSI. :grayno: But I jut hooked up my EZ deflator and bam 28 it was. I think its just what discount does.

 

[cozdude]

lol i know its high im still learning

 

[paychex.308]

There is also going to be some fluctuation in pressure between cold and hot tires. When tires get hot, the pressure will build and then as it cools, will decrease again. Be sure you check your tires when they are cold to get a more accurate reading. the pressures differences are not that much, but since we are talking about 2 or 3 lbs either way, it will make a difference in your wear and ride. just a thought...

 

[cozdude]

There is also going to be some fluctuation in pressure between cold and hot tires. When tires get hot, the pressure will build and then as it cools, will decrease again. Be sure you check your tires when they are cold to get a more accurate reading. the pressures differences are not that much, but since we are talking about 2 or 3 lbs either way, it will make a difference in your wear and ride. just a thought...

yea i set them to 38 warm the other day after playing around with my new tire deflaters. i know there is that difference between warm and cold just never knew it really made that much of a difference in wear. i only have 32's ATM so im sure 35psi will be a solid number if you guys on 35's are running around 30 psi

 

[StrizzyChris]

I wondered about this myself.. So plz allow me to high jack for a moment lol

Discount set my duratrac 33x12.5 15's at about 40 psi. Wonder if that's normal since it sits on a 15 or should I try airing down as well?

also you folks with 35-37's sitting at 28-30 psi, do you have so sacrifice mileage to be that low?

Well no two tires are the same. Like you mentioned a 15 will be different than a 17 with a 35 due to sidewall size difference. The larger the sidewall, the more flex it will allow. Also a thicker sidewall or higher load rating tire will require less psi due to how stiff the sidewall is. The thicker walls are for strength obviously and capable of being used on a 1-ton Ford tow rig, and require less psi on a lighter JK. So for those reasons a Toyo Open Country MT will require less PSI than say a duratrac or MTR Kevlar with thinner walls.

Also milage will always suffer with lower PSI, but I would rather have that than more dangerous steering. Also when your in the 37-40" tire range....MPG has already been shot to shit!

I asked the guy doing the tires to put them at 28PSI and he said yes. I got home and they were at 35PSI. :grayno: But I jut hooked up my EZ deflator and bam 28 it was. I think its just what discount does.

Same here! I think its a liability thing that they dont allow you to leave with too much of a lower than tire recommendation psi? :idontknow:

 

[Majik]

When I hear these discussions I always think back to a fun little high school physics experiment:
figure out the car's weight by measuring air pressure in each tire and the square inches of contact patch of each tire.

Hope I don't bore anyone but I think its useful

The force each tire exerts on the ground is the psi in the tire times the area of contact. There are subtle variables but that's the important part.

If you air down offroad, the portion of the vehicle weight on each wheel is constant. The psi goes down. So the contact patch area goes up. Example:

1200 lbs supported on single wheel. 30psi.
1200 = 30 x a -> a = 40 sq in

Air down to 15 psi:
1200 = 15 x a -> a = 80 sq in

Thus why airing down keeps you afloat on soft sand! More contact area spreading out same weight.

So why high pressures wander on highway with 35"+ tires? Contact patch gets smaller. How? By making the center of the tread bulge out and lifting the side blocks off the ground. Its like standing still on one Rollerblade instead of a flat shoe. Big tires already spread the weight over a larger area than stock. So the only way the physics can hold true if you compare a 31" tire with 35psi in it to a 40x13.5" tire with 35psi in it is for the big tire to disproportionately load (aka bulge) the center of the tread more than the outer edges. That bulge makes that nice wide tire you have act like the Rollerblade...

Hope that made sense. The most accurate way to find your ideal on road pressure for a given tire is unfortunately the most inefficient. You check tread depth on the rear axle. You drive it say 2500 miles. You precisely recheck tread depth at multiple spots across the tread. If you have less tread depth remaining at the center than the outer blocks, then your pressure is too high. If you are wearing the outer edges faster than the center, then tire pressure is too low. Assuming good alignment. I've actually done this informally to figure out ideal front and rear pressures on big tires on baja- inspired truck builds I've done in the past. The weight distribution on a diesel truck, for example, is so different that to make the tread wear evenly requires huge psi differences front to rear.... and it all comes back to...
contact patch area x psi = weight on that wheel



Here's a pic of one of my last projects, no lift (just huge fiberglass fender wells!) on Toyo MT 37s. 46 psi front tires, 27 psi rear. Wore beautifully. Just had to remember to swap pressures when I rotated tires!