In some of the latest cars out there, you can shift gears by simply pressing a button, turning a knob or toggling a little joystick. Yet simultaneously, plenty of different automobiles still require drivers to use one foot for the clutch pedal and another for the gas, all while using one hand to manipulate the gear-shift lever through a distinct pattern of positions. And many other current vehicles don’t have any traditional gears at all in their transmissions.
But Variable Speed Transmission whether or not a vehicle includes a fancy automatic, an old-college manual or a modern-day continually variable tranny (CVT), each unit has to do the same job: help transmit the engine’s output to the generating wheels. It’s a complicated task that we’ll make an effort to make a little 
simpler today, starting with the fundamentals about why a tranny is needed in the first place.
Let’s actually start with the normal internal combustion engine. As the fuel-air mixture ignites in the cylinders, the pistons start upgrading and down, and that motion is used to spin the car’s crankshaft. When the driver presses on the gas pedal, there’s more fuel to burn off in the cylinders and the complete process moves quicker and faster.
What the transmission does is change the ratio between how fast the engine is spinning and how fast the driving wheels are moving. A lesser gear means optimum overall performance with the wheels moving slower than the engine, while with an increased gear, optimum performance comes with the wheels moving faster.
With a manual transmission, gear shifting is handled by the driver via a gear selector. Many of today’s vehicles have got five or six forwards gears, but you’ll discover older models with from three to six ahead gears offered.
A clutch can be used to transmit torque from a car’s engine to its manual tranny. The many gears in a manual tranny allow the car to travel at different speeds. Bigger gears offer plenty of torque but lower speeds, while smaller sized gears deliver much less torque and invite the car travel more quickly.