_SandMan_ via Flickr
Torsion bars are a common technology used for suspension, particularly in truck and SUV applications for virtually all of the major manufacturers.
A torsion bar is available in many formats. But the general idea is that the bar is connected solidly at one end, generally to the chassis, and then connected at the other end of the bar to lower control arm of the suspension via a spline fitting.
The physics is that when the car runs over a bump or anything that causes the control arm to lift, the torsion bar twists. This adds energy and the torsion bar wants to straighten out which pulls the control arm back to the ground.
As mentioned, the torsion bar is commonly in trucks and SUVs that are normally rear wheel drive. In this case the torsion bars are running on each side of the vehicle along the length of the vehicle and connected to the control arms for the front wheels.
 |
 |
 |
| Dorman Torsion Bar | Torsion Leveling Lift Keys | Torsion Bar Unloading Tool |
Benefits of Torsion Bars
There are many advantages to the torsion bar design. The first advantage is that the simplicity of the design offers a significant amount of robustness compared to many other more complex suspensions.
Another benefit is that it places more mass of the suspension closer to the ground, which lowers the center of gravity. This is particularly important in the SUVs and trucks mentioned earlier which have a higher propensity historically for rolling.
The simplicity also allows for easier ride height adjustment, which is often useful for manufacturers to simply compensate for the weight of the engine being installed in the vehicle.
The major downside to this design is that it does not allow for a progressive spring rate, as the twisting of the bar will always provide a constant spring coefficient.
Torsion bars have several factors that are used to make the twisting more or less difficult and effectively changing the response of the suspension.
The main factors are the diameter and length of the bar, the material used and the process used when finalizing the material.
A longer bar is easier to twist than a shorter bar, and would provide a looser suspension.
Also, a larger diameter would cause the bar to be more resistant to twisting.
Some hardening processes could also result in the bar being less likely to twist, but many of these processes also cause the metal to be more brittle, which is to be avoided for obvious reasons. The primary material used for these bars is steel.
In some cases, primarily for performance, hollow torsion bars can be purchased.
Top Rated Brands
There are a few main torsion bar producers when looking to find the right torsion bar for your needs.
Two of the primary manufacturers that show up on Amazon are Hotchkis and Dorman. Dorman particularly has received high reviews, while Hotchkis products don’t show having as many reviews available.
There are also a number available from Mopar performance, although those are primarily aimed at Mopar applications. Another manufacturer that is commonly available for aftermarket is Sway-A-Way, as they offer both a solid and hollow torsion bar offering. Elephant racing has a website that has several other options available as well.
Conclusion
Torsion bars are a very simple, common sense idea that as a result has a very simple design which is quite robust.
The bars are essentially hard mounted to the chassis on one end at to the lower control arm on the other. The control arm has to twist the metal rod to lift, which also means the metal bar wants to twist back to get the suspension on the ground.
Along with its simplicity another advantage is that this allows the center of gravity to be lower which results in the vehicle being less likely to flip, a very critical feature in SUVs and trucks in which this technology is most commonly used.
|
|
|
| Dorman Torsion Bar | Torsion Leveling Lift Keys | Torsion Bar Unloading Tool |