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TECH HEADS- building jim fr diff, whats a good caster angle?
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Author:  kyzermattingley [ Fri Aug 20, 2010 1:43 am ]
Post subject:  TECH HEADS- building jim fr diff, whats a good caster angle?
Hey guys,

Im currently starting a new project front diff housing, that will involve rotating the diff pumpkin.

I want too increase caster, lift pinion angle, plate under shock mounts/pickups, diff armor, etc etc etc while at it.

At present my caster angle is set at 4deg


A mate who's the foreman at Hammand 4x4 recommended around 8deg, he thats what they run on 4"+ lifted Jeep Wranglers.

Part of the reason for this is a continuing problem with caster wobble, at present it only appears lightly occasionally (fitted 9stage adj TuffDog steering damper), the car has been lifted 90mm rear and 110+ front but has only done less than 9000km's and very very little off road work, I have checked kingpins/bearings, all tie rod ends and everything is tight as a nun.



So TECH HEADS preferably, thoughts on a good caster angle, what would be too much caster?



Kyzer

Image
Author:  TZAR [ Fri Aug 20, 2010 1:51 am ]
Post subject:  Re: TECH HEADS- building jim diff, whats a good caster angle?
Bmw run 8 degrees positive for running at 250kph + on the autobarns

Most cars have around 1-2 degrees positive and some even run negative caster ( hq)

The higher the positive then the harder to turn. basically
Image

look at this pic. Castor is basically the shopping trolley effect. When it is negative like the shopping trolley wheel it will return to centre easily and will be very easy to make it change direction. Also the same as a jockey wheel.

When it is positive it is very difficult to turn the wheel as it always wants to go straight ahead. Try pushing a trailer with the jockey wheel pointing the way you want it to go.

I think 3 degrees would be an absolute max for a jimny at road running height
Author:  kyzermattingley [ Fri Aug 20, 2010 2:27 am ]
Post subject:  Re: TECH HEADS- building jim diff, whats a good caster angle?
TZAR wrote:
Bmw run 8 degrees positive for running at 250kph + on the autobarns

Most cars have around 1-2 degrees positive and some even run negative caster ( hq)

The higher the positive then the harder to turn. basically
Image

look at this pic. Castor is basically the shopping trolley effect. When it is negative like the shopping trolley wheel it will return to centre easily and will be very easy to make it change direction. Also the same as a jockey wheel.

When it is positive it is very difficult to turn the wheel as it always wants to go straight ahead. Try pushing a trailer with the jockey wheel pointing the way you want it to go.

I think 3 degrees would be an absolute max for a jimny at road running height


Thanks man,

I realize the dynamics behind caster and the fact that its also there to help your steering to return too center, used too run 7.5deg in my track car

Jim's from memory run around 2deg normally and mine running 4deg isnt noticable.
Thanks anyway TZAR




What I really want advise on is what people have run and have found acceptable, has anyone ever run too much (on a live axle 4wd, not a car) and what was the side effect




Kyzer
Author:  joeblow [ Fri Aug 20, 2010 2:34 am ]
Post subject:  Re: TECH HEADS- building jim fr diff, whats a good caster an
if you want to get rid of wobbles, play around more with toe settings than caster.
Author:  kyzermattingley [ Fri Aug 20, 2010 2:54 am ]
Post subject:  Re: TECH HEADS- building jim fr diff, whats a good caster an
joeblow wrote:
if you want to get rid of wobbles, play around more with toe settings than caster.


OK then, the toe is set at zero at present, what would you recommend then Joe?
Author:  ajsr [ Fri Aug 20, 2010 3:01 am ]
Post subject:  Re: TECH HEADS- building jim fr diff, whats a good caster an
joeblow wrote:
if you want to get rid of wobbles, play around more with toe settings than caster.

X2 4 deg castor would be shit loads and I think about 3-5 mm toe in would be about right too.
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