ASR See traction control
Brake Assist
When the driver puts the brakes on full in an emergency, there is a tendency to reduce the pressure after a few seconds. Brake assist keeps the pressure at a maximum so long as the driver has hid foot on the brake.
Carbon ceramic brake discs
Conventional cast iron brake discs get very hot when used repeatedly, which can lead to brake fade. To overcome this, special brake pads are used, but these require a lot of pedal pressure in normal use.
The carbon ceramic brake discs are made from a ceramic material combined with carbon fibres. The result is a very hard material which can withstand very high temperatures. When used for brake discs, this material provides a very powerful braking whether the brakes are hot or cold.
Cd Drag coefficient
This is a measure of the resistance of the car from the air it moves through. 0.30 is the benchmark for supercars, with a few managing 0.28-0.29. Many are in the 0.32-0.35 range. Anything higher isn’t really good enough. Some caution is needed because all wind tunnel don’t give exactly the same results for a particular shape.
DSC Dynamic Stability Control: see Stability control
ESP Electronic Stability Program: see Stability control
Electro-hydraulic braking
Normally, the braking system is all hydraulic, but with some servo assistance – the vacuum in the intake manifold is used to increase the force you apply to the pedal.
With an electro-hydraulic system, when the pedal is pressed, sensors see how hard you are pressing and how fast. These are converted to electric signals sent to the computer, which takes into account the speed of the car, whether you are turning, and the surface. It then sends signals to a hydraulic pup/accumulator which pressurised the brakes.
The electro-hydraulic system can act very quickly, and can apply the best pressure to each wheel taking into account the loads, etc. It can also maintain a high pressure on the brakes if it detects an emergency and the driver relaxes pressure a little. The system is compact but expensive.
Oversteer
Oversteer is when the rear tires are sliding out more than the front tires. When you start cornering at speed, the tires do not follow the line of the wheel exactly, but run out a little – by a few degrees normally.
When you corner fast at a slow corner in a rear-engine or mid-engine car, or rear-engined car, or most rear-drive cars, the car is likely to oversteer. What happens is that you will feel the back of the car wanting to move out, and then the tires will start to slide. You correct the slide by using opposite lock – turning the wheel in the opposite direction to the corner.
If you misjudge a corner completely in a rear-engine or mid-engine car, the oversteer can come in so quickly that you can spin the car.
Sometimes, you need to induce a little oversteer to cut excessive understeer on a corner.
You can also induce oversteer on a front-wheel drive car by going into a corner quite fast and then lifting off sharply. This is a good safety valve with these cars. The opposite of oversteer is understeer .
Paddle gear control
Sequential gearboxes are usually controlled by a pair of paddles or wide levers mounted in front of the steering wheel. To shift up the driver pulls one paddle toward him, and to shift down, he pulls the other paddle. Usually, if you pull both together, the gearbox is put into neutral.
This is the best form of control because you do not need to move your hands from the wheel, giving greater control. Also, shifts can be very fast indeed. (See also sequential gearbox)
Rack and pinion steering
Rack and pinion steering is the best form of steering gear, as it is the most direct, has least lost motion or 'play' and gives good feedback. It consists of a rack with gear teeth cut into it, which goes across the car. A pinion shaft, connected the the steering column drives the rack to left or right. Jointed track rods connect the rack to the steering arms attached to the hubs.
Roll axis
The axis about which the car rolls when it goes round a corner. When a car corners, the centrifugal force makes it lean outward. It actually rolls about an axis which is usually not quite horizintal between points at the center of the front and rear suspension. The postion of the roll axis is dictatred by the type of suspension. Also, as the car rolls, and goes up and down over bumps, the roll axis can move. (See roll centers)
Roll centers
The roll center is the point about which the car rolls at the front or rear suspension. When the two points are joined together, they make the roll axis.
With a rigid beam axle – at the back of older cars and even the new Ford Mustang – the roll center is high, usually at about the height of the axle. Because the roll center is high the car tends not to roll much.
With parallel trailing links, which are used at the back of many front-wheel drive cars, the roll center is on the ground. With wishbone suspensions, the roll centre is usually 3-6 inches above the ground. Swing axles have a roll center abover the center of the wheel, and although roll is limited they tend to ‘jack up’ – the wheels dig in, and the body lifts up, sometimes resulting in the car overturning.
Stability control
A system that comes to your aid if you try to corner too fast. It uses the equipment and electronics of the ABS with some other sensors which detect steering wheel angle and speed, lateral acceleration and yaw angle – yaw angle is the amount the car is tending to turn about itself – when it is out of control it is yawing and spinning like a top.
W
hen the car starts to get out of control, the stability system applies the brake to one or two wheels – usually one, exerting a turning force opposing the direction in which the car is tending to yaw.
To oppose understeer, the inside rear brake is applied. To oppose oversteer, the outside front brake is applied.
If the situation is serious, the engine torque may also be reduced.
Stability systems tend to mask the handling characteristics of the car, and can behave inconsistently. In most cases, they do allow you to corner faster, but you re less aware of what the car is actually doing.
Sequential gearbox
A gearbox without a ‘gate’ for changing gear. You push a lever in one direction to shift up, and in the opposite direction to shift down. Most sequential boxes are operated by two paddles on the steering wheel – one for up and the other for down. Usually, they re based on a manual gearbox, but the clutch and actual shifting are automated. Many options can be included, such as full automatic operation, a high-speed start, automatic upshifting when peak revs are reached (not a good idea), blipping the throttle when a downshift is made. They shift gears very quickly.
Supercharger
A supercharger is an engine driven compressor or blower which increases the amount of air that can be fed into the engine. Some take the form of screw compressors, and others are nor like fans. In either case, the supercharger increases the pressure of the air fed to the engine, so more fuel can be burned giving more power.
Superchargers deliver extra power at all speeds, the increase in power going up in proportion to engine speed. By contrast, a turbocharger delivers more power over a narrower speed range. Superchargers do not suffer from lag like turbochargers either.
Traction control
Using the ABS system, a traction control senses when a wheel is spinning owing to a slippery surface or too much power being applied, and pulses the brake of the spinning wheel to stop it spinning. If the situation is serious, the engine torque may also be reduced.
Transaxle
A unit consisting of a gearbox and final-drive gears and differential used in front-drive cars and also in mid-engined cars. In mid-engine cars, the engine is usually ore-and-aft, with the differential between the engine and gearbox. In some cases, as on the Pagani Zonda R, the gears are installed transversely in the box so the weight is closer to the axle than with the normal fore-and-aft layout.
Turbocharger
A turbocharger is driven by the exhaust gases. It consists of a turbine wheel and a compressor wheel on a common shaft but in separate parts of a housing. The exhaust gases drive the turbine wheel, which must be made of heat-resistant material, so the compressor compresses the air entering the engine.
The advantage of the turbocharger is that it uses waste energy in the exhaust to drive the compressor. A supercharger absorbs power. The disadvantage of the turbocharger is that the blades operate efficiently over a narrow speed range. This can be overcome to some extent by using a blow-off valve – called a wastegate – so that the turbocharger remains in the efficient range most of the time.
The other disadvantage is that there is some lag when you press the accelerator after slowing down, or just running at a slow speed.
Understeer
Understeer is when the car runs wide on a corner. What happens is that the front tires are gripping less than the rear tires. In fact, once you start cornering at speed, the tires do not follow the line of the wheel exactly, but run out a little – by a few degrees normally.
When a car understeers, you need to turn the steering wheel further to get round the corner, and you feel a lightness at the wheel. If you go much too fast into a car with a front-wheel drive car, the car can understeer so much that it goes almost straight on,hardly turning at all. This can be very dangerous, because hardly any speed is scrubbed off, so you can go straight off the road at high speed.
Understeer is good when you are driving round fast curves well within the limit, but is a nuisance on slow corners because it slows you down a lot. It can also slow the car down at medium speed corners, and in this situation, racing drivers tweak the steering to cut the understeer, and induce a touch of oversteer.
The opposite of understeer is oversteer.
VSC Vehicle stability control: see Stability control
Yaw Angle
The amount the car is tending to turn about its central vertical axis – when it is rally yawing it is spinning like a top.
Twin OHC (or DOHC)
Twin overhead camshafts, which means that there is one camshaft for the inlet valves and another for the exhaust valves. There may be short rockers between the cam and valve, or the cam may act on a tappet sitting on top of the valve. This the system with the minimum mass of valve gear to be operated, so it is needed for high-speed engines.
Single OHC
A single overhead camshaft operates both inlet and exhaust valves through rockers.
Variable valve timing
Traditionally, the valve opening period and lift were fixed all the time. Racing engines had very long opening periods and high lift, but did not run properly at low speed. It was found that by placing a device – something like a helix – between the sprocket and camshaft, the valve opening point could be altered – this is a simple form of variable valve timing.
When the engine is operating at high speed, the timing is arranged so that both valves are open at the same time for some of the time – this gets maximum air into the cylinder. At low speed, the opening is advanced so the valves are not open together. The early part of the opening is not usable, but this improves low-speed driveability.
A better system was pioneered by Honda with VTEC, with similar systems being used now by Toyota and Porsche. It has one cam for low speeds, and another for high speeds, with a switch over at 4,000 to 7,000 rpm, depending on the engine.
One system has a rocker for each cam, and at low speed one cam is not operated, but is free to float. At the change over speed, a pin is pushed into the side of the rocker, locking it to the other one, so it now operates the rockers. The low-speed cam still operates, but because it has less lift than the high-speed cam, it does not touch the rocker.
This system gives excellent low-speed torque and high power at high speeds.
