Let’s dive into the point where the engine meets the wheels. The gearbox and clutch work together to achieve the best efficiency from the car’s engine.

 

Engine Speed and Wheel Speed

Understanding what the clutch does and why we need it will help you use it effectively. Now, for the benefit of your understanding, I’m going to stall the car.

To help you understand what’s happening when I stall the car, you need to understand the difference between engine speed and wheel speed.

 

 

This is your engine speed, and it measures how fast your engine is spinning.

 

 

This is your wheel speed, which shows how fast your wheels are spinning.

Your engine speed is measured in revolutions per minute, or RPM, as you can see here—RPM, or “revs,” times 100.

So, that 10 actually means 1,000; 20 means 2,000, and so on. They don’t add the zeros because it would look messy.

When I come off the gas pedal, the engine speed returns to its minimum, known as its “idle,” which in this car is around 750 revolutions per minute.

That’s quite fast—the engine is spinning at more than 10 times a second right now. Some cars idle a little higher, and some a little lower.

If I press the gas, I rev the engine up, and if I come off the gas, it will return to its minimum speed, its idle.

Meanwhile, your wheel speed is at zero miles per hour. If I press the gas pedal now, it increases the engine speed, but it doesn’t increase the wheel speed because they’re not currently connected.

So that’s your engine speed, and that’s your wheel speed.

 

Stalling for Better Understanding

When I’m traveling at 38 miles per hour in fifth gear, that equates to around 1,500 RPM. If I slow the car down with the brake, you’ll see the engine speed decrease along with the wheels.

The brakes work on the wheels, but since the wheels are currently connected to the engine, it also slows the engine down.

When the revs get to their minimum, around 750 RPM, the engine doesn’t want to go any slower.

If I force it to go slower with the brake and bring the engine speed even lower, once the engine reaches around 500 RPM, it really can’t spin anymore and it just stalls.

The engine can either be on and spinning quickly, or it’s off; there’s no in-between.

 

The Clutch

Petrol and diesel engines have a high minimum speed; they can’t spin slowly and usually need to spin at least 10 times a second, which is very fast.

 

 

Picture this: the electronic screwdriver represents your engine, and the skateboard wheel represents the clutch and all the wheels.

For this demonstration, the clutch and the wheels are directly connected (even though there’s a gearbox and differential in between, we’ll leave them out to keep things simple).

When the clutch is up, it’s connected to the engine, so whatever the engine does, the wheels do, and vice versa.

When you press the clutch pedal down, you disconnect the engine from the wheels. This is important because it allows you to stop the wheels while the engine keeps spinning.

Without the ability to press the clutch down and disconnect the engine from the wheels, every time you stopped, you’d either stall the engine or just keep going until you ran out of fuel.

 

Stopping Without Stalling

Now, I’ll test stopping the car without stalling. I’ll start by using the brake, which slows the wheels and also lowers engine speed.

When the engine speed gets close to its minimum, I press the clutch down to disconnect the engine from the wheels.

This allows me to stop the wheels without stopping the engine. Now, the wheels are at zero miles per hour, and the engine is still running.

If I were to come off the clutch now, the car would try to move. However, since I’m in fourth gear, it’s not the right gear for moving from a stop, so it would likely just stall.

If I want to release the clutch without the car stalling or trying to move, I first need to select neutral.

In neutral, there’s no connection between the engine and wheels, so even if I come off the clutch, the wheels remain stopped while the engine keeps running.

 

Moving with the Clutch

You need to disconnect the engine from the wheels so that you can stop the wheels without stopping the engine, and that’s why you have a clutch.

But you also need to use the clutch to reconnect the engine to the wheels when you want to get going.

If you lift the clutch to about halfway while in gear, it begins to reconnect the engine to the wheels.

This spot is known as the clutch “biting point,” or “half clutch.” Usually, it’s about halfway up, but sometimes it can be slightly higher or slightly lower.

If you press the clutch up and down in neutral, it won’t affect the car’s speed, but you do need to press the clutch down to select a gear.

So, clutch down, into first gear, I’ll take off the parking brake, and as I lift the clutch about halfway, the car will start moving.

Pay attention to the revs, engine speed, and wheel speed. I won’t use the gas this time. Lifting the clutch halfway, the engine actually revs itself a bit to help me get going.

Now, the clutch and engine are both moving at the same speed, so I can fully release the clutch, and now I’m rolling. I can use the gas to keep going.

The reverse sensors are going off because the bushes are sticking out in places, so going near them sets the sensors off at low speed.

Now, I’ll stop the car—clutch down and brake.

 

Gas Before Clutch

This time, I’ll add gas before lifting the clutch. When I add gas, the revs are higher, making the engine more powerful, which is helpful when moving off.

Earlier, when I lifted the clutch without pressing the gas, the car’s system automatically revved up the engine because it needed to.

Not all cars have this system, though; some cars offer more assistance than others.

So, this time, I’ll add gas first for more power to spin the wheels. Clutch up to the bite point—there we go, moving off now.

The clutch and engine are synced, so I come off the clutch completely, and the gas now controls the car’s speed.

 

Changing Gears

You also need to press the clutch down to change gears. Since the gearbox is between the clutch and wheels, if you try to change gears while there’s power going through the gearbox, you could damage something.

 

 

While it’s possible, I highly recommend against it. When it’s time to change gears, press the clutch down, lift off the gas (removing power), shift gears, then lift the clutch up to reconnect the engine to the wheels.

You can then add power through the gears without damaging the gearbox.

I’ll demonstrate that again, this time adding a bit of power as I come off the clutch to avoid slowing down as much.

So, clutch down, off the power, switch to third gear, clutch to the bite point, a little bit of gas to prevent losing speed, and fully off the clutch to continue.

 

In a Nutshell

To summarize: pressing the clutch down disconnects the engine from the wheels, allowing you to stop the wheels without stalling the engine.

The engine prefers to keep spinning, and the clutch lets you smoothly reconnect that fast-spinning engine to the wheels.

If you hold the clutch at the bite point for a few seconds, the clutch gradually catches up with the engine speed, letting you move away smoothly without a jerk.

If you lift the clutch too quickly, it’ll cause a sudden jolt. Pressing the clutch also disconnects the engine from the gearbox, letting you shift gears without power going through, preventing damage.

 

Electric Cars

Electric vehicles and many hybrids don’t need a clutch, because the electric motor spins the wheels and can operate as slowly as needed.

If you want to move at just 0.1 miles per hour, the electric motor can handle that. In contrast, petrol or diesel engines aren’t that flexible.

 

Automatic Cars

Most modern automatics still have a clutch—some even have two—but you don’t have a clutch pedal because the car’s computer controls it.

Traditional automatics and some newer models use a “torque converter,” a different method that lets the engine keep spinning while the wheels stop.

You don’t need to press any pedals or buttons—it’s all automatic.