4WD SUSPENSION
Page 4 of 7
Double-wishbone Suspension
4WDs and good on-road handling are now made reference to in the same sentence due to the increasing number of manufacturers adopting independent front suspension (IFS) in an effort to provide buyers with better-handling 4WDs. Let’s see why. The term double wishbone (also known as double 'A’ arm) refers to the upper and lower wishbones that link the wheel to the chassis. The upper arm is shorter than the lower arm so that the wheel camber (angle the wheel stands up at relative to the vertical) can change in order to keep the tyre contact patch sitting flat on the road when the body rolls during cornering. This makes it the ultimate 4WD suspension for smooth road handling. It is a form of independent suspension that utilises a coil-over shock absorber or a torsion bar. The upper and lower wishbones locate the wheel both fore, aft and laterally.
GOOD POINTS
Double-wishbone suspension provides excellent smooth- and rough-road handling. On 4WDs with a separate chassis, the wishbones and spring mounts can all be fastened very strongly to the chassis rails, making it fairly durable. This type of suspension adds much less unsprung weight to the vehicle, which helps the shock absorbers control spring movements. Unlike live axles, independent suspension allows one wheel to remain unaffected when road irregularities disturb the opposite wheel.
BAD POINTS
On production 4WDs, the length of the wishbones and driveshaft angles limits wheel travel. Narrower 4WDs have shorter wishbones and therefore less travel than wider vehicles such as the 100 Series LandCruiser. Ground clearance to the engine sump and chassis-mounted diff housing decreases under upward suspension travel. These two factors hinder its off-road ability. The camber of the wheels changes with suspension travel in slow off-road conditions where the wheels are moving up and down without much body roll. In this case, the tyres don’t sit flat on the ground, which limits traction. Anyone who has ever seen the vertical angle of the rear wheels on a heavily laden current-model IRS Pajero will understand this. The other problem with double-wishbone 4WD suspension is that it can never be modified to give you as much wheel travel as a live axle can.
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