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Motorsport Wheel Alignment: Lateral Axle Location

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Lateral Axle Location


00:00 - As we've just discussed in the last module, the live axle requires a method of locating it laterally or side to side in the chassis.
00:08 There are a variety of methods for achieving this and at its simplest, lateral location can be achieved by the lead springs, which are also there to provide longitudinal location.
00:19 This is not an ideal arrangement though.
00:21 And as such you won't find leaf spring in the rear of any modern performance cars.
00:26 With a coil over system, another popular option is to use a four link trailing arm design with the two upper links angled towards the centre of the diff.
00:34 These angled arms serve dual purposes of locating the axle laterally and longitudinally.
00:41 In most performance applications however, there will be an independent link, or set of links used for lateral location.
00:47 One of the most popular options here is a panhard rod, which is laterally located across the chassis, attaching to the chassis at one end and the differential at the other.
00:57 This is effective to a point, however as the diff moves through it's bump and rebound travel, the panhard rod also moves through an arc and hence the axle will inevitably move sideways in the chassis a small amount.
01:10 How severe this movement will be is going to depend on the length of the panhard rod, since a longer panhard rod moves through a larger arc, and it will also depend on the amount of vertical suspension movement.
01:22 With a panhard rod, the roll centre is located at the point where the panhard rod crosses the centreline of the axle and hence roll centre height can only be changed by making some significant changes to the mounting points.
01:35 Another consideration here is that to reduce the lateral movement and make sure that the car handles the same in left hand and right hand corners, it's important to make sure the panhard rod is parallel to the ground at normal ride height.
01:49 This can be problematic in lowered cars without adding some degree of adjustment.
01:54 The next step up from the panhard rod is the Watts linkage which uses a pair of lateral arms with a central rotating linkage.
02:02 The idea with the Watts linkage is that it overcomes the lateral movement associated with the panhard rod and the axle will, for the most part, show very little lateral movement as the suspension moves through the bump and rebound travel.
02:15 The Watts linkage can be mounted to the axle itself with the two lateral linkages mounted to the chassis, in which case the roll centre will be the point that the central linkage rotates about on the axle.
02:28 Alternatively the mounting can be reversed and the central linkage can be chassis mounted, while the lateral arms can be mounted on the diff instead.
02:36 In both instances, it's possible to design the Watts linkage to provide the ability to adjust the roll centre height.