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Cornering force

You know that your front wheels turn when you twirl the steering wheel, or turn the handlebar.

india Updated: Aug 28, 2009 11:31 IST
Grease Monkey

You know that your front wheels turn when you twirl the steering wheel, or turn the handlebar. We’ll take a closer look at what goes into making your car or motorcycle go around corners.

We’ll start with bikes, since they’re easier to explain. The front forks (the two tubes that meet your handlebars at the top, and the front wheel’s axle at the bottom) transfer the force you apply to your handlebar to the wheel, and help you steer. If you view the bike from the side, you’ll notice that these forks make a slight angle with the ground. If they were vertical, they’d absorb bumps really well and allow the bike to change direction really quickly, but that’d also make the motorcycle nervous at speed.

Therefore, the forks’ bottom ends are a little in front of the top ends when you view the bike side-on. The nearer the forks are to the vertical, the quicker the bike steers. That is why supersport bikes like Fireblades sport near-vertical forks.

‘Kicking out’ the front forks, or giving them a greater angle with the vertical, adds a lot of straight-line stability to the motorcycle, but this also increases the turning radius and does not allow the bike to change direction readily.

This is why cruisers and especially American choppers prefer this format — they acquit themselves well when presented with miles of smooth, arrow-straight blacktop.

Leaning into bends
Interestingly enough, racers use a technique called ‘counter-steering’ to lean their bikes into bends. Like the name suggests, it involves pushing horizontally on the side of handlebar that’s on the inside of the bend. At low speeds, this will turn the bike away from the corner, but at high speed, this makes the bike lean into the bend.

How do cars do it?
Cars steer with their front wheels, irrespective of which wheels are receiving power to drive the car. It may seem a little unfair to the front wheels in a front-wheel-drive car, to ask them to bear the load of acceleration, braking and steering, but it happens to be the best solution for the public, all things considered. Forklifts steer with their rear wheels because this lends them excellent manoeuverability in the spaces they are used.

This very agility makes a vehicle unstable at speed, which is why the front wheels always steer in normal roadgoing automobiles. This is also why, should you be confronted with a small parking space, you should always back in, instead of trying to make your way in nose first. If you ever see someone driving in reverse at speed and maintaining perfect control over the car, you’re probably looking at a highly-trained driver who can make minute corrections with the wheel.

All-wheel steering
Four-wheel steer has been attempted by a few manufacturers. It has benefits like a smaller turning radius, greater agility at low speeds and better stability at high speeds.

The current BMW 7-series offers four-wheel steer, as did the Nissans.

The rear wheels are able to change direction to the tune of a few degrees, and at low speeds they turn in the direction opposite to the front wheels for greater agility. Up speed, and they’ll turn in the same direction as the front wheels to aid high-speed manoeuvering. Only a few manufacturers have pursued all-wheel steer to the production stage because it’s hideously complex, adds weight and can feel strange to drivers, a reason why many R34 Skyline racecar drivers disabled the four-wheel steer.

Remember, the laws of physics apply to you the same as everyone else. Go slowly and safely around corners, especially on our a-surprise-a-minute roads.