Quote:
Originally Posted by jphughan
Well then just be grateful you're still alive and have an opportunity to check out what you've been missing!  I forgot to mention that the other factor determining the size of the blip you'll need is how high up you are in the rev range in the current gear, since the RPM difference for a given speed between adjacent gears increases as you climb up the rev range.
So for example, let's say you're in 4th gear and want to downshift to 3rd, and you're currently doing 20 MPH. 20 MPH in 4th only has you doing about 1200 RPM, and therefore the required RPM increase for 3rd at that speed is pretty small, about +350 RPM in this car. As a result, you only need a tiny blip, in fact in that case I might not even blip at all. But now let's say you're in 4th gear planning to downshift to 3rd and currently doing 80 MPH. Now you're doing about 4850 RPM in 4th, and there's a bigger RPM increase to get to 3rd, about +1600 RPM in this car. That's over 4x the difference between 4th and 3rd at 30 MPH, so you of course need a correspondingly larger blip. The higher you are in the rev range when downshifting, the larger a blip you'll need to engage the lower gear smoothly.
And if you want to skip shift down, it's even more significant since you're going for an even lower gear where the difference at a given speed will be even greater -- so for example if I'm in 6th doing 60 on the highway and want to downshift to 3rd, even though I'm pretty low in the rev range in 6th (2700 RPM), the fact that I'm dropping 3 gears means I need a blip for a +2200 RPM change. In fact it's so significant that I'll double-clutch that one to spare my 3rd gear synchros. Double-clutching btw is when you shift to Neutral, let the clutch out, THEN blip the throttle (which revs up both the engine and gearbox since the clutch is engaged), then you shift into your desired lower gear. You'll find that the shifter goes into the gate much more smoothly this way when skip shifting down than by just doing a regular 6>3 shift. An alternative that I use if I'm only skipping over one gear, like 6>4, is a double blip. So in 6th, I'll clutch in, blip and move the shifter to 5th, KEEP the clutch in, then blip again and move the shifter to 4th. It's usually easier to get two consecutive smaller blips right than one big one, and passing the shifter through 5th even though I never engage 5th gear makes it easier on the synchros since 5th gear spun the gearbox up partway and then 4th finished the job.
The other thing you'll have to get a feel for is timing. Obviously after that quick blip of the throttle, the revs start falling again since you're not holding the throttle down (nor should you), so part of getting a smooth shift is knowing how quickly to re-engage the clutch. For example, after you get a feel for this, if you accidentally blip too much mid-shift and recognize that before even re-engaging the clutch, you can just hold the clutch in a little longer to wait for the revs to drop a bit more, thereby compensating for the overly aggressive blip. If you don't blip nearly enough though, you have to either blip again or just re-engage the clutch and deal with a bit of a buck since your revs were too low for your new gear.
Again, this all becomes instinct once you get on the road and start practicing, so don't overthink it. But I'm glad you were able to learn a new technique even after all these years! |
What's funny is as complicated as this may read, you actually explained it very well and it makes sense. Do you know if they teach this at HPDE? I still enjoy my DCT downshifts especially with my recent ACM exhaust mod, but I can imagine it's more rewarding with a 6MT.
Quote:
Originally Posted by GVFlyer
Actually -
Coupe: Depending on source - BMWNA -51.2/48.8%, Car & Driver instrumented test - 50.8/49.2
Sedan: BMWNA - 52.2/47.8%
Convertible: BMWNA - 47.2/52.8 %
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I love when people cite the sources, thanks for that. I do find it interesting that the E90 would be a tad more front heavy considering the additional rear doors and windows.