Here is a small excerpt from the Institute of Highways Engineers guidelines for motorcycles. Read the whole document here
4.3 Road Design
4.3.1 It may be of value to the non-riding road designer to briefly explain how motorcycles are different:
- The consistency of grip between tyres and the road surface is critical to motorcycle stability, especially when leaning over for cornering or when braking or accelerating.
- Most braking effort and all steering control for a motorcycle is through the front tyre which means that riders avoid combining braking and steering whenever possible to reduce the likelihood of overwhelming front tyre grip as it attempts to deal with conflicting forces. Any change in this grip, and in particular a sudden decrease, can lead to loss of control during the manoeuvre as the front wheel slides away.
- Loss of front tyre grip on a bend almost invariably leads to a crash.
- All accelerating force is through the small patch of the rear tyre in contact with the road. A sudden lessening of the grip available, for example because of a surface change part-way through a bend, can cause the rear tyre to slip sideways and cause loss of control.
- Motorcycle riders adopt a different line through bends than drivers of twin-track vehicles, traversing the width of the lane in order to maximise grip through minimising steering inputs.
- This keeps the machine as upright as possible, and maximises forward visibility and safety. Anything that forces riders to choose a less-than-optimum riding line through a bend increases the risk of loss of control.
Surface grip and consistency
4.3.2 Motorcycles have a much greater need for a consistent and high coefficient of friction from the road surface than twintrack vehicles, especially on wet surfaces and in areas requiring braking and steering.
Riders adopt an angle of lean to negotiate a corner that is related to speed and bend radius - any change in grip between tyres and surface can destabilise the machine.
Any deviation from a consistently level surface in the same areas can seriously impair the motorcycle’s road-holding ability.
A sudden change in surface level rapidly loads and unloads the suspension, thus reducing the grip between front wheel and road surface. In other words, the wheel rebounds upwards and in severe cases can lose contact with the surface.
Unpredictable changes in the road environment that call for rapid deceleration or braking while cornering can cause the motorcycle to”sit-up” and take a tangential line away from the bend.
GET A GRIP!- from the