Ride Height

Identifying Ride Height Problems

identifying ride height problems

Ride Height adjustment on vehicle systems, either truck or trailer, is a critical part of vehicle suspension performance, meaning identifying ride height problems is also critical. The impact of incorrect ride height adjustment can be profound and results in instability and poor ride, as well as degradation of other vehicle system components.

On trailers with a split group suspension, the ride height of the steer axle also needs to be considered because any deviation from designed ride height will change the caster. Incorrect caster may then cause driveability and tyre wear issues.

Excessive right height can contribute to the following system deficiencies and failures:

  • Poor vehicle stability and balance.
  • Incorrect load share leading to improper brake balance and wheel end loading.
  • Shock absorber catastrophic failure through over extension.
  • Vehicle shimmy and tyre wear. This is because an increase in ride height can change caster in steering and steerable suspensions.
  • Air spring failure through separation at the bead plate.
  • Excessive driveline vibration through substantial change to pinion angles, which can lead to:
    • Damaged universal joints
    • Transmission output bearing degradation
    • Differential pinion bearing degradation
    • Pinion seal failure

identifying ride height problems

Insufficient ride height setting can contribute to the following system deficiencies and failures:

  • Incorrect load share leading to improper brake balance and wheel end loading.
  • Vehicle harsh ride as the suspension is riding on or close to the air spring bump stops.
  • Catastrophic failure of air spring.
  • Catastrophic failure of shock absorbers if the suspension hits a fully compressed shock absorber.
  • Vehicle shimmy and tyre wear due to changes in caster.
  • Fatigue failure of shock absorber fasteners and mounts.
  • Fatigue cracks of chassis frame and cross members.

Ride Height is normally measured from the centre of the axle to the underside of the frame. Vehicle manufacturers may advise of other supplementary methods to measure ride height such as measuring shock absorber length or air spring height. Unless otherwise specified, all ride heights should be measured on the axle attached to the height control valve. On trailers with a split axle group, ride height should be an average of the single axle and the rest of the axle group to take into account any frame slope variations.

Tips

  • Set trailer kingpin mounting plate height to specification before beginning.
  • Ensure there is at least 90 psi (620 kPa) pressure available to the Height Control Valve.
  • To ensure accurate adjustments, first lower suspension and then allow it to rise to set ride height. 
  • Allow sufficient time for the Height Control Valve to operate, as most have a built-in delay of around 10 seconds.
  • identifying ride height problems
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