Engine idles at around 100rpm – connected direct to the roadwheels this would have you doing around 75 mph. Cars need lots of force but little speed to get going but then more speed and less force.
The gearbox lets you use the engine’s speed and power to match the driving conditions – lower gears for more force when pulling away or climbing a hill, and higher gears for higher speed. The clutch allows the engine to keep turning when the car isn’t moving.
On a manual car the driver has to operate the clutch and select the most appropriate gear for the conditions.
With an automatic transmission all you need do is operate the throttle pedal – the ‘clutch’ and gear selection are taken care of automatically.
Many modern autos include a facility for manual gear changes so you have the choice – this may be by nudging the lever or by pulling ‘up’ and ‘down’ paddles (switches) mounted behind the steering wheel.
Automatic gearboxes have become more popular with drivers here in the UK in recent years. They select the gears on their own depending on the revs of the engine. Drivers don’t need to do anything, apart from select ‘Drive’, ‘Park’ or ‘Reverse’.
You don’t need to change gear in an automatic transmission, which comes with lots of benefits. In many circumstances, emissions and economy is improved when analysed against a comparative manual. They can also make driving much more relaxing, especially on a commute or when sat in traffic.
But it’s not all rosy with automatic gearboxes. Some are better than others and not all of them may suit your driving style. It’s best to take a vehicle for a drive to see if you can live with the transmission.
Also, unlike manuals, there are multiple forms of automatic transmissions. Here are the 5 different forms.
Torque converter/traditional auto
This was the first automated transmission used on a vehicle and was made famous by General Motors, Oldsmobile and Cadillac in the 1940s. Using a fluid-filled coupling instead of a clutch, the transmission has stayed mostly the same in layout – with a few changes here and there.
Earlier options tended to lose energy through the fluid coupling that led to lower efficiency and worse performance. But torque converters have improved and modern versions are smooth-shifting and provide a relaxing drive. Some even work well with performance models, showing how adaptable the transmission is.
Rather than the fluid-filled coupling used in a torque converter, a dual-clutch transmission (DCT) uses two robotised clutches. Normally one clutch deals with odd-numbered gears and the other with even-numbered.
You don’t usually lose much performance and economy compared to manual gearboxes, but DCTs can be jerky and strange to use at slower speeds. Different manufacturers in the motoring industry call a DCT different names. Volkswagen Group models have a DSG, Porsche says PDK, Renault uses EDC and Hyundai and Kia go for DCT. All, however, fundamentally work the same way.
Meaning ‘continuously variable transmission’, CVTs don’t have gears in the traditional way and instead have a continually changing ratio to help provide the best power and economy – in theory anyway.
If you’re a keener driver, then a CVT probably isn’t for you, as any hard acceleration can mean the engine revs climb rapidly and it can get very noisy. When driven smoothly, they can be very efficient, making them perfectly suited for hybrid models.
At the bottom end of the automatic food chain is the automated manual. Rather than take the clutch and gearbox operations away, it simply robotises the action. The systems are easy to install and are lightweight.
Some drivers don’t get on too well with the sometimes jerky nature of automated manuals, so make sure you try the car out under a wide range of conditions and road types if you’re test-driving one you’re thinking of buying.
Although EVs don’t technically have a gearbox, they act in a very similar way to an auto. There are no gears to shift, making a switch to a battery-powered model from a normal car with an automatic very easy.
Cons? You do need somewhere to charge it. But with zero emissions produced and a very relaxing driving style, electric vehicles could be for you.