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The Rig: Fire Truck, Fire Apparatus Steering Systems

By Christian P. Koop

Because of the nature of how emergency response vehicles (ERV) are driven during emergency response in heavily congested traffic situations, most rigs’ steering systems take a beating. Keep in mind when considering the safety aspect that they are just as important as the brakes. Many times, situations require the driver to go around stopped traffic, which results in curb jumping, going off the pavement, hitting holes, and a multitude of other obstacles and hazards that can seriously damage the steering system and also the suspension system components. The degree of damage inflicted to the steering system is directly proportionate to how fast and hard the vehicle hits or encounters these obstacles. But in comparison to the old reliable Timex watches, steering systems don’t always “take a licking and keep on ticking!” Most important is to remember that the damage is generally cumulative or adds up over time and can ultimately end up as a catastrophic failure. Because of this, steering systems need to be inspected by trained, conscientious drivers on a daily basis. Failure to follow through and perform these vital inspections properly can result in steering failure and can spell disaster. However, good, diligent, dedicated drivers/operators can prevent failures from ever occurring and can even save the operation down time and serious dollars by staying on top of the rigs’ steering systems. The great part about doing this is that it is not difficult and actually easy to learn if you are not that familiar with it.

The steering system in your rig is designed to provide precise directional control of the chassis, whether it is loaded or not, while minimizing steering effort. Common steering components consist of a steering wheel, column, steering gear, pitman arm, drag link, steering arm, steering knuckle, tie rod, and tie rod ends. All of these components can be damaged during rough use that the vehicle was not intended or designed to endure. In a nutshell, these components, along with others in the suspension, are required to be maintained and adjusted to maintain proper front end alignment, which is crucial for proper tire wear and directional stability. Ensuring all steering systems attaching bolts are tight and that there is no indication of movement should be done by the driver on a daily basis. Any issues found should be reported and the vehicle sent to the shop to have a technician inspect/test further.

The primary steering angles include toe, caster, camber, king pin inclination, and turning angle. The direct benefit of inspecting, maintaining, and keeping the front end properly aligned are longer tire life, easier steering, less wear and tear on the front end components, directional stability, and improved safety—not to mention the dollar savings. Definitions of the steering angles are:

  1. Toe is comparing the distance between the front of the tires to the rear of the tires when viewed from above. It can be measured in a linear fashion or angular. Toe-in or positive toe is when the distance between the front of the tires is less than the rear. Toe-out or negative toe is when the distance between the front of the tires is more than the rear. Toe is generally adjusted positively (toe-in) so when the vehicle is at speed, the tires will move slightly outward because of forces imposed and should be in alignment (also referred to as zero-toe) with the center line of the vehicle. Toe-out will cause rapid tire wear along the inside tire tread and will be easily visible. Striking curbs hard is a leading cause of alignment problems, will knock toe settings out faster than you can imagine, and leads to excessive tire wear and damaged tie-rod ends. If damaged tie rods are not replaced in time, they can separate at the joint and will cause steering loss.
  2. Caster is the forward or rearward tilt of the kingpin when viewed from the side of the vehicle and does not cause tire wear but does provide for directional stability and good steering return. Positive caster is the rearward inclination of the kingpin, and most heavy rigs have positive caster.
  3. Camber is the measure of the angle a front wheel moves away or inward of the frame. Positive camber means the wheels move away from the top and negative means they move inward and is used to help compensate for the wheels to toe out slightly when the vehicle is moving. Most vehicles have a positive setting.
  4. Kingpin inclination (KPI) is the distance the kingpin inclines away from vertical as viewed from the front of the truck and works with the camber angle to place the approximate center of the tire tread in contact with the road. It is not adjustable and generally will only change if the front axle is bent. Hitting large pot holes at speed or going over large bumps or obstacles can damage the front axle. Cost to replace a damaged front axle is considerable.
  5. Turning angle, also referred to as turning radius, is the degree of wheel movement from the straight-ahead position to either extreme left or right. The maximum limits are affected by how far the wheel/tire can turn before contacting the chassis or body and maximum steering gear travel. There are adjustment stops on the steering arm to limit the travel and prevent the steering gear from bottoming and causing damage. Failure to maintain proper adjustment can lead to severe tire damage which won’t be visible unless you inspect the inside tire sidewall. Broken or misadjusted stops can also cause internal steering gear damage. These stops are easily visible, and a trained driver should easily see if they are damaged or missing.

Of all the different types of heavy truck fleet operations, including commercial, government, and military, the ones whose steering systems take a beating on a daily basis are fire and rescue rigs. Having properly trained drivers on staff to inspect these systems on a daily basis is vital in keeping vehicles safe to operate and preventing costly steering system failures.

CHRISTIAN P. KOOP retired as the fleet manager for the Miami-Dade (FL) Fire Department after 35 years with Miami-Dade County and four years in the military. He has been involved in the repair and maintenance of autos, military track and wheeled vehicles, heavy equipment, and emergency response vehicles for the past 40 years. He is a member of the Fire Apparatus & Emergency Equipment Editorial Advisory Board. He has an associate degree from Central Texas College and a bachelor’s degree in public administration from Barry University and has taken course work in basic and digital electronics. He is an ASE-certified master auto/medium/heavy truck technician and master EVT apparatus and ambulance technician. He is a member of the board of directors of EVTCC and FAEVT and a technical committee member for NFPA 1071, Standard for the Emergency Vehicle Technician Professional Qualifications.

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