Over the years, the weight of the car causes the coil spring to lose some of its tension. This results in a lowered ride height. A ride height check can be performed to see if the height of the car conforms to specifications.
Incorrect ride height affects the camber and toe alignment angles. With a short-and-long arm (SLA) suspension system, the car is designed to ride at a height that minimizes changes in tread width. When the suspension system drops due to sagged springs, the upper control arm is in a different place in its arc of travel. This means that there will be even more camber change during bumps.
The position of the control arm changes in its arc due to spring sag. Courtesy of McQuay Norris.
Tires will wear faster and handling is affected.
A vehicle that is too low cannot be aligned properly, so this test should be done before attempting a wheel alignment.
Measuring Front and Rear Curb Height
Check the trunk for extra weight.
Check the tires for normal inflation pressure.
Park the car on a level shop floor or alignment rack.
Find the vehicle manufacturer's specified curb riding height measurement locations in the service manual.
Measure and record the right front curb riding height.
Measure and record the left front curb riding height.
Measure and record the right rear curb riding height.
Measure and record the left rear curb riding height.
Compare the measurement results to the specified curb riding height in the service manual.