Since then I have done a front end rebuild, and installed 315 MTR's. I had a minor death wobble with the 33" BFG at's I had on not too long ago. I'm running 2.5" mediums on the truck with 30mm Slee spacers up front. The angles are very small and the only way to measure is to look at the arc created when the wheel is turned to the right and then to the left. By turning the wheels through the steering arc, the degrees of caster positive or negative can be measured. You can measure this at home, but you need a caster jig to do it. As the arms are pushed down and the truck is lifted up, the angle is reduced. However, when your truck is lifted the axel is rotated around the arc created by the front control arms. Positive caster straightens the wheel when the vehicle is traveling forward, and thus is used to enhance straight-line stability. The same thing happens on a car/truck/80. When the wheel is turned the front of the motorcycle is physically lifted, therefore gravity tends to keep the wheel rolling straight. If the pivot axis is tilted backward (that is, the top pivot is positioned farther rearward than the bottom pivot), then the caster is positive if it's tilted forward, then the caster is negative.Ī motorcycle/bicycle front fork is tilted backwards and has positive caster. By the way, my rig does seem like it tracks slightly straighter with a little weight in the back.Ĭaster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. It seems like if my theory is how they measure castor is correct, then different weights on the same lift would vary drastically with respect to the castor reading.
CC bushing are installed and folks Castor readings are all over the board.
I've read about alot of strange Castor readings in the past with different lifts. If all of my assumptions are true, then the higher the back of the truck is at the time of measurement, then the less positive and or more negative the castor reading would be. If castor is measured at the centerline of the axle, do they use the flat surface or the bolts on top of the knuckle as the centerline/level line of the axle. I've seen the alignment ramp type lift at the shop, am I correct to assume that the ramps and table are level? I understand the concept of positive and negative castor.
I had a thought cross my mind tonight about how to measure castor. Even with tire wear, and the addition of slee sliders. Accounting for tire wear a little bit, the profile views look the just about the same with respect to "amount of coil" visible on the front end. I looked at some old pictures, and went out and snapped a picture. How could my castor had become less positive if the springs were sagging a little bit? Then tonight I had a kind of revelation while sitting in a meeting. I had the alignment checked because of crazy tire wear recently and everything was fine, except the castor was now closer to 0. When my OME was installed with CC the alignment report said I was at 3 deg. I've don't recall seeing THIS aspect of castor/alignment covered before so here we go.