Driver Training Day

The Fundamentals for Driving Fast

Edited by Stuart IlesInformation taken from drivingfast.net

The racing line is the route a racing driver follows in order to take track corners in the fastest possible way. By using all of the available space on the track, cars can travel in a straighter line and travel faster before reaching the limits of grip. Determining the racing line is an essential skill to master for both track days and racing events.

The racing line depends on the braking point, turn in point, apex and the position and direction of the next corner.

NOTE: It is important to remember that there is rarely a perfect line through any corner for all circumstances. It depends on the characteristics of your car, your cornering strategy, and the conditions. You should experiment with different lines and learn from instructors and people who know the track well.

How good are your brakes? How quickly can you reduce your speed from 160km/h to

60km/h? How does your car behave when the front wheels are locked?

How brave are you feeling? All these factors determine your braking point. It's a sensible

strategy to brake earlier as you're learning the track and your car, and progressively shorten the braking area as your experience grows. The rule of thumb is to get most of the braking out of the way before turning into a corner, although a light brake pressure on entry can help to reduce understeer and can give a better turn in (this is known as trail braking).

Threshold braking is the technique you should aim for, but if the wheels do lock, quickly ease off and reapply the brakes with slightly less pressure until you get it right. Try not to turn in if any of the wheels have lost traction.

In some situations on the track, it may be possible to get a better time by leaving your braking to the very last minute, forcing you to maintain braking into the turn. If this is the case, ensure most of the braking effort has been carried out in a straight line, and progressively release the brakes as you approach the apex. The resulting forward weight transfer can reduce understeer and improve 'turn in', however, it can also make the car more prone to oversteer. This is an advanced technique and should only be used once you are very confident with your car, the track and the conditions.

To get the line right, it is vital to turn in at the correct point. Leave it too late and you'll miss the apex, too soon and you'll have to tighten your line mid corner. Get this right and you'll have set yourself up for a good line. Remember that the apex may be further round the turn than you can see, so make sure you learn the track and the apex points before driving in anger.

The apex is the point at which you are closest to the inside of the corner, also referred to as the clipping point. Once you have hit the apex you should be able to reduce the steering lock and increase the throttle. Determining the apex can be tricky but the guidelines below explain how to do it.

There are two different types of apex, the geometrical apex and the racing apex. The geometric apex of a constant radius corner is the central point on the inside and this may also be the racing apex, which depends on the context. Confusing!

This is where your strategy comes into it. There are several generic strategies for cornering including:

Carrying speed in the corner Minimising the severity of the turn Getting the power on early

To carry maximum speed through a corner, you need to take the route that minimises the tightness of the corner arc. This minimises cornering force and frees up precious grip for maintaining speed. This route tends to use the geometric apex of the corner and is usually know as the classic racing line. The turn illustrated is a constant radius 90 degree right hander and the geometric apex is exactly half way around the corner.

Pros of the classic / traditional racing line:

Smoothes out corners in the most efficient way

Maintains momentum (especially useful for low powered cars)

Maximises fuel economy

Reduces the chances of understeer or oversteer

Preserves the life of tyres

Cons:

Not necessarily going to yield the fastest possible lap

Oddly enough, carrying the highest average speed round corners may not actually be the quickest way around a track. If the corner leads onto a straight it can be better to take a late apex, straighten the car out early and get the power on for a high speed exit. This is generally regarded as the best strategy for racing, with a slightly lower entry speed but a faster exit speed. The amount of grip available is the factor which determines how late you can brake and apex.

Pros of the modern racing line:

Increases the chances of a fast lap in a powerful car

Allows the power to be applied earlier

Maximises the use of any straights following the corner

Allows late braking

Useful for overtaking on a corner

Cons:

May not be the fastest route in a low powered car

Places greater demand on the tyres

Common mistake:It's very common for drivers to apex too early due to nerves about the approaching corner and eagerness to take the turn. The racing line apex which is often out of view at the point of turn in, or further round the corner than you expect. This is where experience and track knowledge come in.

A hairpin is a corner which turns 180 degrees. In this case, the apex for the racing line is about three quarters of the way around the bend. A useful guide is that half way through the turn you should be roughly in the middle of the track.

The position and direction of the next corner also affects the choice of line. For example, if the next bend is a left hander you'll need to move over to the right hand side of the track, and thus will need to apex later and take a tighter, slower line. However, if the next corner is another right hander a wider, faster arc can be used

Why do weight transfers occur?

Weight transfers occur as a result of the chassis twisting around the car's roll centre, which determined by the natural suspension setup. When accelerating, braking or steering, the body of the car rotates in the opposite direction, which compresses the suspension on one side of the car, while releasing the weight on the other side.

Acceleration – rear weight transferWhen you accelerate, the weight of the car is thrown backwards. This causes the rear suspension to compress slightly and increases the available grip at the rear tyres.

Advantages of rear weight transfer1. Pulling away in a rear wheel drive carIf you're trying to get a good start, rear weight transfer will be to your advantage in a rear wheel drive car, as the resulting increase in rear grip will provide you with more traction and reduce any wheelspin. In a front wheel drive car, however, you're more likely to get wheelspin off the start, so an extra smooth throttle application is important. 2. Preventing oversteer in a front wheel drive carOversteer is caused by a lack of traction at the rear wheels, but if you accelerate in a front wheel drive car as oversteer is occurring, the resulting rear weight transfer can increase the available grip at the rear wheels and aid recovery. Note: Oversteer in a rear wheel drive car is rarely helped by acceleration, as this will increase the traction demands of the rear wheels, and leave less available grip to oppose the sideways motion.

Disadvantage of rear weight transferCan cause understeerUndersteer results from a lack of traction at the front wheels. If you're accelerating into a corner, the levels of grip at the front wheels will be reduced due to the rear weight transfer, and be more prone to continuing in a straight line despite your steering inputs.

Cars can brake much harder than they can accelerate. Weight transfers under braking are thus more likely to affect the balance of the car.

Advantage of forward weight transfer

Prevention of understeer

If you're hurtling towards a corner, turn the wheel and find yourself ploughing straight on, you've probably approached too quickly. But all might not be lost - easing off the throttle will result in a forwards weight transfer which will increase the available grip at the front wheels. Hopefully this should correct your course. If you're already off the gas, then a light dab on the brakes should help.

Disadvantage of forward weight transfer

Reduction of traction at the rear wheels

If you stamp rapidly on the brakes, you'll find that the rear wheels (in a car without any clever technology) will tend to lock up first. This is the reason almost all cars have smaller brakes at the rear. Despite this fact, the rear wheels are still the most likely to lock when using the brakes aggressively. Braking in a corner should be avoided for the same reason, as this can result in oversteer.

Transitions in weight transfer

To get the best times on the track you need to be either accelerating or braking hard on the straights - any coasting means you're not going as fast as you could. When transitioning between accelerator and brake you'll get exaggerated weight transfers which can further upset the balance of the car.

It's important to consider sideways weight transfers when cornering. If you turn into a corner progressively rather than 'chucking it in', this will transfer the weight to the outside wheels in a gradual manner. As the outside wheels provide most of the cornering effort, the resulting progressive increase in grip can help you take corners at a greater speed before traction is lost. However, if you throw the car into a corner, the sudden weight transfer can unsettle the vehicle and cause the wheels to break traction suddenly.

Take a front engine rear wheel drive car as an example and throw it into a corner hard while accelerating gently. The graphic below shows the levels of grip at each wheel. The size of the circle indicates the total level of grip at each wheel, the larger the circle the more grip is available. Green represents how much of the available grip is being used by cornering, orange by acceleration or braking.

The front wheels naturally tend to have more grip than the back due to the weight of the engine, however in the diagram above, much of this grip is currently being used to take the corner (but the driver still has a small reserve of grip which could be used if the corner tightened). If the level of lateral grip at the front wheels is exceeded, understeer would result. The rear wheels are accelerating gently, but require less grip to corner as this role is mostly performed by the front wheels. If the driver was to accelerate more aggressively the sum of the lateral and longitudinal tyre forces would exceed the level of grip available at the rear and oversteer would result.

When you reach the limits of grip on a corner, two scenarios can result known as understeer or oversteer.

Understeer occurs when traction is lost at the front wheels while cornering, forcing you wide on a bend despite applying the correct steering angle. When viewed by an observer, this action looks as if the driver has applied insufficient steering lock (or under steered). If you're car is understeering, you're scrubbing off speed and missing the optimum line, so it's not a quick way to take a bend.

Understeer is most likely to result from the following scenarios (which are more difficult to correct as you move down the list):Accelerating into a bendBraking into a cornerPloughing into a corner too fastLow traction conditions on the corner such as ice or oil

Passive factors involved Weight distribution Drive layout Suspension & chassis setup Tyre type, wear and pressures Active factors involved Cornering speed Throttle Braking Steering inputs Weight transfer Symptoms of understeer Light steering Drifting towards the outside of a bend Possible tyre noise from the front wheels

1. Accelerating through a bend

Picture the scene, you're in a front wheel drive car on a roundabout about to take the third exit but you think it might be alaugh to go round again. You keep accelerating through the bend and find that the car has a tendency to run wider and wider. The available grip at the front wheels is being used in equal amounts to accelerate and to steer. As you accelerate more, you have less grip to steer – simple. So, reducing either of these inputs will correct the understeer.

This is the easiest form of understeer to correct, and a slight, smooth reduction in power will free up more grip (with the added benefit of a forward weight transfer), and a small corrective input to the steering will get you back on line.

In a rear wheel drive car, in theory the front wheels will be able to resist understeer for longer due to the division of steering and drive between the front and back wheels. However, understeer can also be engineered into a car for safety, and most rear wheel drive cars will also understeer if power is progressively applied mid corner. If you do decide to accelerate aggressively mid corner you're likely to cause oversteer.

2. Braking into a corner

When you apply the brakes, most of the braking effort is exerted on the front wheels due to the forward weight transfer. So if you're braking into the corner you're already using most of your available grip trying to scrub off speed. If you then apply some steering lock, the addition of these lateral forces on the tyre can cause the limits of grip to be exceeded. So, correcting understeer seems simple - stop trying to turn the corner (a better plan might be to get your braking out of the way while you're in a straight line). However, if you happen to be in the middle of a bend as your car starts to understeer, continuing straight on might not seem like the best plan. An alternative strategy could be to reduce your braking effort, freeing up more grip for steering and hopefully allowing you to take the bend successfully.

3. Ploughing into a corner too fast

If you have attempted to take a corner too fast, have turned the steering wheel, and find yourself running wide, you my friend are in a spot of bother. But before you close your eyes and hope for the best, all may not be lost. You've exceeded all of the available grip, yes, but it may be possible to actually increase the level of grip by the slightest, smoothest dab on thebrakes. "The brakes?!", I hear you shout, "but surely that is adding to the demands of the tyres, not reducing them?". This is very true, but if you're not totally out of control by pressing the brakes you're causing the weight to transfer to the front, and thus artificially increasing the levels of adhesion at the wheels. This may, however, not work. The moral is to enter thecorner at a slower speed, then get on the power early on the way out.

4. Low traction conditions

If you've entered a corner at speed and notice a sudden reduction in traction due to oil, black ice or a banana skin, the best course of action (in the immortal words of Douglas Adams) is to consider how lucky you are that life has been kind to you so far.

If life hasn't been kind to you, consider how lucky you are that it won't be bothering you much longer.

Alternatively, be careful, think about the conditions and adjust your entry speed accordingly.

If you have a track car and find understeer a problem, you can complete some relatively easy modifications which can make the handling more neutral. These include:

Reducing the front tyre pressure Softening front springs or anti-roll bar Use softer front tyres Increase front down force (if aerodynamics fitted) Might be worth consulting an expert before doing

anything too dramatic

Oversteer, like understeer, results from the car reaching the limits of traction on a corner. In this case, the rear tyres reach the limit of adhesion before the front. This leads to “the back coming out”. The good thing about oversteer is that you normally go through the hedge backwards, thus preventing expensive repairs to the front of your vehicle! If you manage to performed sustained, controlled oversteer this is know as power oversteer.

The car has turned in normally and is aiming towards the apex The rear wheels have started to lose adhesion, the driver

compensates by steering left to keep steering aligned to the desired driving line.

The driver has maintained control of the car and continues to follow the desired line.

The car is at the limit of left hand lock, a spin is likely at this stage unless dramatic corrections are made.

Oversteer is more exciting than understeer and like most exciting things there is an element of risk involved. Most driver's cars have a tendency to oversteer when on the limit around corners, and this property can be found in a variety of vehicle layouts and drive formats.

Oversteer results from a number of factors, some of which involve the natural handling characteristics of the car, and some result from the way it's being driven.

Passive factors at work (the natural properties of the car): Weight distribution (front or rear bias) Engine and drive layout Suspension & chassis setup Tyre type, wear and pressures Active factors involved (the way it's being driven): Cornering speed Throttle Braking Steering inputs Weight transfer

There are four major active causes of oversteer, but what you're likely to encounter depends on the car being driven. Causes include:

Entering the corner too fast Accelerating into the corner, too early or too

aggressively Braking into the corner or mid corner Lifting off the throttle mid-corner.

Lift-off oversteer is a phenomenon which can occur when reducing the throttle mid corner. This will only happen when driving close to the limit so only experiment when on the track! Sporty front wheel drive cars can be especially prone to this due to the heavy front end and light rear. Reducing the throttle input results in a forward weight transfer, which increases the grip at the front tyres, but reduces levels at the rear. If this is performed during cornering, the combination of the heavy front end and the reduction of grip can cause the rear wheels to break traction and start to slide towards the outside of the corner.

In the image below the driver of a front engine car lifts off the throttle mid corner at A which results in lift-off oversteer at B due to a forwards weight transfer.

Luckily, lift off oversteer can usually be corrected by reapplying the throttle and accelerating. This should pull the front of the car forwards and straighten out the car, but continuing to reduce throttle application can cause the car to spin. Steering in the direction of the intended direction of travel will help keep the car on track.

1. Entering the corner too fast

Enter a corner too fast and you're asking for trouble. Unless of course you have a lovely long run off to play with or if you're driving Silverstone in a go-kart. It’s not the quickest way to take a corner and leads to increased risk of oversteer. If you have entered a corner too fast, ensure that every input you make is incredibly smooth, and take the easiest route. Next time make sure you're entry speed is slow enough to maintain grip, you can build up speed as you gain experience.

2. Accelerating into the corner, too early or too aggressively

If you manage to break traction at the back when applying throttle, you're probably in a powerful car and need to be less aggressive. If you're spinning wheels, the power is not transferring to the road and you're not benefiting from the many horses you have sitting under the bonnet. Gently ease off the gas and you should regain adhesion at the rear wheels.

3. Lifting off the throttle mid-corner

If you are on the power mid-corner and close to the limit, do not lift off the throttle. The resulting forward weight transfer can upset the balance of the car and allow the rear wheels to break loose. In a front wheel drive car, re-applying the throttle can often help in this situation.

4. Braking into the corner or mid corner

You should avoid braking in corners in most situations, however there are circumstances which require the use of the anchors. Ensure braking inputs are especially smooth, gentle and progressive, and if a squirrel has just run out in front of you, try steering around rather then doing an emergency stop. To correct brake-induced oversteer, smoothly (but rapidly) release the brake and adhesion should be reintroduced.

Whatever the cause of oversteer it is important to keep the front wheels pointing in the direction you're hoping to go. If you fail to do this, the most likely result is a spin. This technique is known as counter-steering or applying opposite lock. You should apply enough steering lock to point the wheels in the direction of the slide as shown below. Too little and you're likely to spin as the back continues to come round, too much and the car will rapidly over-correct, often resulting in a spin in the opposite direction. The skill can only be mastered with plenty of practice and should become instinct if you're planning to drive fast on a track.