31 replies to this topic

[chrisuofc]

I'm saving my money and hoping to go to a racing school soon, so I'm trying to learn as much as I can on my own so I don't look like a fool. I've been reading about double clutching, and I hope someone can answer my question. All the sites I've gone to said you do it in this order:
1)depress the clutch
2)move the shifter into neutral
3)let out the clutch
4)blip the throttle to match the revs
5)depress the clutch
6)shift down and let the clutch out again

My question is, why do you have to let the clutch out in between. Why can't you blip the throttle while the clutch is still in (since this seems faster). Any help would be great

[BertlF]

I'm not a technical expert, but AFAIK the blipping of the throttle with the 'closed' clutch used to sync the gear ratios in former non-synched gear boxes. My old beetle for example hat a non synchronized first gear, whenever you wanted to change from second to first and the car was not at a standstill, you had to use the 'double clutching'. Of course, non-synched gear boxes are still used in car racing.

Bert

[brad_d]

Basically, it's because there are two separate "rev-matches" that need to be made. We're all familiar with rev-matching the engine flywheel with the clutch plate when releasing the clutch. But it's also necessary to match the internal gearing of the transmission in order to shove the thing into gear in the first place. Modern passenger cars almost universally have "synchronizers" in the transmission that take care of this for us, which is why double-clutching is not necessary.

This article at howstuffworks.com gives a pretty decent picture of just what's going on.

Basically, with the clutch disengaged and the transmission in neutral, the layshaft and the actual gears in the tranny will spin to a stop, as they're now connected to neither the engine nor the wheels. To physically put the car in a gear, you have to mesh a collar with "dog teeth" on it to a gear fixed to the layshaft. This collar is spinning with the driveshaft.

To match 'em up, you need to "blip" the layshaft up to speed. Since the layshaft isn't connected with the engine when the clutch is disengaged, you need to let out the clutch briefly to "hook them up," and then give the throttle a blip.

Reading through the link I provided will hopefully make things more clear.

This whole practice is purely theoretical to me, BTW. I've never driven a race car, or even a car without synchros so I have zero actual experience with double-clutching.

[lateralforce]

I think for some model of trucks the drivers still have to double clutch to shift smoothly. However, if you are going to a racing school, chances are you don't have to deal with a car that needs to be double-clutched, as since most modern cars have synchros that matches the rotational velocity of the dog gear for a smooth gear meshing.

If the program you are enrolling in has basic drills such as braking, slalom, autocross etc, you might want to do a little excersice on modulating the brake pressure, heel and toe, handling the steering wheel, etc.

You might also want to do a little reading on simple vehicle dynamics such as weight transfer during cornering and braking/accelerating.

[scarbs]

I agree with Lateral Force, unless you are going to a racing school for pre war racing cars, then most important skill is heel and toeing, you will find getting the car down through the gearbox will distract you as you enter the corner. Go out in your road car and practice clutchless down changes to appreciate the rev matching that is needed.
Also you need to practice smoothly applying steering lock and focussing your concentration on every aspect of yor driving for 15 minute stretches.

[AS110]

Hitch a ride in a truck and watch the footwork,it will be slower and easier to follow than a racing driver.

Even a sequental gearbox like a motorcycle needs a blip of the throttle to make a clean downshift.Contry to what you would think fewer and bigger dogs give a quicker and cleaner shift than many smaller dogs,these just feel like a box full of teeth.

[schuy]

Originally posted by lateralforce
I think for some model of trucks the drivers still have to double clutch to shift smoothly. However, if you are going to a racing school, chances are you don't have to deal with a car that needs to be double-clutched, as since most modern cars have synchros that matches the rotational velocity of the dog gear for a smooth gear meshing.

I am sorry, I have to disagree.
Even modern cars would benefit from blipping, as double de-clutching through downshifts make for smoother braking and a more stable car.
I have an Alfa Romeo 33, 1.5, and it's synchromesh is notoriously bad, So blips are very Recommended, but I do it all the time, which makes for a smoother ride, and when driving hard it's much safer to be honest.

Liran Biderman.

[mhferrari]

Originally posted by schuy


I am sorry, I have to disagree.
Even modern cars would benefit from blipping, as double de-clutching through downshifts make for smoother braking and a more stable car.
I have an Alfa Romeo 33, 1.5, and it's synchromesh is notoriously bad, So blips are very Recommended, but I do it all the time, which makes for a smoother ride, and when driving hard it's much safer to be honest.

Liran Biderman.

Indeed, even with a trans with syncros, it is good to double-clutch/double-declutch. You don't have to, but it will help make smoother shifts.

Certain trucks require double clutching as well as aforementioned.

[bobdar]

The driving schools like to teach double-clutching with the dog-ring boxes because, for people who aren't used to shifting this kind of transmission, double clutching is the least damaging to the dogs.
Most racers (using dog-ring boxes) don't double clutch, and, in fact, shifting both up and down without the clutch can be accomplished with no strain on the gearbox. Clutchless shifting allows for left-foot braking, which in turn allows for very precise matching of the lay and pinion shaft speeds, more precisely than possible with heel-toe, in my opinion.

[AlesiUK]

The same process "double de-clutching" can be used in fast driving for another purpose nothing to do with gearbox,it keeps the revs up wich can benifit you depending on the power curve of the car you are driving

[Ross Stonefeld]

ive never understood why you need to release the clutch in neutral. It didnt seem any faster, to have any less wear, and it was just one more thing to worry about. Depending on the throw of the gates and the weight of the flywheel I usually blip whilst im moving the gear lever and its pretty easy to get the timing right. sometimes depending on the car I dont even let the clutch out until im done with the gear selectrion process. Ie i dont let the clutch out in each gear during a 5-2 downchange.

And yeah, most guys shift without the clutch entirely, its remarkably easy in a proper racing gearbox.

[The Tiger]

Forget you even heard about double declutching!

Now at days, and even some 10 to 15 fifteen years ago, race cars, especially formula cars, have syncros which will help you in that department. I being a racecar driver myself, can assure you that most racing drivers do not even use the clutch neither for down nor up shifting. Can you imagine the time and consistency it would take to double clutch down about 1000 times during a single race! WOW!

The technique is old and useless. Of course, blipping is a must if you want to keep the car balanced, but you can still blip without the cluth.

When attending a driving school, keep in mind that you are there to learn and try to get as much as you can out of it. Take it easy and remember it is all about practice and experience. Do not try to eat the whole cake in one bite. Take it step by step. Normally, racing schools use formula cars without wings wich is an excellent way to begin and to learn one of the most important factors in race driving wich is car balance.

[Ben]

Formula cars do not have synchro.

The odd Porsch Group C car had it, but no single seater will FFord, F3, F3000, CART, IRL, F1, etc, etc.

Ben

[AlesiUK]

I being a racecar driver myself, can assure you that most racing drivers do not even use the clutch neither for down nor up shifting.

i would have though most drivers whilst not clutching on upchanges would still need to clutch on downchanges,i admit my single seater experience is limited to a couple of formula ford drives,but i always used the clutch on downchanges and to my knowledge so did everyone else.

Watching the CART race the other nite seemed to show that they also use the clutch on the downshift,the pedal-cam gives a great view of the drivers feet at work.

[F1Johnny]

Originally posted by Ross Stonefeld
ive never understood why you need to release the clutch in neutral. It didnt seem any faster, to have any less wear, and it was just one more thing to worry about. Depending on the throw of the gates and the weight of the flywheel I usually blip whilst im moving the gear lever and its pretty easy to get the timing right. sometimes depending on the car I dont even let the clutch out until im done with the gear selectrion process. Ie i dont let the clutch out in each gear during a 5-2 downchange.

And yeah, most guys shift without the clutch entirely, its remarkably easy in a proper racing gearbox.

Agreed. I am no race car driver, but using heel and toe to change down the box works very effectively to match revs. I do not double clutch, I simply depress the clutch and while shifting down rock my foot over or actually use my heel depending on the pedal layout, blip the throttle and the lower gear engages smoothly, with no obvious compression.

[merlyn6]

Originally posted by AS110
Hitch a ride in a truck and watch the footwork,it will be slower and easier to follow than a racing driver.

Even a sequental gearbox like a motorcycle needs a blip of the throttle to make a clean downshift.Contry to what you would think fewer and bigger dogs give a quicker and cleaner shift than many smaller dogs,these just feel like a box full of teeth.

Its not the size or number of dogs, its the space between dogs that counts. That's the reason Hewland went to narrow dogs some time ago. As long as the dog is substantial enough to carry the torque load, that's all you need.

[ME]

My Car's syncro's are shot so I have to doubleclutch all the time up and down, but I have a trick.

As you are about to change gears, when you let off the throttle apply slight pressure to the shifter
towards neutral. This will throw the car into neutral smoothly without clutching.
Then blip the throttle, stab the clutch, and throw it into gear. Thats it, double clutching with one stab at the clutch, it sure makes for faster shifts.

Oh and blipping the throttle is so necessary in my car, the rears chirp all the time if you don't, it just makes your driving so much smoother.

[schuy]

Originally posted by ME

Oh and blipping the throttle is so necessary in my car, the rears chirp all the time if you don't, it just makes your driving so much smoother.

What car do you have?

[ME]

Ford Thunderbird Super Coupe, its a 3.8L Supercharged V6.

[crono33]

Hi all
i thought i could give my experience, while many years ago i owned 2 fiat 500, which had no synchromesh

double declutching was necessary for downshifting, otherwise loud noises would come from the gearbox, and slaps would come from my dad ;-). the throttle response of the old 360degrees twin cyl 500cc was SLOW. and pedal position was tricky to say the least

using double declutching with syncromeshed gearboxes makes for much quicker shifting, because the syncro doesnt have to do any work; the engagement are already at a very similar speed and this will save a lot of time during downshifting. unfortunatly, my current car (lancia delta integrale) has a very poor throttle response so double declutching is not as effective.

modern cars often have the pedals in positions that make the toe-heel impractical....sometimes toe-toe is possible...(the previous owner of my car bent the brake pedal so it is very close to the throttle)


in bikes, blipping the throttle makes for a smoother downshifting (many bikes will tend to lock the rear wheel during fast downshifting and un derbraking) and avoid the rear whell "skipping", and the rear end coming out of line

also, on bikes, the multidisk clutch always drags a bit so blipping the throttle wont require declutching
blipping the throttle, on bikes u can downshift without clutch. going up in gears doesnt require any clutch at all.

ciao

gm

[AdamLarnachJr]

Originally posted by AlesiUK


i would have though most drivers whilst not clutching on upchanges would still need to clutch on downchanges,i admit my single seater experience is limited to a couple of formula ford drives,but i always used the clutch on downchanges and to my knowledge so did everyone else.

Not always true. I drive a 1990 Ford Ranger at work everyday, and I hardly ever use the clutch for downshifting, I just left foot brake and blip the throttle the instant I get the transmission into neutral and slide it into the next gear, works everytime just about, not the best at low rpm's but its as smooth as silk and works much better than heel toe downshifting on the street.

[Dmitriy_Guller]

I was watching the NASCAR race at Sears Point, and they showed Mark Martin's footwork. Apparently, on downshifts, he just left foot braked and blipped the throttle on each downshift, while on the brakes. On upshifts, he lifted off the gas for a very short moment while using the clutch. It surprised me, because except for using clutch while upshifting, that's exactly the technique most use in GPL that is deemed unrealistic. I was also surprised at that, because Cup cars have notoriously bad brakes for road courses that fade badly towards the end, yet Mark Martin didn't have brake problems while gassing under braking.

[AndyM]

I work on and off for a Junior FFord team here in the UK, and our drivers (all 4 of them as I am aware) do not bother with the clutch on either up or down shifts. Sometimes they find it useful to get into first gear if we are using first for a tighter corner in qualifying, but thats all. Testing at Brands on Friday, one of our clutches went. Apart from stalling in the pitlane between sessios and requiring a bump start, it was no problem.

When I last raced a FFord almost 2 years ago, we were told (Silverstone School) to use the clutch, but I never bothered, as I was having enough trouble synchronising my feet at first for heel and toeing, so I forgot the clutch until I got the hang of it. I reverted back to using the clutch, but didn't bother with it in qualifying and found I could concerntrate on the blipping and my braking much more easily. I now heel and toe in my car (and have done for about 2 years) just to keep my eye in, and it all come naturally now, forget I am doing it. My Corsa gearbox doesn't like me not using the clutch though.....

Similar to the Nascar footage mentioned above, I saw some coverage from one of the Aussie V8 races, and they had a camera looking at Paul Radisich's feet, and he just lifted off briefly to change up, and blipped whilst left foot braking on the downchanges.

[schuy]

Originally posted by crono33
Hi all


using double declutching with syncromeshed gearboxes makes for much quicker shifting, because the syncro doesnt have to do any work; the engagement are already at a very similar speed and this will save a lot of time during downshifting. unfortunatly, my current car (lancia delta integrale) has a very poor throttle response so double declutching is not as effective.

ciao

gm

Try looking for lighter throttle bodies?

[mhferrari]

Originally posted by ME
Ford Thunderbird Super Coupe, its a 3.8L Supercharged V6.

What year?

My brother had an LX (the un-supercharged 3.8L V6), with good ol' rear-wheel drive. The un-supercharging made it underpowered, though it is fun in the snow!

He had troubles with his transmission as well.

[lumepo03]

A purchase of a book by Carroll Smith "Drive to Win" or by
Aryton Senna - Alain Prost - Niki Lauda - Piero Taruffi - Paul Frere or Jackie Stewart, on high performance driving. Any book by Aryton Senna - Alain Prost - Niki Lauda - or Jackie Stewart will be your best bet. After all you have a culmination of 13 world Driving Championships recommending the best solution to driving (braking, steering, shifting, accelerating).



P.S. Carroll Smith is a highly successful and well respected engineer known by successful racers.

[ME]

quote:

Originally posted by ME
Ford Thunderbird Super Coupe, its a 3.8L Supercharged V6.

What year?

My brother had an LX (the un-supercharged 3.8L V6), with good ol' rear-wheel drive. The un- supercharging made it underpowered, though it is fun in the snow!

He had troubles with his transmission as well.


Its A 1991, I've never been in the LX, but the SC's sure are fun, Its great on the highway as well.
I tend to go through a little to many rear tires though.

[mhferrari]

Originally posted by ME
Its A 1991, I've never been in the LX, but the SC's sure are fun, Its great on the highway as well.
I tend to go through a little to many rear tires though.

My brother's was a 1993.
There should be more rear-wheel drive cars on the road!

[just me again]

Originally posted by F1Johnny


Agreed. I am no race car driver, but using heel and toe to change down the box works very effectively to match revs. I do not double clutch, I simply depress the clutch and while shifting down rock my foot over or actually use my heel depending on the pedal layout, blip the throttle and the lower gear engages smoothly, with no obvious compression.

WHAT are you talking about. The porpuse with double clutching is to make the wheels in the gearbox rotate with the same speed before they are engaged in eachother. It has absolutely no porpose to blip the throttle with depressed clutch because there is no connection to the gearwheel you are about to engage.
Bjørn

[bobzdar]

It has absolutely no porpose to blip the throttle with depressed clutch because there is no connection to the gearwheel you are about to engage.

Yes it does, if you don't blip the throttle when you downshift, when you engage the clutch the rear wheels will have to bring the engine up to speed. This can cause the rear wheels to lose traction (especially under braking, which is when you'd use this technique) resulting in a spin or at the very least locked rear wheels. Blipping the throttle ensures that there isn't a sudden jolt on the rear wheels when you release the clutch and is the best way to go about approaching a corner under braking, especially if you trail brake.

[just me again]

Ofcourse you are right Bobzdar, but it is not what this tread is about, what you are writing is not double clutching, but something everybody should do when they are changing gears.
double clutching is about matshing the revs between the gearwheels in the gearbox before engaging them.

Bjørn

[bobzdar]

Ah, ok, I see what you're saying. The way you worded it made it sound like there was no purpose to blipping the throttle on downshifts.