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Racing Tips - Double Declutching

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Note we cannot be held responsible for any damages,  injury,  death or other consequences of using or misusing the information contained here (or on any other part of our website).  This information is for use at your own risk,  and you must assume full responsibility for it.

Double Declutching

Double declutching (sometimes spelt double de-clutching) is a technique that,  if done properly,  allows you to down shift smoothly using a manual transmission.  Double declutching also allows you to down shift when using a gear box that has no "synchros",  or worn "synchros".  If you have trouble getting into one or two particular gears,  especially when down shifting,  you may have worn syncros.  Double declutching will also reduce wear and tear on your synchros even if you have good ones,  increasing the life of your transmission.  Finally,  this technique will also allow you to go into first gear when you are moving at slow speeds (10-30kph) even if your gear box would usually resist such a shift.  Being able to shift down to first while still moving at these speeds can give you that extra push needed when rolling up to a set of traffic lights that change to green before you stop moving,  or in a race where you have to slow down for some reason and then want to take off again in a hurry.

This technique can be used on its own,  or as is more often the case,  as part of the heel and toe technique.  This article will describe the process of double declutching only,  if you wish to learn the heal and toe technique follow the links provided here or on our tips page.  Note however that double declutching is a lot easier to learn than the heal and toe technique and if you plan to do both together you may be better off learning this first,  then moving on to the other.

So,  how do you double declutch ?  There are really two parts to the process,  the actions required to double declutch,  and a second process called Rev Matching.  The actions are quite simple,  even if they do require some practice.  The basic movements are as follows :

  1. Clutch in (press the clutch pedal to the floor) 
  2. Move the gear stick to NEUTRAL
  3. Clutch out (release the clutch pedal to its normal position)
  4. Blip the accelerator (push on the accelerator pedal so the revs rise and fall)
  5. Clutch in again
  6. Move the gear stick to the new gear
  7. Clutch out again

As you can see,  this requires you to depress the clutch pedal twice - hence the name "double declutching".  Steps 4 and 5 should be done almost together,  so the revs are still higher than normal while you clutch in and complete the gear change,  but the 'blipping' must be down with the clutch out and with the gear stick in the neutral position.  How many revs should you use ? That depends on your vehicle,  speed and the gear being selected,  unless you are attempting to 'rev match' however it won't matter if you use too many revs.  If you use too few revs the gear stick will either resist going into gear (in which case repeat steps 3 onward with more revs) or it will shift normally   After some practice this procedure should become second nature,  although we recommend that your initial practicing be done only at race events or where there is no other traffic or hazards on the road.

How does it work ? Without going into too much detail,  increasing the revs while the vehicle is in neutral (and the clutch is out) causes some of the internal parts of the gear box to spin at a speed that allow them to mesh with other parts,  this means that the synchros have to do little of no work.  If the synchros aren't being used then they don't get in the way and/or don't wear out as quickly.

What about Rev Matching ? Rev Matching is a particularly useful skill to have mastered if you wish to learn the heel and toe technique,  and is the main part of the double declutching process as far as smooth driving goes.  When you rev match you are attempting to bring the revs up to the same level as they need to be for the car you're in to do the same speed you are doing at that point in time,  in the new gear you are selecting.  Say you're doing 50 kph in fourth gear, at two thousand revs,  but you want to change down to second for some more power.  If you simply try and change down,  several things will happen :

  1. The gear box may resist the shift,  if it doesn't your synchros are doing their job but you're wearing them out.  The actions we've already covered takes care of this.
  2. The car will need more revs to do the same speed in the lower gear so it will start to engine brake,  unless you apply the accelerator at the same time as you clutch out,  in which case the car is like to take off with a bit of a leap.
  3. You will change smoothly,  but only by letting the revs drop off to a lower level,  resulting in a slower shift.

In either of the cases mentioned in point two,  this will result in a jerky down shift.  In our example, we were doing two thousand revs in fourth,  lets say we need to be doing 4500 revs in second to keep going at 50kph for the vehicle we're driving in.  In order to rev match you must blip the accelerator enough that when you clutch out (in step 7 of our action list) the revs are at 4500.  This means that when the engine engages with the drive system again,  through the transmission,  everything is running at the speed it needs to be at and so there is no braking or sudden acceleration - nor do you have to wait for the revs to die off resulting in a slow shift.  Learning how many revs you need for different speeds and gears in different vehicles takes time and practice,  but when you get it right it will feel so good you'll be grinning well after you stop driving.

Why is it so important to be smooth when driving ? Well,  on the road the smoother your driving the better your passengers will feel and the safer you'll be.  At a race or other event being smooth lets you use 100% of the vehicles abilities for what you want it to do,  rather than for counter acting sudden jerky movements.  For example,  lets says you're racing on a sealed surface but one that doesn't have a lot of traction (maybe its wet or something).  You change down a gear and plant your foot to get more power,  but the sudden increase in power causes the tyres to slip on the track and you spin your wheels.  Even if this only happens for a 100th of a second, you just lost time.  In addition to this,   sudden changes of power while cornering or braking can cause you to spin,  slide,  swap ends or even roll in extreme cases.
If you're a smooth driver you'll be able to get alot more out of any given vehicle than a driver who isn't as smooth. It may take more time & practive before you're faster than a more agressive driver,  but that driver will eventually get to a point where the only way they can go faster is to become smoother (otherwise they're asking the car to do more than it car at the same or lower speeds  than you are).  Its a lot harder to learn to be smooth when you've been racing aggresively for a long time,  so its better to learn to drive this way to start with.

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