Sep 21, 2015, 02:17 PM
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- Jeep Grand Cherokee ZJ 1993 to 1998 Tires General Information and Specs
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All Lift & Tire questions go here!!!
Seasoned Member
Joined: Feb 2010
Posts: 325
Likes: 0
From: Utah
Year: 1999
Model: Cherokee
Engine: 4.0
Yes, 3" backspacing sticks out past the fenders. Think of it as the distance from the wheel mounting surface to the edge of the wheel (inward toward the pumpkin). Hence, the larger the number when referring to backspacing, the more the wheel is tucked in the wheel wells. Hope this makes sense.
Junior Member
Joined: Feb 2010
Posts: 39
Likes: 0
From: Hanover, MD
Year: 2000
Model: Cherokee
Yes, 3" backspacing sticks out past the fenders. Think of it as the distance from the wheel mounting surface to the edge of the wheel (inward toward the pumpkin). Hence, the larger the number when referring to backspacing, the more the wheel is tucked in the wheel wells. Hope this makes sense.
yep.. thanks. had it backwards all these years :-P
Newbie
Joined: Jan 2010
Posts: 19
Likes: 0
From: long island ny
Year: 93
Model: Cherokee
Engine: 4.0 HO
93xj 3" to 5"
i got a 93 cherokee with 31"s n i did a 3" lift from RC, i plan on adding another 2" to my 3" n make it a 5". i got the 2'' front spacers and the rear schackels. what other mods will i have to do. i know i need a sye, track bar, brake lines ect. i also have a set of 35" BFG all terrains, would they fit if i trimed the fenders with a 5" lift
CF Veteran
Joined: Sep 2009
Posts: 4,145
Likes: 0
Death Wobble explained…
Here's an engineering description of DW. I get tired of seeing people guessing at what's causing their DW, so here goes. Hope it helps someone.
First, you've got to realize that the front suspensions on our vehicles were marginally stable, at best, from the factory. DW is a fundamental dynamic response mode of the entire front end...as a system. Lift and larger tires change (increase) the 'gain' associated with what becomes (or even starts out as) a marginally stable dynamic system. The damping factor (lambda) is also affected by larger tires...it decreases as a function of sidewall height/thickness ratio. Hysteresis in any control path (loose tie rod, steering box, track bar bushing) reduces the ultimate stability margin further. The fundamental frequency of DW is determined by the superposition principle where all springs involved are resolved (frame, tire resilience, hub bending, bushing deflection, etc, etc.) into one global spring constant, and all damping factors associated with friction, elastic elements, viscous damping (steering damper and shocks) are resolved into one damping factor. The natural frequency, damped natural frequency, and damping coefficient are then known. Now, if the system is overdamped and the gain is low...no problems...no oscillation. Increase the gain without increasing the damping and you go toward the critically damped, and beyond, specturm of responses. Critically damped means that DW would only 'hint' at being there, but would die out on its own without going totally unstable. This is also known as a decaying response.
Once the system goes beyond critically damped, any excitation, be it an unbalanced tire, a bent wheel, bumps in the road, etc. can set it off and the response will not decay...it will grow in amplitude, quite quickly in some cases, and may be limited only be physical non-linearities like hard stops...or breakage. That's classic Death Wobble.
A truck suspension is designed to stay in the overdamped to critically damped range. That is generally why a truck rides "rough". A Cadillac, on the other hand, is designed to stay in the undersprung range. It just "floats" down the road. Any change in the basic design parameters that affect the gain (e.g., lift, tire size, wheel backspacing, etc.), damping (tire size, steering damper, steering box condition), and hysteresis (any wear point that creates any slop) can push it over the edge and create DW. ANY ONE OR TWO of the factors discussed can do that...which is why everybody then thinks that whatever problem THEY found and fixed is the cause of all DW; it is not. It is plain and simply a marginally stable system in its original form that is easily made unstable by any of the myriad causes discussed already.
If your front end is loose (bushings, bearings, etc.) then you have a situation where your stiffness is removed and any jarring sensation (potholes, unbalanced tires, misaligned wheels, etc.) will cause the suspension to go crazy. It is no longer functioning where it is designed. On the other hand, your suspension could be very tight but an imbalanced tire would be spinning at just the right speed to throw the suspension into a unstable situation.
So unfortunately there isn't only one root cause to the problem of DW. The underlying problem is instability in the front suspension, the root causes can be a multitude of things ranging from bad/loose bushings, to loose bearings, to caster angles, to imbalanced tires, etc.
OKAY, HERE'S THE REALLY USEFUL INFO:
A steering damper only hides (maybe) the effect; it does nothing to fix the root cause.
There are two types of DW. The first typically is speed related. Whenever you reach a certain speed, bam, you get DW, no matter what. This is a vibration/oscillation issue. Look into tire balance, alignment, steering joints, missing bushings (totally shot), loose steering box (either loose bolts or worn internals), etc.
The second is an impact initiated DW. For example, hitting a pothole above a certain speed will start DW. This is more likely a bushings, loosening mounts, flexing components, etc. issue. Basically, something is tight enough that in general straight driving, it is ok, but give it an impact force, whatever is getting loose starts sliding, rebounds and starts going nuts.
Here is how you can tell if the issue is steering related or trackbar related. You are gonna need some ***** for this, but stick with me. Once you have played around with the DW awhile you find you can control it a bit by feathering the brakes. So go find a straight, deserted, bumpy road. Get the truck up to speed and get the DW going. You had it happen a few times, you have already been frantically avoiding potholes, so now go find one, quit whining. At this point, the truck is somewhat violently shaking, and you can keep enough control using the brakes to keep it on the road. Roll down the window and stick your head out and look at the front tire. What is it doing?
1. The front of the tire and the back of the tire are moving approximately the same amount side to side. In this case, the axle is stationary, and the wheel is pivoting on the ball joint during the oscillation. Therefore the problem is likely in the steering. Something in the steering has enough give to allow the movement.
2. The back of the tire is moving MORE than the front of the tire in the side-to-side movement. In this case, the knuckle is pivoting on the steering links, and allowing the axle to move back and forth under the vehicle. The problem here is most likely in the trackbar system.
This doesn't really answer a question about what's causing YOUR DW, but it should give you something to think about in your search for the root cause(s). I'd check the trac bar bushings, make sure your wheel bearings are in spec, make sure your tires are balanced, make sure your alignment is in spec - especially caster, make sure your ball joints & TREs are tight, see if you have play in your steering box, etc.
Here's an engineering description of DW. I get tired of seeing people guessing at what's causing their DW, so here goes. Hope it helps someone.
First, you've got to realize that the front suspensions on our vehicles were marginally stable, at best, from the factory. DW is a fundamental dynamic response mode of the entire front end...as a system. Lift and larger tires change (increase) the 'gain' associated with what becomes (or even starts out as) a marginally stable dynamic system. The damping factor (lambda) is also affected by larger tires...it decreases as a function of sidewall height/thickness ratio. Hysteresis in any control path (loose tie rod, steering box, track bar bushing) reduces the ultimate stability margin further. The fundamental frequency of DW is determined by the superposition principle where all springs involved are resolved (frame, tire resilience, hub bending, bushing deflection, etc, etc.) into one global spring constant, and all damping factors associated with friction, elastic elements, viscous damping (steering damper and shocks) are resolved into one damping factor. The natural frequency, damped natural frequency, and damping coefficient are then known. Now, if the system is overdamped and the gain is low...no problems...no oscillation. Increase the gain without increasing the damping and you go toward the critically damped, and beyond, specturm of responses. Critically damped means that DW would only 'hint' at being there, but would die out on its own without going totally unstable. This is also known as a decaying response.
Once the system goes beyond critically damped, any excitation, be it an unbalanced tire, a bent wheel, bumps in the road, etc. can set it off and the response will not decay...it will grow in amplitude, quite quickly in some cases, and may be limited only be physical non-linearities like hard stops...or breakage. That's classic Death Wobble.
A truck suspension is designed to stay in the overdamped to critically damped range. That is generally why a truck rides "rough". A Cadillac, on the other hand, is designed to stay in the undersprung range. It just "floats" down the road. Any change in the basic design parameters that affect the gain (e.g., lift, tire size, wheel backspacing, etc.), damping (tire size, steering damper, steering box condition), and hysteresis (any wear point that creates any slop) can push it over the edge and create DW. ANY ONE OR TWO of the factors discussed can do that...which is why everybody then thinks that whatever problem THEY found and fixed is the cause of all DW; it is not. It is plain and simply a marginally stable system in its original form that is easily made unstable by any of the myriad causes discussed already.
If your front end is loose (bushings, bearings, etc.) then you have a situation where your stiffness is removed and any jarring sensation (potholes, unbalanced tires, misaligned wheels, etc.) will cause the suspension to go crazy. It is no longer functioning where it is designed. On the other hand, your suspension could be very tight but an imbalanced tire would be spinning at just the right speed to throw the suspension into a unstable situation.
So unfortunately there isn't only one root cause to the problem of DW. The underlying problem is instability in the front suspension, the root causes can be a multitude of things ranging from bad/loose bushings, to loose bearings, to caster angles, to imbalanced tires, etc.
OKAY, HERE'S THE REALLY USEFUL INFO:
A steering damper only hides (maybe) the effect; it does nothing to fix the root cause.
There are two types of DW. The first typically is speed related. Whenever you reach a certain speed, bam, you get DW, no matter what. This is a vibration/oscillation issue. Look into tire balance, alignment, steering joints, missing bushings (totally shot), loose steering box (either loose bolts or worn internals), etc.
The second is an impact initiated DW. For example, hitting a pothole above a certain speed will start DW. This is more likely a bushings, loosening mounts, flexing components, etc. issue. Basically, something is tight enough that in general straight driving, it is ok, but give it an impact force, whatever is getting loose starts sliding, rebounds and starts going nuts.
Here is how you can tell if the issue is steering related or trackbar related. You are gonna need some ***** for this, but stick with me. Once you have played around with the DW awhile you find you can control it a bit by feathering the brakes. So go find a straight, deserted, bumpy road. Get the truck up to speed and get the DW going. You had it happen a few times, you have already been frantically avoiding potholes, so now go find one, quit whining.
At this point, the truck is somewhat violently shaking, and you can keep enough control using the brakes to keep it on the road. Roll down the window and stick your head out and look at the front tire. What is it doing? 1. The front of the tire and the back of the tire are moving approximately the same amount side to side. In this case, the axle is stationary, and the wheel is pivoting on the ball joint during the oscillation. Therefore the problem is likely in the steering. Something in the steering has enough give to allow the movement.
2. The back of the tire is moving MORE than the front of the tire in the side-to-side movement. In this case, the knuckle is pivoting on the steering links, and allowing the axle to move back and forth under the vehicle. The problem here is most likely in the trackbar system.
This doesn't really answer a question about what's causing YOUR DW, but it should give you something to think about in your search for the root cause(s). I'd check the trac bar bushings, make sure your wheel bearings are in spec, make sure your tires are balanced, make sure your alignment is in spec - especially caster, make sure your ball joints & TREs are tight, see if you have play in your steering box, etc.
i'm getting some new 31's and i'm lookin for an aggressive A/t or a well mannered M/t that is cheap and performs. i need on-road handling as well b/c its my daily driver. i know it has probably already been put in this thread but i don't feel like reading 40 pages. any suggestions?
http://www.treadwright.com/shopnow/p...arden-a-t.aspx
Both are good tire. yes they're re-treads but Treadwright has built a reputation for making good tires and they stand behind their product
Last edited by ZachsXJ; Feb 27, 2010 at 06:21 PM.
CF Veteran
Joined: Jan 2010
Posts: 1,062
Likes: 0
From: Fort lewis, wa/ university place, wa
Year: 1999
Model: Cherokee
Engine: 4.0L
You dont have to have anything, but I just installed a 3" rc lift yesterday and you can make the original trac arm work, as long as you dont uninstall it to get something out of the way. I did full leaf springs and new adjustable control arms and went all out. What im saying is you can do a lift with just those things but your ride will suffer most likely. For like two or three hundred more you can upgrade everything (shocks, control arms, leaf springs for the back etc...) and your ride will probably be better. But if you want to put 31's on you will probably have to trim something cause my rubbed until i took a hacksaw to them. Also the arms will work, but it puts everything at the wrong angle.
CF Veteran
Joined: Jan 2010
Posts: 1,062
Likes: 0
From: Fort lewis, wa/ university place, wa
Year: 1999
Model: Cherokee
Engine: 4.0L
i got a 93 cherokee with 31"s n i did a 3" lift from RC, i plan on adding another 2" to my 3" n make it a 5". i got the 2'' front spacers and the rear schackels. what other mods will i have to do. i know i need a sye, track bar, brake lines ect. i also have a set of 35" BFG all terrains, would they fit if i trimed the fenders with a 5" lift
Junior Member
Joined: Jan 2010
Posts: 84
Likes: 0
Model: Cherokee
MOABS ON XJ
I have a 99 XJ / RUSTYS 2" lift. i can get my hands on 2006 16" moabs w/ 255/16 on them or 17" 2008 moabs w/ 255s.Wich will fit my XJ and will have clearence issues with either? THANKS.
CF Veteran
Joined: Sep 2009
Posts: 4,145
Likes: 0
Senior Member
Joined: Sep 2009
Posts: 575
Likes: 2
From: Virginia
Year: 2000
Model: Cherokee
Engine: 4.0 inline 6
aite i got a question i could get a 3.5" RE lift kit for 580$ or i could get a rustys 4.5" lift kit with full packs for less than a hundred more....is rustys really that low quality i have heard some terrible things about them. any one have any thoughts i should know.
Seasoned Member
Joined: Feb 2010
Posts: 325
Likes: 0
From: Utah
Year: 1999
Model: Cherokee
Engine: 4.0