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Thetwist-beam rear suspension (alsotorsion-beam axle,deformable torsion beam, orcompound crank) is a type ofautomobilesuspension based on a large H- or C-shaped member. The front of the H attaches to the body via rubberbushings, and the rear of the H carries each stub-axle assembly, on each side of the car. The cross beam of the H holds the two trailing arms together, and provides theroll stiffness of the suspension, by twisting as the two trailing arms move vertically, relative to each other.
The coil springs usually bear on a pad alongside the stub-axle. Often, the shock iscollinear with the spring forming a coil-over. In many cases, the damper is also used as a restraint strap to stop the arm descending so far that the coil spring falls out through being completely unloaded. This location gives a high motion ratio compared with most suspensions, improving performance.[citation needed]
The longitudinal location of the cross beam controls important parameters of the suspension's behavior, such as theroll steer curve andtoe andcamber compliance. The closer the cross beam to the axle stubs, the more the camber and toe change under deflection. A key difference between the camber and toe changes of a twist beam versus a traditional independent suspension is the change in camber and toe is dependent on the position of the other wheel, not the car's chassis. In a traditional independent suspension, the camber and toe are based on the position of the wheel relative to the body. With twist-beam, if both wheels compress together, their camber and toe will not change. Thus, if both wheels started perpendicular to the road and are compressed together, they will stay perpendicular to the road. The camber and toe changes are the result of one wheel being compressed relative to the other.[1]
This suspension is commonly used on a wide variety of front-wheel-drive cars (mainly compacts and subcompacts), and was almost ubiquitous on Europeansuperminis. When Volkswagen changed from rear-enginedRR layout cars to front-wheel-driveFF layout cars in the mid-1970s, it adopted the system across not just itsAudi 50/Volkswagen Polo supermini, but also the compact-hatchbackVolkswagen Golf andScirocco models.[2][3]
This type of suspension is usually described as semi-independent, meaning that the two wheels can move relative to each other, but their motion is still somewhat inter-linked, to a greater extent than in a true independent rear suspension (IRS). This can mildly compromise the handling and ride quality of the vehicle. For this reason, some manufacturers have changed to different linkage designs. As an example, in 2004,Volkswagen dropped the twist-beam in favor of a true IRS for theVolkswagen Golf Mk5, possibly in response to its rival, theFord Focus's "Control Blade" multi-link rear suspension introduced in 1999 – a first use of multi-link suspension in the segment. It came back on a twist-beam later for small-engine equipped variants of the Mk6 and Mk7 Golf.
General Motors in Europe (Vauxhall andOpel) continued to use twist- or torsion-beam suspension up to the end of GM's ownership of the brand, and it was used on the 1982–1988Cadillac Cimarron,Oldsmobile Firenza, andBuick Skyhawk. The twist-beam provided a cost saving of €100 per car compared to multi-link rear suspension,[4] although the version used in the 2009–2018Opel Astra also employed aWatts linkage at a cost of €20 to address the drawbacks and provide a competitive and cost-effective rear suspension.[4]
Other competitors, theRenault Mégane,Peugeot 308, andCitroen C4 also have stayed with the twist beam.[5] The sportiest models of its brands, such as the Renault Mégane RS and the Peugeot 308 II GTi, have proven that twist-beam rear suspension can provide a high level of performance on a compact car, on the racetrack, but also during theMoose test. The Peugeot 308 II was able to outperform its competitors equipped with multi-link rear axles by passing this test at 82 km/h[6] – only 3 km/h less than the Citroën Xantia Activa's world record of 85 km/h in 1999.[7]
Kia Soul is also using twist-beam,[8] although the largerHyundai Elantra (HD) andHyundai i30 models employed either a torsion beam or a true multi-link independent rear suspension depending on market and also trim level. Most i30 models produced in the Czech Republic have true multi-link independent rear suspension, while those produced in South Korea have torsion-beam rear suspension.
The fourth-generationFord Focus has three rear suspension setups; most hatchback and saloon models have torsion-beam depending on market, while all wagon models have multi-link rear suspension.[9]
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