An excellent explanation of what it is and how it's achieved at TCS Racing - Racing Tips - Double Declutching

Chris

errr....

what's it for??

downshifting smoothly

my dad taught me

surely on a race track with dog-engage gears you wouldn't care tho right??

On a car with a crash gearbox it's essential - the gears won't engage if they're rotating at different speeds. In a modern gearbox with synchromesh, unless the synchros are worn, it doesn't really do anything, other than slow you down, IMHO. There are even people who claim it accelerates wear on your gearbox (I can see why, since you make the synchros do their job twice instead of once). You pays your money ...

Does nothing but slow you down? Pah :P

Chris

Step 4:

Blip the accelerator (push on the accelerator pedal so the revs rise and fall) - In diesel read magazine while waiting for this to happen

In my first car (a Triumph Vitesse 1600) I got this down to a fine art for towing a rally Mini on a trailer, as 1st on the Vitesse was non-syncho :D

Not needed today, IMHO :)

I think it depends what cars you have access to, as some modern cars high performance cars "prefer" DDC gear changes. Certainly a good skill to have in the tool box

Chris

which ones are they? i didnt know some cars prefered this and some didnt.. I've always done it if i need to brake fairly harshly as i just use it as a engine braking....

i made a concious effort to do it today when i was burning along a B road with twisty hairpins etc, and the car does seem to accelerate away faster..

happy days:thumbup:

Always used this for downchanges where engine / road speed matching is needed, particularly dropping into first from highish speeds.

Also use heel an toe a lot in the MR2 (a waste of time in the Fabia). With the new manifold / high flow cat / exhaust, it sounds really crisp when doing this. Makes for easier smoother downshiftng while braking for corners. Pretty essential with a light car to keep things smooth. For snicking into first I heel and toe and DDC, but for all others, I just rev match.

Anyone use heel and toe with block changes? I find it works a treat when really hard on the brakes.

Chris

I heel and toe with block changes (see heel and toe thread) when using a modern syncro gearbox, I'm 100% convinced that block changes - and doing it quite late in the braking zone, are the way ahead. I can't see the point of DDC unless with a straight cut race gearbox, usually a sequential. It can feel quite nice but is something you do for the sake of it IMHO.

When I instruct people on track I find making them concentrate on braking only in the early part of a braking zone, then block changing and letting the clutch out shortly before turn-in, makes their braking vastly better and smoother - whether or not they heel and toe (which is ideal but not something you can learn in an instant). Doing multiple gearchanges during braking, and letting the gears out too early, bringing the revs right up, is not smooth, quick, or mechanically sympathetic.

In fact I find on the road that changing nice and late means heel/toe is not nearly as necessary as it might be.

I heel and toe with block changes (see heel and toe thread) when using a modern syncro gearbox, I'm 100% convinced that block changes - and doing it quite late in the braking zone, are the way ahead. I can't see the point of DDC unless with a straight cut race gearbox, usually a sequential. It can feel quite nice but is something you do for the sake of it IMHO.

I guess DDC is another tool in the tool box so you can make use of it if need be and it does ensure downchanges are nice and smooth (and quick) without resorting to a far less mechanically sympathetic clutch drag gear change....

I see you're local - does that mean you instruct at Thruxton?

Chris

Someone once suggested that I do a bit at Thruxton, but no, I've never done my ARDS instructors qualification - what instruction I do tends to be for friends and friends of friends. Now I'm not racing, or even doing that many trackdays, it's a good way of keeping my hand in from time to time and tbh I enjoy teaching...

Iwork on trucks all day and ive found that the old timer drivers who started driving using the ddc method are always the ones that complain of gearbox problems in their newer trucks. ive known of several instances where gearboxes have been damaged because if them using this style of driving

I drove a 1926 Lea Francis Coupe a few years back and I needed to double de-clutch on that as it doesn't have a syncromesh, never needed to do it on anything else since. Maybe if you were posting on this forum 70 or 80 years ago then you would have had a different responce to this subject

The main benefit on modern gearboxes is when trying to speed match a big difference, sy dropping into 1st or 2nd at 4 or 5000 rpm for a corner. Just using the synchromesh, the gearbox will often baulk trying to do this with the input shaft near idle speed.

Chris

The main benefit on modern gearboxes is when trying to speed match a big difference, sy dropping into 1st or 2nd at 4 or 5000 rpm for a corner. Just using the synchromesh, the gearbox will often baulk trying to do this with the input shaft near idle speed.

Chris

Unless you're on a racetrack, just WTF would you actually do this anyway?

Unless you're on a racetrack, just WTF would you actually do this anyway?

Well, one may be on one of ones favourite stretches of road, slowing for a corner where one wants lots of fun acceleration on the exit, maybe even balancing the car in a bit of an oversteer drift.

Ones engine may be a naturally aspirated item that has little torque low down so one would need to keep it revving to get best exit speed.

Sure there are other reasons, but those will do for now.

Chris

I'm sure a sustained gear change would give the same effect without having to have the car in neutral while you press the clutch again.

I'm sure a sustained gear change would give the same effect without having to have the car in neutral while you press the clutch again.

Of course it will, but over a much longer time frame and with much greater wear and tear on the synchros.

Any reason why not to use it when required?

Chris

No if you find it works for you and is safe and smooth then it's not a problem.

I just don't see a reason to have the vehicle in neutral and effectively coasting while you blip the throttle and wait for the revs to come back down before engaging the gear I think it would encourage rushed gear changes which in turn could affect stability and smoothness.

No if you find it works for you and is safe and smooth then it's not a problem.

I just don't see a reason to have the vehicle in neutral and effectively coasting while you blip the throttle and wait for the revs to come back down before engaging the gear I think it would encourage rushed gear changes which in turn could affect stability and smoothness.

I don't wait for the revs to come back down, I just blip to get the revs I want and engage the gear. Will sometimes do it after braking, sometimes during braking. Takes less time than a protracted gear change and makes progress smoother as the engines internal components wont need to be whipped up to speed as the clutch comes up.

As for fitting it in, the gear change (however achieved) is built into the planning for each corner so it does not cause any issues.

Chris

some people are getting confused and thinking that DDCing is used up the box...