Oct 17, 2006

Positioning yourself

I'd just posted up on positioning yourself on the bike sometime ago. Now I found this at Aprilia's site.


Correct rider positioning is without a shadow of doubt the single most important factor contributing to success in competition riding. Only if correctly positioned can the rider’s body perform the balancing function essential to performance and safety.

It might seem obvious to state that motorcycle handling is totally different to car handling, but a thorough understanding of exactly why it is so different is fundamental to comprehending the dynamics of motorcycle handling. Car driving is totally passive: you sit comfortably in your seat, turn the steering wheel and the car does the rest. Your car is in a state of stable equilibrium, i.e. it remains upright unassisted. Your motorcycle is not: it moves in a state of unstable equilibrium and the speed at which you can negotiate bends is determined by complex physical laws.

It is easy to see that a rider plus his machine add up to form a single mass. The rider’s weight (averaging around 90 kg when full race gear is worn) makes up a large percentage of the total weight of this man + machine system. The rider’s position therefore plays a major role in correct handling, speed and safety. That is why riders shift their position so frequently when maximum performance is required during a race. Race riding is really constant succession of acceleration, high speed travel, braking, and turning. Under most of these conditions the motorcycle is subjected to a shift of load from the front to the rear or vice-versa or from the left to right or vice-versa. During all these load shifts, the rider’s body can and must act to maintain stability. Motorcycle racing is therefore an intensely physical sport, with nearly every muscle in the body in use.

On a twisty circuit, riders have virtually no time to stay still but have to shift their body almost constantly.
So why in particular do riders have to lean in over their bikes on bends? Simply to negotiate them at the highest possible speed without falling off. The inward and downward body shift that we see when race riders tackle bends lowers the bike’s centre of gravity (the theoretical point to which all physical forces can be related) and makes the bike more stable as it travels around the bend. In simple terms, the bike’s own centre of gravity is fixed and unchangeable. You, however, can move your own centre of gravity. You can therefore shift the centre of gravity of your man + machine system by changing your own position. You can negotiate bends at the highest possible speed by moving your weight to the inside of the curve and lowering the centre of the gravity of your man + machine system. This avoids you having to lean your bike to its physical limits.

Another rider going around the same bend at the same speed without hanging into the curve would have to lean his bike at a far more acute angle, with far greater risk of falling off. More acute angles of lean reduce the contact area and consequently the grip between tyres and track. Hanging into a curve is therefore essential to effective race riding, even more so at high speed.
The same principles apply to acceleration and braking. During fierce braking, the bike’s weight is thrown on to its front wheel, and the rear wheel tends to lift. By moving your weight (and consequently the centre of gravity of your man + machine system) further back, you compensate for this shift in load.

Under acceleration the opposite occurs and the bike tends to lift its front end. To counteract this you must therefore move your weight as far forward as possible.
To safely achieve maximum speed under race conditions, the successful rider must therefore shift his position constantly.
The original article is here

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