An Explanation of Camber

see also Dieter Könnecke's technical site

The term tracking incorporates camber, caster and toe. Toe and camber (by the adjustment of ride height) are the only two components of tracking that can be adjusted on the MGF.

What is camber?

Looking from the front of the car looking at the wheels. Camber is the angle that the vertical axis of the wheel makes with the road surface. Negative camber is when the top of the wheel leans into the centre of the car. Positive camber is when the top of the wheel leans out. On an MGF camber should be ±0.5 degree (±30 minutes).

Basic design theory
Figure1: a simple parallelogram- in bump the tyre remains perpendicular to the road

Thanks to Dieter Könnecke for animated figure

 The basic suspension design of the MGF, in common with other sports cars, is by unequal length double wishbones at all four wheels.

Consider the scenario: the car is driving along, and the wheel hits a bump. The wheel is deflected upward.

What wheel orientation will provide the most grip upon the road surface of that deflected wheel? The wheel should remain vertical, with the tyre tread parallel to the road surface to ensure optimum grip upon the road surface.

In this simplest model, equal length wishbones making up a parallelogram will provide the ideal solution.
However, in a corner the body of the car rolls, or leans over. With a parallelogram, the wheel would remain parallel with the vertical axis of the car. Therefore as the car rolls as it goes through a corner the inner edge of the outermost tyres would loose contact with the road. Effectively there would be too much positive camber relative to the road surface, reducing the tyre contact area with the road. The car would easily lose grip especially if a wheel rode over a bump exacerbating the geometry change.

Figure 2: In cornering the simple parallelogram causes the top of the wheel to lean outwards- Positive camber.

Thanks to Dieter Könnecke for animated figure
Figure3: The Unequal length wishbone set-up- allows compensation for roll induced positive camber on the outside tyre.

 To compensate for this roll induced reduction in contact area, engineers derived unequal length wishbone suspension systems. These enable an arc of suspension movement, introducing a degree of compensatory negative camber. This ensures the tyre orientation remains essentially the same with respect to the road surface with maximum tyre contact area with the road inspite of the roll angle of the vehicle. These changes in wheel camber angle occur over a predetermined range of suspension movement.

This essential design has been used to great effect over the years in a number of classic sports cars, and remains a firm favourite with engineers today.

What happens when you lower an MGF’s ride height

The problem occurs when you attempt to lower a vehicle equipped with unequal length wishbones.

Figure4: Lowered suspension with Unequal length wishbones- suspension acts as though in a roll and produces undesired Negative camber.

 By lowering the car, the effect is similar to causing a deflection in the suspension movement- the camber is made more negative. Go round a corner, or over a bump, the camber is made more negative still, putting all the load on the tyre at its inner edge as opposed to the whole tread pattern.

Therefore it is no surprise to find that the inner edge of the tyre wears rapidly away!
What is the solution?

The only way to overcome this problem is a camber adjustment kit- one that would effectively modify the length of one of the suspension wishbones. At rest the wheel would be set to near perpendicular at what ever ride height selected, and ideally would have similar deflection characteristics to the standard set up- but as the ride height is dropped lower and lower this becomes impossible to achieve- without re-locating the suspension pick up points (i.e. where the wishbones pivot from the body work of the car).

In the present absence of a camber correction kit for the MGF, one will have to accept excessive tyre wear as a consequence of lowering one’s car for the potential benefits of better handling (from a lowered centre of gravity) and appearance.