just one more degree of castor. (1 Viewer)

jjdeneen918

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Jul 23, 2008
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Location
Long Beach, CA
 
 
besides the steering box septor shaft tweekness I'm dealing with on my other post, the alignment mecanic said I'm under specs for castor.

I'm even on both sides for castor at 1.5 degrees. Prime is 3 + or - a degree.

I've read numerous posts on the matter but none with my displacement after alreay installing castor plates, usually it's just bushing dilemmas or stock set-ups.

I did Slees 4" lift with the bolt/welded castor plates. Currently running 315/75/16 tires and ARB winch bumper without winch for now.

I'm not exactly mathmatically/engineer-ically smart. I'm still trying to wrap my head around this whole castor idea.

If I installed castor bushings after already doing the castor plates, would I then be way over compensating?
Fabricating a small drop bracet to correct would work? If so at the rear of the radius arm? I would assume that would put me back where I started before the front castor plates..? Dunno, My head hurts.
1 inch spring spacers to drop the axel down a little further? If that worked I wouldn't be opposed, I don't yet have the winch and I'm already a bit lower in the front than the rear.


Maybe after a sixer it will all make sense and come to me. But probably not.
Thanks for reading my rambling and for some possible help and insight.
 
Joined
Nov 23, 2005
Messages
4,099
Location
Birmingham, AL
 
 
Curiously, my 1992 FSM shows two different specs for caster depending on tire size. for 235/75/R15 it is 3 degrees +/- 1 and for 31/10.5 R 15 it is 1 degree 40' +/- 1. I wonder why it changed for the later models?

caster.jpg
caster.jpg
 
Joined
Jul 20, 2004
Messages
24,774
Location
Chandler, AZ
 
 
 
Caster is dynamic, only effective at highway speeds, the only way to “see” it would be on a high speed treadmill. The tires, bushings, springs, etc deflect, flex with the stress/load of the vehicle being driven at speed, the degree angle is a crude way to set it when static/stationary. It can be modeled with software, but the recommended setting is determined by using the “calibrated butts” of test drivers, set it, test drive, repeat, until a comfortable setting is found for the average driver. This is done with the stock setup, tires, springs, bushings, ride height, etc as the vehicle will be sold with.

Tires have a huge affect on the ideal setting, if all other construction details stay the same, a larger diameter tire requires less caster to have the same caster effect. But tire stiffness, ply construction, air pressure, etc all effect the deflection at speed. When I went from 295 Nitto’s to 37” Coopers the caster effect on my rig was greatly increased, to more than I prefer.

Driver has a lot to do with it, some like the “security blanket” of lots of effect, others prefer a lighter wheel. When setting up a vehicle for the sports car racing types, most want little to no caster effect, most street drivers prefer the comfort of more.

Generally speaking a lifted, big tire, linked suspension rig is stiffer, has less axle deflection/angle change power on to braking, so needs less caster to have the same caster effect as a stocker, but driver preference also comes into play. The ideal setup probably isn’t going to be the same as a stock rig, or even the same as someone’s with a slightly different tire/setup. Sorry for the long winded way of saying, you modified your rig, so set the alignment so it drives comfortably for you, regardless of the stock numbers.
 

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