Double Clutching

From what I'm reading on the net, instruction for double clutching is to:

 

1: Depress clutch

2: Shift into neutral

3: Release clutch

4: Blip throttle

5: Depress Clutch

6: Engage next gear

7: Release Clutch

 

My problem is I don't understand why the gear needs to go into neutral (with released clutch) before it goes into the next gear, as opposed to rev matching directly into the next gear.

 

Can someone explain?

The extra clutch out in neutral gets the input shaft spinning at the new engine speed which lessens the amount of work the syncros have to do. I'll usually double clutch the 3-2 and 2-1 (pretty rare) downshift. The 5-4 and 4-3 are done with single clutching. I also seem to have an easier time hitting target RPM with double clutching and adding the heel-toe in there makes me feel like a racecar driver

Wouldn't the input shaft spin at the new engine speed through rev-matching?

double clutching does not include rev matching as you have listed in your step sequence AFAIK. remove #4 from your list and that's double clutching.

So I guess my question is whether there's an advantage to double clutching over rev-matching, rev-matching seems to achieve the same result without going through all the extra steps.

rev matching saves the clutch and is mostly for downshifting, double clutching is easy on the syncros and really is only necessary if you have engagement issues.

 

if either is in good condition, and you keep up with your fluid changes, you dont need to double clutch. Rev matching on downshifts are always a good idea if you do it well.

I don't think double-clutching is used much these days on the race track. Most drivers just rev match while the clutch is depressed during downshifts. Modern synchromesh gearboxes make double-clutching unnecessary. Rev matching is done mainly to avoid axle hop.

 

To better understand rev matching, try driving around without using the clutch. To downshift, you abruptly take your foot off the gas and gently pull the gearshift into neutral. Then you apply the gas while applying gentle pressure on the gearshift until it just falls into the lower gear when the correct rev level is reached. To upshift without the clutch, again you abruptly take your foot off the gas and gently pull the gearshift into neutral. Then you wait for the revs to subside while gently pushing the gearshift toward the higher gear. Clutchless upshifts are actually trickier than clutchless downshifts.

I learned to drive manual on a 1973 Alfa Romeo which the syncros were completely gone so all downshifts had to be double clutch downshifts which I have carried over to my legacy.

 

Whitetiger I'm not sure what you are saying about removing the rev match on the double clutch as you only double clutch on downshifts and the point of the double clutch is to increase the speed of the transmission internals by bringing up the engine speed for that split second in neutral so that when you engage the lower gear the engine will want to be at a higher rpm then it was. For instance 4-3 you might be at 3k rpm in 4th and downshift to third to be at the same speed the engine will have to be spinning around 4k rpm therefore you must increase the transmission internals speed to decrease the wear on the internals.

 

I really only double clutch when I am driving aggressively but for normal driving I just heal toe rev match my downshifts.

 

Edit: Rev-matching does not change the speed of the input shaft to the transmission. Think about it mechanically. The flywheel and pressure plate spin with the engine. The Friction disk is mated to the transmission. So if the clutch is engaged (ie: the pedal is depressed) then when you blip the throttle the engine speed increases but the transmission internals stay where they were. The point of the rev match is to put less wear on the transmission as it only has to sync up with the wheel speeds not the wheel speeds and engine speed.

The point of the rev match is to put less wear on the transmission as it only has to sync up with the wheel speeds not the wheel speeds and engine speed.

 

Don't forget the importance of avoiding wheel lockup while at maximum braking. Especially in rear drive cars, there is very little weight on the rear tires under hard braking, and a botched downshift can easily put you over the threshold of friction. You see this happen all the time at NASCAR road course races.

Don't forget the importance of avoiding wheel lockup while at maximum braking. Especially in rear drive cars, there is very little weight on the rear tires under hard braking, and a botched downshift can easily put you over the threshold of friction. You see this happen all the time at NASCAR road course races.

 

 

Yeah that too. In the Alfa I used to lock the rear tires all the time on downshifts into corners until I really got the hang of what speeds the engine needed to be at to match wheel speed with different gears.

http://s2.quickmeme.com/img/b9/b93f6465a678d0330777dfc372ebf85687b5d64ab6005056431961af76652487.jpg

Modern synchromesh gearboxes make double-clutching unnecessary.

 

This. Double clutching was common for older dog engagement gearboxes. Only time I've had to use it was when a synchro went bad.

 

To better understand rev matching, try driving around without using the clutch. To downshift, you abruptly take your foot off the gas and gently pull the gearshift into neutral. Then you apply the gas while applying gentle pressure on the gearshift until it just falls into the lower gear when the correct rev level is reached. To upshift without the clutch, again you abruptly take your foot off the gas and gently pull the gearshift into neutral. Then you wait for the revs to subside while gently pushing the gearshift toward the higher gear. Clutchless upshifts are actually trickier than clutchless downshifts.

 

The design of synchros will actually pull itself into gear with just slight pressure on the shifter. Like, to upshift, pull it straight towards the next gear but with gentle pressure. It'll naturally "sit" in neutral and pop into gear when the revs match up instead trying to figure out what RPM to shift at. If done correctly, it'll be VERY smooth.

To better understand rev matching, try driving around without using the clutch...

 

Thanks, I will try this in a lot this weekend.

 

Since we're on this topic, does anyone have tips for learning how to heel-toe? With the pedals the way they are I have a pretty tough time getting my foot to both pedals, and I have 11.5 3E feet. Has anyone resorted to adjusting the pedal heights?

I have a size 13 US shoe, and I can't really "heel-toe" in the normal way. I usually have the left side of my foot towards the right edge of the pedal, and sort of just rock my foot over to the gas pedal. My foot is pretty much vertical, and just bridging the gap between the two pedals, using the brake as the pivot point for hitting the gas pedal. If I try to actually use my heel to hit the gas I'll make contact with the center console first.

 

Just start trying it - it takes practice like everything else. Start off when you have extra room to brake (like no other traffic around) as you will inevitably stab/release the brake while trying to figure out the three pedal, two foot dance.

It's not so much "heel-toe", its more off a "ball of foot-side of foot".

 

Watch Senna do it...

 

[ame=http://www.youtube.com/watch?v=96ekbvjyr0g]On-board: Ayrton Senna's - Heel-and-toe - YouTube[/ame]

Senna isn't human though. That footwork should not be possible in slippers

I've watched that video before, pretty incredible.

 

Are you guys able to heel-toe in the Legacy? The right side of my shoe barely grazes the gas pedal even with the ball of my foot on the brake.

For all the complaints I've read about how fragile the 5 speed manual is, I would not recommend rev matching. You'll likely see the results the next time you remove the transmission drain plug.

For all the complaints I've read about how fragile the 5 speed manual is, I would not recommend rev matching. You'll likely see the results the next time you remove the transmission drain plug.

 

 

Rev matching will decrease the wear on the transmission. You are helping the life of the tranny.

Found this cool VHS era video:

 

[ame]www.youtube.com/watch?v=VxGtx9xXhlM[/ame]

For all the complaints I've read about how fragile the 5 speed manual is, I would not recommend rev matching. You'll likely see the results the next time you remove the transmission drain plug.

 

You sure you don't mean driving without the clutch? That does take some getting used to:lol:

You sure you don't mean driving without the clutch? That does take some getting used to:lol:

That's what I mean.

I drove semis for 32 years and the only time I used a clutch was at a stop sign.

I drove semis for 32 years and the only time I used a clutch was at a stop sign.

 

On many rally cars, the clutch is mainly used for staging.

Like the other guy, I disagree with what whitetiger said. Double clutching involves rev matching. That's the entire point.

 

And to the OP (and some others too), here's how a manual transmission works in a nutshell:

http://auto.howstuffworks.com/transmission3.htm

and interactive animation here:

http://auto.howstuffworks.com/transmission4.htm

 

Check the flash animation. The point of double clutching is to spin up the layshaft (and gears) so that when you push the gear selector (and thus the collar) they will be at the same speeds. When you single clutch, you rely on the syncros to do that.

 

I double clutch all downshifts that involve going down more than 1 gear, and always when downshifting to 1.

 

Also, learning heel-toe is just a matter of practice. I have small feet so I have room to work with, so I suppose that makes it easier. After learning heel-toe pretty well, I forced myself to learn how to double clutch heel-toe also. I rarely use heel toe when driving though.... not driving aggressively enough to really justify it.