It takes a fair amount of skill to do it right - without using the clutch. You really have to know your car - and be skilled, accurate, and on your game to do that without damaging your synchros.
But in theory (if you're precise every time), you really aren't hurting anything.

The problem comes when you aren't precise. Everyone has bad days, and one slip can do a lot of damage.
The further you are from the exact RPM, the more stress you put on your synchro (the cone has to absorb the RPM delta). The further you are from the exact RPM, the greater the chance you may chew up the "dog teeth" on your synchro as well.

I'm fairly skilled at shifting, and have a fairly good understanding of the mechanics involved - I just feel better using the clutch. The clutch gives you a much greater slop factor.
I've used the technique you described, with several of my cars. It's fun to test your skill from time to time.
However, I'm only human and I screw up shifts from time to time. More importantly, I really can't afford the steep (and expensive) learing curve!
Sequential shifting (using the clutch), and rev matching is the best insurance for long transmission life.

 

Thanks.

I just got a chance to read your previous post - good stuff.

 

not downshifting through the gears when exiting the highway or slowing down in general is a safety issue. You don't want to be in 5th or 6th gear when you're rolling at 30mph because if you need to accelerate to avoid danger, you're going to have to shift first. You should always be in a gear appropriate for the speed you are traveling regardless of positive, negative, or zero acceleration.

 

Ok slipstream I see what you're saying but I think your whole argument is based on immediate, quick shifting.

I think everyone that skip shifts (everyone I know does it) is doing it leisurely, with ample time between the actual shifts, allowing the rpms to fall.

Here is an example that many of us are likely to experience:
You're annoyed of the meaningless stop sign down your street so after your california roll you floor it on 1st, VTEC (maybe redline), then powershift slam 2nd with a chirp, VTEC, now we're about 40ish MPH at prolly about 6k rpm. Ok common sense kinda comes back and we start looking for the cops so we decide it's better to keep it at 40 to avoid any further attention. At this point we push in the clutch and shift to neutral. RPM's drop to ~1k. So a second or two later all we need to do is keep up that 40mph. I think at this point you can go ahead and shift to 6th and go about your bidniss'. There is no need to go to 3rd, 4th, 5th, then 6th.

The point here is that by the time you let the rpms drop to nothing and you spent a few seconds with the clutch in, your input shaft / synchros are already slowed.

Am I wrong?

I do agree that this would totally screw things up if you quick shifted immediately to an out of order gear.

 

Time is the key, in your example. You've got to realize you're relying on the internal friction of the transmission to slow the input shaft - and there's a lot of rotational inertia to dissipate through that friction. It's hard to tell how long it could take.

I used to skip gears in some of my older cars (many moons ago) until I learned what damage it actually can do. When I learned what was actually going on in a transmission - I changed my shifting techniques and habits (hard to do).
In all, I can guarantee you that it takes me much less time to row through an intermediate gear, or double clutch, than it takes to wait for the input shaft to slow down to a "safe speed" - in order to skip a gear (or more).

Waiting was one of the three techniques I discussed - as more of a side note than anything else. But it works - if you're willing to wait.

Old habits are hard to break - but it can save you some pain down the road.
You won't be the next poor soul to post: "car won't shift into 5th or 6th... HELP!"
Cheers.
Rob

 

So it's cool to skip shift if you slow down the rotation by double clutching?

 

Yes. It's covered in one of my earlier posts on the 1st page along with info put out by 05turboS2k. Read back just a little for more info on that.

 

During any shift, double clutching causes the input shaft to slow down more quickly (thus matching revs for next higher gear) than leaving the clutch disengaged would. When you shift to neutral and re-engage clutch, you are adding more drag from the tranny shafts to the friction already braking the engine.

So double clutching on a down shift seems to be counter-productive at first glance. You are slowing down the input shaft when you really want to speed it up. It means that you have to blip the throttle harder to get the engine speed up to match revs for next lower gear).

Does the extra drag from double-clutching allow better engine speed control while blipping the throttle? Like maybe keep you from over-reving? Otherwise, why not simply disengage clutch, blip throttle to rev match, downshift, and finally reengage clutch.

I have a theory that people double-clutch then coast into a braking zone. As a sort of calm before the storm, in preparation for the action to come. That is, mentally it allows you to focus on braking, turning, and down-shift w/o worrying about anything else like accidentally accelerating the car.

I have done that myself many times. In my quest for better driving technique, I am trying to eliminate that habit in order to prepare for hopeful future track time. It seems like a mental crutch, a big waste of time and driver's energy. Sort of like a hitch in your swing with a baseball bat or golf club.

Of course loafing along on the street with no competitors or stopwatch, it doesn't matter. But it does make me appreciate just how much goes into competitive racecar driving. They never coast. Well, very little.

 

I coast at times during victory laps