[Romer]

Now some want a bigger lift than the 2.5" to 3" lift OME is designed for. They will use the larger springs without the weight or add spacers to increase the height of the lift. Drivibility and Castor issues develop here.


You might ask, what is Castor and why do I care?

The dictionary definition of castor is "a small wheel usually free to swivel used to support and move furniture, trucks, and machines." An example of castor is the front wheel on a shopping cart. When you push a shopping cart, the wheel is forced to steer in the direction you push the cart.
Castor is measured in degrees, the amount the steering pivot (king pin) is angled back from vertical. Because the tire patch is located behind the steering pivot (king pin) the cornering side forces will try to unturn the steering. This is why race cars have power steering.
Castor causes the tires to steer in real cars, also. There is a little difference, however, in cars castor causes camber when the steering forces it off its normal position. These camber changes cause slight changes in tire loads. Many times these small changes are enough to influence the car's handling characteristics. The amount of castor is very often used to adjust the car's handling characteristics coming into a corner.

Any lift kit will have an impact on Castor. Castor problems become drivibility issues and driveibility issues turn into Saftey and Relibility problems.

From the Slee Off Road Web Site:
By lifting the truck, the front axle moves away from the frame. Due to the design of the front control arms, the axle will tilt forward and reduce the caster angle. Stock caster for a 80 Series Land Cruiser is 2-4 degrees positive.

Originally Posted by sleeoffroad

Here is a drawing on how caster changes with lift. The drawings shows the locations of the frame mounted bushing and the two front bushings. The axle center line is shown, as well as the caster angle. The axle was set at 3 degrees positive caster at stock height. The axle was then dropped 2" and the new caster measurements are shown.
We initially estimated about 1 degree of caster loss per 1" of lift. This was from installing different lifts on vehicles and then having the caster measured. Due to a lot of variables involved, this was not 100% correct. From the above you can see that 1.7 degrees of change per inch is more accurate.
Also, when you measure the traditional "2 Degree" bushings from Old Man Emu, you will also see that they actually correct closer to 3.3 degrees. So they are still the correct adjustment for a 2"-2.5" lift.
Our caster plates yield 8 degrees of correction and the current control arms we sell are 11 degrees.

We are aware that a lot of people do not install Castor correction. Mostly this is due to not having the right tools to do the job. They are then convinced that their trucks handle ok, but they are not aware of how good it can handle. We have installed the caster bushings for a lot of customers, that ran the truck without it for a while, and I have yet to meet one that did not comment on how well the truck drives. now.
There are also some that do not install the bushings due to reports of cracked front housings or arm mounts. Indeed this has happened in the past, but we believe that it mostly happened in Australia where the driving conditions are a lot different from here. Also, this might have been from earlier OME bushings where the center metal sleeve was a lot larger and the polyurethane a lot smaller. We have not seen a single case of this in any of the trucks that we have serviced or installed the bushings on. We have seen cases where the center metal sleeve has separated from the urethane.
Caster can also be corrected by some DIY ways of slotting the mounting holes and welding washers on the outside. This accomplishes the same as the caster bushings, in that it rotated the axle back to stock location. The problem with this is that you are limited in the adjustment you can make, and if done to severely, the tie-rod that runs behind the axle, will hit the front control arms when the suspension articulates. This can result in a bent tie-rod or your steering binding up.

Originally Posted by peepers

On the highway the truck does not wander per say. If I can keep the wheel straight it will track straight. But, if I move the wheel slightly the truck seems to "dart" in that location. Is this what out of spec caster angles could feel like?

Originally Posted by Jason Andrews

Yup! Thats what it is. It is especially important for emergency maneuvers. Also when you brake in town your tires and steering will follow the road more....it will veer in a direction if road is slanted etc.