Talk:Double clutching (technique)

input shaft speed vs. engine revolutions

Is it the same in this article's context? Because when I looked at other sites, I find that if I substitute input shaft speed with revs, the instructions become much clearer (its probably just me, though).

Gearbox input shaft speed is not engine crank shaft speed. To prove it to yourself, play with the clutch (which couples engine output to gearbox input) and the throttle. ;)

Paul Jakma

Article title

Does anyone have a reason why this article shouldn't be moved from "double declutch" to "double clutch"? I've never heard the term double declutch before, and from my experience, the term double clutch is quite common in industry and literature. Just for some credibility, I drive trucks for a living. If noone objects, I'll move this article over shortly. -Lommer | ^talk 23:25, 21 July 2005 (UTC)

I've always called it "double declutch", which is in fact more correct since the technique involves the disengaging of the clutch (ie depressing the pedal) twice. I suspect it may be "double clutch" in North America and "double declutch" in the British Empire.--Yeti Hunter 11:49, 12 June 2007 (UTC)

Yep Double declutch for me, I grew up in the UK. — Preceding unsigned comment added by 124.168.92.121 (talk) 18:39, 1 November 2011 (UTC)

Double declutch (or 'de-clutch') is right as I learned it, in UK. Double clutch - what's that? Surely clutch isn't a verb, whereas 'de-clutch' is?
Can we confirm if 'double clutch' really is standard US usage, and if so, note it here?
Onanoff (talk) 20:58, 16 February 2014 (UTC)

This is a frustrating situation. This is the English language Wikipedia, not the American language Wikipedia and the policy is clear that the original editor should never have changed it simply because he (apparently) had no experience of other-than-American English. The same policy also forbids moving it back just for the sake of it. Therefore, despite the clear (but much-belated) support here for the original name this article stands as yet another example of the Americanisation of what should be the English language Wikipedia for all English-speakers. 180.148.179.85 (talk) 12:20, 4 June 2014 (UTC)

I hope you're joking to say that adding de- creates a verb. If de-clutch is a verb, then clutch was obviously a verb all along.

It's pointless to blame this on so-called Americanisation of English. People who live in England don't own English any more than Greek people own democracy. I grew up on Roadrangers, and have only ever heard double clutch. I live in Australia, not America. In case anyone is tempted to claim that Australian English simply follows American usage, there are plenty of examples where they clearly differ. Aboctok (talk) 06:16, 1 September 2018 (UTC)

Rev-matching?

What's the technique called where you rev the engine then let off the gas and as the revs come down you can shift without pressing the clutch pedal i.e. the gears just kind of slip into place? Or am I too dense to understand that this article already describes this technique? Thanks Ewlyahoocom 09:12, 30 July 2005 (UTC)

That's clutchless shifting. You don't rev the engine, you just /very/ quickly close/open the throttle as you shift up - just enough so the revs only drop a small amount, leaving the gearbox without load through it (be it forward or reverse). This is really only feasible on sequential shift gearboxes for a human to do (ie motorcycle gearboxes and race-orientated car gearboxes) - normal car H pattern selector gearboxes would be tricky to do fast enough (never tried myself, so don't know ;)).

On race machinery (bikes at least) the gear selector often is wired to an ignition kill circuit, so that as the rider starts shifting up the ignition automatically is briefly cut - the rider no longer has to manually shut/open the throttle, all they have to do is tap the selector.

The 'rev the engine' thing you refer to is called "Heel and Toe" for cars, throttle-blipping is probably best term for motorcycles. It's done for down-shifts only. However, at least with modern race motorcycles (dont know about race cars), the practice is slowly dying out due to the advent of slipper-clutches - they're appearing even on production road-going sports bikes.

Don't know about other people, but "Heel and Toe" is misnamed for me, should be "Ball and Side" - I use the ball of my foot to brake and the side edge of my foot to blip the throttle ;).

Paul Jakma

The generally accepted term for this (in the US) is 'powershifting', and it's extremely damaging to your car. If I understand correctly (your point being to shift without depressing the clutch?), this is definetly -not- heel-toe technique, which is used to quickly control the throttle during cornering. (Allowing you to brake and accellerate with no time lost to move the foot.) As has been said, this should really only be done on a sequential shift vehicle such as a motorcycle, and even then it's a great way to screw up your tranny. Aspengrey 04:55, 11 September 2007 (UTC)

[Re comment "clutchless shifting" above by Paul Jakma]

I once had a Fiat Uno, whos thrust bearing disintegrated. I drove for another 1200 miles or so before I changed it, clutchless changing all the while. It becomes second nature after a while, but the remnants of the bearing do score the shaft a wee bit. 82.6.1.85 (talk) 21:34, 16 September 2010 (UTC)Lance T.

What about disengaging for starting, stopping, or idling at lights or stop signs? I know you can yank it out of gear into neutral, but is it possible to shift into gear from neutral without the clutch when the vehicle is standing still? — ¾-10 22:15, 17 September 2010 (UTC)

When the clutch cable on my Capri snapped while descending the northern side of the Col du Galibier, I had to go through Valloire where, natch, the traffic lights were red. To restart I switched off the ingnition, bunged it into first and restarted. A bit undignified but it worked. Mr Larrington (talk) 14:09, 26 August 2011 (UTC)

Fuel efficiency

This article says that unsynchronized transmissions are more efficient than synchronized transmissions. Is this true? According to what my uncle Jim said, the earlier unsynchronized transmissions used a lot of gas. He said that the manual transmissions with the synchromesh are more efficient. —Gm1121983 16:36 13 April 2006

I haven't seen synchros in person, but I'd assume this only has an effect while clutching (as opposed to an automatic transmition which really does waste enrgy all the time). If so, it's not very important. —Ben FrantzDale 02:30, 14 April 2006 (UTC)

The main reason that this technique is more fuel effecient is that you don't waste engine power driving a synchro, which matches the RPMs of the transmission and the engine for you. (The synchro also introduces a lot of rotational torque) On a non-synchro transmission it simply isn't possible to shift while the RPMS are very different, so it's kind of a moot point. Aspengrey 04:55, 11 September 2007 (UTC)

Puzzled

OK, I confess I'm a bit stumped. It looks like double-clutching simply means "let the clutch out while in neutral" -- as opposed to my synchromesh transmission, where I match revs with the clutch pedal depressed. But if the only real difference is that a double-clutching transmission doesn't have syncronizers (and hence requires you to match revs fairly well), why does it matter if you're matching revs with the clutch pedal down, or with the clutch pedal up and the gearshift in neutral? Cheers.

With a quck glance, this article appears not to give an answer. From reading various web pages, my sense is that there is a free-spinning shaft between the gearbox and the clutch, like so:

 [engine]----||----[gears]---(wheels)
      clutch ^  ^idler

When you put the car in neutral but with the clutch engaged, the idler is spinning with the engine. If you have the car in gear but the clutch pressed, then the idler is spinning with the wheels. If you don't double clutch, the synchros get that idler spinning the right speed as you throw the shift lever. With double clutching, the idea is to use the engine to do the synchros' job, so you don't have to wait for them to do their thing. That is, when you let go of the pedal while in neutral, you are reconnecting the engine to this shaft and so can get it spinning the correct speed for when you throw it into gear. That's my rough understanding, anyway. —Ben FrantzDale 02:01, 22 May 2006 (UTC)

The main advantage of actually double clutching rather than matching with the clutch in is that the engine will lose or gain RPMs faster while in neutral than just with the clutch depressed. Aspengrey 04:56, 11 September 2007 (UTC)

I find this article very unclear. It does not describe why the word "double" is used in the phrase. Further, the definition seems to allude to some extra action that may lead the novice reader to think that another action is involved and that it was this other action is why the word "double" is used in the phrase yet this appears not to be the case, maybe. Very unclear. Fraberj (talk) 03:07, 26 December 2007 (UTC)

The word "double" is used, presumably, because you press the clutch pedal twice. Hence, "double clutch", or the more accurate "double declutch" since the depressing of the clutch pedal actually disengages the clutch. Yeti Hunter (talk) 10:53, 26 December 2007 (UTC)

Citation

Ok, SERIOUSLY, does that first citation need to be there?! I mean, this is the definition of double-clutching, right there. Anyway, I added 'primarily' in case that was the persons beef, as this is a very useful technique even for syncromesh cars. Aspengrey 04:56, 11 September 2007 (UTC)

Strictly speaking, everything should be cited. However, according to WP:VERIFY, inline citations are only needed for statements that are controversial or likely to be challenged. I don't think any good-faith editor would challenge the lead sentence, therefore I reckon the cite request can be removed.--Yeti Hunter 09:52, 11 September 2007 (UTC)

Apparently the argument is that the term unsynchronized needs to be cited... but it's a link? Here's the edit: 19:07, 18 July 2007 StationNT5Bmedia (Talk | contribs) (3,623 bytes) (cite resource for term unsynchronized) (undo) Aspengrey 02:32, 12 September 2007 (UTC)

Because of your comment, and my adding 'primarily', I think we've cleared up StationNT5Bmedia's concers about the citations, so I'm removing the tag. Aspengrey 15:24, 12 September 2007 (UTC)

Valiant efforts so far but room for improvement

Hi all. There are some conflations and some gaps in the article currently that contribute to readers' not understanding. There are certain distinctions (constant-mesh vs non, meshing the gear teeth themselves versus meshing the dog clutch that's next to the gear teeth, having synchros [synchronizing cones] vs not having them) that are being conflated here. Also, the ideas that the synchros exert tremendous torque on the shafts and thus that they are prone to breaking and require extra fuel to be burned by the engine are off-base. It is only the rotational inertia of the transmission's shafts themselves that the synchros are fighting, at a time when the shafts are disengaged from driving or being driven. The synchros aren't fighting against the linear inertia of the moving vehicle or against the engine, and the engine's not driving them. (Remember, when the clutch is disengaged, the tranny doesn't have a clue what the engine is doing.) And whenever you're shifting at appropriate speeds into appropriate gear ratios, which is most of the time, there is very little shaft inertia to compensate for anyway, because the shaft speed differential is already not too horribly far away from where the next gear needs it to be. The ideas that unsynchronized trannies are either "more efficient" or "more rugged" than synchonized trannies are flawed notions coming from not quite understanding exactly what is or isn't really happening inside the transmission. A ruggedness difference could exist because one tranny design is beefier than another or one tranny's metals were made with better metallurgy than another's, but those are independent variables from any inherent difference between synchro'd vs unsynchro'd. As for fuel efficency diffs between car models, there are many variables that affect them, but the basic distinction between synchro'd and unsynchro'd, by itself, is not one of them. If cousin Bob confounded correlation with causation, he'll (understandably but incorrectly) try to convince you that having synchos caused tranny B to be weaker than tranny A, or car B to get worse mpg than car A.

If I get a chance I'll work on improving the explanations. In the meantime, for those stumped by this double clutch article, some clues are available at Manual transmission#Synchronized transmission, although even there, I think it's a case of "if you don't already know what the writers meant, you probably won't understand what they wrote." It's easier to understand how these moving parts interact with each other than it is to craft a string of words that explains it. For those readers who have a pressing need to learn about this topic ASAP, I suggest going to your library and borrowing a book on transmissions; as of today, that still beats Wikipedia on explaining this subject. Maybe eventually we can make a slow-motion CGI video of a gear shift taking place inside a 1920s transmission and another taking place inside a synchromesh transmission, which would communicate the ideas perhaps easier than words can. Cheers, — ¾-10 20:36, 31 January 2009 (UTC)

Heel to toe

Left foot right foot? Are pedals laid out the same for left and right hand drive? It didn't make sense to me maybe because of this. Australia/UK Vs USA usage. — Preceding unsigned comment added by 124.168.92.121 (talk) 18:46, 1 November 2011 (UTC) Yes the pedals are placed the same way. 188.57.10.129 (talk) 13:54, 29 January 2013 (UTC)

Make Up Your Mind !

In the section on on Manual gear shifting, it says,

"Keeping the clutch pedal (accelerator pedal) pressed while in neutral, ..."

Would somebody please make up their mind ? Darkman101 (talk) 18:49, 1 June 2012 (UTC)

Synchros as a comparison and truck gearboxes

I believe that when contrasted with what a synchromesh transmission does, the process is easier to explain:

With any contemporary manual transmission, changing from one gear to another results in different input and output shaft speeds, which are reflected in the speeds of the selected input and output gears.

Contemporary manual transmissions include Synchromesh http://en.wikipedia.org/wiki/Manual_transmission#Synchronized_transmission friction clutches to ensure gears on the input and output shafts are moving at a matched speed before they are engaged, reducing damage and providing for smoother gear changes.

In gearboxes without synchromesh, the matching of gear speeds must be done by the operator. Double de-clutching is the most commonly taught technique. In double de-clutching the driver shifts briefly into neutral and releases the clutch so that the vehicle's accelerator can be used to adjust the speed of the gearbox input shaft to match the gear that is about to be selected. Once the input shaft is spinning at the correct rate, the clutch is used a second time and the required gear selected.

Double de-clutching is most frequently required on heavy equipment such as trucks which may omit synchronisers in favor of durability and older vehicles before synchromesh was standard. Some drivers may choose to double de-clutch to reduce wear on synchronsier components.

andy — Preceding unsigned comment added by 114.198.117.64 (talk) 12:15, 23 September 2012 (UTC)

"Throttle"

Diesels don't have a throttle. The accelerator controls fuel flow, nothing else. I didn't delete instances of "throttle" because I'm unsure how to word it for maximum clarity for readers accustomed to either gasoline or Diesel engines, but it should indeed be changed as a matter of accuracy. 2607:FEA8:BFA0:47F:49CA:F2FF:C92A:F7D9 (talk) 23:01, 6 June 2019 (UTC)