On many pickups, especially 3/4 and 1 ton applications, using the vehicle as a daily driver with little or no load in the rear creates a rear end high, front end low configuration or "positive frame angle".
Specific vehicles like 1999-2006 Chevrolet/GMC trucks have alignment specifications that require frame angle to be added or subtracted to the caster reading. Basically this means the specifications for these vehicles are written to a zero frame angle.
Illustration courtesy of SPC Performance
Caster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. 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.
Caster is affected mostly when a vehicle has a large front to back difference in ride height. This may also be because of heavy loading in the rear of the vehicle or "negative frame angle". The frame angle will directly affect the caster in a one to one relationship. That means for each degree of frame angle change the caster will change one degree. Positive frame angle will be added to the caster reading whereas negative frame angle would be subtracted from the caster reading.
Illustration courtesy of Grassroots Motorsports Magazine
Caster does not affect tire wear but it can affect how well the vehicle steers. Excessive positive caster will cause an increase in steering effort, especially for low speed maneuvers, such as parking. Negative caster can cause the truck to have poor directional stability, make it tend wander and not return to center. The addition of larger than stock tires or 4WD only compounds these conditions.
If you don't carry heavy loads, a leveling kit can help with steering issues, even if you don't want to put larger tires on your truck. If you do want larger tires, installation of lift and level kits will allow for the use of up to 35" tall tires with 17"-26" wheels and near stock offset, without rubbing, depending on the application.
When shopping for a lift kit for your pickup truck, it is important to keep in mind that there are just a few ways that a lift can be performed. Some systems relocate the suspension brackets and require the removal of all suspension components to do so. Others increase spring pressure and result in a stiffer ride. Tire Rack carries lift and leveling systems by Traxda and Bilstein. Each have their own method of lifting or leveling your vehicle.
Traxda's method relocates the mounting point of the spring that holds the truck up without changing the location of the stock suspension arms. Install is simpler and easier and doesn't compromise the stock ride. Each application is designed to ensure stock compatibility and quality. For example, with a coil-over shock style suspension the strut length is extended while retaining the stock spring pressure. This keeps the smooth ride of a stock truck, with no increase in harshness. For a torsion bar style suspension a re-indexed torsion key and shock relocator brackets are included to change the location of the torsion spring mount without changing the spring tension.
Traxda Lift and Level Kits raise the front of the truck 1.5" to 3" (depending on the vehicle) to eliminate positive frame angle and provide the clearance necessary to run larger wheels and tires. For some applications, the rear of the truck can be raised 1"-2" as well leveling the truck and compensating for the heavy loads used in a working environment (negative frame angle).
Most kits are a direct bolt-in style, simple and easy to install with nothing more than common hand tools and require no modifications to your vehicle. The kits retain stock ride quality. All Traxda kits come complete with hardware, full instructions, alignment specs and dedicated technical support.
The 5100 Series (Ride Height Adjustable) shocks feature multiple snap-ring grooves on the body of the shock to accommodate different spring seat positions, allowing height adjustments from 0" to 2.5", depending on the application. By raising the spring seat position, the factory rake (positive frame angle) can be altered to achieve a level front to rear ride height while accommodating up to 33" diameter tires. Bilstein's self-adjusting valving delivers improved damping control and a smooth ride on all road surfaces at any speed.
You don't have to live with poor steering, tire binding, steering wander and rough ride, just keep it...."on the level."