Cursed by the double-clutch
 

Double-clutching downshifts. Seemed like a good idea. Save a tiny bit on the clutch, preserve the synchros a little bit. Get that awesomely smooth in-the-gate feel from the stick. I do it for a few weeks, now I have a problem. I can't single-clutch a downshift any more.

Blipping the engine with the clutch in feels really wrong now, it's horrible. Obviously upshifting without double-clutching isn't too difficult, since you're not having to hit the gas with the clutch disengaged. But to downshift I have to think about it completely to do it. Then I make contact, feel how off the rev-match was, think about that poor clutch plate and curse the day I learned stick.

Anyone ever in that sort of situation?

David,

You perplexed me with this thread so I had to look it up ( from wikipedia ) :

However, in order to downshift, engine revs must be increased while the gearbox is in neutral and the clutch is engaged. This requires the driver to shift into neutral, release the clutch pedal, apply throttle to bring the revs up to a suitable speed, depress the clutch again, and finally shift into gear. This operation can be very difficult to master, as it requires the driver to gauge the speed of the vehicle accurately and is often conducted as cars in front slow down.

So, how long did it take you to master this ? Sounds tricky...

Nick

Hey Nick. It's pretty easy really, it spreads out the shifting process through more steps, and in a way simplifies it because you'll never really need to precisely vary both feet at the same time. Easy practice is to downshift and upshift while cruising and try to get the revs exact and the stick to slide into the gate with no resistance at all. I guess I worked at it for a week's work of driving before I didn't have to think about it.

At the end of the day it's not really that handy for performance driving, it's obviously more steps and takes a lot longer. It's just nice because it seems to be easier on the tranny.

Waste of time and energy. You'll never double clutch a synchro box as fast as the synchros can do it, unless they're worn.

Let the synchros do their job. They're very durable in these transmissions, and they're there to help ya. :)

Hi,

I agree that today, you don't need to do it, but it's still a good skill to master. Anything which makes you a better driver is worthwhile IMHO.

While the synchros will do the job, I feel it's especially important learning how to match revs for downshifting, this will really preserve both the Box and the Clutch, the Clutch in particular.

And, you never know, you may aspire to Auto-X (rev matching keeps the engine in the sweet spot, an aid toward improving your ETs) or Race someday, and not all race cars have a synchro transmission. My old Formula Ford didn't - straight cut Dog gears. You either double-clutched, or spent your time fodding the Track picking up pieces of your broken tranny...

Happy Motoring!... Jim'99

this sounds like a....you guessed it YOUTUBE momment!

I saw this one a while back I think its Sebring.

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

Well, rev matching and double-clutching are two completely different techniques. Rev-matching is, as you say, crucial to smooth and fast driving. But rev matching isn't about keeping the engine in the "sweet spot." Rev matching is only done to reduce the load on the clutch when shifting to a lower gear - think using your clutch to engage 2nd gear at highway speeds with the engine at idle. Would you rather use the clutch friction to increase the engine speed or use the throttle? I think you'd rather use the throttle, and that's rev-matching.

Double-clutching, in a synchro box, will just slow down your shifts and is a waste of time and energy.

I do know a thing or two about autocross as I do about 20 events a year including multiple National Tours / ProSolos and the Solo Nationals. I've only downshifted once in the past three years!

Hi,

Yes, of course you're right, double-clutching and rev-matching are two different things. I guess my post was more to encourage people to match their revs than to double-clutch anyway. But by double-clutching, you master that technique of stabbing the throttle and matching the revs, as the Lister said, without even thinking about it...

Happy Motoring!... Jim'99

I thought flying helicopters was hard...that just blew my mind.

I am now in the habit of rev matching in both my daily driven Mazda 3 and the boxster however heel n toe is still out of my grasp. I even have difficulty matching revs still.....sometimes I over rev and engage the clutch and sometimes I undershoot the desired rpm. When it works out is feels nice and smooth but it is certainly not easy to master. I am now trying to rev match without looking at the tach and going purely by pedal posistion and sound with mixed results. Practice makes perfect I guess.

Got the Heel and Toe "Blip" shifting down - and do it all the time. And if you haven't learned this technique, I say start practicing. Nothing is more fun then going into a turn in the box, and being able to accelerate immediately through it.

Have always heard mixed reviews on whether double clutching is necessary or not in a car such as ours. Have tried to perfect it along side matching the revs - but really difficult fast.

Regardless - that was a freaking awesome vid - I already shot it out to the fellas - thanks!

- C5150

Amen, brother. I've tried to double-clutch and can't do it quickly like that. I've also gotten so used to (up)shifting very quickly due in part to the short-throw shifter in my R32, that my downshifts are also very quick and I almost always heel-toe anyway. So the synchros don't do much work as I'm generally in about the right rev range while downshifting. Now, if I need to downshift and skip a gear, generally I have a little more time and I can perform a crappy, overthought-out double-clutch because I know it's more difficult to have your revs and synchros lined up if you're skipping a gear or 2.

Keep in mind the synchros are simply used to match speed between the drive shaft and the layshaft in the transmission, so they don't have much to do with rev-matching if you don't engage the transmission in neutral at some point between the starting gear and the ending gear.

Just think of when you shift to a new gear while the clutch is pressed in, the amount of resistance there is on the stick itself is a direct result of how much rpm difference there is between the driving shaft (what the wheels are doing), and the layshaft (a freely spinning shaft that goes from the open end of the clutch to the gearbox). The whole point of double-clutching is to use the engine to change the speed of that layshaft while in neutral so it matches the driveshaft when you shift into it in the new gear. Technically, if you could match it perfectly, you wouldn't even need to press the clutch the second time, you could just engage the dogs on the new gear with the clutch engaged.

I first got annoyed by synchro wear when I would shift from first to second really fast and notice a great deal of resistance. I compared it to a friend's 300zx with a 1-2 shift that was like butter, and wondered if my second gear was just worn or something. Then it hit me 1-2 has the largest general rpm drop, and what I was feeling was the synchros trying to slow down the layshaft so the dogs would engage. Wanting to spare that stress on the synchros, I figured I needed to think about a better technique. The solution for an upshift is simple, move the stick to neutral and wait a little bit for the layshaft to slow down by itself before shifting to the higher gear and voila, much better feeling 1-2 shift. But to downshift...you need to use the engine to speed up the layshaft while in neutral, ergo...double-clutching.

At the end of the day John V is probably right, synchros aren't gonna feel the pain. But it never hurts to know how it's working and what you can do:)

(BTW, the reason the 300zx stick felt like butter is because of a design that uses two synchros instead of one, nice little feature)

-David