We’re all aware of the two main types of gearbox: manual and automatic. Modern cars are usually split between the two but that doesn’t mean they’re the only options. There is another – a semi-automatic gearbox. If this is news to you, then you’re probably wondering what a semi-automatic car is and how it works, right?
Well, that’s exactly what we’re here to explain! We’ll answer all the questions you could possibly think of – and maybe a couple more besides.
Manual vs Automatic
A manual car changes gear through the use of a clutch pedal and a gear stick. Depress the pedal, select the correct gear, pull the pedal back up and carry on your merry way. It always has done, ever since the invention of the combustion-powered motor car in the late 19th Century. Torque drives an engine and crank-started engines couldn’t produce enough torque on their own. As a result, gearboxes were fitted to keep the car moving.
The hassle of gear changes proved too much for one Alfred Horner Munro of Regina, Canada. In 1921, he invented an automatic transmission system to propel a car. Unfortunately, he decided to use compressed air and not hydraulic fluid to propel the car. Unsurprisingly, due to a lack of power, it never took off.
However, the shift away from crank-start engines fuelled the automatic adventure further and, in 1948, General Motors released the Oldsmobile, a car widely credited as the first model to use purely automatic transmission.
Automatic cars, like most super cars, use electronically powered gearboxes to change gear when the computer recognises you need it the most. Nowadays, automatic transmission models are incredibly popular. The ease of slipping the car into drive and then not worry about it appeals to many people.
How does a semi-automatic gearbox differ from the others?
Let’s address the semi-automatic car which, unsurprisingly, fits in the middle of the two.
The main appeal of having a semi-automatic car is that the driver has the option to control the gears manually or automatically, whichever they prefer at the time. The use of electronic components in an automatic car can sometimes mean it struggles to complete gear changes smoothly (unless the car uses a dual-clutch transmission). However, when you’re using a semi-automatic car since the driver can control the gears manually, it can be just as smooth as driving a manual car (given that the driver is skilled and has experience driving a manual car). When you combine this control with potential fuel savings, driving a semi-automatic car starts to make a lot of sense.
How does a semi-automatic transmission work?
A semi-automatic transmission takes the basics of both manual and automatic transmission and combines them.
The kinetic energy produced by the engine helps rotate the wheels, while carefully tuned gear ratios control how fast or slow your wheels spin. The automatic clutch we mentioned connects to a hydraulic motor, which acts as a replacement for a clutch pedal, and controls automatic gear changing for you.
In addition, the layout of your gear stick is very different to a manual one. There’s no fork-like arrangement of the numbers, such as below. Instead, a lever with + and – symbols sits in its place. This is more akin to an automatic gearbox which has four simple settings – Park, Drive, Reverse and Neutral. Sometimes, there’s the option to select 1st and 2nd gears manually. This is for situations where you need to navigate difficult terrain, such as snow, and want the best gear for the situation. For a semi-automatic gearbox, you’re likely to see the letters P, R, N, D & M or A, N, R & M.
What do the letters mean?
P = Park – While your semi-automatic car does still have a handbrake, you can’t rely solely on that. Whenever you get out of the car, make sure you select park. This locks the transmission and stops your car from ending up in a different place to where you parked!
R = Reverse – Pretty self-explanatory, wouldn’t you say?
N = Neutral – Not a great option to select when you’re moving along. It’s the same as knocking a manual out of gear and coasting. Driving instructors frown upon this for a reason, so only select neutral when stopped for a short period of time. It’s important to keep the handbrake on as well, as a semi-automatic car will creep forward if you take your foot off the brake, even in neutral.
M = Manual – This is the biggest difference between a semi- and full-automatic gearbox. Selecting manual gives you more control and takes away most of the automated input, save for the clutch. There are a variety of options where being able to take manual control might be necessary. Sometimes, it’s just because we miss the feel of changing gears ourselves!
D = Drive – Used to keep the car moving forward. Whenever you want to go anywhere, make sure you’re in drive. If you’re not, the computer can’t change gears for you.
A = Automatic – Exactly the same as drive (D).
What is a dual-clutch transmission?
This form of automatic transmission is popular with semi-automatic cars due to the speed and smoothness of gear changes. One automatic clutch will control the even gears, the other, the odds. Two clutches allow for much smoother, often unnoticeable transmission.
A manual car halts the power flow when you change gear. Thanks to two highly responsive clutches, this isn’t necessary in a semi-automatic car.
When compared jerky manual gear changes, a smooth, seamless shift can be very appealing to drivers.
Can I drive a semi-automatic car like an automatic?
Yep. In fact, the default mode is automatic. Think of a semi-automatic as an automatic car which gives manual control when you need it the most. In certain situations, this comes in really useful. Driving in snow and ice as well as navigating steep hills require a different style of changing gear, which a computer can’t understand.
This also means that you can drive a semi-automatic like a full manual most of the time, with an automatic option. This approach works well on long motorway journeys, but why would you want to miss out on all the freedom of an automatic most of the time?
Can I drive a semi-automatic car with an automatic licence?
If you’re worried that your automatic licence isn’t valid because of the manual option a semi-automatic car offers, you can relax.
The Government classes a semi-automatic car as an automatic. Why? Well, even though there’s a manual option, there’s no clutch pedal, which means it isn’t a full manual vehicle.
As long as you have some idea when to change gears should you engage manual mode, you’re can drive a semi-automatic car with an automatic licence. If you’re not confident with a manual, you can just stick clear of that driving mode.
Can I stall a semi-automatic car?
It’s a worry for all of us. Stalling a car is an embarrassing but normal part of driving a manual car.
There’s no need to worry about that in an automatic car!
It’s virtually impossible to stall a semi-automatic car because it has no clutch pedal. Jerky clutch movements are the main cause of engine stalling so, by removing the cause, you thus remove the problem.
The only way we think you could stall a semi-automatic car is if you’re going forward and suddenly select reverse, or vice versa. And we can’t think why you would do that. It’s dangerous and you could cause expensive gearbox damage.
How to drive a semi-automatic car
We’ve touched on several aspects of driving elsewhere in the article but now it’s time to bring it all together.
The default driving mode is automatic. The convenience and ease of driving an automatic is probably what drew you to a semi-automatic car in the first place. So, when pulling away, remove the car from park and put it in automatic or drive. Once it’s there, leave it alone until you either have to reverse or pull up at your destination.
During your journey, you just need to focus on accelerating, braking and steering. The computers will worry about all the fiddly gear changes for you and you can just focus on the road.
If you want to take full control, you can select manual and change through the gears yourself. Always select this when the car is at a complete stop for your safety.
Don’t let the gear stick confuse you: + means change up; – means change down. Easy. The computer tells you when to change gear but listening to the engine works just as well. Those amongst you with manual driving experience will know this best.
We’ve already mentioned that ‘R’ puts the car in reverse and park holds the car in place whenever you pull to a complete stop and get out of the car. Other than that, you now know the basics!
If you’re looking to drive a semi-automatic car, check out Wikihow’s detailed, step-by-step guide for more information.
Semi-automatic cars are a great example of successfully having the best of both worlds. You get the ease and convenience of an automatic as well as the control of smoothness of a manual. It’s a win-win. Hopefully, you’re now all clued up on what a semi-automatic car is. However, if you have a specific burning question that we haven’t answered, just ask it in the comments! Alternatively, if you found this guide really useful and you want us to do one on another topic, we’d love to hear from you too!