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fig.7
4.3.
FronT wheel seT-BaCK
front wheel set-back is a check used to determine the position of the front wheels with reference to a line placed perpendicular to the
vehicle's centre line. Ideally the left hand wheel should be located directly opposite the right hand wheel. However, a tolerance of 5mm is
allowed on all new cars, and on older cars a set back of 10mm is acceptable. Whilst conducting a routine toe check on vehicles,
noting any excessive set back provides a good indicator, which suggests closer inspection is required, as collision damage or
suspension problems may be present. Please note: Most alignment equipment does not indicate which wheel is at fault, just that there is
a difference across the centre line. However, positive set-back indicates that the off-side wheel is set-back further than the left. negative
set-back indicates that the near-side wheel is set-back further than the right (fig.10).
4.3.1. Place the turnplates centrally in front of each front wheel with the curve facing downwards. Drive the vehicle onto the turnplates (fig.2).
nEVEr attempt to carry out any wheel alignment without positioning the vehicle correctly on the turnplates.
4.3.2. turn the steering wheel to the straight-ahead position and lock it in position with the spring loaded wheel clamp positioned between it
and the driver's seat (fig.3).
4.3.3. Mount the laser measuring heads onto the front wheels with the toe scales to the front of the vehicle adjust to fit - see 4.1.4.
4.3.4. using the bottom scale labelled sEtBAcK, record the readings for the near and off side of the vehicle. A difference of more then
10mm will require further investigation for any damage to the suspension.
fig.9
4.4.
rear wheel alignMenT
noTe: toe readings are reversed when the laser measuring heads are on the rear wheels i.e. Toe in = Toe out and visa versa.
4.4.1. Place the turnplates centrally in front of each rEAr wheel with the curve facing downwards. Drive the vehicle onto the turnplates.
Make sure the front wheels are in the straight ahead position. Place the alignment assemblies on the front wheels and position
correctly.
4.4.2. Place the laser measuring heads on the rear wheels, position correctly and ensure the toe scales are at the rear. turn the units'
switches to position I, note the front wheel scale readings. e.g. left front wheel reads 1, right front wheel reads 4. the difference is 3 to
the right.
4.4.3. transfer the laser measuring heads to the front wheels and the alignment assemblies to the rear wheels. Adjust the track rods equally
to give a rear scale indication of 3 lines to the right i.e. 1.5 lines on both scales. the steering wheel is now set to the vehicle thrust line.
4.5.
rear wheel Toe angle (TraCKing)
rear wheel toe angle, either in or out, is an individual measurement. front wheel toe angle can be measured as a total, because the
steering system will allow unequal adjustments on either side to self centre. With rear wheel toe however, each wheel can affect the
steering as there is no compensating steering wheel for the rear axle. It is the rear wheel axle alignment that controls the steering wheel
position. When adjusting rear wheels for toe in or toe out, the angles must be exactly equal for both sides, if not, the vehicle will be
steered away from it's centre line. the rule of thumb, when making rear wheel adjustments, is to firstly adjust both wheels to equal toe
with respect of the centre line, then equally increase or decrease them to the manufacturer's settings. the vast majority of modern
vehicles have a toe in or toe out of no more than 1mm per wheel. More than that and tyre wear occurs at unacceptable levels.
With the introduction of the front wheel drive vehicle, rear wheel toe adjustments have become more common place. It is easier to build
an average tolerance body shell and trim the rear wheel alignment to suit, to give acceptable tyre wear and steering capability, as
opposed to building a close tolerance body shell (fig.11).
4.5.1. Place the turnplates centrally in front of each rear wheel with the curve facing downwards. Drive the vehicle onto the turnplates. Make
sure the front wheels are in the straight ahead position. Place the alignment assemblies on the front wheels and position correctly (fig.12).
fig.8
fig.10
Original Language Version
fig.11
GA60
Issue: 1 - 23/02/10
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