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Why Fit Sway Bars To A 4WD

Toyota Hilux

Fitting larger swaybars, particularly in the rear, has two main effects, vehicle balance in terms of understeer and oversteer, and increased roll resistance. Both of these effects can provide increased overall handling and safety benefits in a 4wd vehicle.

As most factory vehicles are biased towards understeer, fitting of a larger rear swaybar, or the addition of a swaybar, helps in providing a more neutral characteristic in the handling. This is due to the increase in roll stiffness at the rear, which changes the loading of the rear wheels under conditions of increased cornering load.

At the same time, as the rear end is resisting more of the roll, the front end resists less in proportion, leaving the front wheels more evenly loaded, producing more available front end grip. In the end an increase in overall stability can be achieved by balancing the vehicle.

Another effect of introducing larger rear bars is a reduction in chassis roll. This reduces the effects of “roll camber”. Roll camber is the variation in the wheel and tyre camber setting due to chassis roll. During cornering the presence of chassis roll usually results in the outside wheels gaining positive camber. By increasing the roll stiffness and reducing roll camber effect, the wheel and tyre combination stays closer to its optimal setting.

As an alternative, this could be remedied by starting out with large amounts of static camber to counteract the positive camber gain. The trade off however is the resulting increased tyre wear, and reduction in straight-line handling.

Now that the basics are covered, imagine a Nissan Patrol, Toyota Landcruiser or Toyota Hilux that has been lifted 50mm with a bulbar and winch package. It has been fitted out with a draw system, roof rack and tows a twenty foot caravan! This may be the extreme, but somewhere between this and a standard, off the showroom floor vehicle, is where most of these vehicles operate. The factory swaybars were never designed to control anything other than the standard vehicle at standard ride height and with something less than being loaded to their GVM limit.

The modern 4WD Dual cab utility, almost the family sedan of this century, is normally coil sprung, strut front end and leaf sprung rear with a front but no rear swaybar.

They typically suffer from understeer and can be very unstable during high speed directional changes. Load the vehicle with accessories or people, change its height or tow and the problem only gets worse.

Upgrading swaybars is the only way to compensated for:

  • The change in centre of gravity of the chassis
  • The increase in vehicle mass
  • The change in the Yaw Moment of Inertia of the vehicle

Upgrading swaybars will

  • Improve the stability of the vehicle at high speed
  • Neutralise the factory understeer
  • Increase tyre life
  • Control the roll in load carrying applications
  • Improve safety with no loss of comfort

The biggest resistance to the fitment of bigger swaybars to 4WD vehicles is the flawed concept of the loss of articulation in the suspension. If the replacement swaybars are designed correctly and the swaybar links are lengthened, replacement swaybars can be fitted with minimal or no loss of articulation. However, the improvements to stability, safety and driveability will far outweigh any loss of articulation.

So without reducing comfort or articulation, a swaybar will make the suspension system and tyres perform better, making the vehicle more responsive while neutralising understeer. Fitting a swaybar offers all round improvements in handling, tyre wear, comfort, safety and load carrying. It is one of the best handling improvements you can make.

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