GRM expert watching The Fast & The Furious?

Did I read this right? In this month's advice to young race drivers, it seemed like a "well credentialed" (sorry, can't recall his name) Miata expert was recommending double-clutch downshifts for a raced Miata. For a moment, I heard Vin Diesel's voice in my brain and had flashbacks to the days of DSM's with giant triple wings. My understanding was that proper care of a synchro'd manual simply required a rev match on the downshift. I've been working on that with my "new" (1994) Miata as I am planning a few HDPE events for it next year, but I'm curious if anyone knows why a double clutch would be called for? Since Vin Diesel rarely makes appearances here, I thought I'd ask you guys.

All jokes aside, it's not BAD advice per se. In a heavier gearbox, double clutching would indeed let the transmission live longer. If E46 M3 guys double clutched, their synchros wouldn't go bad so relatively soon. But I really don't see it making much difference in a Miata. The only thing it could do for performance driving is slow you down. I guess it's a skill to brag about though.

Ill double clutch the escort, but more out less to keep the revolutions up. Just how I prefer to do it. Heat remember, rookies don't use nitrous.

I've seen how you drive, rookie. You'll blow yourself to pieces.

My fuel map still has a nasty hole.

I used to double clutch when I drove heavy trucks, and still do with my Ford tractor, but neither of them had/have synchronizers. I've never done it with any of my cars, street or track, and have never managed to blow my synchros. I guess it would depend on the design of the trans, but for my cars I've never seen the need, and it just slows down the downshift and if not done perfectly can also upset the chassis under hard braking/downshifting. And frankly, I have a hard enough time heel and toeing without thinking about double clutching at the same time!

I blew the welds on my manifold after missing a double-clutch upshift once.

Did your floorboards fall out?

I double clutch transmissions on the downshift if there's time to do it.

A bit of extra effort makes the synchros last longer.

My '67 Jeep -needs- to be double clutched for 1'st.

Shawn

I'm in the habit of double-clutch downshifting when I'm not driving fast as it's a lot easier on the synchros (an issue with Mustang gearboxes), but if I'm getting on it, I don't have the heel-toe control to do anything but a rev-match.

After driving a car with dying, crunchy synchros for too long, I have trouble not double-clutching...

If the car has mohr horsepower and a button clutch I always double clutch, in the Elantra I wouldn't waste the effort

Some one walk me through a double clutch. I've read what wiki says and that doesn't jive with my preconceived notion. I do like to heel and toe in the miata, though.

In reply to RossD:

For a 3-2 downshift:

1 depress clutch
2 move shifter from 3 to N
3 release clutch
4 blip throttle to match revs between engine and 2nd gear
5 depress clutch
6 move shifter from N to 2
7 release clutch

Obviously the timing on some of these is critical/overlapping. The important item achieved by having the clutch engaged and the trans in N when you rev-match is that the input shaft is spun up along with the engine.

If you just blip while downshifting without double-clutching you're matching the engine with the rear wheels, while the synchros are taking care of matching the input and output shaft speeds in the transmission.

If you double-clutch, you're matching everything up. (the engine and input shaft are a unit, and you're matching them to the output shaft/wheels "unit")

Thats what I thought, but wiki seemed to say something different... Thanks.

DukeOfUndersteer wrote: My fuel map still has a nasty hole.

Are you dumping in third?

I double-clutch on the street to save wear but on the track I usually just rev-match and straight shift. I don't see how double clutching could help you drive any faster.

200k miles of NOT double clutching the Miata and its fine.

Joey

PS, I once beat up a guy with a pipe. Now hes a janitor.

Joey

I live my life a quarter mile at a time. For those 5-10 minutes of slomo and 10 gear shifts, I'm free.

Here's a nice in-car video that demonstrates double-clutch downshifts:

http://www.youtube.com/watch?v=0j-3xIZK-Bk

I'm thinking the need to double-clutch is totally dependent on application, like some racing/high-performance situations, worn synchro's or no synchro's. In racing, there was a time when few transmissions had synchronized gears, so double-clutching was necessary to preserve the box and to maintain speed and momentum. Take another look at the movie Grand Prix; there is some great footage of the process. I'm thinking of the scenes from Monaco where Garner was experiencing shifting issues.

With the exception of my truck, every car i've owned since 1968 has been a manual; the only one that ever needed double-clutching was the Sprite as it had a non-synchro first gear. Heel-and-toe (with rev-matching) has always been the norm for every car and I've never had a problem/situation that dictated the double-pump technique.

I tend to double-clutch my downshifts. The old Land Rover taught me how (no synchros on some of the gears, and it's an old crunchy 'box anyhow) and the Miata gearbox in my Locost has a questionable synchro in 2nd. So I got in the habit, and never got out. It works fine and doesn't seem to slow me down at all - my lap times in the Locost are very close to Brandon's, and he's got a flappy paddle bike gearbox in his car. I know he's at least as fast a driver as I am, so it's a reasonable comparison.

BTW, if you want to learn how to double-clutch a downshift well, try dropping into 1st gear in low range with no sychros. Very high skill level required. I'm at about a 75% success rate.

You know, for a movie that's universally mocked, a whole lotta people here are able to quote and describe multiple bits of the movie...

I may eventually work on double clutching the downshifts on my 98k mile E46 M3, but for now I need to work on heel-toe technique first.

In reply to ransom:

Thank you for that explanation I never understood the reasoning behind the double clutch but that makes complete sense. I don't see how anyone can do that quick enough to be fast. It seems like a lot of work when trying to get around a track as fast as you can.

pigeon wrote: You know, for a movie that's universally mocked, a whole lotta people here are able to quote and describe multiple bits of the movie...

Because everyone loves corny movies. Twister is my favorite. Do you have any ideas how many bloopers and non-truths are in THAT?!