TYRE COMPOSITION
Softer tyres increase grip while harder tyres decrease grip.
DRIFT ANGLE
This is the angle between the tyre direction and the car (wheel) direction.
It may be observed on rallies, when the car direction is pointed outside
the curve while the tyres are pointed inside.
This angle increases the grip until some value when it begins to decrease.
The optimum value is between 5 and 8 degrees.
TEMPERATURE
The rubber viscosity, and therefore the grip, increases with the temperature
until the optimum value between 90 and 100 degrees Celsius. Outside of
these values the tyre degrades.
VERTICAL WEIGHT
If we increase weight inciding vertically to the tyre, its grip decreases
somewhat. More the weight, less the grip.
This is very important in curves, where there is weight transfer. This means that, when we brake, the car weight is trasferred to the front (due to inertial forces) and the front tyres grip decrease. If the curve is right-handed, the inertial forces increase the weight on the outside tyre and reduce the weight on the inside tyre. So, the grip of the inside tyre is somewhat enhanced and the grip of the outside tyre is reduced. This unballanced behaviour reduces our steering performance, and we will have greater turn radius than if we had no weight transfer.
TRACTION CIRCLE
If we represent the force made by the tyre in all directions as a circle
with tyre in the centre and the radius as the maximum amout of the force
without losing grip, we can represent the tyre force evolution as a chart.
The force may be longitudinal (braking and accelerating) and lateral (steering
and gliding). The vector of these forces draws a chart around the circle.
If the combination of these forces is greater than the radius, the
car will lose grip. Good drivers combine these two forces and stick to
the circumference of the circle as closely as possible.
The conclusion we may make is that the tyre will work better with only
one type of force at once, because it can reach maximum without being reduced
by the another force.