I know there are many variables to consider in getting adequate caster when lifting 4Runners. I want to share some thoughts on one variable, and that is frame rake, specifically when lifted.
Review and Discuss!
Theory: When considering two trucks, Truck A with a 2" front lift and a level frame and Truck B with a 2" front lift and a 1.5" rear lift with near factory frame rake, that Truck A will have a better positive caster when maxing alignment components.
Assumptions
- Both trucks have the same Maximum steering angle relative to the truck frame. In this case 87 degrees relative to truck frame.
- Both trucks have the same alignment components
- Manufacturing differences between trucks is ignored
Analysis
Triangulating everything from a level truck, Truck A, I then input a 1.5" rake and solve for the Caster of Truck B. Level Truck A has 3 degrees of Caster.
Result
Caster is 2.22 degrees when steering angle to truck frame is 87 degrees on a 1.5" rake truck.
That is a 0.78 degrees of Caster penalty per 1.5" rake, or about 0.5 degree per 1 inch.
Speculation
Based on forum speculation, a 2" front lift might get good alignment with stock UCA, but a 2"F/1-1.5"R lift with some rake, might push alignment out of spec.
I currently have 2.125" of front lift, and 0.75" of rear lift and my caster is out about 2 degrees at best.
Review and Discuss!
Theory: When considering two trucks, Truck A with a 2" front lift and a level frame and Truck B with a 2" front lift and a 1.5" rear lift with near factory frame rake, that Truck A will have a better positive caster when maxing alignment components.
Assumptions
- Both trucks have the same Maximum steering angle relative to the truck frame. In this case 87 degrees relative to truck frame.
- Both trucks have the same alignment components
- Manufacturing differences between trucks is ignored
Analysis
Triangulating everything from a level truck, Truck A, I then input a 1.5" rake and solve for the Caster of Truck B. Level Truck A has 3 degrees of Caster.
Result
Caster is 2.22 degrees when steering angle to truck frame is 87 degrees on a 1.5" rake truck.
That is a 0.78 degrees of Caster penalty per 1.5" rake, or about 0.5 degree per 1 inch.
Speculation
Based on forum speculation, a 2" front lift might get good alignment with stock UCA, but a 2"F/1-1.5"R lift with some rake, might push alignment out of spec.
I currently have 2.125" of front lift, and 0.75" of rear lift and my caster is out about 2 degrees at best.
