What is double clutching? Well, as on many occasions, we begin with a quote from Vin Diesel and the much-loved film The Fast and the Furious.
You almost had me?! You never had me. You never had your car.
Granny shifting, not double clutching like you should. You’re lucky that hundred shot of NOS didn’t blow the welds on the intake. Almost had me?!
As we will come to look at, this sentence doesn’t carry a whole lot of weight. It doesn’t actually make that much sense. If The Fast and the Furious is the only reason you’re here, click here to jump down to the section where we examine Vin Diesel’s words to Paul Walker.
Today, we will take an in-depth look at the concept – and the reality – of this driving technique.
So, what is double clutching? How should it be done? Is it useful for everyday conditions on the roads? And what’s Dom Toretto on about?
- What is Double Clutching?
- Advantages and Disadvantages
- Should I Do It?
- Heel and Toe
- Fast and Furious
What is Double Clutching?
Known as “double de-clutching” around the world outside the US, double clutching is a technique used when driving a car with a manual transmission. In short, it involves pressing the clutch pedal twice.
When thinking about the question “what is double clutching?”, it depends whether you are upshifting or downshifting. The techniques are slightly different for each of these:
- When upshifting: after pressing the clutch down first, put the car into neutral. Release the clutch. After that, press the clutch pedal down again and pop the car into the next (higher) gear. Finally, release the clutch for the last time.
- When downshifting: press the clutch pedal down and move the gearstick into the neutral position. As soon as its out of gear, you will need to tap the throttle – firmly, but not too harshly – to raise the revs of the engine (rev matching). Once the revs have raised, press the clutch down again, moving the gearstick into the next gear down.
The difference between these two is the extra blip on the throttle when downshifting.
The whole idea is to match up the rotational engine speed with the speed of the transmission. There are several benefits of doing this, which we will examine in a later section of this article. Of course, as with anything, there are also some potential drawbacks.
Check out this YouTube clip from milanmastracci for a great, detailed explanation on how to double clutch.
As you will have been able to see from the video, the main benefit of double clutching is “smoothness”. In the world of mechanics, engineering and motorsport, the smoother something is, the better.
When I Double Clutch, What’s Going On Mechanically?
This video from Engineering Explained on YouTube explains nicely what happens when you double clutch.
Perhaps the most important thing to recognise, if you aren’t familiar with internal combustion engines and powertrains, is the fact that the engine, the transmission (also known as a gearbox) and output shaft, which goes to the driven wheels, are all independent systems.
This means that, when the clutch is disconnected from the engine, the engine speed is independent of the transmission. As a result, the driver can manually adjust the engine speed (increasing the revs when downshifting, or allowing them to naturally decrease when upshifting) to match the transmission speed.
This makes for a nice, smooth gear change, as the flywheel and clutch have much less “catching up with each other” to do.
Almost every modern car in the world will have synchros now, making this process almost redundant (but not quite).
This guide from HowStuffWorks will give a great, brief overview of what’s going on.
A Recap – How Does a Powertrain Work?
The engine turns the reciprocal (up and down) motion into a rotational force, using connecting rods (known as con rods). This causes the crankshaft to spin. On the end of the crankshaft, we find the flywheel and a pressure plate.
When the pressure moves away from the clutch plate, the flywheel is no longer connected to the transmission, therefore the power isn’t going anywhere. This is what happens when you press the clutch pedal.
For a full explanation on how the powertrain of a standard manual car works, check out this video.
What are Some Advantages of Double Clutching?
Okay, so here’s where the truth of the matter comes in. Almost every modern car with a manual transmission has synchronisers, known as “synchros”.
These synchros make the whole process of double clutching virtually completely unneeded. Over time, synchros have become more and more sophisticated until, in modern cars, they are so advanced that you are unlikely to feel almost every gear change.
Click here to be taken to a link to Tremec’s website and an overview of how synchronisers work.
Alternatively, this 3-minute video provides a clear explanation.
We will look at why double clutching is no longer particularly relevant in the section “Should I Ever Double Clutch While Driving on the Road?”
However, in the meantime, there are a couple of advantages.
- Double clutching might make a difference in any car if you are redlining the vehicle before shifting. The shift will feel smoother. Slightly.
- In terms of double clutching, when you shift gears smoothly it means there is less stress on both the clutch and the synchros. This means that they’ll last longer, which is better for your bank account. However, under normal driving conditions, this benefit is likely to be virtually negligible.
- Another advantage of smooth gear changes is passenger comfort. The smoother your ride is, the more confident your passengers will be in your driving ability. This is great for them, great for your confidence and great for having a nice, relaxed journey.
- If your clutch or synchros are on the way out, double clutching is much kinder to them and your transmission as a whole. This will – hopefully – mean that they last a bit longer before you need to get them changed.
- In some modern situations, the principles behind double clutching can be useful. For example, if you had the transmission in neutral whilst slowing down (let’s say when approaching a red light), but then need to put it back in gear before bringing the car to a halt (let’s say the light turns green), you will typically notice heavy jolt, especially in the lower gears such as 1st and 2nd. Instead, you should blip the throttle before putting the car in gear. This will more closely match the engine speed to the transmission speed, making this gear shift much smoother and nicer to your clutch and transmission.
- Being ready to drive an older car.
As in everything, where there are advantages there are disadvantages.
What are Some Disadvantages of Double Clutching?
Aside from double clutching being almost completely unnecessary in almost every driving situation, there are some important reasons you should be wary of double clutching, especially if you haven’t done it before.
- Perhaps the main disadvantage is the possibility of losing control of the car. Whilst this is unlikely, especially if you’re unfamiliar with the action, it might be possible to accidentally miss the next gear, meaning your car is either stuck in neutral or only half in the gear. Being in neutral at the wrong time can lead to a whole array of problems. The root of the matter is that you’re no longer in control of the vehicle – the engine is not connected to the wheels. If you don’t get it back in gear quickly, you could easily crash in unfortunate circumstances.
- On this note, it might be worth only practising on abandoned, straight roads near your house. Or, to be even safer, when the car is switched off and parked up.Getting familiar with the feeling of the clutch and doing the process quickly will mean that it’s much less likely you’ll make a mistake when doing it for real.
- Although you will technically be avoiding wear on your synchros and clutch, you are using the clutch pedal twice as often. This technically puts double the strain on all the other clutch components, making the whole process – essentially – futile.
- Modern cars are built to shift normally. There’s no real need to double clutch.
Should I Ever Double Clutch While Driving on the Road?
This YouTube video by Speed Secrets is right on the money.
If you drive a modern car, the short answer is – no, probably not.
This isn’t for any reason other than it’s not really necessary in most situations in modern cars. Technology has advanced to the point where double clutching is rarely needed.
In situations where, once upon a time, double clutching might have been necessary, there are now more relevant driving techniques which will work more effectively. One such example is the “heel and toe” technique, which we will explore shortly.
In our opinion, the only time it might be worth employing a double clutch technique is when accelerating hard and when there’s nothing in front of you. This way it’s safe, enjoyable and (in a small way) good for your transmission.
If you drive an older car, the answer is – perhaps.
Transmission synchronisers were invented and introduced to cars in the 1920s and was first installed on a production car in 1928 by Cadillac. That’s almost 100 years ago.
Before this, gearboxes were non-synchronous. These are often referred to as “crash gearboxes”. This is due to the difficulty of changing gear smoothly. It’s also why driving a car in those days was much more of a speciality skill.
What is Heel and Toe?
Heel and toe is a technique which should be mostly limited to the racetrack. Using this technique allows you to slow down (using the brake pedal) whilst smoothly downshifting.
When driving on the road – just popping to the shops or home from work, for example – you probably aren’t going to need to use this. However, it’s good to know, and especially useful on the racetrack.
Using the double clutching technique, when downshifting, doesn’t traditionally involve any braking. In fact, it’s verging on dangerous because it takes too long. If you were braking, you would need to combine it with this heel and toe move. You would be more likely to double clutch down a gear in preparation for hard acceleration.
To brake, you can use the heel and toe technique.
When using the heel and toe motion to slow down, follow these steps (as shown in the video above):
Heel and Toe Technique
- Depress the brake pedal with the ball of your foot to begin to slow down.
- Depress the clutch.
- Rotate your right foot so the side of it blips the throttle. Keep the brake pressed down. Simultaneously, change gear. There is no need to stay in neutral along the way.
- Move your right foot back to being straight. At the same time, release the clutch. How quickly you release the clutch depends on 2 things: 1. the quality and type of clutch, and 2. whether or not you care about your clutch. For your average road car, be gentle.
- Once you have sufficiently slowed down, release the brake.
- If necessary, continue to do this through the gears, repeating steps 1-4 as many times as necessary. Of course, this is dependent on how many gears your transmission has.
The mechanics of this are very similar to double clutching.
Here is another video from YouTube by Engineering Explained to help you understand.
The Fast and The Furious
Okay, so let’s examine the reference to double clutching in The Fast and the Furious.
Let’s not knock this film as a film – it’s one of the best and most popular series ever made, containing some incredible performances from some very talented actors.
Mechanically, practicality has been outvoted by Hollywood drama. While it’s an amazing set of films, some of the racing depicted is so, so, so far away from real life.
Take this clip for example. It’s the quarter-mile drag race at the end of the film.
The drag race begins at 0:40. At exactly 2:15, Dom and Brian cross the railroad track which, in Dom’s words, is “exactly a quarter mile away”. That’s 95 seconds.
Using basic physics, we can work out that their average speed to cover this distance in this time is a mind-blowing… 9.5 mph. A relatively fit person could sprint a quarter mile faster than that.
Now, you might argue that some of this is in slow motion, and that it’s important to see everyone’s expressions and everything that’s happening with the individual cars. And you’d be right. But you can see how the feeling of speed can get somewhat lost, in favour of dramatic Hollywood moments.
What is Granny Shifting?
We’ve included this just to explain what that Fast and Furious quote is all about. This section comes before the part about double clutching just so you’ll know what it is likely referring to.
Granny shifting isn’t a defined term. So far as we can tell, it’s a term that the film writers made up. Most people disagree over its exact meaning – however, we suspect it means “to shift normally”.
“Granny shifting” is (probably), in short, driving normally. It’s changing the gears either 1 up or 1 down at a time by pressing the clutch pedal in to disengage it, moving the gear selector straight into the next gear, and releasing the clutch.
If this definition is what Vin Diesel meant, when you learnt to drive, you’ll have learnt how to “granny shift”.
This topic is widely debated on forums such as this one across the internet.
What is Double Clutching in The Fast and the Furious
It’s a somewhat similarly-unrealistic situation for the “double clutching” moment in the film.
The quote comes after the drag race, which you can watch here.
The whole scene is awesome. But it’s factually… challenged. To name just a few, Brian would never have recovered from that start. Again, it takes a solid couple of minutes to complete the quarter mile. Also, in no drag race, ever, should the cars set off one by one. Finally, the warp speed effect is one of the standout things about the film, but it makes you think more of hyperspace from Star Wars than real-life racing.
Coming to the point, Dom tells Brian that he should have been “double clutching” instead of “granny shifting”.
Here is a link to the Fast and Furious Wiki giving all the stats on Brian’s hyped-up Supra he uses later in the film.
In a drag race, you would never double clutch. You would just smash the gear in as fast as possible.
Well, perhaps you could double clutch if you were just having a nice one off race and really badly wanted to look after your car, but not other than that. And, in The Fast and the Furious, Brian clearly doesn’t care too much about his car – he uses excessive amounts of NOS. He just wants to win.
In short, it’s impossible for double clutching to be faster than normal shifting. It’s nicer to the synchros and the clutch, especially at high rpms, yes, but that’s all.
In fact, in drag racing, it might even be fastest to ignore the clutch completely and just ram the gear in. Again, this isn’t too friendly on your transmission. It also requires a highly-skilled driver.
There are twice as many steps involved as a normal shift. This means that, so no matter how fast you can double shift, normal shifting will always be quicker, as long as you’re willing to just throw the gear in, rather than be gentle. It’ll be harsher on your synchros and clutch, yes, but in a high-stakes drag race that’s unlikely to be your main concern.
Basically, Brian is right to be granny shifting, and to not be double clutching. Dom’s wrong.
As the final nail in the coffin, watch the video carefully at exactly 36 seconds in. You’ll see Dom shifting normally. Bit of a hypocrite there.
What is the Best Way to Change Gear?
All of these bits of information may be making you wonder about the above question.
In short, we recommend the following:
- If you drive a relatively modern car, shift normally. As in, press the clutch pedal down, move straight into the next gear, and then gently release the pedal. The car has been built with this in mind. You aren’t doing anything wrong. In fact, it’s probably better for your car to shift this way.
- If you’re driving a relatively modern car and redlining it, double clutching may help you have a smoother shift and look after your transmission. However, there is no need to do it in most situations.
- If you’re driving an old car (we’re talking “somewhat vintage”), double clutching will be necessary for driving.
It’s always worth remembering the mechanics. Match up the engine speed with the transmission speed, and this will lead to smooth shifts. In almost every car on the roads now, synchros will do that for you – but, on rare occasions, they made need a small amount of help.
Double Clutching Facts:
- Double-clutching is a driving technique used solely in manual transmission vehicles.
- Three systems are involved in double-clutching: the engine, the clutch, and the transmission.
- The purpose of the clutch is to act as a buffer between the engine and transmission.
- Each system can rotate independently.
- Double-clutching means releasing the clutch while the transmission is in neutral, raising the engine RPM, and then shifting into the next gear.
- Nearly all modern manual transmission passenger vehicles have synchronizers, which makes double-clutching unnecessary.
- Heavy-duty freight truck transmissions do not have synchronizers.
- Synchronizers match the rotational speed of the gear being selected to the speed of the transmission output shaft.
- Double-clutching can be useful in specific scenarios, such as extending the life of synchronizers or shifting into first gear while already moving.
- Double-clutching provides a smooth downshift.
What is Double Clutching? – In Conclusion
To round up our thoughts then, we’ve looked at double clutching, how to do it, whether it’s relevant today and the reference from The Fast and the Furious. We’ve seen that, while it’s a neat trick, chances are you’re never going to have to use it.
Perhaps the other main lesson is to treat Fast and Furious as the incredible film it is, rather than a driver’s manual. There are plenty of interesting references in the films, but this one is just a bit off.
We hope you have found this article useful and that you know a little more about your transmission and this driving technique.