On 2006-05-04, k. ote penned:
I think this is the first time anyone's mentioned specific RPM numbers on this thread. What you're describing is what I do, but I suspect the folks worried about engine damage are thinking of downshifts that cause much higher spikes.
free to engine brake in normal driving.
This is most reassuring... I'm the OP of this thread, and am finding much of the discussion very useful.
In my case, when I do downshift, I basically never spike it above 5k. Most of the time when I gear down, it maxes out at a little over 4. I agree that the issue would be a much bigger concern if I were continually red-lining the motor as I slowed down, but that's far from what happens with me.
I agree that 'technically', if the motor is used to brake, it will result in additional wear than if it were not. But I think that if a driver is not a complete cowboy about it, that kind of driving habit should not be a real detriment to the car.
I don't think it's hard on the engine at all at normal speeds; in terms of additional wear as in "normal wear you see when the engine is engaged" I suppose that's correct: but certainly no "undue" wear and tear. Additionally, if you just use the brake to slow down, then you're most likely in the wrong gear by the time you stop and in an emergency situation you are screwed in your reaction times by an additional clutch-shift-clutch sequence that could mean the difference between life and death.
Therefore, even from a safety standpoint, it seems to me that it's in the driver's best interest to keep the gears reasonable and downshift properly when coming to a stop. I'd hate to be doing 15kph in 4th and suddenly see a semi coming at me full-tilt from the side.
That would suck--especially since I can't actually downshift to 1st until I'm around 12kph or slower unless I do a full double-clutch (rev-matching does nothing in that case.) The car just prevents it.
Anyway, good luck with your engine, and I sincerely hope you all have a nice weekend!
On 2006-05-05, k. ote penned:
By the way, why is this? It's incredibly annoying in stop and go traffic, not to mention on certain very steep roads with switchbacks.
And what is this double-clutch maneuver? I know there's such a thing as a double clutch transmission, but double clutching in a modern car? What's that?
No wonder you don't downshift. It's the way almost all truck drivers and high performance drivers downshift any manual transmission smoothly.
Double clutch by letting out the clutch as you shift the transmission through neutral, then rev match by the difference in gear ratios, then clutch in and shift into the lower gear. Much less wear and strain on the tranmission since the gears are spinning at about the same speed before they're meshed. Then letting out the clutch the second time causes almost zero clutch wear because there should be almost no difference in speed between clutch plates. The car won't jerk when you clutch out the lower gear since you've already used the gas pedal to bring the engine up the the correct RPM for that gear and your current speed. You can use the tach to measure whether you've blip'd the RPM's up by the right amount for your selected lower gear.
Some drivers can do it so fast you can barely see them hit the clutch pedal twice, but you might be able to hear the blip of the gas pedal in between clutchings as the shift lever rapidly passes thru neutral.
I hope I have that right, since that's how I've been downshifting my Toyota for over 300K miles.
IMHO. YMMV.
Take a look here:
Er, I'm not the one who doesn't downshift. But it sounds like I can learn a thing or two about it, anyway.
My technique has been to hit the throttle (clutch out, in neutral) to ensure the rpm is somewhat above the speed it will be in the next gear down, then catch the shift as the gears slow down by maintaining light pressure on the shifter. Same concept, just the quick and dirty version.
In either case, the technique involves shifting into neutral and letting out the clutch, using the engine to bring the gears up to speed, then shifting into the lower gear.
Mike
Hrm. I'm not sure. I do know that the STi's gears are pretty tall, especially for the lower gears. At around those speeds, being in first requires the engine to rev at around 4,000 rpm. It could be a (slightly over-)protective measure to ensure that I don't accidentally shift dangerously into a gear that would push the engine unsafely beyond the redline.
Clutch down, shift to neutral. Clutch up. Rev engine about 1.5K (or less depending on how fast you are.) Clutch down, shift to lower gear. Clutch easy up.
Spins up the gears so the engine mates nicely with the transmission, lessens wear, doesn't use the clutch as a brake pedal, and in tight cornering it can help reduce unwanted weight transfer which could mean the difference between keeping enough grip to finish the corner and sliding.
Course.. I don't travel at those speeds even on the track, but I was told it was good to get into the habit now.
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