Driving can be a difficult thing to get the hang of when you are just starting, but once you have some experience it becomes easier to pick up new skills. Some of these skills can be very useful, like rev matching and double clutching. However, it is important to know when and how to use them.
The main differences between rev matching and double clutching are:
- Rev matching is an action before re-engaging the clutch
- Double clutching involves more usage of the clutch and gear stick
- Rev matching is more relevant than double clutching nowadays
If you have never heard of either of these techniques before, this may sound very confusing. However, we will outline each technique below in much more detail and give you some information as to why and when you might want to use rev matching instead of double clutching, or even both at once.
What Is Rev Matching?
In simple terms, rev matching is the process of matching the speed of your engine with the speed of your transmission. The two parts are essentially made up of cogs that connect when you are in gear, and disconnect when the clutch is disengaged. When you are in gear, both the engine speed and the transmission speed are matched, as the cogs are locked into each other.
When the clutch is depressed, the two parts become disengaged, and if you were to keep your foot on the gas the engine speed would remain at the same RPM while the speed of the transmission would decrease. Essentially, the two parts begin to spin out of sync, and this is where the rev matching comes into play.
The best way to illustrate this is with an example. If you were driving along in fourth gear and quickly shifted down into third, you would probably notice a jolt. This is because you might be going from an engine speed of around 3000 RPM to one of 5000 RPM, due to the way that the gear ratios work. This can cause grinding of the gears and can damage the car.
Therefore, in order to make a smooth downshift at this kind of engine speed you will need to apply some of the gas pedal in order to lift the revs to 5000 RPM. The process is essentially depressing the clutch, applying some throttle while the clutch is disengaged to bring the revs up, and then releasing the clutch to engage the transmission again, leading to a smooth gear change.
If you were to do the opposite and change up from third gear at 5000 RPM and into fourth, you could in theory hold the clutch in for longer to allow the engine speed to decrease to the same speed as the transmission in order to get a smooth shift. The technique is most commonly used for downshifting however, as upshifting rarely requires much in the way of rev matching.
What Is Double Clutching?
Double clutching on the other hand involves more of the clutch pedal as well as the gas pedal. It differs from rev matching as a technique, although it essentially involves it as one of its steps. It is another way to reduce engine wear that can be caused by careless shifting of gears and was a very popular technique until cars implemented synchronized transmissions.
There Is More Involved
The double clutch method of changing gears involves dipping the clutch pedal, going into neutral and then releasing the clutch pedal, before then carrying out a rev match as described above. Then, once the revs are matched, the driver shifts into their desired gear – down or up, although like rev matching it is usually only used for downshifting – and releases the clutch once again.
Not Really Effective For Upshifting
The reason you would rarely need to use double clutching to upshift is that it would just take too long under normal circumstances. You can apply the throttle to lift the revs when downshifting, but the only way to drop the revs is to wait for them to drop themselves. The main way this would happen faster is if you were driving uphill, in which case you would probably be looking to downshift anyway.
Double clutching is commonly used nowadays in trucks and other special vehicles that do not have synchronized gearboxes. A synchronized gearbox essentially has a system already built into it that helps to make both down and up shifts easier and smoother, by keeping the transmission shaft rotating so that its speed doesn’t drop rapidly.
Why Use One Over The Other?
The first difference between rev matching and double clutching is the way they are physically put into practice. As rev matching only really involves more action on the throttle rather than the clutch, it is often much easier to do even for a first-time driver. If you are not overly confident with the clutch, double clutching may seem like quite a daunting task.
Rev Matching Is Easier To Learn
Rev matching isn’t necessarily easy to do without experience. However, it is much easier to juggle the task of driving, watching or feeling the revs, and then changing gear accordingly, than to do all of these things while also depressing the clutch pedal twice and moving the car from one gear into neutral and then into the next gear. There is just more involved in double clutching.
With that being said, if you are fairly confident with the clutch, and want to get the ultimate in smooth transitions between gears, double clutching can be the better option. As we have said already, it essentially involves rev matching as part of the process, and so once you learn how to match the revs properly, double clutching will become much easier.
Why Rev Matching Is Arguably More Useful Nowadays Than Double Clutching
We have already touched on the idea of a synchronized gearbox, and this is the main reason that the techniques of rev matching and double clutching are becoming less common. These kinds of manual transmission use meshing to keep the transmission shaft rotating while the clutch is disengaged, leading to a smaller drop in its speed when the clutch is depressed.
The Car Does It For You
This means there is less need to rev match, as the car helps do this for you in an indirect fashion. Some cars even have automatic rev matching, which eliminates the need for manual rev matching entirely. However, even without this system it is fairly easy to quickly down or up shift without the need to use either technique.
Even though modern cars have this technology, rev matching can still be useful. Drivers can definitely get away without double clutching in a modern car, provided they aren’t changing gears too carelessly. However, every driver could definitely benefit from being able to judge gear changes through some basic rev matching, and it can still help to reduce any unnecessary wear and tear of your car.
Other Times These Techniques Are Required
Although these techniques are not essential to the driving process, they can have a dramatic effect on the lifespan of your engine and transmission shafts. If you have an older car, you may have an unsynchronized gearbox. This means you will have to do a bit more rev matching, or else you may find yourself unnecessarily crunching through gears.
Trucks & Other Special Vehicles
A lot of heavy goods vehicles still use unsynchronized transmission boxes, and there are several reasons for this. Importantly, unsynchronized gear boxes are less prone to general breakdowns, as there are basically fewer moving parts at play because there are no meshing components to keep the transmission shaft rotating when the clutch is disengaged.
So, if you are driving a heavy goods vehicle, you will probably at least need to learn how to rev match effectively, but more than likely it will prove to be extremely beneficial to learn how to double clutch as well. The techniques can not only make for smoother transitions between gears, but also faster ones too when used correctly.
Rev matching and double clutching are two techniques that used to be a lot more common than they are now, but there is still use in knowing which is which and why you might want to use one over the other. Generally speaking, rev matching is easier than double clutching, although double clutching involves rev matching within its process.
Rev matching can take some time to get used to, but it will allow you to make much smoother gear changes. Double clutching is much less common due to improvements in vehicle technology, but it can still make for very smooth transitions as well. Once you get more comfortable with each technique, you will be able to make faster and smoother gear changes.