Different Types Of Gear Transmissions: Know The Difference
Most people think that gearbox types depend on if you have to change gears yourself or if it is done automatically. However, there are more differences in the underlying mechanisms, driving feel and the best application.
This is why we decided to give our readers a quick overview of the most common transmission options and help them decide what is the closest to their needs and desires. We will talk about the general concepts, their pros and cons and the best applications. There are, of course, exceptions to the rules, but in general, this is it.
How Many Types Of Transmissions Are There?
There are 5 different types of transmissions that we will be discussing in this article:
Automatic Transmission with Torque Converter
Dual-Clutch Transmission (DCT)
Continuously Variable Transmission (CVT)
Single Speed Transmissions
We feel that these are the more common ones that are being used by modern car manufacturers. It is useful as a car owner to understand which transmission your car has and how it can affect the way you drive.
Manual gearboxes require the driver to operate the clutch to disconnect the driving force of the engine from the wheels and thus enable a change in the gear ratio. While manual gearboxes are beloved by many driving enthusiasts, they are less comfortable than the other options.
Sadly, the manual transmission is a dying breed. What once was by far the most common option now is reserved for a smaller number of vehicles, usually in a lower trim as a cost-saving option.
However, there are a few respectable vehicles out there that still keep the manual and are very fun to drive. Many hot hatches are equipped with a manual and its nature fits them perfectly. Also, some other driver’s cars still offer manual options, including the likes of the Ford Mustang or Mazda MX-5.
After the invention of the auto transmission, driving a manual car can be rather tiresome for city driving. Especially when you have to stop and move off many times throughout the journey. Drivers might find having to operate the clutch a pain.
However, there are certain benefits that come with driving a manual like a better feel of your car, cheaper maintenance and better fuel economy
Automatic Transmission with a Torque Converter
This is the most common kind of gearbox that shifts gears automatically. It uses a torque converter that is filled with liquid to accommodate the shifts. When the torque converter is not locked, the gearbox can change gears without any violent jerks as the liquid is used to cushion the change in ratio.
Many people see this option as the best of all worlds as it gives comfortable shifts that can be very fast and smooth at the same time. It is the perfect blend of comfort and performance.
However, there are some downsides. The most familiar one is a reduction in fuel efficiency. It is not huge, but it does make a difference. In most other options a single rotation of the engine crankshaft gives a set number of wheel rotations, depending on the particular gear ratio. However, the liquid that enables smooth shifts produces some losses as the connection is not as firmly set.
Simply put, with the liquid transferring the power to the wheels, the crankshaft rotation does not give the same fixed number of wheel rotations. These losses mean that sometimes you need more throttle for the same result and it means you use a bit more fuel.
The second downside has to do with performance applications. While these gearboxes can be amazingly efficient and while we do see them in many stunning performance vehicles, generally speaking, dual-clutch gearboxes offer faster shifts and a better, more continual use of the engine power.
Still, torque converter automatics seem here to stay. Their versatility seems unmatched and amazing solutions like the ZF’s 8HP automatic does wonders with reducing or eliminating the downsides.
Moreover, some of the most revered transmissions are of this kind, including Tiptronic used in VW and Audi vehicles, Steptronic used in BMW, 5, 7 or 9G-Tronic made by Mercedes-Benz or Skyactiv-Drive made by Mazda.
Dual-Clutch Transmission (DCT)
Imagine having two manual transmissions in one car. One is used to drive the gear you are in right now and the other one pre-engages the next gear. The moment you decide to change gears, the shift happens instantly because the second transmission is already locked and ready to take over.
Now imagine this shift from one transmission to another is controlled by a computer that can do it with higher precision than any human being. This is exactly what dual-clutch gearboxes are and the two clutches are used to engage one set of gears or another.
The computer is used to pre-determine which gear you want to shift to (for example, if your revs are rising and you are accelerating, it assumes you want to go to a higher gear) and also to control a number of other aspects such as shifting points and shift speed.
There is no torque converter and the power delivery can be very smooth and uninterrupted. This is why dual-clutch gearboxes are perfect for many sports cars. Porsche’s PDK, Mercedes-Benz’s 7G-DCT or Audi’s S-Tronic are the perfect examples. Such technology allows for small SUVs/MPVs like the Mercedes GLA 200 and Mercedes GLB 200 to have quick accelerations.
However, it’s not all good news. The chase for lowers emissions and the best fuel economy have made many manufacturers offer dual-clutch gearboxes in cars that are far from any performance application. VW has been doing this with their DSG for more than a decade now.
While the logic behind these choices is sound, DCTs are also notorious for being jerky and harsh at low speeds as the computer tries to lock the clutch as soon as possible to prevent wear. Volkswagen’s DSG is probably the most famous example of this, especially in its early days. While you will not drive a racing car in a stop and go traffic very often, your VW Golf may actually spend most of its days like that.
Another downside comes from the predictions of the computer. The gearbox keeps two gears ready to go at all times – the one you are in, and the one it thinks you want to shift to. But if you want to overtake someone on a busy road and you start off from the fourth gear, rising revs, you may actually want to shift down to make the pickup more immediate and not up, as the computer thinks. The computer will pick up quickly, but the lag is noticeable.
However, with the latest applications in ‘normal’ cars, DCTs are becoming more and more refined.
It is worth noting that there are also multi-clutch gearboxes like the one used in the Koenigsegg Jesko which has seven clutches, or several generations of AMG MCT gearboxes.
Continuously Variable Transmission (CVT)
CVT, or continuously variable transmission, is like a cone with a belt. As the belt moves up and down the cone, it changes the gear ratio continuously. There are no set gear ratios, but a range of ratios that constantly change giving you the best efficiency at any given point.
If you are accelerating hard, the CVT will put you in the most efficient revs for that purpose in a second. If you are cruising peacefully, it will give you the lowest efficient revs to reduce the engine noise and improve fuel efficiency. It sounds perfect, doesn’t it?
The downside is that CVTs give a very disconnected driving feel. For example, you may be accelerating but your engine revs will be at the same level despite the change in speed, as the acceleration will not come from a faster work of the engine, but a change in the position of the belt over the cone. Many driving enthusiasts are not a fan of this.
Manufacturers have done wonders in trying to make CVTs feel more natural, even providing something like simulated shifts that resemble fixed gear ratios, but the disconnected feel is still there.
CVTs are still reserved for cars with efficiency as their priority, including many hybrids or low-powered city cars. The latter feels more powerful as CVTs get them to the best revs instantly, so they are a good choice for these kinds of vehicles. A popular car in Singapore with such a transmission is the Honda Shuttle.
These are found almost exclusively on electric vehicles and the likes of the uniquely stunning Koenigsegg Regera. As electric motors can spin at much higher revs, they don’t really need to change their gear ratios to provide efficient operation.
So, What Should You Choose?
If you are buying an electric car, you don’t really have a choice. If you are up for a mix of comfort and performance, a torque converter automatic seems like the best choice in most cases. If you want some high-performance gear changes, dual-clutch will give you the fastest shifts. If you have a low-powered car and you aim for the best efficiency, get a CVT. And if you want some old-fashioned, all limbs, heel & toe fun, go for the manual.