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XJ wandering - everything seems correct.

yossarian19 said:
Has anyone said "tire pressure" yet? Sometimes the obvious ones get missed.
Click to expand...

I think this was discussed already, although maybe that was another thread. I am running on the higher side, at 32psi right now. I've never been able to get a straight answer on tire pressure :) I figure the max psi is only 35 with the km2's and max load divided across all 4 is something like 3x my weight, so I'm probably over pressure :).

Will set toe back to 1/8 in, drop PSI to ??? and give it another test before trying 1/2" toe in (which I'm not comfortable with as it seems like a massive over-compensation for something else being wrong).

Also, I suppose the pulling did start with bigger tires as well. I went to 33's the same time I did the lockers.
 
pitman arm loose at the steering box? happens A LOT. throw a wrench on it. Also, check to make sure the steering box isnt loose on the frame.
 
blistovmhz said:
Also, I suppose the pulling did start with bigger tires as well. I went to 33's the same time I did the lockers.
Click to expand...

Wider tires for me have always pulled more, or amplified any irregularity in the rest of the system. For whatever reason on mine if it pulls mostly left it's toed in too far, if it pulls right it's toed out too far.

I would go to 28# in the front, 25# in the rear. Decent starting spot. Won't change anything other than road feel, wont' affect pulling.
 
Vanimal said:
pitman arm loose at the steering box? happens A LOT. throw a wrench on it. Also, check to make sure the steering box isnt loose on the frame.
Click to expand...

Nope. All tight. This ain't a situation where I just bought my first Jeep from some guy, and thought I got a really good deal and the only problem is that it drives like shit :).
I've been building this rig up for most of 5 years. I know every nut and bolt and rust pot :p.

I even just swapped out pitman arms last night to get my draglink/track bar angles within 0.5 degrees of each other (was about 2 degrees off with the drop pitman).
Steering box bolts hold on my bumper so if they ever came loose, I'd know pretty quick.

I actually just remembered the timeline.

* 31", stock steering, long arms, front and rear lockers installed - no pull.
* Add - 33" - no pull.
* Add - WJ Knuckle swap and 1 tonne steering - No pull.
* Re-gear to 4.56 which required pulling both axles - Pull starts (I think).

I thought when I took it for it's first test drive after re-gearing, that I must have somehow changed my upper CA's length, but I'm positive I did not. I purposefully left the torque nuts installed on the uppers when I removed them for paint (while waiting for parts for the re-gear).
That said, I'm also positive I was at 85.5 degrees caster (measured at the diff cover bolts), and that's where I sit now.

So, I think it comes down to one of the following:
1. Tire inflation. I didn't change the PSI when I swapped gears, but I did go wheeling the first day after getting them installed. I probably aired down on the trail, and back up on the way home. I'm pretty sure I aired back up to 30psi which is where I ran them before.
2. Somehow I ****ed something up with the axle while it was out of the Jeep. Either long arms or axle mounts. Can't imagine how.
3. Bigger gears + lunchbox lockers = lockers want to lock a little earlier due to tighter tolerances with the new gears being setup properly, or perhaps just the larger gears causing lockers to engage more often.

Anyone else running 35's with 4.56, and lockers front/rear, on their DD?
 
All I can think of with the lockers is that, if it's totally locked when you are on the gas, any slight variation in side / side tire diameter (treadwear, pressure) would turn into a steering effect as the same shaft speed is applied to different diameters. Right?
So... set tires @ 26 psi or so, plus minus 1 psi. Ideally they'd be exactly the same side / side. Measure as accurately as you can the diameters at all 4 corners. If you can detect side / side differences, arrange the tires to minimize variances. See how that works.
 
blistovmhz said:
Nope. All tight. This ain't a situation where I just bought my first Jeep from some guy, and thought I got a really good deal and the only problem is that it drives like shit :).
I've been building this rig up for most of 5 years. I know every nut and bolt and rust pot :p.

I even just swapped out pitman arms last night to get my draglink/track bar angles within 0.5 degrees of each other (was about 2 degrees off with the drop pitman).
Steering box bolts hold on my bumper so if they ever came loose, I'd know pretty quick.

I actually just remembered the timeline.

* 31", stock steering, long arms, front and rear lockers installed - no pull.
* Add - 33" - no pull.
* Add - WJ Knuckle swap and 1 tonne steering - No pull.
* Re-gear to 4.56 which required pulling both axles - Pull starts (I think).

I thought when I took it for it's first test drive after re-gearing, that I must have somehow changed my upper CA's length, but I'm positive I did not. I purposefully left the torque nuts installed on the uppers when I removed them for paint (while waiting for parts for the re-gear).
That said, I'm also positive I was at 85.5 degrees caster (measured at the diff cover bolts), and that's where I sit now.

So, I think it comes down to one of the following:
1. Tire inflation. I didn't change the PSI when I swapped gears, but I did go wheeling the first day after getting them installed. I probably aired down on the trail, and back up on the way home. I'm pretty sure I aired back up to 30psi which is where I ran them before.
2. Somehow I ****ed something up with the axle while it was out of the Jeep. Either long arms or axle mounts. Can't imagine how.
3. Bigger gears + lunchbox lockers = lockers want to lock a little earlier due to tighter tolerances with the new gears being setup properly, or perhaps just the larger gears causing lockers to engage more often.

Anyone else running 35's with 4.56, and lockers front/rear, on their DD?
Click to expand...
Stupid question, but are you sure the 88.5 degrees is in the right direction?

I run 37's, 5.38's, and auto lockers in my xj, and it's a DD. I do get some slight pulling at times with the rear locker, but it isn't too bad. it could be that i'm just used to it. On the highway, i can let go of the wheel and it drives just fine. i could probably add a little more toe (1/8" in), but other than that, not much i can do with it. I do notice air pressure has a lot to do with the locker pulling, i have to make sure they are all the same.
It is a lifted jeep on big tires, i don't think you're ever going to get the road manners of a stock vehicle. It's very light for the tire size, so i think small stuff effects it more than it would in a big truck.
 
Vanimal said:
Stupid question, but are you sure the 88.5 degrees is in the right direction?

I run 37's, 5.38's, and auto lockers in my xj, and it's a DD. I do get some slight pulling at times with the rear locker, but it isn't too bad. it could be that i'm just used to it. On the highway, i can let go of the wheel and it drives just fine. i could probably add a little more toe (1/8" in), but other than that, not much i can do with it. I do notice air pressure has a lot to do with the locker pulling, i have to make sure they are all the same.
It is a lifted jeep on big tires, i don't think you're ever going to get the road manners of a stock vehicle. It's very light for the tire size, so i think small stuff effects it more than it would in a big truck.
Click to expand...

Heh. Yea, definitely castered the right direction. Wouldn't self center otherwise, and my pinion points almost parallel to the ground right now. Just enough angle to ward off any DL vibes. I'm a bit annoyed though that RC's long arms (upper) are so long. At 6.5" lift, I have to pull the uppers in as far as they'll go to get 88.5. Even if I was only at 2" lift, I'd only be turning the uppers out 5 or 6 threads, but there's 4 inches of thread available. Seems like they should've made the uppers almost 2 inches shorter to accommodate a larger range of lift. 2" shorter on the uppers, and you'd be able to set caster for 0 - 10" of lift easily and safely. As it stands, 6.5" lift is the absolute maximum you could use these for, without chopping an inch out. WTF.


What shoes are you running, and what pressure? And what's your rig weigh? Trying to get an idea of what PSI's work for what sizes/weights.
 
blistovmhz said:
Heh. Yea, definitely castered the right direction. Wouldn't self center otherwise, and my pinion points almost parallel to the ground right now. Just enough angle to ward off any DL vibes. I'm a bit annoyed though that RC's long arms (upper) are so long. At 6.5" lift, I have to pull the uppers in as far as they'll go to get 88.5. Even if I was only at 2" lift, I'd only be turning the uppers out 5 or 6 threads, but there's 4 inches of thread available. Seems like they should've made the uppers almost 2 inches shorter to accommodate a larger range of lift. 2" shorter on the uppers, and you'd be able to set caster for 0 - 10" of lift easily and safely. As it stands, 6.5" lift is the absolute maximum you could use these for, without chopping an inch out. WTF.


What shoes are you running, and what pressure? And what's your rig weigh? Trying to get an idea of what PSI's work for what sizes/weights.
Click to expand...
toyo mt's, 37x13.5x17. i'm lazy with the psi, i just make them all the same (sometimes lol). i try to run between 32 and 35 though. My jeep is on 1 tons so it's about 4800lbs without me in it, but with tools and gas.
 
Vanimal said:
toyo mt's, 37x13.5x17. i'm lazy with the psi, i just make them all the same (sometimes lol). i try to run between 32 and 35 though. My jeep is on 1 tons so it's about 4800lbs without me in it, but with tools and gas.
Click to expand...
You're a bit over a 1000lbs heavier than me. Bad comparison :)

iluv83vettes said:
How are your bushings or whatever ends you have?
Click to expand...

All bushings and joints look good. As I said, I can't find any play in anything. I've jacked up and dropped the truck and recorded everything in slow motion from all angles, and there's no give anywhere that I can see.


Really wish I could find some science to tire pressure vs. load vs. load rating. Everything I find tells me I should be running at either 13psi or 50 :)
I figure this tire is rated for 2500lbs @ 35psi. I have 4 tires, and weigh 3800ish. I'm sure that means I should be less than 35psi, but no formula's I've found thus far, make any sense. I figure the number should be somewhere around 26psi. Will just try that this afternoon after I reset my toe to 1/8 in, then take a drive to the border for more jeep rations :)
 
blistovmhz said:
You're a bit over a 1000lbs heavier than me. Bad comparison :)



All bushings and joints look good. As I said, I can't find any play in anything. I've jacked up and dropped the truck and recorded everything in slow motion from all angles, and there's no give anywhere that I can see.


Really wish I could find some science to tire pressure vs. load vs. load rating. Everything I find tells me I should be running at either 13psi or 50 :)
I figure this tire is rated for 2500lbs @ 35psi. I have 4 tires, and weigh 3800ish. I'm sure that means I should be less than 35psi, but no formula's I've found thus far, make any sense. I figure the number should be somewhere around 26psi. Will just try that this afternoon after I reset my toe to 1/8 in, then take a drive to the border for more jeep rations :)
Click to expand...

My last setup was on 35's and 4.88's, and also 1000lbs lighter. not much of a difference....
 
Thrust angle? - If the axles are misaligned setting the toe can be a genuine pain - Easy enuff to check with a tape measure & someone other'n your Mrs. to hold one end of the tape - - If the axles are not parallel the vehicle will pull/drift to the shorter side under acceleration on smooth/level & go the other way when you let offa the gas - - My MJ had this prob - - A few shims cured it after much head scratching & grief caused by 3 dif so called alignment shops - Worn LCA bushing on one side can also cause TA probs from what I've read, but I see all yours are tight/new. Anyway, just a thought - More stuff I wish I didn't know
 
blistovmhz said:
Really wish I could find some science to tire pressure vs. load vs. load rating. Everything I find tells me I should be running at either 13psi or 50 :)
I figure this tire is rated for 2500lbs @ 35psi. I have 4 tires, and weigh 3800ish. I'm sure that means I should be less than 35psi, but no formula's I've found thus far, make any sense. I figure the number should be somewhere around 26psi. Will just try that this afternoon after I reset my toe to 1/8 in, then take a drive to the border for more jeep rations :)
Click to expand...

What seemed to make at least a little sense to me was a rationale of taking the max weight loading on the tire and divide by the max PSI. (e.g. 3250 pounds at 35 PSI, for 93 pounds per PSI) Then take the estimated corner weight and apply the pre-determined ratio to get a minimum target PSI (e.g. 1500 pound corner weight with previous example would be about 16 PSI). I added about 5-10 PSI to that for comfort and that's what I run.

The other concept I saw was based on cold versus hot pressures. The recommendation was that there should be a 4-5 PSI gain hot versus cold. If you only gained 2-3 PSI for a hot tire versus cold, then it is overinflated. If you gained more than 5 PSI, then it is underinflated. I tried that for a while and it was ok.

There is also a difference between what you would run for a narrower tire versus a wider tire, but I've never worked that out yet.
 
SolarBell said:
What seemed to make at least a little sense to me was a rationale of taking the max weight loading on the tire and divide by the max PSI. (e.g. 3250 pounds at 35 PSI, for 93 pounds per PSI) Then take the estimated corner weight and apply the pre-determined ratio to get a minimum target PSI (e.g. 1500 pound corner weight with previous example would be about 16 PSI). I added about 5-10 PSI to that for comfort and that's what I run.

The other concept I saw was based on cold versus hot pressures. The recommendation was that there should be a 4-5 PSI gain hot versus cold. If you only gained 2-3 PSI for a hot tire versus cold, then it is overinflated. If you gained more than 5 PSI, then it is underinflated. I tried that for a while and it was ok.

There is also a difference between what you would run for a narrower tire versus a wider tire, but I've never worked that out yet.
Click to expand...

Yup. did the same calculation, and got 13psi :) There's no way that's anywhere near correct and arbitrarily adding N psi defeats the purpose of the calculation :)
 
DANBYRAMBLER said:
Thrust angle? - If the axles are misaligned setting the toe can be a genuine pain - Easy enuff to check with a tape measure & someone other'n your Mrs. to hold one end of the tape - - If the axles are not parallel the vehicle will pull/drift to the shorter side under acceleration on smooth/level & go the other way when you let offa the gas - - My MJ had this prob - - A few shims cured it after much head scratching & grief caused by 3 dif so called alignment shops - Worn LCA bushing on one side can also cause TA probs from what I've read, but I see all yours are tight/new. Anyway, just a thought - More stuff I wish I didn't know
Click to expand...

Hadn't considered this. Will measure. Very well could be an issue.
 
blistovmhz said:
Yup. did the same calculation, and got 13psi :) There's no way that's anywhere near correct and arbitrarily adding N psi defeats the purpose of the calculation :)
Click to expand...

I would consider this number to be the minimum PSI for the weight the tire supports at highway speeds, hence adding a value <10 PSI for stability and cooling.

If you want a more scientific answer I could suggest a ouija board. :)
 
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