Whats double clutching & whats the reason to use it - Team-BHP

_Crazi4Speed_ · 4th March 2004, 05:48

Hi, I am not much knowledgable about the mechanics of cars and dont know about this technique used while racing, why does one use and how does it help and do any of you use this while racing on the road or on a empty strip??

it was used in F&F..

Thanks

Rehaan · 4th March 2004, 07:33

Hey C4S,

Firstly, in my opinion the guys from F&F were talking crap... (or maybe there is a reason i am completely unaware of?)

Nowadays cars have syncromesh's on all forward gears, so this makes it pointless to double clutch. Let me try and explain why -

Let me just say once again i am going to simplfy all the processes so the concept can be clearly understood.

Lets say we have 4 main rotating parts
1 - Clutch
2 - Input axle to gear box (between clutch and gearbox)
3 - Output axle from gearbox
4 - the actual gear selector cog(s) (this is the simplified part). When u select a gear all you are doing is moving this "part" around, allowing it to make contact with different gears of different sizes, hence giving different gear ratios.

This is a diagram (just try and realize that the opening on the TOP where the gearlever is connected is connected to a lever in the gearbox that moves around the "moving part"

Lets do a hypothetical upshift from 1st to 2nd without doubleclutching (in a car with a syncromeshed gearbox -ie any car in the last 10++ years)
You are in 1st gear, the engine is at 5,000Rpm, you press the clutch and almost simultaneously release the accelerator.
Shift the gearstick into Neutral, and then continue to push it into second. (where the engine will only be revving at 2,500Rpm)
(Now the part that u are shifting in the gearbox was spinning really fast when u were in first and is still freewheeling very fast in neutral, so when u are pushing into 2nd this is where a syncro comes in....it is like a mini-clutch or think of it as a "Cushion" on the gear that basically gets the moveable peice spinning at the same speed so that when you push into 2nd gear it slides in without any problem.

Hope that was clear!
If you got that it should be quite simple to understand double clutching now - (remember u want to double clutch when there are no syncros)

ok, so you are doing the same 1st to 2nd upshift using dblcltching..
You are in 1st gear, the engine is at 5,000Rpm, you press the clutch and almost simultaneously release the accelerator.
Shift the gearstick into Neutral, and THEN RELEASE THE CLUTCH (this completes 1 "clutching").
By releasing the clutch and having stepped off the accelerator, now the engine is spinning at 2,500rpm which is similar to what is will be revving at in 2nd gear at this speed (u are controlling engine revs). Since the clutch is not pressed and the car is in neutral the "moveable peice" spins at a speed relative to that of the engine.
then PRESS THE CLUTCH AGAIN (2nd clutching) and continue to push it into second. (where the engine will only be revving at 2,500Rpm, which is the speed that the "moveable peice" is aldready spinning at!

Thats basically the basics of it!
As you can now see...double clutching in modern cars is just a waste of time (i cant think of a reason to.....) except sometimes when u are going a bit fast in 2nd and u try and put the car in 1st and it doesnt slot in (i assume u guys know what i am talking abt?) then u just leave it in neutral..leave the clutch...revv the engine...press the clutch and it slots straight into 1st!..there...you just double clutched. I guess in this scenario the syncros were just having a hard time bringing the "moving peice" up to speed??

Im sorry i didnt explain the way the gearbox works in any detail..but it is complicated...so find a good site with pics and.wait...here..this seems to be a great one.....Howstuffworks "How Manual Transmissions Work"
check out the whole site...you will learn a lot...and they have some awesomely helpful flash animations to explain things.

Gearbox's are truly amazing peices of engineering! just try in your mind to create one...even if you aldready know how they work and its still incredibly tough!

cheers.....
Rehaan.

Rehaan · 4th March 2004, 07:36

Im not sure, but in cars without syncros, i dont think it was absolutely neccessary to double clutch unless u were taking the engine quite high before changing, hence causing large discrepancies between rotational speeds of parts.

cya

ajmat · 4th March 2004, 10:40

It makes a Ferrari sound good

v12 · 4th March 2004, 11:17

hey guys, correct me if i'm wrong. Our BEST buses need double clutching, right???

ajmat · 4th March 2004, 12:07

yes - no synchromesh - frankly it is times our Tata / AL trucks moved from the ambassador age to the volvo age

GTO · 4th March 2004, 13:07

Boy thats a superb explanation Rehaan (and how stuff works). I had a couple of doubts myself, Thanks for clearing that up.

GTO

Shan2nu · 4th March 2004, 14:09

I don't think we need to worry about double cluthing anymore. I'm happy as long as i can shift

The reverse doesn't have syncro right. Is that the reason why the RG makes that irritating sound when revved?

Regards...
Shan2nu

Regards...
Shan2nu

Rehaan · 4th March 2004, 14:37

Hey Shan2nu,

Im not a 100% sure if reverse has a syncro or not........BUT

the noise you hear is because reverese gear is a "straight-cut" gear and not a "helical cut" gear.

Helical gears are the ones pictured above (ie my first post).....with the diagnolly "slanted" teeth. They greatly reduce noise, but are believed to be slightly weaker (this is debateable).

Hence, since reverse is straight cut u hear that noise. Also, in WRC if you listen carefully, some of the noise amongst the engine, exhaust and turbo is from the straight cut gearbox.

cheers

Shan2nu · 4th March 2004, 14:54

Ya i've noticed that in WRC cars. ven that hissing noise, that must be the turbo right?

Regards...
Shan2nu

Rehaan · 4th March 2004, 15:10

The turbo makes a sounds like a whistle.

If u listen to a octavia TurboDeisel go past u on a quiet night and u pay attention u will notice it. Any TC car for that matter! ;-P

toyota · 4th March 2004, 21:24

THe WRC cars makes this hissing nose bcoz of two reasons
1. Turbo
2. MOdified airsuction ports

rgowani · 18th March 2004, 21:08

Yea the Turbo is letting of Excess Air through the Dump Valve. I love that sound

Stratos · 19th March 2004, 00:24

A simple explanation of Double Clutching would be... push the clutch.. put the gear in neutral...remove leg... then again press the clutch and put it in the appropriate gear... This method is done to prohibit Grinding between the gears ... and on cars that dont have a Synchromesh...
I hope my explanation is kinda correct

Stratos · 19th March 2004, 00:29

Quote:

Originally Posted by [b

Quote[/b] (v12 @ Mar. 04 2004,09:47)]hey guys, correct me if i'm wrong. Our BEST buses need double clutching, right???

The new BEST buses do have a Synchromesh... there are automatics also

4th March 2004, 05:48	#1 (permalink)
_Crazi4Speed_ BHPian Join Date: Feb 2004 Location: Shuffling between chicago and delhi Posts: 753	Whats double clutching & whats the reason to use it Hi, I am not much knowledgable about the mechanics of cars and dont know about this technique used while racing, why does one use and how does it help and do any of you use this while racing on the road or on a empty strip?? it was used in F&F.. Thanks __________________ _Crazi4Speed_ Dont dress for the position you are at, dress for the position you want to be in...

4th March 2004, 07:33	#2 (permalink)
Rehaan Team-BHP Support Join Date: Feb 2004 Location: Bombay Posts: 10,334	Hey C4S, Firstly, in my opinion the guys from F&F were talking crap... (or maybe there is a reason i am completely unaware of?) Nowadays cars have syncromesh's on all forward gears, so this makes it pointless to double clutch. Let me try and explain why - Let me just say once again i am going to simplfy all the processes so the concept can be clearly understood. Lets say we have 4 main rotating parts 1 - Clutch 2 - Input axle to gear box (between clutch and gearbox) 3 - Output axle from gearbox 4 - the actual gear selector cog(s) (this is the simplified part). When u select a gear all you are doing is moving this "part" around, allowing it to make contact with different gears of different sizes, hence giving different gear ratios. This is a diagram (just try and realize that the opening on the TOP where the gearlever is connected is connected to a lever in the gearbox that moves around the "moving part" Lets do a hypothetical upshift from 1st to 2nd without doubleclutching (in a car with a syncromeshed gearbox -ie any car in the last 10++ years) You are in 1st gear, the engine is at 5,000Rpm, you press the clutch and almost simultaneously release the accelerator. Shift the gearstick into Neutral, and then continue to push it into second. (where the engine will only be revving at 2,500Rpm) (Now the part that u are shifting in the gearbox was spinning really fast when u were in first and is still freewheeling very fast in neutral, so when u are pushing into 2nd this is where a syncro comes in....it is like a mini-clutch or think of it as a "Cushion" on the gear that basically gets the moveable peice spinning at the same speed so that when you push into 2nd gear it slides in without any problem. Hope that was clear! If you got that it should be quite simple to understand double clutching now - (remember u want to double clutch when there are no syncros) ok, so you are doing the same 1st to 2nd upshift using dblcltching.. You are in 1st gear, the engine is at 5,000Rpm, you press the clutch and almost simultaneously release the accelerator. Shift the gearstick into Neutral, and THEN RELEASE THE CLUTCH (this completes 1 "clutching"). By releasing the clutch and having stepped off the accelerator, now the engine is spinning at 2,500rpm which is similar to what is will be revving at in 2nd gear at this speed (u are controlling engine revs). Since the clutch is not pressed and the car is in neutral the "moveable peice" spins at a speed relative to that of the engine. then PRESS THE CLUTCH AGAIN (2nd clutching) and continue to push it into second. (where the engine will only be revving at 2,500Rpm, which is the speed that the "moveable peice" is aldready spinning at! Thats basically the basics of it! As you can now see...double clutching in modern cars is just a waste of time (i cant think of a reason to.....) except sometimes when u are going a bit fast in 2nd and u try and put the car in 1st and it doesnt slot in (i assume u guys know what i am talking abt?) then u just leave it in neutral..leave the clutch...revv the engine...press the clutch and it slots straight into 1st!..there...you just double clutched. I guess in this scenario the syncros were just having a hard time bringing the "moving peice" up to speed?? Im sorry i didnt explain the way the gearbox works in any detail..but it is complicated...so find a good site with pics and.wait...here..this seems to be a great one.....Howstuffworks "How Manual Transmissions Work" check out the whole site...you will learn a lot...and they have some awesomely helpful flash animations to explain things. Gearbox's are truly amazing peices of engineering! just try in your mind to create one...even if you aldready know how they work and its still incredibly tough! cheers..... Rehaan. __________________ The memory of you will ride by our side forever. Last edited by Rehaan : 24th July 2008 at 13:20.

4th March 2004, 07:36	#3 (permalink)
Rehaan Team-BHP Support Join Date: Feb 2004 Location: Bombay Posts: 10,334	Im not sure, but in cars without syncros, i dont think it was absolutely neccessary to double clutch unless u were taking the engine quite high before changing, hence causing large discrepancies between rotational speeds of parts. cya __________________ The memory of you will ride by our side forever.

4th March 2004, 10:40	#4 (permalink)
ajmat Team-BHP Support Join Date: Feb 2004 Location: Bangalore Posts: 6,357 View My Garage	It makes a Ferrari sound good __________________ Rice is cheaper than German Potato's

4th March 2004, 11:17	#5 (permalink)
v12 Team-BHP Support Join Date: Feb 2004 Location: Mumbai Posts: 3,467 View My Garage	hey guys, correct me if i'm wrong. Our BEST buses need double clutching, right??? __________________ Enfield Cafe Racer completed. Yamaha Cafe Racer started.

4th March 2004, 12:07	#6 (permalink)
ajmat Team-BHP Support Join Date: Feb 2004 Location: Bangalore Posts: 6,357 View My Garage	yes - no synchromesh - frankly it is times our Tata / AL trucks moved from the ambassador age to the volvo age __________________ Rice is cheaper than German Potato's

4th March 2004, 13:07	#7 (permalink)
GTO Team-BHP Support Join Date: Feb 2004 Location: Bombay Posts: 18,785 View My Garage	Boy thats a superb explanation Rehaan (and how stuff works). I had a couple of doubts myself, Thanks for clearing that up. GTO __________________ GTO Work backward from your imagination, not forward from the past! Please don't PM for support. Use the Contact Form instead. Please read the NEW Team-BHP FAQ section for all your queries.

4th March 2004, 14:09	#8 (permalink)
Shan2nu Distinguished - BHPian Join Date: Feb 2004 Location: Hubli - Karnataka - India Posts: 4,788 View My Garage	I don't think we need to worry about double cluthing anymore. I'm happy as long as i can shift The reverse doesn't have syncro right. Is that the reason why the RG makes that irritating sound when revved? Regards... Shan2nu Regards... Shan2nu

4th March 2004, 14:37	#9 (permalink)
Rehaan Team-BHP Support Join Date: Feb 2004 Location: Bombay Posts: 10,334	Hey Shan2nu, Im not a 100% sure if reverse has a syncro or not........BUT the noise you hear is because reverese gear is a "straight-cut" gear and not a "helical cut" gear. Helical gears are the ones pictured above (ie my first post).....with the diagnolly "slanted" teeth. They greatly reduce noise, but are believed to be slightly weaker (this is debateable). Hence, since reverse is straight cut u hear that noise. Also, in WRC if you listen carefully, some of the noise amongst the engine, exhaust and turbo is from the straight cut gearbox. cheers __________________ The memory of you will ride by our side forever.

4th March 2004, 14:54	#10 (permalink)
Shan2nu Distinguished - BHPian Join Date: Feb 2004 Location: Hubli - Karnataka - India Posts: 4,788 View My Garage	Ya i've noticed that in WRC cars. ven that hissing noise, that must be the turbo right? Regards... Shan2nu

4th March 2004, 15:10	#11 (permalink)
Rehaan Team-BHP Support Join Date: Feb 2004 Location: Bombay Posts: 10,334	The turbo makes a sounds like a whistle. If u listen to a octavia TurboDeisel go past u on a quiet night and u pay attention u will notice it. Any TC car for that matter! ;-P __________________ The memory of you will ride by our side forever.

4th March 2004, 21:24	#12 (permalink)
toyota BHPian Join Date: Feb 2004 Location: bangalore Posts: 138	THe WRC cars makes this hissing nose bcoz of two reasons 1. Turbo 2. MOdified airsuction ports

18th March 2004, 21:08	#13 (permalink)
rgowani BHPian Join Date: Mar 2004 Location: Mumbai Posts: 239	Yea the Turbo is letting of Excess Air through the Dump Valve. I love that sound __________________ Don't Immitate, Innovate®.

19th March 2004, 00:24	#14 (permalink)
Stratos Team-BHP Support Join Date: Mar 2004 Location: San Jose, CA - Mumbai, MH Posts: 1,937 View My Garage	A simple explanation of Double Clutching would be... push the clutch.. put the gear in neutral...remove leg... then again press the clutch and put it in the appropriate gear... This method is done to prohibit Grinding between the gears ... and on cars that dont have a Synchromesh... I hope my explanation is kinda correct

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