Vehicle Ride Height
Vehicle riding height is a vital measurement and should be checked before alignment. This measurement affects the toe, caster, and camber. Measurements are taken with a tape measure or special tool from the ground to the fender well, bumper, control arm etc.
Typically sagging coil/leaf springs, suspension air bags, or the torsion bars are the culprit. Check the control arm bushings for wear or damage before condemning the spring. Vehicle manufacturers have different specifications and techniques for measuring ride height. Usually if the vehicle sags more than an inch from front to rear or side to side it is out of specifications. Always check the sticker in the door frame for the correct tire size. A larger or smaller diameter tire will effect the curb ride height measurements.
The vehicles ride height affects several other alignment angles. When a vehicle sags in the rear increased steering effort and rapid wheel return is noticed. This is because the caster is now more positive. If the vehicles front end is sagging the vehicle will wander because its directional stability has been reduced. The vehicle now has negative caster.
Sometimes if the ride height is within a certain amount, a shim is used to restore ride height to specifications. This increases the harshness and increases the chance of the spring bottoming out. It’s always best to replace worn springs with new ones and in pairs.
Variable rate springs provide a soft ride when traveling with light loads and a firmer ride when traveling with heavier loads. This is accomplished by using springs of different thickness and spacing between coils. A linear spring is squarer and has equal spacing and thickness throughout. Often technicians replace the manufacturers sagging linear springs with aftermarket variable rate springs.
