Sharp Drive Discuss Vehicle Control
Effects of Adverse Conditions: The grip or friction between the tyres and the road is what allows the vehicle to respond to the driver inputs – accelerating, braking or steering. That grip is limited by the conditon of the tyres and of the road’s surface. When there is a maximum contact between a good tyre and a good dry, smooth road surface, such as dry asphalt or hotmix, then there is maximum grip. Chip seal is not as good as it lacks continuous smooth contact with the tyre.
At the opposite end of the scale is an
unsealed road made up of dirt, which has very little grip, with loose stones or
gravel which simply act as little rollers between the tyres and the road.
Anything that contaminates a sealed road surface, such as dirt, cattle
crossings and spills, like oil or chemicals greatly reduce the grip. Wet autumn
leaves are very slippery hazzards. Watch for gravel swept from the shoulder
onto the sealed corners. It is like driving on little rollers, causing an
instant loss of grip.
Water, in any form, mist or fog, snow or
ice will make any surface more slippery, and is worse when combined with any
other contaminants, such as dirt or oil. Pools of standing water from heavy
rain cause acquaplaning. Asphalt is more prone to acquaplaning than chipped
seal, which allows a certain amount of water to escape, forming little valleys
between the stones. To avoid aquaplaning don’t drive through water. If
unavoidable, slow down.
A common and dangerous loss of grip occurs when
there is a very light shower of rain, or after a very hot spell. We become used
to the good grip of a hot, dry road, but a film of moisture will make the
normal accumulation of dirt and oil on the road surface very greasy. One
benefit of heavy rain is that it washes the road surface clean. With good tread
depth, and avoiding pools, grip on sealed roads in rain can be quite good.
In any conditions less than a good, dry
sealed road braking distances will be longer, acceleration grip will be less,
allowing wheel spin, and cornering grip will be reduced. Unexpected
transisition between different road conditions is very hazardous. Keep a sharp
watch out and reduce speed for any changes. In these conditions the slightest
lack of smoothness in braking, steering or accelerating can result in a loss of
control slide.
When cresting a rise, or a loss in road
camber can cause a slight un-weighting of the wheels, effectively reducing the
grip. Combined with other conditions that could be enough to push the vehicle
beyond the limits of control.
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