What the clutch is exactly for is misunderstood by probably more than 95% of drivers (It’s not just for moving off and changing gear). How to use it correctly is probably not known by the same proportion of instructors, which is why learners frequently have problems using it.
Many instructors confuse their pupils because they themselves are confused. This leads to low speed control problems and jerky gear changes. Many also confuse engine braking with clutch braking causing further issues.
The biggest mistake uninformed instructors make is telling pupils that they are coasting when they have the clutch down. This is wrong. We frequently need the clutch down to maintain proper control of the car. The detail that many instructors are unaware of is that coasting only happens where the clutch is down unnecessarily.
How come we at Road and Track understand the Clutch when others don’t, you might ask. Well, many explanations of how cars work are based on half-truths and ‘Chinese whispers’. Our background in race car engineering means we fully understand and can explain how the car works rather than evade the answer to questions.
The benefit to you is that you can learn to drive expertly in a short time. While the benefits to us is that our days are spent being driven around smoothly. The increased efficiency of learning means you learn more while you spend less.
Both ‘Wikipedia’ and ‘How stuff works’ leave out the same information as most instructors. But, when you know what to do, you can drive a manual car as smoothly as an automatic.
The clutch, as a device has been around for hundreds of years, having been used in windmills and waterwheels. It was designed so that a power source can generate and, very importantly, also store some energy before supplying that energy to do work such as turning gears or a wheel. It also enables the power delivery to be minutely varied. Both of these features are very important if you want to control a car smoothly.
Unfortunately, because it’s not part of our training before we qualify, many of our fellow instructors aren’t fully aware of these properties of the clutch. They are therefore unable to teach their pupils to use the clutch to its best advantage.
A clutch comprises of two discs. One, the flywheel, is attached solidly to the rotating parts of the engine via a very short shaft. The other is able to slide along a shaft attached to the gearbox. (This gearbox shaft runs up to the engine but doesn’t connect to it so the two shafts can turn at different speeds).
When the clutch pedal is pushed down the clutch disc is brought apart from the flywheel..
. Flywheel Clutch
Engine –]—[— Gearbox
As the pedal comes up the disc and flywheel are brought together .
Engine –]–[—- Gearbox
Engine –]-[—– Gearbox
Engine –][—— Gearbox
As the two surfaces touch (known as the biting point), the spinning flywheel begins to transfer power to the clutch disc through friction, and the clutch itself begins to spin. This in turn turns the gears, which turn the wheels.
If the clutch pedal is moved slightly up and down at this point you can minutely vary the power going to the wheels. It is this skill that allows you to move off jerk free, manoeuvre at low speed and change gear smoothly.
Sadly many instructors don’t teach this vital skill as they confuse it with coasting. This means most people that we see, who have had lessons elsewhere, can’t use the clutch properly and have to relearn it .