Double clutch on downshift during aggressive driving

[kyngfish]

So I’m a double clutch convert. A quick double clutch between 1-2 does make things a split second faster. For what it’s worth though I’ve never really had issues with a normal 1-2 shift.

But I hear a lot of people using the double clutch on downshift. And here I’m having more issues. When I’m double clutching during aggressive driving - up shift is fine but downshift doesn’t really work well. I’m better off rev matching. Is this because I’m doing it wrong or is aggressive downshift really more for heel toe?

[kyngfish]

FWIW double clutch during downshift when I’m driving more normally it’s totally fine.

[Noah930]

I don't understand exactly. When you are downshifting, you are always double clutching, correct? But you are not always heel-toeing when downshifting? So you can double clutch at "regular" speeds (with no heel-toe), but when you throw in the heel-toe while "aggressively" double clutch downshifting you're having problems?

No heel-toe: no problem.
Heel-toe: problem.

[Bill Verburg]

All you need to do is rev match on the downshifts

[yelcab1]

Practice, practice, practice.

[midnight911]

I don't double clutch during downshift most of the time but I do have to blip twice to rev match as my engine rev falls too fast while I carefully find the next gear in my 915. Occasionally I would lift the clutch during that process double clutching. But i think there is no need for double clutching as the synchro mesh would have done the job by the time I reengage the clutch. And if you have a healthy synchro, then double clutching is adding minimal value even when shifting up. Synchro would mesh with the next gear way before you engage your clutch.

[kyngfish]

I rev match fine. It thought double clutching was better for downshifts. But during aggressive driving it doesn’t really work.

[Solamar]

I always double clutch with rev match when downshifting from 3 to 2, I don't even realize I'm doing it anymore. Regardless of how aggressive I'm driving the double clutch/rev match 3 to 2 is smoother, quicker and un-settles the car less than without.

I'm sure this is a reflection of my transmission state of wear more so than anything else but I find it comforting that it's easier on my tranny doing it this way.

[Bill Verburg]

Originally Posted by kyngfish

I rev match fine. It thought double clutching was better for downshifts. But during aggressive driving it doesn’t really work.

At track speeds there isn't time for double clutch, rev match saves wear and tear mostly on the clutch

also uses the brakes to slow the car, you only shift later, after most of the braking is done to have the right gear for power on. It depends on the exact situation but I will often do most of the brakeing, then skip a gear, i.e. go from say 5 to 3 w/ a rev match of course then power on

[LIRS6]

I don’t track, but I ALWAYS double clutch when downshifting - spirited driving or otherwise. Started doing this with my 911 35 yrs ago after learning the technique while driving a Formula Ford at Lime Rock, due non-synchronized tranny. I’ve never heard of double clutching for up-shifts. What am I missing?

Jason

[stownsen914]

Originally Posted by kyngfish

It thought double clutching was better for downshifts. But during aggressive driving it doesn’t really work.

What about it doesn't work? I'd think that double clutching during pretty much any street driving should be possible. Bill is right that on track there often isn't time if you're pushing it, but I argue that with practice it should be possible driving on the street. At least most of the time.

[michael lang]

Using the brakes slows the car... using the transmission to slow the car breaks the transmission.

You'll be much smoother and way faster (if that's your goal) to brake, heel & toe and then start accelerating again. Plus it will sound so cool, especially if your car's exhaust is on the aggressive side.

[Evan Fullerton]

I double clutch every downshift in old cars and don't feel it affects my shift speed in a negative way. When you get it right, you can really feel the reduction in shift effort by making synchros not have to work as hard. Takes years to master though.

https://www.youtube.com/watch?v=Ns6nEPXHrFo

[creaturecat]

it's all part of the joyous experience of finessing a sorted 915, for me.
don't miss the old Grandmother 50 one iota.

[H-viken]

Could someone please walk me through both processes step by step so I can follow?

[thetorch]

Doesn't get much better than this explanation from Ian:
https://www.youtube.com/watch?v=0TYD4aOvN80

[Evan Fullerton]

Downshift

On brakes
Clutch in
Shift to neutral
Clutch out
Heel-toe Rev match over shooting the revs quite a bit
Clutch in
Shifter down a gear
Clutch out

You need to over shoot the rev blip so that when the second half of the shift is done and the clutch is out for the second time the engine speed and road speed for that gear match. Takes a lot of practice to do all that seamlessly and fast. The amount of blip you need also changes with every gear as the gear ratio spacing is a bigger gap the lower you go. For Autocross, sometimes you have to downshift to first, that takes a massive blip. If you have a light flywheel and are “racing” often you just peg the rev limiter during the neutral blip phase to time the RPM drop when you get it into the next lower gear.

When you get really good at it, you can skip 2 gears if you want. A 4 to 2nd shift can save some time and allow you to push the braking zone a little farther as even the best struggle to maintain 100% threshold braking during a heel-toe blip. You just better know your car and the corner extremely well to not have a mechanical over rev. A 4th to 2nd downshift is where I find a 2 gear downshift feels the most natural.

Only reason to double clutch an up shift is if you can shift faster then the natural RPM drop of the engine. With a heavy flywheel or some throttle hang due to poor carb tuning and a decent transmission, it’s not uncommon to be able to shift faster from 1st to 2nd then the engine speed drops. Adding a double clutch on the 1-2 up shift can help save some wear on the 2nd gear synchro if this is the case. I have a MGB GT with a T5 gearbox and a Chevy V6 that needs a healthy pause or double clutch on the 1-2 up shift if you take it to redline in 1st due to slow rev drop from a heavy flywheel and oversized carburetor.

[kent olsen]

The only time I "had" to double clutch at a track day was from 5th to 4th. My old linkage was a little vague and once or twice I touched reverse. Sooo I would double clutch giving the linkage a second to move over to the 3-4 plane.

I have heel/toe shifted ever since I grew up lusting for my neighbors 356. So 60 years and I have never used up a clutch. Of course I always replaced the disc, throwout and pilot bearing with each engine pull but never the pressure plate.

Third engine on my Porsche, 2.4 then 2.7 and now the twin plug 3.0. Last week she went over 247,000 miles.