Double Clutching

[blind_elk]

the point of double-clutching is to match the GEARBOX output shaft with the GEARBOX input shaft  (which at the same time matches the gearbox & engine speeds)

AND to match the rotation of the gearsets so the teeth mesh cleanly on engagement - this is what the synchros are supposed to do, but don't do it so well when they wear out.

Im not trying to start an argument, but explain *why* the heel-toe technique "has no benifit and is a waste of time"?

The benefit of heel-toe is to match the engine speed up to the road speed of the wheels. By matching these, the stress on the whole drive train is minimised, and therefore wear-and-tear on the drive train is reduced, resulting in longer life of the components.

Anyone who claims they will be long gone by not heel-toeing is deluding themselves, and obviously not driving correctly - heel-toe is all done under braking, and therefore is done BEFORE the corner while travelling in a straight line, so there can be no time lost "changing gears in the middle of a corner". Heel-toe is really not that much slower than a non-heel-toe gear change (fractions of a second), because the general movement of the gearshift and engagement of the gears is not interupted, as it would be with a double-declutch. And because it is done under braking, it doesn't matter that it takes a bit longer. With heel-toe, you can actually have the lower gear engaged before giving the blip on the throttle.

[Duncan]

hahaha this thread is funny....some uninformed comments in here among the gold

hahah by the time you double clutch your car around corners and on the staright, i would have left you by miles. what a waste

So you are saying that under brakes you will be changing gears longer than braking, are you? Maybe you need to stop granny shifting and start driving properly.....in every track I have driven there is time to double clutch down thru the gears while you are still braking 100%....probably the best example in NSW is Eastern Creek turn 2 where you change from 5th back to 3rd (or 2nd for some cars/tyres)

[MerlinTheHapyPig]

i've forgotten what we were arguing about!

all i disagreed with was the comment that heel-toe "has no benifit and is a waste of time"

lol

[blind_elk]

i've forgotten what we were arguing about!

all i disagreed with was the comment that heel-toe   "has no benifit and is a waste of time"

lol

So are you now saying you support the idea and practice of heel-toeing? Because that is not the interpretation I got from the piece I quoted in my previous post.

[(B1) MR_fanny]

merlinthepig had always supported heel toe. 26gts seemed to have questions about it vs double de clutching.

*stands back on the sideline and continues watching*

[MerlinTheHapyPig]

yes i do support heel-toe, and always have. I don't double clutch though.

hmm, i can't be bothered reading back through my posts.... but i don't remember mentioning what i personally preferred at all.

26GTS seems hung up on the idea that if you can't double-declutch like he can - (coz he's a much better driver then all of us - and heaps cooler too) - then you don't deserve to drive a car....

[MerlinTheHapyPig]

oh yeah, in the post of mine you quoted, i was quoting 26GTS, he said that

[heel-toe technique] has no benifit and is a waste of time

i was asking him to explain that.

[Sydneykid]

Hi guys, it seems to me that there are two techniques being discussed here...

#1 blip thottle on down change without lifting clutch.

#2 blip throttle on downchange while lifting clutch

#1 matches the engine RPM to the road speed and lets the synchros match the gearbox input shaft rpm to the engine rpm.

#2 matches the engine rpm to the the road speed and also raises the gearbox input shaft rpm.

#1 stops rear wheel lock up (compression lock) when you lift the clutch with zero throttle on, but doesn't save the load (rpm differences) on the synchros or the gearbox input shaft. So it is OK if you have a gearbox with good (single or double) synchros.

#2 also stops rear wheel lock up (compression lock) when you lift the clutch with zero throttle on, but it also saves the load (rpm differences) on the synchros and the gearbox input shaft. So it is necessary if you have a gearbox with dud synchros or a dog box (no synchros).

The bigger the gearbox, the more inertia in the input shaft and the more important it is to use technique #2. This also aplies to standard/wide ratio gearboxes, where the rpm differences are large. Not so much to close ratio gearsets where the rpm differences are small.

Bottom line, neither technique is wrong, it is simply a matter of horses for courses.

[geno8r]

I heal & toe but not really the heal part.. its more just toe & toe.... Half the top of my foot on brakes, the other half on accelerator. angle left half of my foot to brake, pop clutch pedal in, right half of foot revs up a couple 1000 revs, clutch pedal out into new lower gear, revs match at fly wheel = smooth shifting

[Abo Bob]

I just put one size 13 boot sideways across the pedals.

My car doesn't need double clutching anyway. It's much better than any of yours.

[eXc]

haha this is gold.

I heel toe or toe-toe depending on if i am wearing shoes or not.

I also tried double clutching in the good ol' applause (daily driver) and it makes it smoother....i am getting faster...haha i dont think i will really bother tho, i just wanna be able to say i can do it, and then i can be like Vin Diesel, cause he's my hero, and i can be all like "not double clutching when you should be" and then i will be full sik mayte.

[geno8r]

My car doesn't need double clutching anyway.  It's much better than any of yours.

Not with those rims it aint... :shake: lol

[discopotato03]

Lots of personal opinions here so I'll add my own .

I believe the earliest multi ratio gearboxes had gears that moved sideways on the mainshaft to engage with those on the layshaft or the back of the ist motion shaft (input shaft) for top gear . Engines of the day had a very narrow rev range compared to todays designs and road speed was slow .

Generally these gearboxes had large gears and shafts with lots of innertia or flywheel effect . To change down we had to dip the clutch change to neutral , off the clutch and rev the engine to bring the geartrain up to the sort of speeds where the desired mainshaft gear could slide into mesh with its matching layshaft gear . Off the clutch and maybe we could coax our Model T Ford up that savage 1 in 100 grade . Later designed gearboxes had the mainshaft gears running on bearings so that all the mainshaft/layshaft gear pairs could be in mesh but none of the mainshaft gears locked to the mainshaft . The mainshaft also had coupling sleeves with dove tail shaped dogs on the side that could move sideways to engage the dogs on the sides of the mainshaft gears to lock them and allow drive . These are called constant mesh dog boxes and still exist today in trucks and competition car gearboxes . The coupling sleeves eventually grew baulk rings and cone clutches and are known as syncro boxes .

To be continued , out of time .

[discopotato03]

As engine torque increased with capacity (and forced induction) the shafts and gears get heavier to cope with the increased loads . In some cases double and triple cone syncros have be used to reliably slow down or speed up the mainshaft gears to allow smooth quiet engagement . Trouble is the syncroniser assembly gets bigger and heavier creating more fly wheel effect making the syncros work harder and wear out faster .

In a perfect world the shafts/gears/syncro hubs/ clutch plate would weigh nothing and changing gears would be easy all the time . Because they aren't and we use big revs and wide ratio (production gearboxes) the syncros get a hard life . They are not designed to be taken to the rev limit in 1st and bashed into 2nd etc .

Road cars are designed to have a broad spread of torque starting at lowish revs and with 3000 rpm , change , driving they work fine .

We've all been in that situation of putting along at low revs in high gear and desire acceleration . So we go back two gears asking the syncros to accelerate the layshaft and 1st motion shaft/ clutch plate up to the speed of the lower ratio for the same road speed . Cone clutches in gear oil only work so well so if we beat the bault ring and force the coupling sleeve ito the gear at big speed differences it going to go crunch .

Double de clutching brings the engine and gear train up to speed , reducing the work and load on the cone clutch AND has the engine in the right speed range to accelerate the vehicle . Often double de clutching can speed up a gear change when the ratio spread is wide . My experience is that syncro boxes hate clutchless changes so I don't do it , its probably to do with the fine dogs on the gear/coupling sleeve . Dog boxes have big gaps in the dogs so handle it much better . With a bit of practise they are lightening quick to up change , gentle pressure on the stick and slight lift off on accelerator to unload the coupling sleve and snick . One thing you will notice with them is the bang and clang , they are noisy and have a fair bit of backlash which people would never put up with in road cars if if Joe average could change the gears .

Close ratio boxes help as the speed difference between the gears is less .

Some company's in the US do half dog boxes ie 1st - 2nd dog change and the rest syncro .

I've never driven a production six speed car box such as S15 , R34 or the B Double box that the Vomit Doors get's . Are the Nissan ones fairly close ratio and do they change well with a boot full of revs .

The above epic is my interpretation but feel free to comment , the discussions on this site are really good .

Cheers A .

[someonestolecc]

Lemme get this straight.

blipping on downshifts to match revs with the clutch pedal in isn't effective and I should be doing it in neutral with the clutch pedal out ?

If that's true I'm going to watch myself next time I do it cos I don't know which I do

Otherwise, I occasionally double-clutch going changing gears up in my car because anything over 4-5k grinds but shifting around that rpm range doesn't keep it on boost long enough to go fastest it can. I think that's only my car though

One thing I have noticed is that when I'm trying to go faster, I blip. When I'm trying to deccererate, I'll double de-clutch. I find the engine braking is better. Is that bad?

[Beer Baron]

firstly I haven't read this whole thread (just pages 1 and 3) but what discopotato has said was very well explained and matches pretty well with my limited hands on experience with gearsets. good stuff mate.

[MicK51]

i heel and toe all my downshifts simply so i can release the clutch quickly without the nasty jolt. I also double clutch but only when i skip a gear, eg on the street u do alot of tight 90deg turns (side street off a main rd ect) so i'll be cruising at 60 in 4th, when i get to the corner i double clutch straight to 2nd and turn in.

I do this all the time on the street but when i tried it in the race car (trying to do a skaifie )i found it a little to teddius and was getting lost in neutral. So i figured it best not to skip gears on the track.

Works great on the street though

[Gts-t]

You lot still carrying on hey..... :wassup:

[260Z]

Just to add my late 2 cents, since its something I feel strongly about.

I started double declutching my car (not a skyline), because the second gear synchro was shot. If you have a shot synchro, or one thats slow to work, only then can you really understand the value of double clutching and heel and toe. Try and engage second from third, and you'd have to lean hard on the gear lever to do it, and when it did drop in, it felt clunky and horrible.

But, if you double declutch it right, when you go to second from the slight neutral pause while you lift the clutch, the gear lever will actually fall away from your hand into gear, and the first time you get it right, it feels like you've just found neutral again. So, in any gearbox where you feel a slight notchiness or resistance when changing down a gear, it will assist you there. I assume skyline boxes are too slick though, so you probably can't feel any difference.

Heel and toeing. Why wouldn't you? Before that, I used to double clutch down the gears through every corner, and whenever i came up to lights - it was crap, because I had to let go of the brakes every time I changed gear. But with heel and toe, you never let go of the brakes, and you can change down gears much earlier in the corner, as you actually come into it, rather than having to slow down enough for your snychros to be able to work effectively before you change. I double de-clutch in my heel and toe, because i'm braking anyway, it doesn't affect my cornering speed, but i get a much smoother change.

And for all you drifters out there, you should know by now the advantages of heel and toe - come in mod speed in 4th, heel and toe through third to second, but delay releasing the clutch until you're past the apex, then feed clutch out fast (not drop!), and enjoy the back sliding under nothing more than the engine braking on the rear wheels