Transmission

Gearing and traction are necessary to turn power into speed. The part of the drivetrain have a massive impact on driving performance.

An engine revolves at anywhere between several hundres and several thousand times a minute. This would be too fast to turn the wheel directly, so an intermediate mechanism is needed. This is where the transmission comes in. the transmission uses different gears to transmit the appropriate amounts of power and speed to the wheels for any given situation.

Lets look at how gears work. If a small gear is driving a larger gear, the larger gear will rotate slowly, but it’s torque will be increased. Conversely, if a large gear is driving a smaller gear, the smaller gear will turn faster, but with less torque.

The transmission can make use of these principles to fit the appropriate gear to the appropriate situation. A car need most power when accelerating from a standstill, and conversely, only need a small amount of power to maintain a steady speed. Thus, when accelerating from zero, a large gear (with slow rotation but high power) is used to transmit enough power to set the car in motion.

A large gear will create a lot of torque, but will rotate slowly. This means that in first gear, even revving to the limit will only produce speed of several tens of kilometers per hour. This is why several gear are used, gradually getting smaller as the driver shift up, and producing more speed and less torque. The ability to move freely between these gears allows the driver the use the right gear for the right situation.

automatic transmission

On an actual car, in addition to the gears of the transmission which are connected directly to the engine, the overall gear ratio is determined by combining with another “final gear” that is between the transmission and the drive wheels. The gear ratio can greatly affect the driving characteristics of a car, and especially in circuit racing, the selection of the proper gears suited for the course will be a major key in improving your lap time.

Valve Configuration

In a four stroke engine there are two types of valves : the intake valves that open during the intake stroke, allowing the air-fuel mix into the engine, and the exhaust valves that open during the exhaust stroke, releasing the waste gases. The valves are located in the cylinder head, and play an important role in connecting and blocking off the combustion chamber.
 

Modern engines typically have camshaft at the top of the engine, which allow more reliable valve movement. Most modern engines have 4 valves per cylinder with 2 intake valves and 2 exhaust valves, but engines that focus on combustion efficiency at the low RPM range with 2 valves per cylinder, consisting of 1 intake valve and 1 exhaust valve, will probably be making a comeback in the future.

The latest trend is towards variable valve timing. Initially, this allowed valves two timing – one for low revs, and one for high revs – but more recent development allow valve timing and lifted to be varied continuously to match the engines’s revs. In the latest valve mechanism of the “valvetronic” BMW engine, power adjustment is accomplished without using the throttle valve, achieving greater efficiency.

Types of Valve Configuration

DOHC (Double Overhead Camshaft)

In a DOHC engine, one camshaft operates the intake valves and one camshaft operates the exhaust valves. Other than ensuring stable operation by sharing the work over two camshafts, it also means that there is less reciprocating mass (inertia) in the valvetrain, and this make it possible to achieve higher RPMs with the engine. This is turn allows better power output, which is why this layout has adopted in most of today’s high-performance engines.

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    SOHC (Single Overhead Camshaft)

A single overhead camshaft is engine with a single camshaft operating the intake and exhaust valves. Depending of the type of combustion chamber, the camshaft can either directly operate the valves, or it can operate the valves through rocker arms. Compared to an OHV engine, valve movements are more reliable, and higher revs are possible. Compared to a DOHC engine, valve movement are not as smooth, but high rpm SOHC engines exist, so they are not also inferior.

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         OHV (Overhead Valve)

An overhead valve is, as its name suggest a system where the valves are mounted on the cylinder head. Unlike an SOHC or DOHC setup, the camshaft is located to the side of the cylinders and the camshaft operates the valves with long arms called “pushrods”. This structure is simple, and it is easily maintained. However, valves operations of this types of engines are not as reliable at high RPM, and is not generally suited for high power.

Dimensions

A Car’s Performance is Dependent on Its Dimensions and Weight

A vehicle’s frame and the basic layout of its operating parts are the most basic specifications, and are decided during the initial stages of development, making them the hardest to change later on. These specifications have a crucial effect on the three main functions of driving, turning, and braking. Any deficiencies are difficult to compensate for with tuning, and just a slight difference can have a huge effect on performance. Furthermore the effect gained from tuning are also greatly affected by the car’s base potential. To get the most out of your car, you should be familiar with how these basic specifications affect driving performance.

Wheelbase

The wheelbase is the distance from the center of the front wheels to the center of the back wheels when viewing the car from the side. This length has a large impact on the stability of the car. The longer the wheelbase, the less affected the vehicle will be by undulation of the road surface and crosswinds, and it will tend to be more stable in a straight line. On the other hand, although a shorter wheelbase reduce stability, steering responsiveness is improved, and the car will be agile around corners. In terms of comfort, a longer wheelbase is generally considered better

Overhang

The front overhang is the length of the car that extends beyond center of the front wheels to the foremost end of the front bumper. Rear overhang is the length of the car that extends beyond the center of the rear wheels to the end of the rear bumper. If the parts of the car in this overhang are heavy, the yaw moment of inertia (resistant to turning) increases, and maneuverability is reduced. Because of this, components of a car with significant weight should be placed within the wheelbase whenever possible. This is especially true for heavy components such as the engine. However, an overhang of some length is important for aerodynamic purpose, so it cannot be avoided altogether.

Track Width

Track width refers to the distance between the left and right wheels of a car. Increasing track width will lower a vehicle’s center of gravity. Generally speaking, increasing track width improves traction when cornering, and increasing the track width of the drive wheels will increase contact with road surface, and thereby improves the vehicle’s ability to transfer its power to the road surface. A smaller track width, on the other hand, will offer quicker handling, but will reduce stability. It’s common for racing cars to have different track widths for the front and rear wheels to improve handling.

Height

Height is measured from the road surface to the highest point of a vehicle. Lower heights means a lower center of gravity, reducing roll when cornering, and increasing turning speed. However, lower height also means less room for passengers and shortened suspension stroke (the amount of room that suspension springs have in which to expand and contract), and increases the risk of bottoming out of the suspension.

Weight

Weight is a crucial factor in determining vehicle performance. The lighter the car, the less demand on the engine, and the more power can be used for the movement. Other benefit include reduces brake wear and more efficient cornering. The weight of a car divided by its maximum power output is known as the power-to-weight ratio. The smaller this ratio, the faster acceleration will be, and the sportier the ride. This also has a major effect to fuel economy, and reducing the weight of a car is now an important factor in designing new cars in term of environmental impact and performance.