Race Truck or Off-Road Truck: Tacoma Coil Overs

Coil overs are a special type of shock absorber. The shock body is usually made of aluminum and the exterior is threaded. The upper spring perch is adjustable, and threads onto the body. The lower spring seat is fixed.

A jamb nut also threads onto the body to lock the upper spring perch into place. Springs are positioned around the shock body, and between the spring seats. The ends of the coil over are attached to the body and the suspension with rubber bushings.

Coil over shocks usually are charged with nitrogen gas to provide additional control of the hydraulic fluid. Unlike stock shocks and struts, the upper spring seat is adjustable, which allows for precise adjustment. By lowering the upper spring seat, the coil over compresses the spring further, raising the front of the truck. Many coil overs also have a damping adjustment on the shock absorber. These adjustments allow for customization of ride height, suspension stiffness, rebound, and damping.

Coil over ride height adjustment is a fairly easy endeavor. You’ll need a special spanner wrench, which is usually included in the coil over kit. Depending on the design/style/manufacturer, you may need additional tools.

1. To get started, with the truck on the ground, measure from the center of the wheel hub to the bottom of the fender opening. This will be your ride height pre-adjustment.
2. Then lift the truck off the ground and allow the suspension to hang out fully. Repeat the measurement from hub center to fender bottom. This will be your droop measurement. Keep both these measurements for later.
3. Next, use the spanner wrench to loosen the upper jamb nut. Mark the current position of the upper spring seat on the shock body.
4. Measure from the top of the upper spring seat to the top of the threads on the shock body. Save for later. 
5. Turn the upper spring seat clockwise to compress the spring further, increasing preload and raising lift height. For approximately every 4 turns, ride height is increased by ½ an inch. From its lowest setting to its highest setting, the total amount of adjustment is somewhere between 2 to 3 inches. 
6. Measure again from the top of the upper spring seat to the top of the threads. Compare with specifications to be sure maximum preload isn’t exceeded.
7. Once your adjustment is complete, retighten the jamb nut down against the upper spring seat. Return the truck to the ground, and move it around a bit to allow the suspension to settle.
8. Once again, measure from the hub center to the fender bottom. This is your new ride height. 

When you are finished, compare your droop measurement to your new ride height measurement. The difference is the amount of down travel available from ride height. For best handling and response, this measurement should be no less than 2 inches. 

To adjust rebound and damping, locate the adjuster knob at the top of the coil over assembly. One way will be softer, and the other harder. Turn the knob in the appropriate direction for the change you wish to make.

Dialing it in just right make take a few attempts. You would generally want a stiffer suspension for on-road handling and comfort. For off-road applications, a softer adjustment will allow for more travel and increased comfort over rocks and obstacles.

The valving of the shock portion of the coil over is also adjustable internally. This requires disassembly of the shock absorber. Once the shock is apart, you can change the valves inside in order to tailor the damping and rebound to your specific needs. This is a more specialized procedure, so first-timers should defer to a professional.

You may also further customize your suspension to your specific vehicle by adjusting the spring rates of the coil springs. The amount of weight each coil spring will support can be nearly perfectly matched to the weight of your vehicle. This results in a much more controlled, predictable suspension response.

Coil overs perform far better off road than a stock shock absorber. The increased spring preload allows for greater ride height, more tire space, and a level vehicle. Adjustable damping and rebound allow you to simply dial in the proper suspension for the task at hand. Combining that, with internally adjustable valving, and different spring weights, the adjustments are almost endless.

There are two main types of coil over shocks. An emulsion shock contains the oil and nitrogen charge in the same area inside the shock. Emulsion shocks are designed for slow speed off-roading and on-road use.

A dividing piston shock has a second floating piston that separates the oil and nitrogen. The piston can be located in the shock tube, or in either an attached reservoir or a remote reservoir. The dividing piston shocks are geared more towards off-roading at speed. By moving the floating piston into a reservoir, the travel of the shock is increased. Without the second piston taking up space inside the shock body, the shock can travel further, while still maintaining the same collapsed length.

Another upside to reservoirs is cooling. As the piston moves up and down in the hydraulic fluid, it transfers physical energy into heat energy that is absorbed by the fluid, and then transferred to the shock tube. The additional fluid in the reservoir, as well as more room for expansion of the fluid inside the reservoir, allow the heat to transfer out of the fluid more quickly. That allows you to off-road at a higher speed, with less chance of overheating and failure of the shock.

Reservoir shocks contain valving specific to your particular application, as opposed to stock style shocks, which can be generic. If you need to adjust to even more specific variables, the valve shims inside can be swapped out in order to customize rebound and damping to your specific needs.