The Physics of Cornering: The Tyre vs Isaac Newton
Sir Isaac Newton’s Third Law of Motion asserts that no object can develop a force greater than that being applied to it. However, by stretching in two directions when introduced to a corner, the modern tyre develops forces with a combined value that can exceed the loads being applied to it. Clever. However, while celebrating its capacity to multi-task, one shouldn’t forget that it can never do two jobs as well as it can do one. We therefore separate the cornering process into three phases in order to maximise their potential:
1 - Best braking takes place in a straight line, because weight transfers to the front tyres, which aids braking and initial turning power.
2 - Best cornering takes place with no braking or throttle. You reduce braking as you start steering. The body of the car will lean over and the weight transfers to the outside tyres, creating maximum cornering power.
3 - Cornering power reduces as acceleration begins, and best acceleration happens in a straight line.
Pursuing this sequence is a whole lot more reliable, and comfortable, than dancing on the pedals.
Racing drivers are known for being prima donnas with custard for brains and a heavy right foot. But in 1958, a Formula One driver called Piero Taruffi became momentarily possessed by the spirit of Einstein and he spat out an equation for predicting the maximum cornering speed of a car through any given corner: F=mv2/r.
Your car’s tyres have four potential enemies, excluding your erratic enthusiasm, during the cornering process: the nature of the road surface, the vehicle’s weight, speed and the tightness of the bend.
In true game-show-host style, I will not reveal which of these vital elements is missing from brother Taruffi’s equation until later on. For now, just consider that your car’s tyres have to create an equal or greater amount of grip than the centrifugal force - the F - of cornering.
The weight, or mass, of the car rounding an arc creates a centrifugal force, just like spinning a conker on the end of a string. As any conker champ will tell you, it doesn’t pay to rely on big nuts for conkering because the heavier the conker, the greater the force trying to shear it away from the string and off into next door’s garden.
When you swing through a corner, the centrifugal force wants to throw the car off the road in the same way, but it meets resistance from the tyres, which cling to the road surface. If you were to let go of the steering wheel the car would instantly go straight, because the only things forcing it to turn are the front tyres. The heavier the car, the more work the tyres have to do.
Alarmingly, the effect of your speed on your cornering force is exponential, so driving twice as fast more than doubles the cornering force. In the cornering equation, your weight is multiplied by the square of your speed!
In a perfectly planed curve, the apex is exactly halfway through the corner. However, the time advantage you gain by travelling faster down the straights significantly outweighs any short-term gains from screeching through the bends. So although it’s been fascinating to swallow a geometry book, you’ll be glad to know that taking a corner is a lot more artful than driving by numbers.