Double clutching and rev matching are two driving techniques that are used in different situations. Beginner drivers may not know when to use each one, or may even think they’re the same thing. But there are some key differences between double clutching and rev matching.
The 3 main differences between double clutching and rev matching are:
- Rev matching is an action before re-engaging the clutch
- Double clutching involves more use 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 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 pedal is depressed, the two parts become disengaged, and if you were to keep your foot on the gas the engine speed would increase (as there is now less load on the engine) 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.
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 involves use of the clutch pedal and 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 it 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 matching the revs as described above. Then, once you match the revs, you shift into your desired gear – down or up, although like rev matching it is usually only used for downshifting – and release 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 most commonly used 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 upshifts easier and smoother, by keeping the transmission shaft rotating so that its speed doesn’t drop rapidly.
KEY POINTS• Rev matching is a technique used to make for smoother gear changes
• Double clutching involves rev matching, but it is rarely used nowadays
• Modern synchronized gearboxes remove the need to double clutch
Rev Matching vs Double Clutching – Which To Use?
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 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.
Rev Matching vs Double Clutching – Which Is More Useful?
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 less common than they once were (outside of racing anyway). 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 an 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 breaking down, as there are 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.
KEY POINTS• Both rev matching and double clutching are fairly obsolete practices in normal, everyday driving
• Some vehicles may benefit from the use of one or both of these techniques
• Each of them can make for smoother gear changes when done properly
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.
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