Am I the only one who double clutches?

EvanB wrote: Everyone is granny shifting, not double clutching like they should.

You had to say it, didn't you?

Double clutch my Dodge W250 with Cummins and Getrag, especially when towing or hauling. It's really a good feeling when the trans slips right into gear.

Occassionally 2xclutch my Volvo Amazon, but those old cast iron 4 speed boxes are so tough they can run a whole race full of water and still work fine (ask me how I know...)

Mine is more of a 1.5 clutch. It's really just a quick tap on the clutch pedal as I pull it out of gear, then rev-match, and clutch-in to finish the downshift.

I've gone six years in a Spec Miata without EVER having double clutched. It has 197k miles on it, and the original transmission still shifts smooth. The street Miata has 214k on it, and it never gets double clutched. The original transmission on that one is smooth as well. And it even got hit from behind at a light on two different occasions.

In reply to David S. Wallens:

i enjoyed that thsi morning.

thank you.

Some times I double clutch, some times I rev match.

Mguar said it better than me. Yes you may be heel-toe braking but you could be braking a lot more effectively if you dedicated a foot to the task.

Used to be good reason for double declutching. I had an early VW and early MG that had no first gear syncro. Early Porsches with the down and back 1st gear and typically weak 2nd gear syncros. I ran FF and Super Vee for a while - straight cut boxes. Now it's really unnessisary except for fun. I will admit that I've gotten lazy and just rev match now.

I don't see the point in any car made in the last 10 years or so. Old cars? Sure.

Mongo requires it, the 11 Elantra doesn't, the others vary according to power, use, and components.

The (Hydraulic) 5.0 RX7 doesn't need it but the (Cable) Challenge Mustang likes it.

I double clutch the ProStar.

I don't double clutch anything, but i do heel-toe downshift. Not because it's better in braking (it's probably not because i'm compromising a foot), but because it means i'm already in the gear i want when i'm ready to get back on the gas again.

aussiesmg wrote: Mongo requires it, the 11 Elantra doesn't, the others vary according to power, use, and components. The (Hydraulic) 5.0 RX7 doesn't need it but the (Cable) Challenge Mustang likes it.

I've experienced the sounds that require this in person.

racerfink wrote: I've gone six years in a Spec Miata without EVER having double clutched. It has 197k miles on it, and the original transmission still shifts smooth. The street Miata has 214k on it, and it never gets double clutched. The original transmission on that one is smooth as well. And it even got hit from behind at a light on two different occasions.

I was wondering when someone that has been racing for some time would chime in and state that they don't bother with it. He even uses a car whose transmissions are made out of glass.

I don't bother with double clutching, too much going on to learn a new trick that really doesn't benefit me. I guess it sounds cool to tell people you can do it but I don't think its as beneficial as rev matching unless you have a sychro that is shot.

mguar wrote: In reply to DaewooOfDeath: Older cars with weak syncros or non-syncro-ed straight cut gears require double DE-clutching in order to save the gears.. Newer gearbox's aren't as delicate. Take a video of you double clutching and you'll find that it takes you 2 maybe 3 seconds per shift.. that's 2 maybe three seconds the car is effectively coasting.

http://www.youtube.com/watch?v=jKIP-YnC6Yw&feature=plcp

Here's a video of me double clutching every time. I'm on the brakes for every single instance, never coasting and I don't think my down shifts are excessively slow. In fact, I'll bet nobody would know I was double clutching unless they watched my left leg or unless I told them.

In my personal experience, double clutching actually makes down shifts faster. The only exception I've ever had to this was a BMW Z3, and that thing had super-smooth synchros.

Next downshifting as a means of slowing down is really pretty obsolete. Modern braking systems should be effective enough so using engine braking to slow the car means that you will not be threshold braking. (braking at the edge).. Plus the rate of DE-acceleration varies under engine braking requiring additional pedal modulation as the compression* varies throughout the camshaft range. That additional modulation makes extreme DE-acceleration more difficult to achieve especially should the track be slippery due to rain or oil etc..

So you are arguing against rev matching, not double clutching?

* yes I know we're talking about BMEP and not compression. Why use a clutch? up-shifts/downshifts, gas and shove.. (the lever that is).. which is the way you shift a transmission with dog rings.. A slight lift of the throttle on up-shifts and a definite pressing of the throttle on down shifts.. The speed the lever is moved is the trick. Any hesitation and the dog rings will be smacking each other until they can finally drop in.. Use the clutch in any shift and you start damage. but shift speed become measured in tenths of a second rather seconds per shift.. on a track with say 14 corners requiring downshifts/up-shifts we can be talking about lap time differences of several seconds per lap.. Add the potential for better threshold braking and the potential lap time savings become really significant..

Here's what I don't understand about the supposed braking liabilities with double clutching on a car with conventional synchros.

Let's say I'm simply rev-matching. With my right leg, I press the brake with my big toe and blip the throttle once with my little toe. With my left leg I press the clutch once.

Now I'm double clutching. With my right leg I'm still pressing the brake with my big toe and blipping the throttle once. The only difference is with my left leg, which is now pressing twice. This, seemingly, has nothing to do with the brakes.

I double clutch.

I'm still at a loss as to how holding the clutch in the whole time vs letting it go in the middle and pushing it in again makes any difference whatsoever in wear and tear. If you're rev-matching, isn't THAT what relieves the synchros? Can someone 'splain it to someone without an intimate knowledge of manual transmission internals?

foxtrapper wrote: Depends on the gearbox and the driving conditions for me.

Yerp.

I rally. I can be as sloppy as I want with the shifting and clutch action, whatever gets it into the gear I want as quick as possible.

Same with heal-toe. I don't do that either (especially because I am left foot braking constantly).

When I go on track, I find no difference in the driving style's. I've also found that some transmissions (5 speed wrx) suck no matter what you do, which has made me question the effectiveness of the double clutching.

And finally, daewoo, you're downshifts seem quite slow to me. No, I wouldn't know you are double clutching (how could someone, it's a soundless action...) but those weren't quick downshifts.

^You can hear him matching revs on the downshift. See also: McQueen double declutching his Mustang in Bullitt.

scardeal wrote: I'm still at a loss as to how holding the clutch in the whole time vs letting it go in the middle and pushing it in again makes any difference whatsoever in wear and tear. If you're rev-matching, isn't THAT what relieves the synchros? Can someone 'splain it to someone without an intimate knowledge of manual transmission internals?

Going to take a crack at this even though I'm neither a truck driver nor an engineer.

Let's say you're braking into a corner while still in gear. The engine, input shaft, output shaft, and wheels are all locked together. When you come out of the corner, you want to be in a different gear, and the engine should be spinning faster, since you want some power coming out. Typically you do this by pressing in the clutch and blipping the throttle This brings the engine up to speed. The output shaft is still locked to the wheels, so nothing needs to happen there. The input shaft, however, is spinning at a speed that's more appropriate for 4th gear than 3rd gear, since the gear ratio changed. It's not a huge difference, and the mass of the input shaft isn't nearly that of the engine, so the synchros are able to eat the difference.

If you didn't have synchros, or if they were shot, you'd want to pop the car intro neutral before blipping the throttle. This locks the input shaft to the engine, so they're both turning at the same speed. If you do it perfectly, they're also both turning at the same speed as the output shaft, so everything slots together in perfect harmony. This requires two clutch presses (one to get the car out of gear and into neutral, and another to get it into gear once you blip the throttle).

The only time I've ever even noticed the difference is when you're coasting down the highway in neutral. On a normal downshift, the input shaft doesn't have much time to slow down, but if you're doing 80 or so and you coast down a hill in neutral, the input shaft lopes along at the engine idle speed. If you rev-match with the clutch in to get back in gear, the input shaft has to get yanked up to speed by the synchros. It's noticeably jerky if you don't rev match with the trans in neutral.

In reply to steronz:

You sir get an A for the day

And I usually rev match instead of DC, my truck trans takes so long it's easy to do on the shifter's part and does make a noticeable difference in smoothness of shifts, but my clutch is ridiculously heavy so my leg gets tired of doing it...

When I'm not in a hurry I double-clutch the T-5 in the Mustang because the 2nd and 3rd gear synchros are wonky (known to be weak in those trannies anyway).

DaewooOfDeath wrote: I've been watching a lot of race videos from GRM members and it looks like everybody rev-matches but nobody double clutches. Considering speed is really not that important on a downshift, that double clutching is easier on the transmission and that the whole exercise makes it easier to get the car in the desired gear, what's the downside?

I double-clutch on the street.

On course, I don't lift to upshift, and I don't rev-match downshifts - I use a harsh downshift to set up for the corner.

My WAG is that double clutching is more necessary, if at all, on cars with longer gears. Such as, say, a Daewoo versus a Civic Si. The longer the gears, the greater the speed difference between the input and output shafts.

scardeal wrote: I'm still at a loss as to how holding the clutch in the whole time vs letting it go in the middle and pushing it in again makes any difference whatsoever in wear and tear. If you're rev-matching, isn't THAT what relieves the synchros? Can someone 'splain it to someone without an intimate knowledge of manual transmission internals?

When you rev the engine with the clutch engaged and the box in neutral, it speeds up all the internals so that when you do shift the transmission gears and the engine are already going the same speed.

Basically, it does the work the synchros would normally do.

Knurled wrote:

DaewooOfDeath wrote: I've been watching a lot of race videos from GRM members and it looks like everybody rev-matches but nobody double clutches. Considering speed is really not that important on a downshift, that double clutching is easier on the transmission and that the whole exercise makes it easier to get the car in the desired gear, what's the downside?

I double-clutch on the street. On course, I don't lift to upshift, and I don't rev-match downshifts - I use a harsh downshift to set up for the corner.

All of my mechanical sympathy is bleeding!