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-   -   What PSI to run with 31x10.5 15 BFG KM2 (http://www.wranglerforum.com/f282/what-psi-to-run-with-31x10-5-15-bfg-km2-145780.html)

AsylumTJ 03-12-2012 03:22 AM

What PSI to run with 31x10.5 15 BFG KM2
 
So I've had these tires on for about 30k so and it just rides hard. I noticed when at the beach and going on and off road I aired down to like 38 or so and the ride was a lot nicer. Anyone have input about what PSI I should run with these tires?

AsylumTJ 03-12-2012 03:41 AM

Oh and right now i'm running the 50psi that is says for max on the side wall

pjfargo 03-12-2012 03:47 AM

Can't say for those specific tires, but we always ran 10-12 psi in the snow up in Iceland. Guys with 36's and larger ran 8 ish. I've run 10 psi on 32's and 33's with no issues. When we got ready to travel back on the main roads (thats funny that), we filled them back up to regular psi levels. Seen guys do this with stock tires, they were like 28 or 29's and skinny, on stock rims. You just have to know you cant make sharp turns or go real fast, comon sense stuff or you will pop the bead. But if you have a decent compressor and some straps you can reseat it and continue on. I popped one bead hitting a hidden boulder, wasn't fun to re-seat in the cold but no harm was done.

AsylumTJ 03-12-2012 03:51 AM

Well what would be a "regular tire levels"? I should have clarified that it would be the PSI for street driving.

Umbra0101 03-12-2012 04:02 AM

38 Is even a little high for the street. Just use normal tire pressure. It'll tell you on a tag inside the door jam, or you could call a few tire places and ask until you get one overwhelming answer. I run mine at 36 psi right now. Could go lower. 28-32 is about normal for most vehicles.

When you air down for sand, your tires should look a little less than half flat. A little saggy at the bottom.

The closer to max pressure in the tire, the better mileage you're likely to get, but the center treads will wear faster and you'll have less tread in contact with the road. At ideal pressure the tread will wear evenly and you will have more treadin contact with the road, which is safer. Less than ideal and the shoulder treads will wear more and your mileage will decrease. Far too low and it will get squirmy on the road and not be safe.

XJ Knight 03-12-2012 04:26 AM

Yeah for the street you should be running like around 32 psi.. 50 is way to high

pjfargo 03-12-2012 04:39 AM

Ah, I see. I always run at stated max psi on the sidewall for street use. When she starts feeling soft, I know it's time to add more air. If you go down to the low 30's or whatever, you will have that softer ride at the expense of MPG as Umbra0101 said.
I guess the other question would be what shocks do you have? If stock, are they the tow package version? Those are a bit stiffer.
The ideal answer is also the most expensive. Run at manufacturers recommended psi and purchase tunable shocks.

Beachcomber 03-12-2012 08:24 AM

Your running much to high for street use. 28 to 32 would be the max and 12 to 15 for off road. The max rating on the the sidewalls is not what you should be running at as a norm.

s14sh3r 03-12-2012 08:39 AM

The 50 psi is for maximum loads. It should say what the max load is on the sidewall of the tire. You're no where near that in the jeep.

billybobjoe 03-12-2012 09:13 AM

The recommended street pressure is in a label on the doorjamb of every motor vehicle sold in the USA for at least the the last 10-12 years or more. I have 31's as well and I run 30-32 PSI

wwch99tj 03-12-2012 09:46 AM

Quote:

Originally Posted by billybobjoe
The recommended street pressure is in a label on the doorjamb of every motor vehicle sold in the USA for at least the the last 10-12 years or more. I have 31's as well and I run 30-32 PSI

That is for the stock size tires ...

I have 31" Goodyear tires and run at 30 psi

johnnyleo11 03-12-2012 09:58 AM

You could always do a chalk test on your tires. This will allow for proper wear over the life of the tires.

AsylumTJ 03-12-2012 12:05 PM

I appreciate the help guys, i'm going to try to run between 28-31 after I do the chalk test. The shocks I have are BDS but will be replaced by OME soon.

TheTJRod 03-12-2012 01:58 PM

I bet the center of your tires are going bald! We will never run max pressure on tires in our Jeeps. 38 is real high still, and expecially for sand. When you go offroad you should bring the PSI to at least 20 if not lower. I run at 12 with no beadlocks and haven't popped a bead.

Also glad someone said it. You can't rely on the door jab pressure either, that is for stock tires. The bigger/wider the tire the less air pressure you need to run.

I'm still surprised you were running 50, would have expected the tires to give out after 30k of that.

MikeMTJ 03-12-2012 02:05 PM

Quote:

Originally Posted by AsylumTJ
I appreciate the help guys, i'm going to try to run between 28-31 after I do the chalk test. The shocks I have are BDS but will be replaced by OME soon.

You're going to notice a big difference. You might even decide it won't be worth it to change your shocks out, although OME shocks are very comfy.

TjWranglerMan 03-12-2012 02:10 PM

Quote:

Originally Posted by AsylumTJ
I appreciate the help guys, i'm going to try to run between 28-31 after I do the chalk test. The shocks I have are BDS but will be replaced by OME soon.

OME r very comfortable my tj feels like a Cadillac really smooth

Sherpa 03-12-2012 11:17 PM

I only run 26 psi on the street in my 31x12.50 Goodyear MT/Rs. I have done this for three years now on these tires (I've run them on two different Jeeps in that time). When I go out to play in the rocks, I air down to 15 psi.

My tires wear evenly at this pressure, and I observe stock-like fuel economy (16-17 mpg). FYI

the great moo 03-12-2012 11:34 PM

I notice a lot of you run off road aired down. When I first started wheeling I did the same but I found, in Arizona that with the right tires I never air down any more. I would live to know what kind of terain you guys run and why you air down. I wonder if I'm missing something staying aired up now?

TjWranglerMan 03-12-2012 11:39 PM

Quote:

Originally Posted by the great moo
I notice a lot of you run off road aired down. When I first started wheeling I did the same but I found, in Arizona that with the right tires I never air down any more. I would live to know what kind of terain you guys run and why you air down. I wonder if I'm missing something staying aired up now?

I run bfg mud terrain wit a lot of tread and I air down to 8-15 psi depending wht I'm doing the reason I air down is the tire molds better round things instead of bouncing off of it

Jerry Bransford 03-12-2012 11:45 PM

Quote:

Originally Posted by the great moo (Post 2133986)
I notice a lot of you run off road aired down. When I first started wheeling I did the same but I found, in Arizona that with the right tires I never air down any more. I would live to know what kind of terain you guys run and why you air down. I wonder if I'm missing something staying aired up now?

Not airing your tires down while offroad is a mistake. Airing down below 15 psi gives a number of benefits... a smoother ride is the least of them which also helps prevent shaking your Jeep so much which helps reduce the likelihood of introducing rattles.

The other benefits, which are the main benefits, include MUCH better traction since more tire is in greater contact with the terrain which gives much better traction, and an aired-down tire is less likely to get damaged when rolling over sharp obstacles... it will conform to the sharp obstacle without damage instead of presenting a harder/stiffer more easily cut surface to the sharp obstacle.

I had a Rubicon in a group several years ago and he was having a lot (!) of trouble on the trail. His tires were spinning on rocks and obstacles that the rest of us were not having any problems on. It turned out after many attempts to get him to tell us how far he had aired down, that he finally admitted he had only aired down to 20 psi which he thought at the time was "a lot". Once we got him down to 13 psi, which is still not aired down a lot, he had no more problems on the trail.

On an easy trail, I air down to 12-13 psi. For a really difficult trail, I may take it down as low as 6-8 psi though that's a bit too low for most tire and wheel combinations.

Sherpa 03-13-2012 12:16 AM

Quote:

Originally Posted by the great moo (Post 2133986)
I would live to know what kind of terain you guys run and why you air down.

Here are a few pictures of my current Jeep I have lying around on my server:

http://dempseybowling.com/cars/98sport/pose-50.jpg

http://dempseybowling.com/cars/98sport/98_lm2b.jpg

And here are some shots of former Jeeps:

http://dempseybowling.com/cars/pastcars/tg_ratl.jpg

http://dempseybowling.com/pix/jeeping/con_sh02.jpg

http://dempseybowling.com/pix/jeeping/con_sh07.jpg

I love rocks.

Jerry Bransford 03-13-2012 12:20 AM

You don't need to be offroading on rocks to benefit from airing down. Any offroad trail that is more difficult than a dirt road will present conditions where an aired down tire will do better than a tire that is still inflated to its street pressure.

the great moo 03-13-2012 09:49 PM

4 Attachment(s)
I live the pics thanx. When u was wheeling my Toyota I aired down a lot, best way to get traction but since I traded up to the Jeep I just have never had a need anymore. Guess I need to keep challenging my jeep some more.

Was trying to add some pics but it keeps crashing on me.

neverfastenough1 03-13-2012 10:26 PM

You should always air down at the drag strip, too! Use what the door says. It is for your vehicle weight and will give you the best footprint. A little less will ride smoother, but the more you run under, the worse the mpg's.

TheTJRod 03-14-2012 12:32 AM

Quote:

Use what the door says. It is for your vehicle weight and will give you the best footprint. A little less will ride smoother, but the more you run under, the worse the mpg's.
Maybe you should reread what was said above. The door sticker may be good for stock weight but it's also only good for stock tire size. Tire size, tire width, wheel size, wheel width, and weight all play a part. Change them from stock and you can't use the stock pressure. The chalk test will tell you if you're under or over pressure to keep from wearing your tires uneven.

the great moo 03-14-2012 11:26 AM

The chalk test is the only way to set your tire pressure right. Without it you can't account for your vehicles individual traits add ons and so forth.


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