Cornering Force — It Drives You Around The Bend

When trying to help people understand what we are talking about, particularly when referring to potentially tricky topics, we find it really useful to refer to ordinary everyday objects with which to illustrate the point. For this one we are going to use the humble conker, or to give it its proper name, the Horse Chestnut, and of course, a piece of string.

Find yourself a conker, or anything of a similar size to use as a small weight, drill a neat hole through its centre and thread it onto a piece of string of about 2–feet in length. Now, knot the string at one end and allow the conker to slide to the knot whilst holding the other end in one hand. You now have the apparatus that we are going to use to illustrate the subject matter of this article — cornering force.

If you whirl the conker around over the top of your head like a helicopter rotor the string will remain taught, and the faster you whirl, the more stressed the string becomes. The question is, does the conker pull on the string or does the string pull on the conker?

To get to the answer to the riddle ask yourself what would happen to the conker if the string should break, or if you let it go? It would no longer orbit the top of your head, that’s for sure, but fly outwards on a straight–line course away from the circle that it just been drawing in the air. That change to a straight–line course occurs at exactly the point where the conker is released from the force that it making it travel in a circle, whereupon it will head off in whatever direction it was facing at that moment.

The Cornering Force Acting Upon a Vehicle

Every inanimate object on the planet, when subjected to acceleration, will travel in a straight line unless it is subjected to an interfering force that acts upon that object to change its direction of travel. In the case of our conker on a string, it will fly off in a direction that is at a tangent to the circular path it came from.

If you think about it, the thing only travelled in a circular path to begin with because it was pulled in that direction by the string. The string therefore represents the interfering force, but how does this have any relevance to you driving your car?

Accepting that contrary to some opinions, cars do not have a mind of their own any more than does any other solid object, and they do not experience emotions, it does help us to understand this subject a little more easily if we imagine they do. With that in mind we can say that objects are always happiest when travelling in a straight line, because a straight path is the line of travel that nature always intended for them.

For a vehicle to drive around a bend is an unnatural activity

When you steer the car around a bend you are asking it to perform an unnatural act, and that requires an amount of effort that is stronger than the desire of that vehicle to keep going straight ahead. When you drive a bend your tyres are the conker string, as it is only the grip of the tyres upon the road that will steer the car around a bend. Therefore, we can say the car represents the conker.

That being the case, if we try and negotiate a corner too quickly our conker string (tyre grip) may snap, or slip from our grasp, releasing it from the only force that was making it steer away from a naturally straight course. This means that we are restricted to cornering only at a rate that is within the breaking strain of our string, or within our ability to keep hold of the string (grip of the tyres), if we are to be successful in emerging on the other side of the bend.

Every Part and Everything in The Car Travels With The Car

If you are not convinced of this concept, then think of this scenario. If we put a ball in the centre of the passenger floor foot well of a car, assuming the car is level enough for the ball to remain there whilst the car is driving at a constant speed in a straight line, that ball will travel with the car in the same direction and speed. However, you will be aware that if we steer into a left hand bend we can expect the ball to begin to roll, but which way does it go?

If the car is travelling at 30mph along a straight road, then the ball in the middle of passenger floor foot well is also travelling at 30mph, but that is only its speed relative to the road surface over which the car is driving. If we are talking about the relationship the ball has within its mini–environment, i.e. the interior of the car, then it remains stationary.

Continue to keep your eye on the ball

If we now apply the brakes, and because the ball is free to move, it will continue to travel at 30mph. What is happening here is the ball begins to leave the car behind, this being due to the car reducing its speed. The visual effect we have from within the car, however, is the ball has begun to roll forward. It is only once it has been stopped from doing so by coming up against the end of the foot well is it forced to decelerate at the same rate as the car.

Now apply this theory to a car that is steering into a corner. When the car steers to the left the ball appears to roll to the right, but in reality it has remained on the original course of straight ahead. It has only appeared to roll to the right because of its relationship with the interior of the car, as the car has changed its orientation by rotating about its axis towards the left.

The ball, in reality, will continue on its original course relative to the ground beneath the car, until it meets with some obstruction such as your centre console or transmission tunnel, and it will be that obstruction that will gather the ball and then take it around the bend with the car.

How Many Cornering Forces Acting on The Car?

It is easy to think that there are many different forces pulling and pushing on a car during cornering, but really there is only one, and that is the force that pulls it away from its natural line of travel of straight ahead.

In the diagram the arrow is pointing towards the axis of the circular path through which the car is travelling as it orbits that point. This pulling force is known as centripetal force, and not centrifugal force, which is a completely different thing and should never be confused or associated with cornering motorcars.

Centripetal force is the only thing that is pulling the car away from the straight ahead position and into the corner and that force is created by the grip of the tyres on the road.

Whilst it is not possible to change the laws of physics it is possible, by gaining a better understanding, to work more closely with them, and therefore not to fight with them. This is one of the reasons why The System of Car Control works so well, because through this method the driver will set the car up to its maximum level of stability before making any change in direction

By use of The System fo Car Control, when the direction change takes place, it is achieved with the car at its most stable attitude. This will be with the cornering force applied progressively and whilst maintaining the vehicle balance as evenly as possible over the whole car.

The Car Leans Over Whilst Cornering

We all know that when we steer a car around a bend it will heel over towards the outside of the curve, but think of it more this way. The mass of the vehicle is intent on going straight ahead at all times, and the tyres, through their grip of the road surface, are hauling it away from that course to follow the direction of the road.

All the time the tyres are winning their battle the car will be forced to obey. However, because the connection between the chassis and the wheels allows a certain amount of free movement (suspension), once steering is applied, the wheels will change direction momentarily sooner than the rest of the car.

Think again of the conker on the string, but this time with a second conker attached to the first by a piece of elastic. The one on the string is the car wheels, and the second is the chassis and body. The first one responds immediately, but the second, the one attached by elastic, does not initially respond, and is only forced to do so after the elastic (suspension) has stretched to a point when it has managed to exert enough pull to haul the weight of the conker (body) to follow the arc.

By developing a better understanding fo what is going on within the car
you will get better driving performance

Every component of your car is being subjected to the laws of physics, but if you are a really silky–smooth driver, and you balance the car up nicely prior to entering the corner, you will get the best performance out of whatever it is you are driving in terms of its cornering potential.

If you are rough with the controls, or shift the balance of the car a second time after you have begun cornering, then you will diminish its ability to deal with what you are asking it to achieve.

When a vehicle is cornering, every part of that car is being forced to go around the bend against its will, and therefore any part that manages to break free of that cornering force, such as the rear wheels and axle for example, will automatically assume its natural line of travel, taking with it whatever it is attached to.

It is why, when the rear tyres lose their purchase on the road surface, the back of the car appears to step outwards. What it is really doing is changing from travelling through the arc you had intended, leaving it at a tangent, and if that direction is to the tall oak tree on the outside of the bend, then to that tall oak tree the car will go.

Confused? Well don’t be, because all you need to know is, if the car has left the road at a bend it is because you have expected too much from the car at that time — and that’s why you are now in the hedge!

Julian Smith
Ride Drive Limited

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Thursday, 27-Jan-2011

ornering Force — It Drives You Around The Bend