Double Clutchng - Please explain

[blueoval]

I have heard this terminology used in racing terms for manual vehicles.

Can someone shed some light on what the benefits are for 'double clutching' and why some racers do it?

If there is another thread on this subject, please direct me to it.

[olfella]

Used to be common in the good old days; before syncros and was used to 'line up the cogs' at each gear change.

[blueoval]

Thanks olfella, is it a necessity for todays gearboxes or a thing of the past?

[Nathan&Amanda]

it is a method of changing down normally

you push clutch in, pull out of gear release clutch rev, re clutch and put in gear,


pretty simple but hard to master

not needed today normally, as gearboxes have synchros etc to allign gears and allow to engage

Yep, it's pretty simple. Clutch in, neutral, clutch out, match revs, clutch in, select new gear and the release.

Much more satisfying to not clutch non synchro boxes at all, but that takes getting used to and can sound very bad if you get it wrong.

Many trucks use non synchro boxes, cars started using synchro's in about the 30's. Some race boxes still use no synchro's, but they don't double clutch the shifts.

If you're thinking fast and the furious, that was just rubbish. Double clutching had nothing to do with anything. Stupidest line ever.

-
edit.
You can practise it on your normal cars, but it will just wear the clutch out twice as fast. You won't know if you've got it right because the synchro's will match it all up for you. So very little benefit, other than getting the basic co-ordination.

If you've ever heard a truckie talk about a road ranger, it's a non synchro box they were referring to.

If you can't find it, grind it.

[olfella]

Originally Posted by blueoval

Thanks olfella, is it a necessity for todays gearboxes or a thing of the past?

Previous post also answers this. With good syncros you should not need it however I have driven some cars with worn syncros and it does make the downshift a bit smoother.

[V3RSAC3]

Takes ages to master Shav ... but u have an Auto : ... i'll teach ya when i update to a manual bro :P

Originally Posted by olfella

Previous post also answers this. With good syncros you should not need it however I have driven some cars with worn syncros and it does make the downshift a bit smoother.

Good point. The synchro's are a bit worn on the 2nd gear of my other car. I have to get the revs pretty right when I shift into second.

I could also double clutch if I wanted, but why bother.

[olfella]

Originally Posted by Shounak

Many trucks use non synchro boxes, cars started using synchro's in about the 30's.
If you can't find it, grind it.

Mmmm must be older than I feel :evil3: but I can still do it!! :

[Smoke Pursuit]

Its easy to master once you got it.. I drive 13 - 18 speed road rangers quiet easily now..

[Sloth]

Originally Posted by Shounak

You can practise it on your normal cars, but it will just wear the clutch out twice as fast. You won't know if you've got it right because the synchro's will match it all up for you. So very little benefit, other than getting the basic co-ordination.

Haha, I did just that. Got the co-ordination for it in my EB a few months back, no point, purely out of curiosity. And now I drive an auto anyway.

[schnoods]

Originally Posted by Fast and the Furious

You almost had me? You never had your car. Granny shiftin’, not double clutchin’ like you should. You’re lucky that hundred shot of NOS didn’t blow the welds on your intake. Almost had me? Now me and the mad scientist gotta rip apart the block and replace the piston rings you fried. Ask any racer, any real racer. It don’t matter if you win by an inch or a mile, winning’s winning.

Hehe, thats the only time I really heard it.

[aussiblue]

I always called it double declutching and it was the only way to drive the old Jeep we had on the farm when I was a kid. Non synchro gearboxes were old technology even then - out 1950's farm tractor even had a 5 speed sychro gearbox. The Willy's also had synchomesh originally it was just that they had worn to the point that they no longer worked.

Through lack of practice I have forgotten how. Though as I found out several years ago when asked to drive a similar old jeep, my sub-concious still knows how. I automatically double declutched fine without being aware of it until someone commented on what I was doing and I became concious of what I was doing - after that I couldn't do it - I think I was thinking too hard about how to do it and waiting for the inevitable gear grind each time.


See http://www.madabout-kitcars.com/kitcar/kb.php?aid=190

Double declutching technique

A double clutch (also called a double declutch) is a driving procedure used for vehicles with an unsynchronized manual transmission. Before the introduction of synchronizers and automatic transmissions, double declutching was the only way to drive an automobile. Due to the difficulty involved in learning the technique, it has largely fallen into disuse. However, drivers of large trucks still use double clutching, as those vehicles are usually equipped with the older, more efficient, and more durable unsynchronized gearboxes.

The purpose of the double clutch 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.

When shifting up on a double-clutched vehicle, the clutch pedal is pressed and the gearbox shifted into neutral. The clutch pedal is then released. As the engine idles with no load, the rpms will decrease until they are at a level suitable for shifting into the next gear. The driver then depresses the clutch again and shifts into the next gear. The whole manouver can, with practice, take no more than a fraction of a second, and the result is a very smooth gear change. However, in order to downshift, engine revs must be increased while the gearbox is in neutral and the clutch pedal is released. This requires the driver to shift into neutral, release the clutch pedal, apply throttle to bring the revs up to a suitable speed, depresss the clutch again, and finally shift into gear. This operation can be very difficult to master, as it requires the driver to gauge the speed of the vehicle accurately and is often conducted as cars in front slow down.

A related technique is called Heel-and-Toe, during which the brake and accelerator pedal are pressed by the right foot while the clutch pedal is pressed by the left foot. Note that Heel-and-Toe can be used with any downshift clutch operation, not just with double-clutching. Though difficult, mastering Heel-and-Toe in conjunction with Double Clutching is essential for high performance driving (e.g., Rallying) where straight-cut gearboxes are often used to minimise the wastage of power.

[blueoval]

cheers for the info fellas. Thats explained a few myths for me.

Yeah I have heard it from a few sources including fast and furious and other films. But I was never sure if it was something worth doing. Obviously not by the sounds of it.

[whiteELXR6]

Yer not really something that is really applicable for today's cars, still widly used to drive trucks though. Mind you I prefer to not use the clutch in the truck but it does take alot of practice and soem ordinary sounds lol.

[XHUTE6]

In my old Freightliner and Mack, due to my long legs i had trouble reaching the top of the steering wheel and often had to lean forward to turn corners if i wanted to use the clutch. I was forced to drive without the clutch up and downshifting. Now in my Powerstar i can sit very comfortably, still down low in the cab and and can use the clutch and turn corners without leaning forward. I feel much better about my driving now.
Talking to an engineer at Allison one day about this and he said to me that the clutch is there for a reason. It should be used. While you may appear skillful driving without the clutch, any employer would prefer someone who prefers to use the clutch.

[smally289]

As well as using it to help engage gears by equalising the speed of the gears so they mesh more easily, race drivers use it on downshifts to prevent 'compression locking' and help stabilise the car during braking.
Imagine if a V8 supercar driver went flying into the chase at Bathurst at full noise, hit the brakes, selected 4th gear and popped the clutch. The back end would lock up quicksmart!

[snakeoil]

Just a small point if you cannot double declutch you probably cannot heel and toe which means that you cannot balance a car at its ragged edge

Even heel and toe with a blip on the down change is better than slamming down a cog then back on the brakes etc

Riding bikes /cars quick is all about balance and controlling the weight shift

Dude next time V8 supercars is on watch very carefully when they do the footwell shot it shows how they balance the car

if you are driving an auto learn left foot braking...........the first time you do it you will either break your nose on the dash or slam into the car in front but keep practising

Driving cars is a foot skill not a hand skill.......cheers

[FPV8U]

Still Learning the Art of Heal - Toe to be honest, i find it much easier in alot of friends older smaller cars (E.g TX3 AWD Turbo) than in my BA Falcon and i have decent sized feet (Size 12-13), is is just me or does it seem like the Brake sits just a touch high to give the throttle a proper Blip with the Less than sensitive Electronic throttle in these cars?

Maybe an Edit will help or am i missing something?

[NudgE^SIKBRO]

In the K-Dub im double clutching all day long, its a to learn correctly but once you do its really quite simple, Tacho is your best friend... when learning

[sprjenkins]

Originally Posted by FPV8U

Still Learning the Art of Heal - Toe to be honest, i find it much easier in alot of friends older smaller cars (E.g TX3 AWD Turbo) than in my BA Falcon and i have decent sized feet (Size 12-13), is is just me or does it seem like the Brake sits just a touch high to give the throttle a proper Blip with the Less than sensitive Electronic throttle in these cars?

Maybe an Edit will help or am i missing something?

No your right, the brake pedal sits higher in my BA XR6T, makes it hard to blip the throttle with your heel and when you do hit the throttle the throttle response is crap because its electronic and not very sensitive.

I'm kinda wondering if its even worth learning in the BA because its so hard to do.

[lukep]

some people ive spoken to say this and they mean when in wet or dry and want to drift without the handbrake or other means,as you come into a corner and the weight of the car(if your goen quick enough)starts to offload and your given it throttle punch the clutch and be ready to catch it.I used to do this(and still do)with my first car a xf 3.3 carby,open diff in my pops paddock.doen circle work and no crapy keyholes but huge controlled drifts around a goat track and when it started to oneleg i would smash the clutch or feather the brake to get both wheels to spin again.unless youve got a safe place to practice i recommend not to this as ive had a lot of practice and was shown a few tricks by a couple of my uncles.highway patrol officer and driver instuctor for the sydney police force.both are extremly good steerers.retired now.

Start riding a motorbike, where heel toeing is much easier. If you don't rev match the downshifts, you'll end up on your . Unless you've got a slipper clutch.

[Peuty]

Originally Posted by Shounak

Start riding a motorbike, where heel toeing is much easier. If you don't rev match the downshifts, you'll end up on your . Unless you've got a slipper clutch.

I'm confused. I ride a motorbike myself, but I can't understand how you would "heel/toe" on one...

[FPV8U]

Originally Posted by sprjenkins

No your right, the brake pedal sits higher in my BA XR6T, makes it hard to blip the throttle with your heel and when you do hit the throttle the throttle response is crap because its electronic and not very sensitive.

I'm kinda wondering if its even worth learning in the BA because its so hard to do.

Good to hear im not a total dud then

[nat_daly]

it's used alot in racing, especially drifting. when u do it alot, it becomes habit and people get in the car and ask what the hell your doing.

Originally Posted by Peuty

I'm confused. I ride a motorbike myself, but I can't understand how you would "heel/toe" on one...

You rev match your downshifts. When you switch down a gear, you clutch in, throttle up to the right revs and then put in gear.

You don't physically heel-toe, but you do the same thing as heel-toing in a car. Using the clutch, brake and gas at pretty much the same times.

It's like saying you floored it at the lights in a motorbike. You don't physically floor it, you just twist it or snap it. But everyone knows what you mean.

[Peuty]

Yeah thats what I thought. I would hardly call it heel toeing though.

[3vXT]

Originally Posted by blueoval

Can someone shed some light on what the benefits are for 'double clutching' and why some racers do it?

Not sure about racing but for someone driving a modern car on the road the main benefit is that it increases the size of the drivers ego and is a good skill to boast about on the internet and other places.

I'm not seriously having a go at anyone but whenever this subject comes up on an internet forum the responses seem to descend into some kind of primitive, body part measuring contest :

Like i said, i'm not having a go at anyone, its just something amusing that i've noticed.

EDIT: I've tried it a few times in my BA but as someone posted earlier, the brake feels way too high. I've got bigish feet but it feels like i need clown shoes on. Tried it once or twice in my old work car (90's rodeo) and while the pedals in that felt perfect, i was still pretty bad at it

EDIT2: I guess that means i don't measure up

[Dezza]

Originally Posted by aussiblue

I always called it double declutching and it was the only way to drive the old Jeep we had on the farm when I was a kid. Non synchro gearboxes were old technology even then - out 1950's farm tractor even had a 5 speed sychro gearbox. The Willy's also had synchomesh originally it was just that they had worn to the point that they no longer worked.

Dad's tractors don't have synchro. He has 77' and 78' International tractors. I don't double clutch though. You basically need to be firm but don't slam it straight in. It seems to slide in to the right gear pretty easy with this method. It's kind of like getting reverse in the EA. It doesn't have a reverse synchro, so if I try to force it, it'll crunch. Be gentle and it usually goes in pretty easily.