Wheel Alignment Elements
Tracking – (1 angle measured)
This is a linear measurement of the vehicles two front wheels, they are checked for alignment compared to one another in one horizontal plain only ( relative toe).
This single measurement method makes the large and foolish assumption that the wheel being measured is correct in all other plains (camber, caster, KPI etc) and makes no attempt to measure the rear wheels at all.
Four wheel alignment – (2 angles measured)
This is again a simple linear measurement where the rear wheel alignment is simply assumed to be correct and the rear wheels are then used as a scale to centre the front steering rack, the front toe left and right is then individually adjusted.
This is mildly more useful but still highly floored as it makes a dangerous assumption regarding the rear wheels alignment to the actual chassis and again it completely ignores the many other important plains of geometry.
Four wheel Laser alignment
Exactly the same process as above! The addition of the word “Laser” is a simple marketing ploy to make a simple process seem more technologically advanced.
Primary Geometry – (8 angles measured)
This system will accurately locate the rear axle centreline allowing both the front and rear axle to be centred, in addition front and rear wheel cambers will be measured. Whilst this system is acceptable we still consider it rather basic.
Full Global Geometry, Primary and Secondary – (15+ angles measured)
This system measures every necessary wheel angle and therefore the vehicle geometry can be set or corrected absolutely from scratch with no assumptions being made.
These systems are very powerful but are also complicated to both use and to understand. Unfortunately all too often these systems are operated by technicians who do not fully understand the relevance of many of the measured angles and so the system can be totally wasted in the wrong hands.
The important wheel alignment measurements include:-
- King Pin Inclination/ SJI/ SAI (terminology differs)
- Scrub radius
- Included angles
- Toot/ Ackerman
- Delta curves
A real problem in this industry is that the full global wheel alignment systems, along with the relevant staff training are invariably quite expensive for a company, so this leads many companies to implement the cheaper and far less adequate systems. This problem combined with the fact that the average customer is blissfully unaware that there is anything more their cars setup than simple “tracking” can often result in unhappy customers after poor customer service and poor results.
Be aware of the differences in the systems and make sure that the service you are paying for next time is actually capable of giving you results!
Positive or negative camber angle is determined by the distances ‘A’ and ‘B’, depending on whether or not these two distances are the same, and by the position of the arms relative to the ground under normal use conditions of the vehicle, if, for example, it is decided that the wheel should have a zero camber angle under normal load conditions, then obviously it must be at the mid-point in the range of movement between complete compression and complete release, the camber will then tend towards positive when empty, and negative when fully loaded, when the suspension system is in a classical position, the condition described above will be satisfied,
In fact, with the suspension system in this arrangement, which means that the distance ‘A’ will be different to distance ‘B’ for any minimum upward or downward, movement the wheel camber angle will inevitably change, for a large number of reasons, it is not always possible for the manufacturer to follow the classical arrangement rules, and a complex number of possibilities arise from this regarding the geometrical arrangement of the suspension systems.