63expert

Caster and trail are what provide stability and the ability of the steering system to center itself.

Obviously different from a jeep, but the principals apply

If you look at the picture of the dragbike you can see the forks are "raked" out. This is a function of steering head angle, or caster. The dragbike uses extreme caster because stability is valued above all else.

The roadracer on the the other hand uses a very steep steering head angle, or very little caster. This is because stability takes a back seat to agility.

Trail, the distance that the tire contact patch lies behind the imaginary intersection of the caster angle with the ground, is what gives the steering the ability to center itself when no input is applied to the steering system.


ETA:

I should have stated, when you lift a JK you move away from the drag racer and toward the roadracer. Less caster, quicker steering, less trail, less stability.

jedg

hahaha!!! I forgot about this... perfect!!

63expert

I could tell the difference in caster going from a 16/54 spring set to a 19/59 set on my JKR.

That is why a lift needs a proper caster correction. I bought a set of Rancho brackets, but before I even installed them I decided I didn't want something hanging that low.

I'll go with adjustable LCAs

Rednroll

That's a good example. This is my favorite demonstration of the concept.

Edit: I see Resharp already posted my favorite Demo. LOL.

prelucir

I say, it is good to know what is causing my problems. I get now why my Jeep turns so well with so little effort. Although it is not bad going down the road. I am afraid that in high wind I will get pulled over as it almost looks like I am driving drunk.

I guess the next questions is, how do I measure the caster and how do I adjust it? I will see if I can Google more about it.

Thanks again,
John

resharp001

Getting an alignment is really the only way to get a dead on accurate reading. The best way to adjust caster is by having adjustable control arms. If you can't go that route due to budget, control arm brackets are a solution, but will eat a bit in to your ground clearance. Brackets cost ~$100, and if you go that route, I'd buy some with multiple mounting positions so you have a couple options in regards to adjusting. Technically cam bolts are an option, but should never really be considered on these things.

Also, even if you have adjustable control arms.......this is something the alignment shops would typically charge you extra to adjust as it's some extra work for them. Typically you'd just adjust them yourself at home, take it in and get it scanned to confirm you're correct.

Rednroll

As I mentioned previously, if you had an alignment done, then the alignment shop should have measured your caster and that will be your most accurate measurement.

The way it can be be adjusted most commonly is through the use of increasing the length of your front lower control arms, if you have adjustable control arms or through geo correction brackets. If can also be done through adjustable upper control arms. Without knowing your components of the lift you have, it will be difficult to determine what your options are to adjust.

Which lift did you add and what did the lift provide if anything for caster correction?

You mentioned you moved to 37s, so I'm assuming you have a pretty fair amount of lift and typically, the higher you go in lift then the more caster correction you will need.

Rednroll

As I know all too well.

Unless you have the TF Alpine or Synergy adjustable LCAs, adjustment isn't a simple task as it requires pulling the arms off, adjusting them, then mounting them back up, which sounds much simpler than it actually is.

prelucir

I went back and re read this page. It is beginning to make more sense to me now. I am however, afraid to get under the Jeep and start turning on the control arms as I do not know what I am doing.

I now feel better about talking with the shop that I have been using. And, after reading the page on caster angles, I see where others, who wrench, do not know as much as they seem to think that they do. I have noticed that some folks have opened a shop because they own a tool box.

Also, I read that putting the Jeep on an alignment machine will measure the caster angle. But the folks that do front end alignments do not adjust caster do they? There is a Les Schwab down the road from me. They have done the front end alignment for me before. Can they adjust the caster? I am thinking these are guys off the street with minimal knowledge of their jobs.

-John

I have the Rubicon Express 3.5 inch lift kit. This summer I swapped the axles and put on Danytrac 44/60 and upgraded to 37 inch tires.

Rednroll

Most shops when they do an alignment will not adjust the caster because the ONLY thing that is adjustable on a JK from the factory in regards to front end alignment is the toe and that's what they will adjust. If you added adjustable control arms, then this allows for caster adjustment where this will be a separate charge from a shop and in regards to accepting to do the work, is typically done on a shop by shop basis. In other words, some shops may tell you no they won't do it. Likely because if they don't do it regularly, it ends up being a lot of trial and error guess work on their part where they need to adjust the arms, put them on, take the alignment measurement, pull them off, re-adjust, rinse, wash, repeat. There's only a couple arms that are on the market which are adjustable while still mounted and those are the Synergy and TF Alpine's that I mentioned previously. You don't have those.

This RE 3.5in kit?
https://www.extremeterrain.com/rubic...T5_Var4=J10324



If so, then that kit has upper adjustable control arms to adjust caster.