Transmission Basics: How Does a Transmission Work?

Not exactly sure what a transmission is or what it does? Don’t really care? We’ll pretend we didn’t hear that and your car won’t ever have to know. But we’re going to tell you anyways, because you should have an idea of how cars get you from place to place. It’s the least you can do because your car works hard for you and it deserves a little attention. So, how does a transmission work? Well, we’ll explain it to the best of our ability.

How Does a Transmission Work?

In layman’s terms, your transmission is the powertrain that converts the engine’s force into a controlled source of power. It acts as a mediator between the engine and the wheels, and converts the high power the engine produces into torque (rotational force), which is then transferred to the axles which in turn rotates the wheels. So without the transmission, your car would literally be a hunk of junk.

You see, the engine of your car creates power and sends it to the crankshaft, but the power produced is too high and too variable to produce a usable speed for the driver. The engine operates at a high rotational speed (anywhere from 600 to 7000 RPMs), while the wheels rotate at a slower rate (anywhere from 0 to 1800 RPMs). Sure, you could try to slap some wheels on the crankshaft but not only will you be subject to high speeds, you also won’t be able to control the speed or even be able to come to complete stop. And that’s where the transmission comes in. The transmission is able to 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. It does this all through the use of gear ratios, but how do gear ratios work?

What Are Gear Ratios?

A transmission uses toothed gears that interact with each other in order 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. In order 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 in order to tell how many times the output gear must rotate for the input gear to make one full rotation.

how does a transmission work - gear ratios

There are many gears in the transmission with different sizes, which allows for many gear ratio combinations. And gears don’t only have to interact in combinations of two either, more gears can interact together as well. 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.

As an example, here are the gear ratios for a manual transmission 6-speed 2004 Chevrolet Corvette C5 Z06:

GearRatio
1st gear:2.97:1
2nd gear:2.07:1
3rd gear:1.43:1
4th gear:1.00:1
5th gear:0.84:1
6th gear:0.56:1
Reverse:3.38:1

Besides 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.

How an Automatic Transmission Works

There are two main types of transmissions: automatics and manuals (but there are different types of automatics too). But when answering the question “How does a transmission work” we were mostly referring to a manual transmission in our explanation. Remember, automatic transmissions came after the manual transmission and if you know how a manual works, you’ll get the basic idea of how an automatic transmission works. While a manual transmission requires the driver to manually change gear ratios, an automatic does this on its own through the use of 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 gearset 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!

how does a transmission work - planetary gearset

So transmission fluid enters the torque converter which then activates clutches and bands. In turn, those 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.

Automatic vs. Manual Transmissions

Now that we answered your question “How does a transmission work?” we can compare the automatic versus the manual. 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.

Manual TransmissionsAutomatic Transmissions
Pros:Pros:
  • Less maintenance
  • Manual transmissions tend to have better fuel economy
  • Cheaper repairs
  • Less servicing required
  • More control
  • Easier to use
  • More widely available (95% of car sales in North America have an automatic transmission)
  • Parts are easier to find
  • More convenient
  • Automatically changes gears
Cons:Cons:
  • Steeper learning curve
  • Not as widely available
  • Less convenient
  • More expensive repairs
  • Requires more maintenance
  • Develops issues more often than manuals