Double Clutching the Upshift

[AusStreetRacer]

Another thread prompted me to put this idea forward. Please not this isn't really a 'drifting' technique. Atleast I don't think it is.

I've been trying to work out if there's any advantage to actually double clutching on the upshift. I have heard from alot of people that this is completely useless in cars with synchros- but apparently it's actually used amongst some drivers and it's supposed to enable you to get better acceleration.

This is my theory:

When you're making the shift to neutral - you can pretty much bring the clutch straight up - because the only thing the engine is fighting is the weight of the layshaft and gears, compared to the entire weight of the car like you would experience under a normal shift in normal driving conditions.

This is one split second shift.

So assuming that shifting to neutral can be done as fast as possible without damaging anything, and the fact is that now that the lay-shaft is spinning at the right speed, you should be able to put it into gear and dump the clutch without any jolt or causing any extra wear.

This is a second split second shift.

So when you think about it - double clutching the up shift means that yes - you hit the clutch twice - but by doing that, you're enabling yourself to bring up the clutch much faster than you would normally. So you're actually reducing the lag between putting the car into gear and making the power connection from the engine to the wheels.

You're basically replacing one long shift with two split second shifts.

I mean yeah sure - you can always just change gears and dump your clutch - but that creates that JOLT effect which creates a lag on your engine.

In effect you end up keeping your revs up around wear you'd want them more effectively, and therefore accelerating faster.

Whaddya think?

Guh... I haven't had a good nights sleep in a few days and it's currently 1:02 AM.

I swear driving needs to be a job. I'm studying Commerce and I spend too much time playing Initial D, watching Initial D, looking for a new car and looking at my finance options, when I could be studying, or sleeping so I can study better.

I've just got a new job and most my money will be going towards the car - I don't think I'll have text-books next semester. I'll probably sell my old ones to help save for my car too the way I'm going. LOL.

I'll probably read this when I wake up and think: "WTF?!"

Anyone wanna point out any holes in my theory?

[malcolm]

well, double-clutching on up-shifts makes your gearbox last a ***little*** bit longer, it's not worth doing because it wastes time. It almost triples the amount of time that you aren't accelerating, and thus losing time to those around you.

basically, only do it if your gearbox is dead, and all the synchros have stopped working.

[Drifterlunchb0x]

plus double clutching was what old classics had to do with alot of the gear boxes...it doesnt apply to todays cars at all,well unless ur sykroz are blown . moving on....

[AusStreetRacer]

Neither of you actually commented on the theory I put forward.

I've heard what both of you have said a million times over.

Did you actually read my theory?

I'm gonna leave it for a while... and come back to it in a day or two... see if my theory still makes sense to me.

When I get another manual car I'll actually test it.

Damn auto's.

[malcolm]

yeah, I read it... but two kicks of the clutch will always be slower than one. Also, you don't quite "dump" the clutch on fast single-clutch upshifts, but you can let it up quite fast without making the car shudder (just takes a bit of practice).

There is a technique I used on my old MR2 that had a blown syncro in third gear. I would select neutral, from second, with the clutch out, and then quickly hit the clutch just as I put the lever into third. Worked quite well.

Also, I don't get what you mean by the "lag" you're talking about.

[SidewaysGts]

Not going to bother reading what was said though im pretty sure malcom was right on.

Double clutching on an upshift will make you take logner when shfiting. Keep in mind when you up shift your revs need to fall, theres no point in raising them in neutral (which takes time to do) only to let them fall (and take time while they fall) again. Why be in neutral even for a short time, lining up your gears when you could already be in the next gear and accelerating?

The only point in doing it is to prevent damage to your synchros/dog teeth, or if you dont have them/theyre broken.

___

Added: You can bring the clutch up as fast when your upshifting as you could while your going into neutral. Just depends how smooth you are on it.

The key to double clutching being slow, is your revs -need- to fall when you upshift. Go watch the drift bible and watch out fast tsuchiya upshifts, now tell me if you could use the clutch twice while linging up the gears between the clutch uses, in the same time he moves his foot once.

[AusStreetRacer]

Yeah. Probably.

I'm just thinking...

Your clutch would be able to bring the layshaft up to speed faster than the synchros. But the time it takes to make the second shift from neutral to the next gear would greater than the time you'd save by using the clutch instead of the synchros to get the layshaft spinning at the right speed.

So yeah I guess the only advantage of double clutching is that it'll save your synchros, clutch, and transmission from some abuse - especially if you have a high-powered car, and it also disrupts the balance of the car less when down-shifting - but so does rev matching anyway.

So I dunno - maybe people who think they can get better acceleration by double clutching already have *Censored**Censored**Censored**Censored*ed syncros or are just idiots.

Or maybe there's just a whole bunch of try hards out their that took The Fast and The Furious as a definitive guide to street racing. LOL

I'm gonna keep putting more research into this until I find out a definitive answer from someone with a qualification or something.

Might see if I can get in contact with a professor at my uni who specialises in automotive engineering and physics or maybe the UQ Racing Team.

Anyone else got any input into this?

[SidewaysGts]

or are just idiots.

Or maybe there's just a whole bunch of try hards out their that took The Fast and The Furious as a definitive guide to street racing. LOL

You hit it dead on I dont have any "professional" experience myself, but malcom here races what was it again? Formula bmw? Hes as creditied as they come on these forums.

[Parry]

Originally posted by AusStreetRacer
I'm gonna keep putting more research into this until I find out a definitive answer from someone with a qualification or something.

Might see if I can get in contact with a professor at my uni who specialises in automotive engineering and physics or maybe the UQ Racing Team.

Anyone else got any input into this?

If you need a professor to tell you that double clutching is slower, than you're beyond the help of ANY professors.

Get over it.

[SidewaysGts]

^--Cold as ice

[AusStreetRacer]

LOL.

Thanks Parry

I'm done with it

[conandd]

double declutching to upshift ?
I do it all the time in the morning run to school and office......

Do it only when you need it only..... or it just make u slower ....

I think with a normal gearbox, a faster shift ( I upshift without giving any gas...I know some of u do but some give gas when they are engaging the clutch ) is a clearer and smoother shift

but for downshift I do 2declutching all the time ......just for fun but not for fast ...and it help the synchros more when u downshift than when u upshift

[SaintDrift]

Ross Bentley basically said it would waste a huge amount of time, but any complete race car driver should be able to do it and also shift without a clutch. You never know when your clutch or syncros will go bad. Also, in endurance races it may be worth it to do all the double-clutching.

[malcolm]

for upshifts, no... you don't want to double-clutch, ever. Think about it. You waste 2 tenths of a second a shift. 10 shifts a lap, that's 2 seconds. 800 laps in a 24 hour race, and that's 1600 seconds, or 26 minutes. It's just not worth it. For endurance racing, double-clutch on downshifts, because it doesn't really cost you any time.

[SidewaysGts]

Normally when downshifting you need to ease up on the clutch (unlike upshifting where you can pretty much go as fast as you can as long as your smooth) to some extent, go as fast as you can and the car will jerk (big no-no for racing! dotn want to upset your balance at the most important time, right before a corner)

Double clutching on a downshfit rev matches (gets the engine speed where it should be for that next gear down and the speed your going) so you can work fast on the clutch.

But then again, hey thats why we have the ever so popular heel-toe right?
__

On a side not the ONLY time ive ever used double-clutching was on downshifting, and in specific the only 2 situations i use it.

One is when i want to pass and need to downshift.

Two is when im slowing down slowly in traffic, talking so slow just taking my foot off the gas and coasting is enough to slow down, and i double-clutch when id downshift, more for "fun" then being nice on the tranny or being smooth