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by Dhruv Behl
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Welcome to the third edition in our series of driving tips. I hope you found last months cues as easy to use as the first.
This time, we look at how the weight of your car shifts when you drive and how this affects driving dynamics. We also explain understeer and oversteer, and how best to counter both.
Weight transfer
It's safe to say that a car would handle at its best, whether in braking, accelerating or cornering when weight is evenly distributed over all four corners of the car. Such solid-state behavior can be achieved only by exceptional computer wizardry that doesn't exist on today's cars.
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In the mid 90s, this was a reality in Formula 1 and was referred to as Active Suspension. This was subsequently banned or else would have, in all probability, made it onto high-end road cars of today.
With conventional suspension systems, when you brake, weight is transferred to your front wheels, when you accelerate, weight is transferred to the rear. This is important because weight on the front wheels helps you turn in as you brake and head into a corner.
This relationship can be applied to everyday driving in Indian conditions. Ask yourself what happens when you come up, unsighted, to a pothole in the road ahead - you brake all the way to, as well as through, the incongruous pothole. In terms of technique, this is head and shoulders above the alternative of not slowing down at all, although it may not be the most effective way of handling the pothole in question. As I just mentioned, when you brake, weight moves forward (not an entirely complex relationship).
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The images above demonstrate a simple relationship, which is, the weight of a car shifts backwards, on the rear wheels, when you accelerate (top). And conversely, moves forwards onto the front wheels (below) when you brake |
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Therefore, what happens when you have the majority of your cars weight over the front wheels as you go through a pothole? In short, it makes for a harder impact. If you release the brake pedal right before you go through this unavoidable obstruction, it'll do just enough to rock the weight backwards and make the whole encounter a little less bone jarring - this simple and unobtrusive technique can also be applied to the numerous speed breakers you encounter on a daily basis.
Before we go any further, there's a need to expand on the basic handling traits of front and rear drive cars. In cars that apply both power and steering through the front wheels, it's safe to assume that this set of wheels are more stressed than the rear, and as a result, tend to loose grip before the rear. Consequently, when a front drive car exceeds its limits of adhesion, it tends to push or understeer, which is to say it diverts from its intended course and goes straight on instead. Another disadvantage of a front drive car is that both engine and drivetrain are located in the front of the vehicle and add to the weight over the front wheels - causing them to be under additional strain and therefore recede grip sooner. This begs the questions, why are 99% of the cars on our roads of this configuration? Truth be told, the accountants beat the engineers on this occasion.
Despite these intrinsic flaws, there is one very tangible advantage of a car that has understeer as an inherent handling characteristic. In order to get the car back in line, all the driver has to do in most cases is take his or her foot off the accelerator pedal. Needless to say, this is an automatic reaction and doesn't take much practice - it slows the car and transfers weight forwards onto the front wheels, helping them regain grip and return the car on its intended course. On the other hand, in a rear drive car that looses its grasp on the tarmac, this reaction doesn't always yield the desired result.
In a rear drive car, if you accelerate too much coming out of a corner and overwhelm the grip levels of the wheels applying power to the ground, the rear end will start sliding. As an automatic reaction, if you simply lift your foot off the accelerator pedal, this will in all probability make the situation worse as weight is transferred away from the rear to the front of the vehicle - making it harder for the rear wheels to reclaim any form of equilibrium with the road surface. The right way to correct an oversteering car is to release power slowly while applying counter steer or opposite lock - this is referred to steering into the skid because you're steering in the same direction as which the rear end is sliding. Imagine that you're taking a right turn and the car begins to oversteer, which means the rear will slide to the left in an effort to swap ends with the front. In order to get the car pointing straight, the driver needs to steer in the opposite direction (the left) until the rear is in line once again. At this point, its crucial to straighten the steering wheel at exactly the right time in order to avoid the car sliding the other way by which time it becomes progressively harder to correct the situation.
Needless to say, an oversteer slide is harder to correct and requires a certain level of skill and practice to perfect. And since many of the well-heeled buyers that drive high performance cars without really knowing how to handle them, car manufacturers now try and make their cars idiot proof by adding invasive traction control systems and high levels of default understeer. Take the Porsche Boxter as a case in point it's not only one of the best handling cars in the world but also one of the easiest cars to drive fast. Although once its high levels of grip are breached, the car attempts to understeer off the road as if being dragged by an econobox. This is largely inexcusable with a mid engined, rear drive configuration, which is the ideal set up for a high performance road car - as evidenced by most super cars and single seater racing cars.
A few closing tips, try and look at where you want the car to go and not what you want to avoid. If you focus only on the obstacle in your way, you're likely to end up becoming a part of it. Also, always use all your mirrors and maintain a peripheral vision. Be aware of your surroundings and try and anticipate, not only how the car will react, but also how other drivers will as well. In closing, drive safe and keep learning - let's hope, if only by an act of god, traffic conditions follow a somewhat similar pace of progress as the cars on our roads.
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