Creative Car Control Handbook
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Managing Grip at the Limit of Adhesion
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Developing technique is an important part of driving. Practising what works best is more important than practising anything else. Many people are exactingly good at practising what to do when they make their most often fundamental error.
Whole driving philosophies have been bound up in techniques that don't work as well as others that don't look "good" or "right". This is often because some out dated philosophy was difficult to master and became a party trick of the instructor society in which it was prevalent. It still goes on in some circles of advanced driving and it makes no difference to the teaching that better, more useful techniques exist.
Find out what works best in the dangerous situations and practise practise practise.
Having good technique minimises mistakes. In competitive situations on track it is particularly important to minimise mistakes; people tend to pay for their errors more than once on track, their competitive side pops up and makes them try to compensate for the error. The thus pay twice; once for the original error, and once when they overdo the correction or next time they arrive at the same place they try to make up for the last time they made a pig's ear of it.
Having a reliable technique that is metronomic is crucial; people who do this let nothing affect their demeanour, they know what works best and they do it systematically time and time again. When something goes slightly wrong or they get bullied into a situation by another driver they just go back to their technique, metronomically doing what works best because it minimises the errors.
For tyres and suspension systems to work well they need to be treated properly - it's like any relationship. Dropping hints is crucial to smooth relationships. The better we get at hinting, the more subtle they become.
Braking is a classic example. We have learnt that braking on the straight and level with heavy braking in the early phase followed by reduced braking effort as the car slows is important, as is the gentle trailing off as the transient into steering takes place. But what else?
Hinting to the brakes sounds like nonsense. How do you do that? What does that do for you?
The braking system is a hydraulic network of pistons and pipes that starts at the driver's foot and ends up at the four extremities of the vehicle having negotiated multiple valves and other paraphernalia on the way. Optimum operation requires that braking surfaces come together evenly.
The brake rotors are mounted effectively on the wheels and the brake pads effectively on the suspension. The wheel bearings provide small amounts of clearance and this causes the pads to be "knocked back" from the braking surface of the rotor. When we stomp on the brake pedal, the hydraulic pressure in the system increases and the pads start to move into contact with the rotors in line with developing pressure in the brake lines. Shorter lines mean pressure develops at the nearest brakes earlier than those further away - even more so when sophisticated ABS and brake balance valve systems get in the route. Uneven braking results initially in and the balance of the car can be upset significantly as weight shifts around in response to brakes coming in at different times and intensities. This is often compounded as suspension elements settle into braking position and dampers operate.
The solution is to start the initial braking softly (the hinting phase). This brings brakes into play by evenly taking up the clearances and delays in the system and moving suspension elements across their working clearances as bushes move in response to initial light braking. Hard braking at maximum intensity followed by a reduction in pressure as the vehicle slows down and careful phasing out as steering is applied is the optimum braking technique. "Soft - Hard - reduce off softly".
As braking is reduced to a minimum the vehicle is "prepared" for cornering by "hinting" to the steering system, this is done by very slight movement of the steering in the desired direction on the approach to the corner. This is followed by and blended into the "steering proper" phase of the corner.
The hint has the effect of waking up the tyre from its relaxation period and needs to be completed earlier as speed increases because the tyre relaxation period is a constant quantity of time. The resultant vehicle response is sharpened dramatically (often at low speed to the point where oversteer is induced). Steering can continue to be applied into mild understeer which is a stable condition.
Careful attention to desired direction and monitoring of weight transfer leads to accurate judgement of throttle application and subsequent removal of steering. Appropriate throttle should be applied carefully and judiciously to optimise exit speed. Too early application of throttle lifts the weight off the front wheels providing instant loss of frontal grip in the corner. In practice this loss of grip cannot be regained in the same timescale by lifting off throttle and often results in lift off oversteer which requires steering dexterity and freedom from panic to be negotiated fluently.
Optimum performance on track demands smooth transitions. Gear changes are no exception and it may be necessary or desirable to change down under braking for a corner so that the optimum accelerative performance can be obtained on exit. This can be achieved easily by matching engine speed to road speed for the gear being selected.
In order for this to happen it is necessary to operate the brakes, throttle and clutch simultaneously. This is achieved by using the clutch and gearlever in the normal way and operating the brake and throttle simultaneously with the right foot.
The brake pedal is partially covered with the ball of the foot and effective braking is prioritised. At the same time the right foot leans over to the side and operated the throttle in a subtle and convenient way to increase the engine speed to that required for the smooth gear change which goes on in the background.
With practise these gear changes happen seamlessly and can add valuable engine braking to the high speed slowing down of the vehicle (when the brakes cannot lock the wheels any additional braking is valuable). When the transition from braking to steering to throttle application takes place the vehicle is in the right gear with the engine on song.
Sometimes it is desirable to change gear in the middle of a corner and in this instance the engine speed must accurately match the road speed for the gear selected. In mid corner near to the limit of adhesion the torque reversal due to errors in crude throttle operation and poor gear selection can have a catastrophic effect upon vehicle stability. It is imperative that gear changes under these conditions are made smoothly.