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Old 03-26-2009, 03:47 PM   #1
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Tire Pressure - Remedial Review

Hey guys,

Thanks for all your help on the other thread I started. I just wanted to start another thread for the newbies (like me). Tire Pressure.

Bought my Jeep a few weeks back, and it is a blast. Having driven a few before, I knew what to expect. Noisy, rough ride, etc, etc. Big deal. What I didn't expect was how much the thing would be all over the road. It seemed to bump steer pretty bad.

I have read a ton of things and was preparing to start replacing all kinds of stuff, even though inspection of components didn't seem to show anything as being wrong.

Finally weeks into thinking it was just a "Jeep thing" I noticed my tire print on light layer of mud on the road to work. Seemed like not all of the tires had a full "footprint" layed down.

Having just bought it, I ASSUMED that tire pressures were, you know, taken care of by the dealer. Just the same, I went out and bought a nice tire guage and started checking pressures.

FR- 60psi
FL- 65psi
RR - 35psi
RL - 30psi

WTF??? At that time, I didn't even know where to begin with them. I put them all at 40psi, came home, got on this forum and saw that people seem to like anywhere from 27-35psi. I adjusted to 35 and boom. Rides betters. Steers properly (no bump steer). I can drive with one hand now. Quieter ride (for some reason).

DO NOT OVERLOOK TIRE PRESSURE AS THE #1 SOURCE OF WEIRDNESS ON YOUR RIDE.

That said, I have Goodyear MTR (I think) mounted on Rubicon wheels. 245/75x16. Anyone have a recommended pressure for that set up?

Thanks for reading. I feel like an idiot. I will now fade into the mist.

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Old 03-26-2009, 03:56 PM   #2
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Good to know. I am getting my Jeep on Saturday and totally forgot about checking the tire pressure.

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Old 03-26-2009, 03:59 PM   #3
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Having never had a vehicle with tires of that size, tire pressure becomes an afterthought. Buy a nice gauge and keep in the Jeep. I am now a believer in all this tire pressure talk. I always thought that my body was not calibrated enough to sense a difference in tire pressure.
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Old 03-26-2009, 04:39 PM   #4
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Another note.

My jeep is not a DD. So after airing down while out wheeling I would park it at home and run around in it every now and then. With 15 pounds of air it was a smooth ride. I would air them back up eventually though. However, those few rides took a tole on my tires. The tread on each tire started to wear very uneven. Fortunately/unfortunately someone decided they wanted my Jeep more than me and stole it. I got it back with no wheels and tires. So have new rubber on there now.

Cliff notes…while on the road, run your tires at what the manufacturer recommends, not wants rides the best.
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Old 03-26-2009, 04:53 PM   #5
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Quote:
Originally Posted by BSing View Post
.
Cliff notes…while on the road, run your tires at what the manufacturer recommends, not wants rides the best.
Or you could do the chalk footprint test to see optimal pressure...
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Old 03-26-2009, 05:11 PM   #6
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Originally Posted by innocent bystander View Post
That said, I have Goodyear MTR (I think) mounted on Rubicon wheels. 245/75x16. Anyone have a recommended pressure for that set up?
That is roughly equivilent to a 31x9.50x16 and I'd be running roughly 29 to 31 psi with that size tire. 29 with the jeep mostly unloaded like with just you and a passenger, 31 with it fully loaded with passengers, gear, etc. 35 psi is a little too high for that size tire and weight of vehicle.
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Old 03-26-2009, 05:13 PM   #7
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Jerry, for everyone do you mind posting what you recommend for the basic tires 31,32,33,35. I have always wondered and I know everyone respects your opinion.
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Old 03-26-2009, 05:21 PM   #8
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That would be helpful!
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Old 03-26-2009, 05:51 PM   #9
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I personally run 28 psi on the street and 10-12 psi while off-road. Jeep runs nice on 33x10.5 BFG MTs on stock Gambler wheels.
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Old 03-26-2009, 06:03 PM   #10
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i run the psi written on the side of the tire, im sure they put it there for a reason.
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Old 03-26-2009, 06:06 PM   #11
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i run the psi written on the side of the tire, im sure they put it there for a reason.
You are right, it is there for a reason but not the reason you think it is.

The pressure molded into the sidewall is only that tire's maximum allowable air pressure to be used only when the tire is carrying its maximum allowable weight it can support without failure. Since a Jeep is nowhere near that weight, usually only about half of that for safety reasons, you should never run the pressure on the sidewall. That's why tires on a Jeep may say 50 psi on the sidewall, for example, but the recommended tire pressure typically on the doorjamb sticker is only perhaps 30-31 psi.

The heavier the vehicle, the more tire pressure you need. The lighter the vehicle, the less air pressure that should be run. The correct tire pressure is dependent on the tire size, load rating, and weight of the vehicle, not the maximum allowable air pressure that is molded onto the sidewall.
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Old 03-26-2009, 06:08 PM   #12
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good to know, thanks.
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Old 03-26-2009, 06:23 PM   #13
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Jerry, for everyone do you mind posting what you recommend for the basic tires 31,32,33,35. I have always wondered and I know everyone respects your opinion.
That's a harder question than it may seem since there are so many variables including the weight of your Wrangler and especially the Load Rating of the tire. Like the E Load Ratings on the MT/Rs that come on 16" Rubicon wheels make them a lot stiffer so they typically need less air pressure. The Goodyear MT/Rs that I use on my 15" wheels are C load ratings so they don't ride as stiff and would normally use a tad more air pressure.

But for 15" wheel radial tires where a C Load Rating is common, these are close...

35" 25-26 on the street
33" 26-28
32" 28-29
31" 29-31
30" 31-33

The first figure is for an unloaded Wrangler, the second is for when it is fully loaded.

Bias belted tire pressures will be lower...

Those are just ballpark figures. If you want to run the chalk test, you can get a better idea for what works best for your particular tires and weight of Wrangler.
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Old 03-26-2009, 06:46 PM   #14
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Peaked my interest Jerry...chalk test???
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Old 03-26-2009, 07:02 PM   #15
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Peaked my interest Jerry...chalk test???
Using a piece of chalk, draw a heavy line across the tread of your tire and drive it a short distance. If only the center of the chalk line is worn away, the tire is overinflated. If only the outer edges are worn away, the tire is underinflated. Proper tire pressure results in the chalk line being evenly worn away.
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Old 03-26-2009, 07:43 PM   #16
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Wow. I am actually at 35 right now. I will try coming down to 31-32 tomorrow after my drive to work.

Is it plausible that the super high pressures found in my front tires would cause that disgusting bump steer?
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Old 03-26-2009, 07:47 PM   #17
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Jerry, thanks for the great tip...I'll give it a shot tomorrow
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Old 03-26-2009, 10:26 PM   #18
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Wow. I am actually at 35 right now. I will try coming down to 31-32 tomorrow after my drive to work.

Is it plausible that the super high pressures found in my front tires would cause that disgusting bump steer?
Yes, it is very possible. The slightest change in tire pressure can cause many differant things to happen.
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Old 03-26-2009, 10:57 PM   #19
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Thanks for the tip Sb. I will play around a bit more. I think I am onto the cheapest wander fix ever.
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Old 03-27-2009, 07:33 AM   #20
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The chalk test is the best way to find your optimum tire pressure. In my case with the tires I have now 25 psi for an all around tp gives me full contact and I gain 3 psi while road driving.
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Old 03-27-2009, 08:06 AM   #21
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I have 30x9.5 15's BFG AT's and found that 23 all around gives the best ride and wear. In fact I am still running 2 from my YJ on my TJ and the TJ has almost 70k. My guess is these have 85-90k on them and still have plenty of tread. Keep in mind I run 100 miles a day commuting on almost all highway.
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Old 03-27-2009, 09:51 AM   #22
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jerry knows his stuff..

all the old guys in my jeep club runs their psi at the MAX tire pressure.. really ticks me off, they get crappy with me when i air up to 25-27 psi.. then my gfs dad wonders why my jeep handles 10x better than his and his daughters.. well they shouldnt be airing up to 45-50 psi..

heck ive stated this more than once.. they even get mad at me when i air down to 12 psi when offroading.. they air down to 20-25 psi when we go out offroading.. im like WTF.. but then again im 21 (in 6 days) and they are almost 50.. what do i know about jeeps? ive just been driving around in one since i was 14 and done EVERYTHING to it besides rebuild the tranny when it went out.. heck when i first got with my gf, her dad and i got to talking and he said he saw me driving my jeep (when i was 16) and he had to get one, this was 4 years before i met his daughter and him.. we'd pass each other EVERY day on my way to school LOL.. hes had his jeep longer than most in our jeep club too
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Old 03-27-2009, 10:24 AM   #23
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Ride into work this morning with morning was MUCH MUCH better. At 35psi, the ride was very very good. I am dropping to 30psi for the ride home. I work at a wind farm, so the road in is pretty rough in most places... so it is a good test.

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