Tire Pressure?

[Sparky-Watts]

Anybody out there have any advice of what pressure to run my Mud King 31x10.5x15 tires? Originally, the dealer inflated them to 32 PSI. When I got my new rims, they inflated them to 50 PSI, because that's what the "Maximum Pressure" rating is on the side. At 50 PSI, only the very center part of the tread lugs touched the road, and the ride was awful. So, now I'm running them at 35 PSI, which appears to have a good contact patch and much better ride. There isn't any heat build-up, either. I was just curious what you guys thought. I went to the BFG site (they make the Mud King), but couldn't really find anything there for the size of vehicle. If I was driving an F250, or some other full-sized vehicle, 50 PSI probably wouldn't be too far off, but not on a little Wrangler.....

 

[88Wrangles]

I'd stay between 28 and 32 on the road. That's where my Jeep liked it's pressure when it had 31's. From there, you can play around with the pressure till it's perfect.

 

[Sparky-Watts]

How was the tire wear in that range? Seemed that pressure (32) was a little soft on the contact patch, putting more strain on the outer lugs. The ride was good, but it felt pretty soft going through the curves. On the other hand, with it up at 50, going around corners, it felt like the rear end was wanting to jump out. Now, at 35, it feels pretty neutral front to rear in the turns.

 

[88Wrangles]

RE: ROLL OVER Angle??

Well all vehicles/tires will like a little different pressure. I had BFG Mud Terrains and they wore excellent at about 28 psi. I only had them on for about 10,000 miles, but they still looked brand new when I took them off.

A way mny people use is put a line of chalk on the tires and drive a tiny bit. Then look at how the chalk wore, and you can see the high/ low spots.


Maybe someone else has another idea.

 

[Sparky-Watts]

RE: Re: RE: safari bikini,duster,deck cover

Well all vehicles/tires will like a little different pressure. I had BFG Mud Terrains and they wore excellent at about 28 psi. I only had them on for about 10,000 miles, but they still looked brand new when I took them off.

A way mny people use is put a line of chalk on the tires and drive a tiny bit. Then look at how the chalk wore, and you can see the high/ low spots.


Maybe someone else has another idea.

I've heard of that, and also driving in a little water and seeing how the wet tracks fade. Think I'll try the chalk thing tomorrow. How will it look if I'm over or under inflated? I would think if it's under inflated, it will wear on the outsides first, and vice versa for over, right?

 

[BigDaddys88YJ]

I dont know if this will help but I run my jeep at 35 psi and I have done this on two sets of BFG M/T's and seems to work for me,but its not my everyday driver. On the other hand I have a F250 superduty, 4x4, diesel,Crew cab(heavy bastard) that I run at about 5psi higher than recommended, due to the fact that in my opinion I get better fuel milage and longer tire life, and it also has BFG M/T's on it. Hope this is some help. BDYG

 

[Sparky-Watts]

Thanks, BigDaddy! I agree on the fuel mileage. With the harder tire and less contact patch pressure, the engine doesn't have to work as hard to turn them. Basically, with low pressure, the tire deforms more, making it harder to turn.

 

[88Wrangles]

How will it look if I'm over or under inflated? I would think if it's under inflated, it will wear on the outsides first, and vice versa for over, right?

Yes.
underinflated= more wear on the edges of tires (less chalk left in those areas).

Overinflated= more wear in center of tires (less chalk will be in the centers).

If 35 feels good to you though, you'll be fine leaving them at that. My Jeep was completely stripped down and I always carried the neccessary tools and equipement in it, which is probably why such a low air pressure worked for me.



Now with my Chevy....I usually run 17 lbs on the street with it :wink:

 

[_(OIIIIO)_Jeeper]

RE: Cat shoots Owner

When I got my new rims, they inflated them to 50 PSI, because that's what the "Maximum Pressure" rating is on the side.

Sounds like you need to find anouther shop that actually knows about tires. :roll:

I ran the 31x10.50 I had at 30psi...my 36x14.50 at 35 psi

 

[TwistedCU]

So, now I'm running them at 35 PSI, which appears to have a good contact patch and much better ride. There isn't any heat build-up, either.

There you go Sparky. All tires are different, as are the weight of vehicles.

If 35 works on the road and you have good contact and ride, stay with 35.

I run 35psi on my MT/R's on the street, and 20 psi for on the trail. I tried 30 psi and noticed the tread blocks started to cup a bit, so I rotated them and went back to 35 psi. Glad I was keeping an eye on them as I would've kicked myself for screwing up my mudders.

Stick with what works. You'd hate to try a lower pressure and have uneven wear as a result, especially after knowing what already worked for ya.

My $.02

 

[Sparky-Watts]

Well, this has been just what I was wanting....everyone's opinions and some justification that I wasn't wrong! Thanks!!! I remember now running one set of Kumhos on my Toyota at 32 and they cupped really bad, ruined them before I realized what was happening.

 

[LVRockCrawler]

I've found its a trade off (3-way) with fuel economy, tire wear and comfort... i'm running 25psi in mine to make the ride a bit softer - the more pressure the harsher the ride... just my $.02

 

[TwistedCU]

Again, there are so many factors that play into the correct tire pressure... Wheel width, make of the tire, load rating, weight of the Jeep...

My 32" BFG's on the old YJ were on 7" wheels. I had to run them below 30 psi or they would wear in the center. My MTR's on my XJ are on 8" wheels and they need to be at 35 on the street or they'll cup. Those situations may have differed if I had heavy bumpers or a 6 cyl and hard top on the YJ as opposed to a 4 banger and soft top. This is why you have to experiment, do the chalk test to see the contact with the road, and look at the wear of the tires to see what works best. Seems like Sparky has done that.

Ride quality is nice to have, but I'll put up with a few more bumps to save my expensive mud tires from prematurely wearing out.

If it ain't broke don't fix it.

 

[Sparky-Watts]

Ride quality is nice to have, but I'll put up with a few more bumps to save my expensive mud tires from prematurely wearing out.

My thoughts exactly. I didn't buy a Jeep wanting a Cadillac ride. I knew going into it that it would be a kidney buster. If I wanted a soft ride, I'd still have my Camry.

 

[LVRockCrawler]

have to agree w/the wheel width also - with my 33's on 8" rims i'm running on all but about 1/2" one each edge of tread with no cup in the middle - and at 25psi have a "decent" ride - yea youre all right - i could drop to 18-20 psi and get more cushy but get the cupping and too much sidewall flex (lets not forget that!!) and when u delete the sway bar and rear trac bar, sidewall flex aint much fun on the road!!!!

 

[Junkpile]

1989 jeep cherokee

It all depends on your exact setup. It sounds like you have got it covered fairly well already. I'd guess your going to get the best results at 30-32psi in those 31s, if those are 8" rims.

I didn't buy a Jeep wanting a Cadillac ride. I knew going into it that it would be a kidney buster.

Even a Cadillac wouldn't ride like a Cadillac if it had a 93" wheelbase. A factory YJ does ride like crap, but a quality spring/shock combo along with a tire that has a taller, softer sidewall improves things quite a bit.