Suspension and tire questions

2001 XJ, AW4, 4.0 I6, 4WD, Stock height
18 months ago I put on Duratrac Tires (235/75/15 LT) and got a full alignment. These tires were slightly larger than the 225/75/15 I normally use and they cupped badly on the front. So I rebuilt most of the front end and replaced the following:

Ball Joints (Left side old balljoints had some play)
TRE's (Some play in old joints but not excessive)
Draglink
Pitman Arm
Steering Box (some play in the old box)
Axle shaft U joints (some play in old joints)
Wheel bearings
Rotors (old ones warped)
Front differential carrier bearings (one was badly worn, some heavy pitting on the race)
Front Shock absorbers Rancho RS 5000

After doing this work I replaced the tires with Firestone Destination A/T (235/75/15 LT) and got a full alignment. After 8000 miles rear tires look great but the front tires are starting to show cupping wear especially on the outer edges.

When I rebuilt the front end I didn't replace the lower or upper control arms or the coil springs. I am not sure if replacing these would help or not. Looking at my lower control arms it does look like the bushings have gone.

Regarding the coil springs Jeep doesn't service these anymore. According to my build sheet the front coil codes are:

Left front ZFKP
Right Front ZUJP

Crown automotive have a standard duty 16.5" coil Code ZVF and ZGF
and they have a heavy duty coil 17" Code ZGV, ZVJ and I'm not sure if these would be acceptable or not. I am fairly sure the coil springs I have on my vehicle now are original and not sure if they need replacing or not.

One last point regarding shock absorbers: I put on a slightly larger tire diameter 28.86" (235/75/15 LT Firestone Destination A/T) than normal and I wonder if I need a different length shock absorber for this modest increase in tire size? As I understand cupping is where the tire is hitting the road repeatedly and is often shock related and I also read that the control arms act a secondary shock.

Any advice / help would be greatly appreciated as this is really getting frustrating and expensive.

You should have rotated your tires 3-4K miles ago.

Several thoughts,
One: bad shock absorbers. No need for length change unless Jeep is lifted.
Two: bad control arm bushings. Often it is hard to tell if they are good or not unless you pull the arms. Since everything else is mostly new I would check the control arm bushings.
Three: Weak springs will just sag the front end but not usually cause cupping. The alignment should compensate for any geometry changes from sagging.

Something that helps a little is a couple of more pounds of air pressure. Stiffens up the sidewalls a little and you get a little more weight to the center of the tire.

And it is always a trade off between soft rubber compounds for winter and harder compounds that last longer.

One reason I stopped using Goodyear tires was front edge wear. Good tires but seem to wear quicker than some others.

Rotate your tires, IMO the wear on the fronts is nearly triple the wear in the back.

Cupping is a symptom of suspension problems.

No, more aggressive tires cup all the time if they are not rotated religiously. I rotate mine every oil change, they wear great.

lawagoneer said:

Cupping is a symptom of suspension problems.

Click to expand...

trippled said:

No, more aggressive tires cup all the time if they are not rotated religiously. I rotate mine every oil change, they wear great.

Click to expand...

Both statements can be true. Replace the control arms (or at least the bushings) and rotate the tires more often. For complete stock control arms I have found MOOG to be best as they still use Clevite bushings. NAPA and O'Reilly's are not Clevite anymore. Look for better pricing from Rock Auto or Amazon or places like that. For axle side bushings, O'Reilly's Master Pro K3128 are the cheapest I've found and they were Clevite the last time I bought them, so their rubber will match that in the MOOG control arms. NAPA ones are not and I've broken them trying to install them. I've used BFG A/T KO for at least 10 years and around 400,000 miles on Jeeps, Toyotas, and Dodge Ram trucks, though mostly the Jeeps. They may not be the quietest, smoothest, or cheapest but they are indestructible and you can run the miles up on them particularly if you do lots of highway. I've got upwards of 90,000 miles on a set on my XJ's. If it's a grocery getter in town expect closer to the warranty miles (about 50,000). I change them when they start to loose breaking performance or don't perform well in heavy rains.

Thanks for the advice.
Regarding the coil springs Jeep doesn't service these anymore. According to my build sheet the front coil codes are:

Left front ZFKP
Right Front ZUJP

Crown automotive have a standard duty 16.5" coil but Codes are ZVF and ZGF
and they have a heavy duty coil 17" Codes ZGV, ZVJ. Would these be Ok to use?

I would go with the taller (Up-country spring) and chance any height change and deal with that later by the rear springs!

What is wrong with your current springs?

At the moment I am not sure if there is a problem with the springs. I think they are the original ones on the vehicle i.e. 15 years old and I am not sure if they are weak and if they are making some contribution to my cupped tires.

Springs do not have anything to do with "cupping"! You said it was aligned, but you didn't give the specs?

Firestone did the alignment these are the results

Left Front
Camber -0.6 (Spec -0.8 to 0.5)
Caster 5.3 (Spec 5.3 to 8.5)
Toe. 0.18 (Spec 0 to 0.23)
SAI. 12.5 (No Spec Listed)
Included Angle Turning Diff 11.9 (No Spec Listed)

Right Front
Camber -0.5 (Spec -0.8 to 0.5)
Caster 5.4 (Spec 5.3 to 8.5)
Toe. 0.15 (Spec 0 to 0.23)
SAI. 18.8 (No Spec Listed)
Included Angle Turning Diff 18.4 (No Spec Listed)

Front
Cross camber 0.1 (Spec -1 to 1)
Cross caster -0.1 ( Spec -1.3 to 1.3)
Cross SAI. -6.4 (No Spec Listed)
Total Toe. 0.33 (Spec 0 to 0.45)

Rear Left
Camber -0.1 (No Spec listed)
Toe. -0.05 (No Spec listed)

Rear Right
Camber -0.6 (No Spec listed)
Toe. 0.12 (No Spec listed)

Rear
Cross Camber 0.5 (No Spec Listed)
Total Toe 0.08 (No Spec Listed)
Thrust angle -0.09 (Spec -0.15 to 0.15)

Tryfan said:

Thanks for the advice.
Regarding the coil springs Jeep doesn't service these anymore. According to my build sheet the front coil codes are:

Left front ZFKP
Right Front ZUJP

Crown automotive have a standard duty 16.5" coil but Codes are ZVF and ZGF
and they have a heavy duty coil 17" Codes ZGV, ZVJ. Would these be Ok to use?

Click to expand...

Any further comments on suitability of these coil springs???

Crown sells a lot of garbage. Given that there is no known defect with your current springs I would look at other causes of your problem.

My tire guy (at an actual specialized tire shop) warned me that most popular AT tires are designed for trucks and heavy SUV's in the 5000-6000lb range. Because the XJ only clocks in at about 3000lbs, these tires are going to be very prone to cupping. He implored me to rotate them frequently, basically every oil change if I could. Basically stated, the XJ is not heavy enough to keep these heavy/stiff load rated tires firmly planted on the ground over road bumps at highway speeds. So they cup.

Actually, his first and best advice was to go with something more appropriately load rated for the XJ. Which would also be way cheaper (for example, Goodyear Wrangler radials), but the choices in that class are not very attractive from an All-terrain point of view. A lot of cheap light-truck tires with smooth featureless road treads. I told him, that I was going to go with a more aggressive AT tire no matter what (for looks), so his next best advice was to rotate like crazy.

When I bought my XJ, it had BFG/AT KOs on it. I loved them (the way they looked), but they were cupped. So I eventually took them off, and replaced with some cheap Wranglers while deciding what I really wanted on there. It was during this time that he warned me that I would experience cupping again quickly if I did not take his advice on the new tires. He also warned that the higher the load rating, and ply count, the more I would need to be on top of the frequent rotations.

So now I rotate 5-8k miles, and I can feel/hear the tires getting more cuppy/noisy around the 7-8k mark. I can do the job in about 15 minutes these days.