Questions on Double Clutching

[Cactus]

As I unserstand double clutching:

Say I am going 45 mph in 3rd gear (~3k) and I want to downshift to get some more acceleration for whatever reason, so I am going down to second (~4.5k). To double clutch you depress the clutch, drop into neutral, let the clutch out, rev the RPM's up to 4.5k, depress the clutch again, shift into 2nd and away you go.

I understand that matching the engine RPM's to match the gear saves the syncros in the transmission. My question is why put the car in neutral and let the clutch out. If I depress the clutch it has the same effect as being in neutral (the transmission is disengaged from the engine, right?) so why not just push the clutch in, rev the engine, shift into 2nd and be on my way? That would be faster than double clutching, so why double clutch?

[SoySauceCb7]

no its not the same as putting it in neutral, in neutral you are not matching input and the output shaft thats why you want to relase cluth in neutral, to match speeds.

[DrLove'sKuDang]

damn you fast and furious!!!!! got everyone wantin to double clutch now... just be careful of those welds on the intake, wouldnt wanna blow'em

[Sho Nuff]

lol

[Boost_Lee]

I would watch your passenger floor panel too...things come loose like no other. Thats why im an auto

[92accordlx]

just be careful so you dont have to rip apart the block and replace those piston rings that can fry

[92accordf20a]

yeah but,

you can win by an inch or a mile, winning is winning! :lo:

[mayberry]

so whos giving me a ten second car?

[H23Accord]

He ain't worried about all that nonsense...he lives his life a quarter mile at a time...and nothing else matters.

[DrLove'sKuDang]

wow, damn did we come to the rescue... bet he can doubleclutch like a pro now

[deevergote]

Ok, WHO'S being influenced by The Fast and the Furious now? The question is a very valid one about double clutching.

Double clutching, unlike the elusive MoTeC System Exhaust, has been around for a long time (before synchros) and is NOT a product of that blasted movie. So c'mon, give the guy a break. He's not asking how to beat an RX-7 in a drag race by double clutching. He obvously knows what it's really for. Well, sort of.


Double clutching in our cars isn't really all that useful. The technique was mainly used in older cars before sycnchronizers were invented/used. By using this technique now, you may save the sycnhros a little bit, but at the expense of other parts (like the clutch)

As far as I can tell (I'm no mechanic, nor am I a racer) holding the clutch in does the same thing as far as speed matching goes.

[cb7-R]

Re: Questions on Double Clutching

Originally posted by Cactus
As I unserstand double clutching:

Say I am going 45 mph in 3rd gear (~3k) and I want to downshift to get some more acceleration for whatever reason, so I am going down to second (~4.5k). To double clutch you depress the clutch, drop into neutral, let the clutch out, rev the RPM's up to 4.5k, depress the clutch again, shift into 2nd and away you go.

I understand that matching the engine RPM's to match the gear saves the syncros in the transmission. My question is why put the car in neutral and let the clutch out. If I depress the clutch it has the same effect as being in neutral (the transmission is disengaged from the engine, right?) so why not just push the clutch in, rev the engine, shift into 2nd and be on my way? That would be faster than double clutching, so why double clutch?

OK first you wont get any more speed out of 2nd gear it will actually slow you down as the gear is sized for torque not speed. Also double clutching is totally usless in modern automobiles. The point of d-clutching was to match the speed of the mainshaft to the counter shaft in order to engage in a smoother shift., however with the adition of snychronizer gears, rings and hubs the work is placed on them to do all the work. Basiclly the ring slows down the countershaft to match the speed of the mainshaft.

[mixmatch]

actually if u downshift from 3rd to 2nd you can gain acceleration thus gaining speed faster as if you had stayed in 3rd. but it depends on where u are at in the power band in 3rd gear and where the shift puts u at in 2nd. u can test it yourself. go 40-45 in 4th gear then try to accelerate to 60. next go 40-45 and downshift to 3rd or even 2nd and again accelerate to 60. you should be able to tell a noticable difference.

and i believe double clutching is still a technique used in some road racing but a race transmission is NOTHING like what we have so maybe that is why.

[cb7-R]

You are NOT gaining speed you are gaining torque. But you must give up some speed to gain this torque. The second gear drive gear is sized to move our heavy vehicle from a standing stop. So the 2nd gear drive gear is about 3:1 roughly to the 2nd gear driven gear. 3rd and 4th gears are completely diffrent from 2nd. They are closer in size to their respective driven gears. And thus are sized for speed and fuel economy in most modern passenger sedans. 5th gear is usually under 1 so it is the overdrive gear and pretty usless in 1/4 mile racing.

[Ronald_Type-R]

Allright, that whole thing with letting go of the clutch in neutral??? You only do that if you're driving those big trucks...Hehe...That's not how you do it....You just pretty much push in the clutch, match the RPM while downshifting, and then let the clutch go when the RPM is where it's supposed to be...

As for rev matching when you downshift to accelerate, it does improve the overall performance...I know I know, the synchros are there.....But if you downshift without rev matching, I'm sure that all of you would feel the car pulling back on ya....Come on, admit it, I'm sure all you ppl that don't rev match are familiar with that feeling..Hehehe.. But if you actually match the RPM before you let go of the clutch in the lower gear, you won't even feel the synchros trying to match those shafts or whatever....Stepping on the gas revs up the engine faster to the desired RPM rather than waiting for the synchros to match up those two shafts...Therefore, smoother and WAAY faster downshifting....Same goes with the whole heel-toe technique....It's all about matching the RPM...The only difference with heel-toe is that you're braking WHILE you're trying to match the RPM....

I've always hated the feeling of the car jerking back because of downshifting....That's why I wanted to master the whole matching RPM thing pretty bad...Took me about 2 months to get used to it, but since then, whenever I'm driving other ppl, and they're sitting in the back seat, they won't even know that my car's standard until they ask....Hehehe

Anyways...Hope that helps...I could've sworn I've explained this before....Meh.. I wish I can post up one of these videos where ppl in Japan race on the track with one camera pointing at their feet, and the other one pointing at the RPM...It would explain this whole thing soo much better..I have it in my comp., but it's a big file, and I don't know how to host a file this big...But I'll try my best tho..And if I can make it smaller, then I'll post it up..

Ronald