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tire pressure for 31s- chalk test no good

srimes

NAXJA Forum User
Location
Cabot, AR
So I have new 31x10.50 wrangler duratracs and 15x7 rims on a basically stock, 4.0 aw4 XJ. I just did the chalk test on the front tires only, and don't see any use in the results. I started at 30 psi, where the chalk rubbed off to about 1.5" from the edge, and worked my way down all the way to 15 psi (!), where it rubbed off to about 5/8" from the edge of the full lugs and 1/4" from the scalloped lugs. I didn't bother going lower.

Any suggestions? I guess I'll try the temp-increase method. What's the target rise, 4 psi?
 
There are some factos you have to take into consideration. If you are doing the chalk test with a cold tire wersus warm, also if it is a brand new tire that hasn't broken in. With that size I would go right to 32 and leave it. That size with the belt design and structural stiffness should wear best at that. Any less at regular driving could cause more friction and heat, particularly in the side wall. We have done many of those tires at my shop, this appears to be the best for that style.
 
I would run them at about 32-33 psi. I usually put 1 psi more in the fronts for normal driving as there is more weight up there. I have had pretty even wear running this just over 30 psi with 32s.

If you wanted to get better mileage on a long road trip you could bump up to 35 but I wouldn't keep it like that forever. How many trucks do you see with BFG ATs and such that are worn bad in the center of the tread and still have great tread depth at the edges?? I see them around pretty frequently.
 
FWIW I run 26 PSI in my 31s on Ravines. (15X8)

(I run 14 psi in the sand)

Terrific ride and good wear so far. I do add air (32 PSI) to the rear tires when I tow my boat.

32 PSI is too rough a ride and bows the tire to much for my taste.

This advice is worth what you paid for it.
 
There are some factos you have to take into consideration. If you are doing the chalk test with a cold tire wersus warm, also if it is a brand new tire that hasn't broken in. With that size I would go right to 32 and leave it. That size with the belt design and structural stiffness should wear best at that. Any less at regular driving could cause more friction and heat, particularly in the side wall. We have done many of those tires at my shop, this appears to be the best for that style.
^x2
On new tires I usually run them at 10-12 lbs for 10 or 15 minutes to break in the sidewalls on tires that I use for wheeling. Then air up and see the difference in the way the tread lays. The Cherokee is light so it may take a couple of drives to get the sidewalls broke in so they flex good.
 
I'd say 30-35 psi is a good number. If you plan on carrying extra weight or using the truck hard keep it with in 20 percent of the maximum psi rating on the side wall.
 
So this morning my tires were at 24 psi. After driving to work they went up less than 2 psi, to just under 26. It was a bit colder outside than in the garage, so that probably reduced the pressure rise a little. Before driving home they were just over 26. It was quite a bit warmer out than when I drove in, maybe 30* or so. When I got home the tires were at 28 psi, a rise of 2 from driving and 4 from this morning.

So should I let some air out and try a lower pressure? It sounds low already but it isn't the 4 psi rise that's mentioned on gojeep's site.
 
Do you trust your air gauge? I would check it against another one just to be sure yours is somewhat accurate.
 
Do you trust your air gauge? I would check it against another one just to be sure yours is somewhat accurate.

I think it's good, but I'll find another to compare it too. It's a 0-60 dial.

I set the tires to 22 this morning. Drove to work and they were at 25.
 
Do you trust your air gauge? I would check it against another one just to be sure yours is somewhat accurate.

Turns out it's pretty good, just a little low. We got a new, calibrated, 0-30 gauge and rigged it up and it measured 24, while mine measured about 22.5-23. So it's about 5% low.
 
If you continue to have trouble setting the air pressure, I would try setting them at something that 'seems' about right based on ride quality, handling, and the look of the tread contact. Then consider buying a tread depth gauge and measuring them now and then at your next oil change to see how they are wearing and make adjustments from there. Ideally, you'll be able to make adjustments based on uneven wear and get pretty close to your ideal pressure that way.

I am actually going through the same thing with my new Falken 31" tires at the moment. They are on 15x8 Ravine wheels. But, I don't trust what my tire gauge is telling me, so I verify with a different one when I get the chance.
 
your not going to get a correct chalk tune with proper air pressure while running those tires on 7" wheels. im not saying its bad to run them if you do alot of offroad driving. the narrow wheel will help hold the bead if you lower the pressure for traction. but those tires are supposed to be mounted on an 8" wheel for proper street performance. the fact of the matter is that if you plan to run those wheels with those tires, they ARE going to wear faster in the center of the tread. its a trade off. run the correct width wheel and have the tire wear better, or run a narrower wheel and have a better chance of not throwing a bead when running low pressure.
 
How quickly are you checking the pressures after pulling up? Drops pretty quickly and find jumping out after driving on the highway for 1/2hr and just doing the one side the best. Temps, and therefore pressure, can drop while just driving around in the burbs before pulling up.
 
your not going to get a correct chalk tune with proper air pressure while running those tires on 7" wheels.

Yeah, that's what I figured after trying it :roll:.

How quickly are you checking the pressures after pulling up? Drops pretty quickly and find jumping out after driving on the highway for 1/2hr and just doing the one side the best. Temps, and therefore pressure, can drop while just driving around in the burbs before pulling up.

Pretty quick in the morning at work: the parking lot is just off exit, no stoplights. Probably 60-90 seconds or so. Coming home there's a couple of lights and the house is about 3 miles from the highway, so that reading probably isn't good.

Does outside temp matter when looking at pressure rise?
 
I have 33" duratracs (on 15x8) and I have tried to get a flatter contact patch as well... it didn't flatten out all that much at lower psi so I said screw it and put it back to 30psi. Now thinking about it and seeing other peoples ideas it's probably due to the rim puckering the tire.
 
I have 33" duratracs (on 15x8) and I have tried to get a flatter contact patch as well... it didn't flatten out all that much at lower psi so I said screw it and put it back to 30psi. Now thinking about it and seeing other peoples ideas it's probably due to the rim puckering the tire.

x2 on the setup.i am at 28psi till i see everyone elses thoughts/experiences. i'm happy with the duratracs(owned the for a week now)
 
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