Mizuno

A big part of 993 highway fun for me is to shift to a lower gear and enjoy the sound and rush of driving in the 5000+ rpm range.

I was wondering ...

1. if many of you double-clutch down shift in the same highway circumstances?

2. If double-clutch down shifting or regular shifting is the best way to downshift to limit wear and tear of the clutch/ transmission/ synchro?

Thx!

Quadcammer

do I, not a chance.

Do I rev match the downshift, yes, but I don't double clutch.

2. double clutching doubles the cycles on the pp springs, tob, etc, but it is the best for the synchros.

just rev-match and don't worry about it.

Jim W

Single clutch with throttle blip to rev match for me.

ca993twin

I double-clutch most of my downshifts because I am a really old geezer and habits are hard to change. No doubt it is easier on the synchros, but modern synchros are better than they used to be.

DanL993

Ditto. I do it from long habit and looks like I'll have to break that. Thanks for the input and the question....I've wondered for a long time.

Rinty

Won't the clutch plates wear out before the springs and throwout bearing?

I'm a double clutcher; used to drive trucks with square boxes, as a student.

P-daddy

Ditto for me. Plus, it's so good to hear the Stage IIIs when I blip

Quadcammer

the springs almost for sure, throw out bearing could go either way.

The point is that with a proper rev match, there is little benefit to double clutching, which takes time.

Is there anything wrong with doing it...spose not. Is there any real benefit over a proper rev match...not in my view.

EMBPilot

i do this. try to anyways... some better than others

Resident Sicko

I double clutch the car before it warms up and that is it. More of a need than desire as it take a while to wake her up. Double down gearing when everything is at operating temp only needs a rev match for the fun to begin.

ca993twin

Not to belabor this point, but rev matching helps your clutch and your vehicle dynamics in a downshift... it does NOT help the synchros. The synchros are barely even needed with a proper double-clutch downshift. And, if it is taking more time then a "blip", you are doing it wrong. But as I said, new synchro designs are better, so this may be about nothing. But then again... maybe not.

Quadcammer

steve, i have to disagree. If you rev match properly, it greatly reduces the amount of "rpm compensation" the synchros have to do.

Furthermore, you may be more practiced than I, but comparing: clutch in (blip and gear change at same time) clutch out vs. clutch in (shift to neutral) clutch out, clutch in, (shift to gear) clutch out, it seems like the first would be quite a bit quicker.


I'd also say that rev match doesn't really help your clutch either. The clutch disk is still getting slammed against a moving flywheel (and in the case of a downshift, a much faster spinning one). Clutch health to me, has to do with how much clutch slip occurs, and thats more the result of your pedal work.

Quadcammer

that said, after thinking on it more, unless you are really hamfisted, i guess you would nhave to feather the clutch quite a bit on downshifts if you dont rev match, and doing that would affect clutch wear

Dplus

Blipping the throttle on a downshift, with the clutch depressed; what exactly are you "rev matching"?

The reason to double clutch is to get the gears on the input and output shaft spinning the same speed in the transmission prior to engaging the gears. Blipping the throttle with the clutch depressed only spins the motor.

The output shaft is spinning due to wheel speed, depressing the clutch, shifting into neutral, releasing the clutch, blipping the throttle will spin the gears on the input shaft, match them to the speed of the gears on the output shaft and make the gear engagement easier/smoother. This was necessary prior to syncros and still necessary on some large/older trucks. You can also rev match and shift without the clutch at all, it's called floating.

ca993twin

Dplus has it right. Rev-matching (done correctly) eliminates the speed differential from the flywheel to the clutch disk, making the downshift smoother and without unsettling the car, especially in mid-corner. This can also greatly reduce clutch wear.

The synchros wear when being "forced" to match the internal gear speeds. Everytime this is done, there will be some (perhaps infinitesimal) wear on the synchros. By double clutching properly, the gear lever will almost fall into the down gear with almost no pressure on the lever. No "force", no wear. Same thing on the upshifts, except there is no need to double clutch an upshift, unless you are REALLY slow on the lever. By pausing slightly before engaging the next higher gear, you are matching the gear speeds, and the lever just falls into place. Try upshifting quickly and see how much more force is required... force equals synchro wear.

Here's another trick to save your first gear synchro: I assume that at signals you are putting the gearbox in neutral and releasing the clutch (saving wear on the throw-out bearing). When the light changes, engage 5th or 6th gear before you select 1st gear. Selecting those higher gears will stop the input shaft, allowing you to select first gear with very little pressure on the lever. The synchros on those higher gears wear very little.

As to the speed of a proper double-clutch downshift? If it is taking longer than the blip, you need more practice.