How Do Torsion Bars Work?

Torsion bars are an important part of many vehicles. They help provide a smooth and comfortable ride. Here are the key things to know about how torsion bars work:

Torsion bars act as springs to absorb bumps in the road. They twist and bend to cushion the ride.
They are made of strong metal rods anchored at one end. The other end is connected to parts of the suspension.
When a wheel goes over a bump, the torsion bar twists. This absorbs the energy from the bump.
Torsion bars can be adjusted. This lets mechanics change the ride height or stiffness.
They provide good durability and performance at low cost compared to other springs.

What Is A Torsion Bar?

A torsion bar is a long metal rod used in the suspension of vehicles. It works as a spring by twisting under load. Here are the key parts of a torsion bar:

Rod – The bar is made of spring steel. It can twist and return to shape without permanently bending.
Mounts – The bar is anchored firmly at one end to the vehicle frame. This is the mounted end.
Torsion Key – The other end has a perpendicular lever called the torsion key. This connects to the suspension parts.
Arms – On some vehicles, short arms link the torsion key to parts like the control arm or spindle.

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How Does The Torsion Bar Twist And Bend?

When the wheel hits a bump, the torsion bar absorbs the impact by twisting:

The wheel moves up, pushing the suspension and torsion key up.
This lifts the lever and makes the bar twist slightly along its length.
The hard spring steel resists twisting. This provides cushioning to absorb the bump.
Energy makes the bar twist, instead of directly jolting the vehicle.
When the wheel moves back down, the bar untwists and returns to its original shape.

Why Are Torsion Bars Used In Vehicles?

There are some key reasons torsion bars are used for suspensions:

They provide good shock absorption and a cushioned ride over uneven road surfaces.
The bars are durable and withstand repetitive twisting without damage.
They are compact and take up little space compared to coil springs.
Torsion bars allow easy height adjustments, by changing the bars or arms.
They are a lower cost option compared to other suspension spring designs.

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How Are Torsion Bars Adjusted?

An advantage of torsion bars is their adjustability. Mechanics can change the ride height and suspension stiffness:

Swapping Bars – They can install thicker or thinner bars to raise or lower the vehicle.
Torsion Keys – Longer or shorter torsion keys affect how easily the bar twists.
Fore/Aft Arms – Adjusting the angle or length of connecting arms changes the force on the bar.
Preloading – Manually twisting the bar before attaching the torsion keys sets an initial preload.

These adjustments help balance vehicle handling and comfort. They are also used to level vehicles loaded with different weights.

Where Are Torsion Bars Used On Vehicles?

Torsion bars have been used in many vehicle suspension designs:

Independent Front – Often used for front wheel independent suspension. Each wheel has its own torsion bar.
Solid Rear Axle – Usually used for solid non-independent rear axle suspension. A single bar crosses the axle.
Trucks And Vans – Widely used for front suspension in light trucks and vans. Provides greater load capacity.
Off-Road – Some off-road vehicles use long travel torsion bar suspension for high articulation.
European Cars – Torsion bars were common on European cars like Volkswagen, Audi and Citroën.

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What Are The Advantages Of Torsion Bars?

Torsion bars have some notable benefits compared to coil springs:

Provide smoother ride with elastic bending properties.
Are durable and withstand repetitive high loading without sagging.
Compact size takes up less space than coil springs.
Allow easy ride height adjustments by changing parts.
Cost less than multi-link and air suspension designs.
Work well for independent front suspension systems.
Require less maintenance than other spring types.

What Are The Disadvantages Of Torsion Bars?

Torsion bars also come with some downsides:

Harsher ride than coils, especially with solid rear axle suspension.
Limited duration before metal fatigue leads to failure.
Front and rear suspension need separate torsion bars.
Rubber bushings tend to wear faster.
Rear bars can’t easily provide progressive spring rate.
Independent wheel travel limited by bar length.
Adjustments require a garage lift to access parts.

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What Are Some Key Torsion Bar Terms To Know?

Here are some helpful terminology about torsion bars:

Travel – The distance the wheel can move up or down. More allows for bigger bumps.
Twist Angle – The number of degrees the bar rotates under suspension movement.
Windup – Turning the bar with an external force to preset the ride height.
Preload – Suspension force with the vehicle at rest and wheels straight.
Torque Rate – How much torque is needed to twist the bar a certain amount.
Deflection Rate – The change in wheel position per degree the bar rotates.

How Are Torsion Bar Suspensions Maintained?

Like other suspension types, torsion bars need periodic maintenance:

Lubrication – Key pivot points should be greased to prevent wear.
Inspections – Mechanics should check for loose components or damage during routine servicing.
Adjustments – Arm angles, torsion key length, and ride height may need adjustment.
Replacement – Torsion bars may eventually need replacement if they fatigue and crack.

Proper maintenance helps ensure the torsion bar suspension keeps providing a smooth and controllable ride.

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Conclusion

In summary, torsion bars are an important automotive spring design. They work by twisting along their length to absorb bumps. Torsion bars offer advantages like adjustability and durability. They help provide a comfortable ride. With routine maintenance, a torsion bar suspension can reliably serve vehicles for many miles.

Here are some key FAQs about torsion bars:

What is a torsion bar made of?

Torsion bars are made from tough high-carbon steel alloy that can resist twisting force without permanent deformation. The metal has high yield strength and elasticity. Common alloys used include EN45A, EN47, and high-carbon SAE 1045-1060 steel.

How long do torsion bars last?

With proper maintenance and bushing lubrication, torsion bars typically last 80,000 to 100,000 miles before needing replacement. More rugged bars on trucks may last 150,000+ miles. Damage from rust or overloading can shorten bar life.

Can you adjust torsion bars yourself?

Yes, ride height can be adjusted by changing torsion bar parts. But this requires lifting the vehicle and disassembling suspension components. Only experienced DIY mechanics should attempt torsion bar adjustments. Most owners will need a professional shop to correctly adjust bars and alignment.

What lubricant is used on torsion bars?

Torsion bars should be lubricated with high quality chassis grease during installation and maintenance. This prevents seizing and allows the bars to twist freely. Molybdenum disulfide grease or lithium complex NLGI 2 grease are good options.

How do you remove torsion bars?

Removing torsion bars requires raising the vehicle, removing the wheels, disconnecting the torsion keys and arms, and unbolting the bars from their mounted ends. New bars are installed in reverse order. An alignment is necessary after new bars are installed.

Are torsion bars better than coil springs?

There is no definitive answer, as both have pros and cons. Coil springs tend to give a softer ride, while bars allow easy height adjustments. Overall durability is similar. Torsion bars have fallen out of favor modernly in favor of coilover shocks, especially on rear suspension.

Why do torsion bars make noise?

Excessive squeaking or popping noises from torsion bars usually indicate worn rubber bushings. Replacing the dried out, cracked bushings with new rubber parts will allow the bars to twist quietly again.

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