Sorry for asking this non engine related question about my Jeep but i need help before i run outa tire tread... so im asking this everywhere and you guys are awsome so maybe you can help.. This is my 98 5.9 Grand cherokee.

So after 3k miles of driving when i got this vehicle a year ago i noticed the outer tires wore down quickly. both tires. I had an alignment done and they checked everything underneeth used prybars on my front wheel to check the joints and everything was good.. The alignment came back at

Toe (No higher then 0.25 max)

0.20
0.15

Camber

-0.4
-0.4

Caster

5.4
5.7

Specs say caster needs to be 6.5 to 7.5 but the mechanic said caster doesnt affect outer tire wear so i dont need to get an alignment as everything was within spec.. so he charge me only half for checking everything..

So i suspected it was my viscous coupler in my quadra trac 249 transfercase .. so i replaced it.. Rotated tires... its been another 3k miles and my tires that were in the rear which are now in the front wore down on the outside just like the previous front tires did... So if my VC is brand new... and my joints are OK, and my alignment was OK.... im starting to think maybe caster really does affect outer wear..

Or can it be something else ? At this rate im going to need to replace the tires in 2 oil changes.... and thats BS cause they are fairly new.. so i mneed some serious help here... does caster affect tires wear ? From what i researched it just affects how the wheels return to center... but i have seen some ppl say it does affect outer tires wear but i cant get a positive on this...


Measured my tires are they are 6/32 on all 4 on the outside, 7/32 middle on all 4, and 9/32 on the inside on all 4.... So obviosuly since they were rotated once now the front is wearing them down exactly the same even with a new viscous coupler... so it cant be the VC it has to be something else... The tires i have are Firestone Destination LE 225/70/16 (i think)

 

I am not 100% certain - only about 90%. I don't think caster effects outer edge wear. It has more to do with steering. An extreme positive camber will cause outer edge wear. I would get a second opinion. That much wear in a short amount of driving is excessive. If another alignment shop gives you something that conlict with the first one, I would get it in writing and ask the first one to pay for correcting the problem - and maybe replacing the tires as well. I would almost think you could see that much error visually.

 

Going too fast around corners will accelerate outer tire wear as well. Go to your local grocery store, clothing mall, or high school and look at the front tires there, you'll see what I mean.

However, my front right tire on my Ram wears the outer edge excessively and I don't go too fast around corners...

In other words, I'm going to be keeping a close eye on this thread.

 

Get a new mechanic. If spec is 6.5-7.5 and your not within these specs and the mechanic say's it's ok move on. Your out of factory spec and what's the camber spec that sounds like alot for such a small tire. On a straight axle i believe one effect's the other..

 

On a straqight axle caster will absolutely affect outside edge tire wear. When you turn and have caster out it will cause the outside tire in a turn to be up on its edge, and that will wear it out, and fast. It will usually make it chop also before its toally bald.
The mechanic prob said is was fine because its no adjustable, can only be fixed by wither changing your shackle length, or using degree shims between your leafs and axle.
Remember that your caster angle is much more important the you front pinion angle. So don't worry if that is not perfect.

 

My caster is about 2.5 degrees neg, which does not affect handling much but does tire wear. Here is showing my pass front tire while turned, I am on a lil hill to dramatize the effect for the picture sake..

 

Camber and toe have more affect on tire wear. Caster is more about your steerings tendency to want to self-center. On a solid axle suspension, what you are seeing there really isn't all that unusual. What do you run your tire pressure at, and what load range tires ya got?

 

This is true, but the "want to self steer" indicates an incorrectly place contact patch in relationship to the fulcrom of the knuckle, which will therefor create unusual tire wear.

 

Erm. No..... Caster is the angle as measure thru the balljoints (difference from vertical.) as viewed from the side of the truck. Changing caster will not have much affect on contact patch. (changing CAMBER on the other hand, most certainly will, but, unless you have adjustable ball joints, camber isn't adjustable on a solid front axle.) The 'self steering' is how bad your truck wants to go STRAIGHT, not wander all over the road. Stock setting is about 1 degree, which really isn't enough..... From what I have read, 3 degrees is the sweet spot.

 

You are correct about your definition of caster, but the contact patch will change as the caster increases. Imagine an axle with tires on it just sitting there not bolted into a truck. The yoke side of the diff will drop casing the cover to be pointed straight up (as long as tires are big enough to allow this) now pull on a tire to create turn. Those tires are gonna go up on the edge. that is a dramatic example but that is still caster in relation to the ball joints, and the contact patch clearly cganges.Even at 6-7 degrees neg like he is describing will cause a les dramtivc version of the same result of that example.

I have done a lot of sas and 4x4 custom lift work. I know this to be true.