Counter steering is an amazing technique used by many bike riders, and is very useful when making a quick turn and doing some bike stunts. The very first thing you should know is, counter steering looks counter intuitive, you turn the handlebars to the left, but the motorcycle makes a quick right turn. Can you guess what is the physics behind this strange phenomenon? In this article I will explain to you the interesting physics behind the counter steering.
Before understanding the concept of counter steering, let’s first understand the concept of normal motorcycle steering, which basically leads to no-slip wheel condition. The wheels always try to attain a non-slip condition, which means that the wheels should have no relative motion with the road. But, since the road is at rest, the wheel contact point should have zero velocity. How is zero velocity possible for a moving wheel? It is possible because the wheel has two kinds of motion, a translational motion along with the vehicle, and a rotational motion on its own axis. As when the translational and rotational velocities go in opposite directions (refer fig 1), it is possible to make the resulting velocity zero at the contact point.
In a normal steering, to make a right turn, what we do is just turn the handlebars towards the right and lean the motorcycle inwards. Assume that even after turning the handlebars the vehicle moves straight ahead. Here, if you check the front wheel, it will not meet the no-slip condition since the wheel and vehicle velocities do not cancel each other out. The only way to solve this problem is by making the translational velocity inclined as well. This is possible when the whole motorcycle makes a turn around an instantaneous centre (refer fig 2). The instantaneous centre should be at the intersection of both the wheel's normal lines. It is clear that when the motorcycle makes a turn in this manner, both the wheels easily satisfy the no-slip condition. In short, the no-slip condition forces the motorcycle to make a turn.
How do you normally turn the vehicle? You turn the handlebars, to balance the torque produced by the centripetal force just lean the motorcycle, you also have to adjust the body position to achieve the lean of the motorcycle. The important thing here is that the handlebars turning and the leaning operation happen simultaneously and are in perfect balance. A centripetal force is needed for any object to make a turn. This centripetal force is provided by the frictional force between the tire and the road (refer fig 3).
Let’s do the torque balance of the motorcycle at one point during the turn. You come to know that the vehicle is not stable in this position. The torque produced by the frictional forces will turn the motorcycle down. The only way to balance this torque is by leaning your motorcycle inwards. You find the gravitational and normal forces act in the inclined motorcycle position (refer fig 4a). This will produce another torque, which can counter the torque formed by the centripetal force (refer fig 4b).
In counter steering you turn the handlebars but you do not lean the motorcycle. Obviously, this is an unstable condition. The torque produced by the centripetal force will topple the motorcycle in the opposite direction. In short, the motorcycle achieves a lean in the opposite direction for a moment. This lean is sufficient to achieve a perfect turn in the opposite direction. According to me one thing to be noted here is that during the lean operation, the driver cleverly adjusts the angle of the handlebars so that it is suitable for a perfect no-slip condition.
In case of normal steering, the lean of the motorcycle is achieved by shifting your body weight, whereas in counter steering the lean is achieved by the motorcycle’s instability caused by the centripetal force (refer fig 6). Counter steering is a quicker operation, but slightly risky. If you don’t steer the handlebars back to the proper angle during the leaning operation, you will fall down. This is why proper practice is needed to master this instability steering trick.
Counter steering is a quicker method to avoid sudden obstacles.
I hope this article will help you to gain knowledge with respect to motorcycle steering.