Torsion Bars & Suspension Coil Springs

What Do Torsion Bars & Coil Springs Do?

The suspension system in your commuter vehicle is designed to deliver more than just a comfy, pleasant ride. Without a system of torsion bars or springs, your vehicle cannot turn corners without lifting off the ground on one side. There are many functions of a torsion suspension or spring suspension system, including supporting the weight and height of your vehicle, absorbing bouncing from bumps and dips in the road and protecting the very important points of contact your tires make with the road, which allows for proper maneuvering and optimal traction.

Most modern sedans, pickup trucks, minivans and SUVs incorporate an independent suspension system (containing coil springs or a torsion bar) where the vehicle's wheels are not linked together by a solid axle and each is equipped with its own shock absorber and spring. This means each wheel is free to move up and down independently to better maintain correct suspension balance, especially across uneven terrain.

Torsion Bars vs. Coil Springs

A torsion bar system supports the vehicle's weight with a twisting bar. However, in a coil spring system, the vehicle's weight is supported by a set of springs with a specific spring rate. Constant rate coil springs are ideal for standard situations. These suspension coil springs are tasked with contracting and expanding (rebound), depending on the constant changes in force. Variable rate coil springs use 'progressive spacing' of the coils to handle normal loads, as well as the occasional heavy-duty haul. The tightly wound coils take care of the everyday commute, while the widely spaced coils provide the additional load-carrying capacity when the entire family is loaded up for a road trip down unfamiliar highways and byways.

Signs of Bad Suspension

Suspension problems typically happen slowly throughout a long period of time. Warning signs include excessive bouncing while driving, lack of ability to tightly turn a corner and loss of contact with the road on a windy day. If you are concerned, try the 'bounce test' to test your shocks. Pick one corner of your vehicle and push down as hard as you can. Once you release, your vehicle should bounce up and then depress back down again. If your vehicle bounces up and down a few times, you might need to replace worn-out parts of the suspension system.

Suspension Sag & How to Assess

If you delay in addressing these suspension repairs and upgrades, your vehicle may start to sag, which means your springs are not maintaining your vehicle's proper height like they are engineered to perform. Sagging can cause you to lose control of steering and handling while on the road. It can also cause uneven wear to your tires, which greatly reduces their lifespan, as well as misalignment of your headlight beams, thus risking your visibility and safety. Coil springs themselves can collapse too. This will cause the vehicle to bottom out and create a loud thud when the undercarriage smacks the pavement.

Additionally, a sagging car can push your steering components and other critical systems out of alignment. Most steering linkage systems are designed so that the tie rod assemblies connect to the center link or rack at a specific angle. A sagging suspension will force the tie rod outward and cause a "toe-out" condition. However, if the linkage is positioned behind the spindle on these vehicles, the outward force of the tie rods caused by the drop in suspension height will cause a "toe-in" condition.

Before you visually inspect your vehicle for dreaded sag, make sure to park on a level surface, inflate all the tires to the correct pressure and empty the vehicle of all cargo and supplies. For accurate front-to-rear comparison, you should check measurement points against the manufacturer's recommendations for your specific model. While under the vehicle, look at each end of the control arms for damage from road debris, worn rubber bumpers or shiny (rubbed) spring coils. If your inspection reveals a weak coil spring on either side, keep in mind that you must replace it on both sides. Luckily, this repair rarely needs done more than once during the life of a vehicle.

Torsion Bar & Coil Spring Replacement

Control arms, shock absorbers, springs and struts may come to mind when you're looking at suspension components, but don't forget about all the small parts that make up the entire system. Check out NAPA's entire catalog, including shackles, spacers, bearings, bushings and bolts, pins, friction pads and wear pads, mounting plates, brackets and lock pins. And of course, NAPA is your go-to shop for a new steering and suspension parts. If needing professional torsion bar or coil spring replacement, look no further than your local NAPA AutoCare Center.