Double De-clutching & your clutch

[Anonymous]

O.K. I know the process for double declutching, however there is always a step that has seemed unnecessary, i.e. shifting into neutral before bliping the accelerator...

If i attempt any such manuvour I simply blip the revs with the clutch down which is no different from doing it in neutral, or is it  s:? :? s:?  . I can't help but think it is wearing on the clutch or some other part of the car.. why else would neutral be a part of the process?

Anyone know?  s:? :? s:?

[Anonymous]

Hope this explains things for you.

Double declutch
The double declutch (or, more simply, double clutch) is a driving technique that is somewhat harder to describe than to learn how to do. At one time, it was a very common practice, because gearboxes had no synchronizers. Now it has largely fallen into disuse, except by drivers of large trucks, who still have to deal with the older, unsynchronized, type of gearbox.
The purpose of the double declutch is to match the speed of the rotating parts of the gearbox for the gear you wish to select to the speed of the input shaft being driven by the engine. Once the speeds are matched, the gear will engage smoothly. If the speeds are not matched, the gears will "crash" or grate as they come into mesh. A modern synchromesh gearbox accomplishes this automatically.

To perform a double declutch, the clutch is pressed and the gearbox shifted into neutral gear. The clutch is released, the throttle is blipped which applies power to the disengaged gearbox, thus speeding it up internally. The clutch is pressed for the second time and the gear lever moved (smoothly) to the desired gear. The clutch is released again, and the drive continues. This operation is suitable for a down change. For an upchange, it is usually sufficient to allow the gear lever to rest momentarily in neutral and no "blip" is applied. The whole thing can, with practice, take no more than a fraction of a second, and the result is a very smooth (and satisfying) gearchange.

A related manoeuvre is Heel-and-Toe, in which the double declutch is performed while braking (braking and changing down on entry to a bend for example). Because the left foot is operating the clutch, the right foot must operate the brake and accelerator pedal (for the blip) simultaneously. Mastering this is very rewarding, and is essential for high performance driving (e.g. Rallying) where straight-cut gearboxes are often used to minimise the wastage of power.

[SteveJ]

Or just get SMT - it double de-clutches AND rev-matches in the blink of an eye (sounds cool on downshifts too   s8) s8)  )

[Liz]

When I was learning to drive HGV I really really tried to get along with the double declutch but was unable to, its great seeing someone drive who can do it properly though, my instructor was well impressive. I tried it in the two once but failed, roll on the jokes about females and co-ordination   s:roll: :roll: s:roll:

[Slacey]

....roll on the jokes about females and co-ordination   s:roll: :roll: s:roll:

I think your coordinating of the Hunt squashes that one  s:wink: :wink: s:wink:  
Back on topic though, is there any real need for this in a modern car? I can't say I've ever tried it - or ever will for that matter. I do blip on downshifts (feet too big to H&T) as I was taught to do so from my early biking days, so honestly don't see the point of this. Sounds too complicated for my liking anyway  s:oops: :oops: s:oops:

[GSB]

There is also another reason its done, although not usually by mere mortals...

D-D-C'ing is also handy if you are a highly skilled rally or tarmac racer, who is barreling into a corner at speeds beyond what would be considered sensible, and you need to change gear. Not only does D-D-C'ing guarantee it'll go in (missed gears arent just embarassing, but can blow engines up too), but done properly the matching of engine speed to gearshaft speed means that no positive or negative torque is applied to the driveline during the change. Thus, no sudden surge of engine braking or accleration to un-balance a car that is clearly already on the edge of control...

Like I said though... "highly skilled" & "racer". Not "commuter", or "shopper in Tesco's car park". This technique is for the exclusive use of the sort of people who need windscreen wipers on the door glass, and not by mere mortals such as ourselves.  s:wink: :wink: s:wink:

[noddynurdle]

when i had my spitfire i found i had to learn how to double declutch especially when i went from first in to second i found once it is learnt it is very easy to use well for quick starts but i dont have too now cos i got my MR2  s:D s:D    s:D s:D

[dieamond]

On a track, when you come into a U shaped corner, a quick brake and quick heel-toe down shifting gives you a fair advantage.
Downshifting is smoother, you cancel the shift lock and limit the parasite in weight transfer.

I say on a track, but you can use it on open road.
On road, it implyes going way too fast to be legal, thought  s;-) ;-) s;-)

[Anonymous]

Just going back to the original post, the only thing we have to do is to blip the throttle on down changes - this can be done with the clutch in and without doing the full double declutch since all we need to acheive is to match the engine speed to the lower gear ratio. As Steve said the only reason for doing this on a modern car with synchromesh gears is when changing down through the box quickly when approaching a corner quickly. If you acheive a perfect blip and downchange then when releasing the clutch there will be no change in engine revs and thus the attitude (front to rear) of the car will not change. Again, as Steve said, it really only applies if you are pushing the car really hard and on the ragged edge of cornering adhesion and you don't want to upset the car by down changing - on the other side of the coin, if you've not mastered the technique it could be as detrimental as it can be beneficial but we're probably talking 10/10ths driving here.

Sorry if i repeated a few things but I've tried to give a rounded answer to the whole question - if you get my drift (no pun intended).

[Anonymous]

One of the things the Advanced driving (and Police Drivers "Roadcraft" book) suggest is not changing gear while cornering.  Partly for this very reason.

[Anonymous]

That answers my question thanks guys for the full on explanaition  s:) s:)   I does cover my origional post very well, Really i wanted to know whether IF i D-D-clutch can I just blip the engine with the clutch down without damaging the clutch or something. It seems that a) it is unnecessary in modern cars unless trying for 10/10ths and b) not a problem to simply:

press clutch
blip engine
switch into gear
depress clutch

Rather than:

Press clutch
put gear into neutral
blip engine
put into desired gear
depress clutch

And so is quicker  s:? :? s:?  

Thanks again

[Anonymous]

During my Grade 1 Advanced Police Driver training they recommended that you use double declutching not only when changing down, but also when changing up.

Whilst it is not strictly necessary with good synchromesh gearboxes, it does mean that you do not 'over-rush' a gear change, risk a missed gear and preserves the synchros in the 'box.

It sounds very long winded, but once mastered gear changes can be performed quickly and slickly, and very positively.

The main down side is that your left foot works overtime and you might wear out the floor mats a little quickly. When doubling up the 'box you don't blip the throttle, just double pump the clutch.

One point worth bearing in mind is that Toyota boxes aren't reknowned for the strongest of synchros and a bit of care might pay off in the long term.

At the end of the day we all adapt our driving technique to suit ourselves, and to the specific conditions and type of driving being undertaken.

I tend to mix and match a lot of different styles and techniques, learnt over many years of driving and competition.

Andrew