A vehicle’s transmission is the “powertrain” that converts the engine’s combustion force into a controlled source of power. It acts as a mediator between the engine and the wheels by converting the high power produced by engines into torque (rotational force) -which is then transferred to the axles which rotate the wheels. Without the transmission, vehicles have no way of transforming the energy from the engine to the drivetrains. Combustion energy to the crankshaft is too high and of a variable to produce a usable speed for the driver. The engine operates at a high rotational speed (500-to-7000 RPMs), while the wheels rotate at a slower rate (Zero-to-1600 RPMs). The transmission can keep both your engine’s RPM and the RPM of the wheels at optimal rates, and it sends power to the differentials which turns the wheels.
Transmissions use toothed gears that interact with each other to produce torque, and the gear ratio refers to the gears’ relation to each other. Say you have an input gear with 20 teeth that interacts with an output gear that has 10 teeth. To spin the gear with 20 teeth once, the 10-tooth gear must make two full rotations. A gear ratio is calculated by taking the number of teeth on the output gear and dividing it by the input gear. Thus, the gear ratio in this example is 1:2 but it’s usually simplified to 0.5:1 to tell how many times the output gear must rotate for the input gear to make one full rotation.
Transmission gear ratios will always differ from car to car because there are a variety of gears and transmission sizes all of which allow a larger gear ratio combination. Gear ratios must be changed in relation to the speed of the car and that’s why there are multiple gears which are able to switch, and these gears working together is exactly what allows you to achieve different speeds. Aside from “forward” gears, there are also neutral, reverse, and park selectors. In neutral, the engine disconnects from the drive wheels. In reverse, the drive wheels run in the opposite direction. Then there’s park, which allows a latch mechanism to lock the drive wheels and prevents them from turning.
There are two main types of transmissions: manual and automatic (but there are different types of automatics too, c4 transmission, , cvt transmission etc.). A manual transmission requires the driver to manually change gear ratios, automatic’s do this on their own using fluid pressure. Automatic transmission fluid provides the necessary pressure to activate clutches and bands that in turn determines what gear the vehicle should be in. The planetary gear-set is what’s responsible for changing gear ratios, and it consists of a sun gear surrounded by smaller planet gears carried by a planet carrier enclosed in a ring gear. Whew, that was a mouthful!
When transmission fluid enters the torque converter which then activates clutches and bands. These determine what gear ratio should be engaged and the planetary gearset can then be configured to the right gear combination. All the parts in the planetary gearset can be locked or unlocked to determine the gear ratio. The video below will help you understand the different gear ratios that can be achieved. When comparing the automatic versus the manual transmissions. There’s really no basis of truth when someone says one type of transmission is better than the other. Automatics and manuals both have their pros and cons and it really just boils down to a matter of preference in the end.