Drivechain 

Clutches

 A clutch is a device for transmitting rotational forces, with the ability to engaged and disengaged, creating the functionality to be able to modulate power input. Normaly the clutch is connected via two rotating shafts. One normaly the input shaft from the engine flywheel and the other the output driveshaft normally connected to a differential.

 The actual "clutch" is made up of three main components. The clutch disc which is the part that is spinning around inside the gearbox/transmission and it transfers engine power to the flywheel and the rest of the drivechain.The disc fits in between the flywheel on the back of the engine and the pressure plate. The release bearing is what moves the disc on and off the pressure plate as you operate the clutch pedal inside the vehicle with your foot. It is advisable to replace all 3 components when replacing the "clutch" assembly.

 The most basic explanation of a clutch would be of a hand held drill. One shaft is driven by the motor, and the other drives a drill chuck. The clutch connects the two shafts so that they can either be locked together and spin at the same speed (engaged), or be decoupled and spin at different speeds (disengaged).

Modifications of the clutch are needed in mild to high performance engine increases over standard equipment. This is required to help make use of the power hikes and improve drivability. Otherwise all that extra power will be lost in the drivechain and never get to the driven wheels. There is no point in having a high performance engine, without the ability to get that power onto the road.

Gearbox / Transmission

A good example of this is trying to pull away from a standstill in 5th gear, in a low powered vehicle.The engine will most likely try to stall and the throttle will be unresponsive. Due to the fact that both in everyday driving and on the racetrack we will come across a combination of both slow and fast corners. It becomes necessary to have a system to keep the engine in the optimum rev range.

A gear box is required to keep the Engine in this powerband at different given speed. Maximising the engines RPM and engine power to keep acceleration at it's optimum and having enough available Torque to propel the vehicle forward.

The Engine needs be operating in the optimum RPM (Revolutions Per Minute) range to get the best horsepower also. Different engines develop maximum Power at different Revs, depending on the overall goal and use of the engine. 

Outside the powerband and the engine falls out of the desired rev range of a selected gear, then acceleration, power and torque are effected. Acceleration is sluggish until the revs build again.

A Honda Civic for example needs to be kept high up in the Rev range and doesn't have the low down grunt of a Diesel engine for instants. Horses for Courses as the old saying goes.

In normal everyday driving shifting gear is a simple and normally effortless experience. Clutch in, move gear selector knob and release the clutch peddle.In basic terms the engine spins the flywheel, clutch assembly and with the clutch peddle released (off the clutch peddle) the engine is connected Directly to the input of the gearbox/transmission.

When you change gear and disengage the clutch (foot on the peddle) depending on the selected gear, a synchromesh will match the input and output shafts via the gear ratio selected and a new final drive will be achieved (well if you have a modern car). The clutch peddle is released (foot off the peddle) and the flywheel clutch assembly and clutch gearbox/transmission assembly are Directly engaged again and the process is complete.

 When the gearbox or transmission is engaged, a pair of gears are working Directly together. Both on the input shafts and also the output shafts. Broadly speaking in most gears other than top Gear, a different RPM of the input shaft and output shaft is achieved. The lower the gear the faster the input shaft is relative to the output shaft. In top gear it is normally a 1:1 ratio to maximize top speed and economy.

The output shaft will then transmit the power to the differential which connects these rotations to the driven wheels. Diff ratios are normally 3:1 or 5:1, so there are 3 or 5 revolutions to 1 wheel rotation. 

Most Racing Gearboxes/ Transmission have the ability to change the Ratios and adjust the desired acceleration versus overal top speed.

 Differential 

This is essentially a device normally consisting of three shafts, one being driven by the Engine. The others run off this shaft ( driveshaft/ propshaft) and their job is to spit the Torque equally while allowing each wheel to rotate at different speeds. Designed to help maximise cornering efficiency, due to the nature of the inside wheel having to travel less of a distance then the outside wheel on a corner. With out one, the inside wheel will spin and the outside wheel will be dragged along. This set up produces unpredictable handling characteristics with more strain on tyres/ tires and the drivechain which could result in failure.

The differential in a normal Road car (Open) is designed to allow each side of the car's wheels to rotate at different driven speeds while having the same torque transmitted to each of them. Since the inside tyre/tire rotates faster on a corner then the outside. If the wheels did not have a Open differential and was Locked then the inside wheel would spin and reduce overall grip and traction as describe above.

There are also Limited-slip diffs which locks at a present point to limit the difference in the rotational speed.This is in a bid to maximise traction and grip for acceleration and deceleration, or even cornering forces. But have a look at Drivechain Upgrades to view a full list of the different Differentials available and their advantages and disadvantages.

The settings can be adjusted on some designs to achieve different handling characteristics (this is sometimes electronic). Reducing the acceleration setting on a FF and AWD car can reduce understeer at the front of the vechicle. While an increase on the rear, will result in more oversteer for AWD and FR cars. 

High powered performance cars may have to have a certain amout of acceleration lock in place to maximise grip, but sometimes at the cost of handling. In all cases small increments are needed rather then large adjustments.

Drivechain Layouts

 Over the Year cars have tranformed the way we live and travel, along with these changing times the car has had rapid evolutions as well. This includes the way the power is transferred to the driven wheels. Different applications yield different results and below is a list of the Advantages and Disadvantages associated with them.

Front wheel Drive 

Front-wheel drive or FF as it is commonly known, is a form of engine/ transmission layout used in most modern cars. It saves space and can maximise cabin space. The engine drives the front wheels and the rear wheels just roll along and aid in some braking.Most front wheel drive vehicles have a transverse engine as apposed to the the conventional longitudinal engine arrangement generally found in rear wheel drive and four wheel drive cars. Due to all the weight being over the front of the car, FF cars are generally labled with the oversteer Handling characteristics 

Release of the throttle while the car is Understeering, can help to cure this and it also makes this a stable platform for everyday driving. Lift off oversteer can be produce by rapidly releasing and reapplying the throttle , which can aid the corning process and produce Oversteer to aid turn in response. Also due to the less machanical part used in construction, the overall weight and cost of the vechical is kept to a minimum. So is a favoured design for Hot Hatches and Small Hatch Backs.

When engine upgrades or engineers started to increase the performance of this type of car, the layout tended to produce Torque steer.This makes the car pull to the left or the right under heavy acceleration, which isn't an ideal situation when exiting a corner. By fitting Limited slip diffs and other suspension Upgrades, it is possible to help reduce these undesired tendencies.

The FF car due to it's compact engine compartment and complex design, can have issues with a restricted turning circle and increased wear of CV joints. Also unlike the benefits of RWD cars under acceleration with weight transfer, the FF car can have problems getting maximum traction. This is due to the weight shifting to the rear of the car taking away some of the traction from the driven wheels.

Also in icy or slippery driving conditions, FF cars can again have issues getting the power down on a slope. But are generally considered more stable then FR cars, due to the increased weight on the front tyres/tires aiding in corning and the stable and predictable handling characteristics.

Typically smaller light weight engines are used, in FF cars partly due to the better space savings and also too much weight at the front produces bad handling.

Rear wheel Drive 

Rear-wheel drive (RWD) cars, typically places the engine in the front of the vehicle and the driven wheels at the rear via a Drive Shaft. This configuration is also known as  Front-engined, Rear-wheel drive (FR). The Rear mid-engined and Rear engined layouts are also used, but more on that later. 

Through out history the RWD or FR layout was the traditional automobile Design for most of the 20th century. Rear-wheeled drive is a good balance in terms of a performance package, as a 50:50 weight ration is achievable. The front end deal with most of the braking ( aided by weight transfer) and the steering, while the back is predominantly getting the Power down.

So a great package is achieved and a good handling car where the front deals with steering and the back looks after the power delivery. In the dry this layout can yield greater performance then FF cars due to the more equal share of the loads on wheels in terms of Braking and Acceleration.Typically you would see inline straight 6, V6, V8, V10 and V12 engines due to the increased room in the engine compartment and maximisation of the extra power.

Advantages under aceleration are gained due to the weight transfers of a car under power, causing the rear tyres/tires to have more traction due to the weight pushing down on the Tyre/ Tire. Also these cars tend to have larger turning circles due to the fact that they have less complicated driveshafts then a FF car. This type of layout is favoured in drift racing, as this is a more balanced layout and it has good oversteer handling capacities. Controllable Powerslides are achieved with gentle feathering of the throttle on the limit of traction  (and maybe a little bit of opposite lock).

Also the layout is normally cheaper for maintenance, or easier to gain access to components then FF cars which have everthing crammed in. Due to geometry and packaging constraints, the universal joints attached to the wheel hub have less of a tendency to wear out quicker than the CV joints found in FF cars. 

The significantly shorter drive axles on a FF drive car causes the joint to flex through a much wider degree of motion. Compounded by additional stress and angles of steering, while the CV joints of a rear wheel drive car regularly see angles and wear of less than half that of front wheel drive vehicles.

But the RR car is not with out it's flaws, firstly weight for weight this layout is normally heavier then it's FF counterparts. Due to the addition of the drive shafts feeding the rear wheels. Also the internal cabin space is normally reduced due to the transmission tunnel running through the middle of the cabin.

 Four wheel Drive 

In terms of performance, traction and sometimes handling; the AWD or 4 wheel drive car has the best of both worlds compared to FF and FR layouts. Traction is nearly doubled compared to 2 wheel drive variants and this is even more evident in slippery or low grip driving conditions such as Ice or loose gravel. hence the reasons for Modern Rally cars adopting this design layout.

The AWD system was finally perfected for rallying with the Audi quatro, as before then military vehicals had poor cornering capacity due to the front and rear wheels been locked by the Differential during cornering. Audi developed the differential to let the front and rears operate at different speeds, finally solving the handling issues normally associated with the design.

The AWD layout can be set up to emulate FF or FR layouts with both under and oversteer characteritics. However at the limit of grip, a well balanced 4WD configuration will resist extremes of either understeer or oversteer. But it may take a more aggressive driving style to achieve a four wheel drift and get the back end out. Central diffs can be Upgraded to send more Torque to the Rear wheels to have more Oversteer friendly handling characteristics, but it depends on the Engine location also.

It is possible to make all 4 wheels drift, with modern electronic driving aids.This flexibility allows production car engineers the freedom in selecting handling characteristics that will allow a 4WD car to be driven more safely at higher speeds by inexperienced motorists than 2 Wheel Drive designs.

Due to the complex transmission layout and components, normally AWD cars will result in a higher maintenance and initial costs. Also due to the extra complexity, there are larger drivchain losses; so these cars can be less ecomonical then FF or FR cars. Also weight for weight, heavier to to the more componets present.

Power normally comes in the form of a Turbo charged 2.0 litres inlines Engine, even though the original Audi was a 5 cylinder inline Engine. In a Front engine car, this reduces the weight at the front and increases handling.

But there seems to be a trend of Supercars now adopting AWD with a Mid Engine layout, creating the ultimate layout in this class.

 Mid Engined, Rear wheel Drive. 

The mid-engine layout is typically chosen for its favorable weight distribution, and is consider the ultimate layout for Racing cars. As the heaviest component (the engine) is nearer to the center of the vehicle, reducing the vehicle's moment of inertia and making it easier and faster to turn the vehicle to a new direction.

Also the engine weight is more evenly carried by all the wheels with this layout resulting in a more balanced handling chassis. Vehicle stability, traction, and ride quality are naturally improved when turning, braking, and accelerating.

Mounting the engine in the middle of the chassis instead of the front of the vehicle, puts more weight over the rear tyres/tires. This results in more traction and provides increased grip to the front tyres/tires in braking. 

Also with less chance of rear wheel lockup and reduced chance of a skid or spin due to the weight loads. The added weight on the rear tyres/tires can also improve acceleration on slippery surfaces. Providing much of the benefit of a AWD car without all the added weight and expense of the components. The mid-engine layout makes ABS brakes and traction control systems work more efficeintly, due to the weight loads over the Rear Tyre/ Tires.