Double-Clutch Heel/Toeing
#31
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Since this is the Racing forum, we must remember that racers usually have a budget for scheduled gearbox rebuilding. Thus, if your are one, shift in any manner that decreases lap times.
Driving a piece of transportation, for most people, requires some restraint in the way pieces of a car (like a gearbox) are used. So in this environment, it's always better to not speedshift and to double-clutch so the equipment lasts longer. Or.... you take your racing or recreation budget and plug it into periodic synchro replacement.
MHO,
Sherwood
Driving a piece of transportation, for most people, requires some restraint in the way pieces of a car (like a gearbox) are used. So in this environment, it's always better to not speedshift and to double-clutch so the equipment lasts longer. Or.... you take your racing or recreation budget and plug it into periodic synchro replacement.
MHO,
Sherwood
#32
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Wow, that video is fascinating Geza. I've not seen an example like that. Thanks for posting. I wish I could slow it down a bit, remove his right arm, and see the shifter better. It appears he never really lets the clutch pedal out completely. How long before the clutch goes?
Roger
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Last edited by InThePocket; 01-10-2006 at 09:13 PM.
#33
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Originally Posted by Geza
The process I listed is double de-clutching (DDC). What you described is a conventional downshift where the syncros speed up the “input shaft” (while shifting into the lower gear) to allow for the smooth mating of the lower gear. In DDC, once in neutral with the clutch released, the “input shaft” is directly connected to the engine, allowing the driver to speed up the input shaft to the right RPM for the downshift with the first blip of the throttle. Now, the clutch can be depressed and the lower gear selected smoothly without using the syncros (to speed up the input shaft). The rest is just rev matching the engine speed to the drive wheel speed to make sure things are smooth once the clutch is released. Hope this helps.
http://www.teamsmr.com/movies/Footbox%20Small.wmv
http://www.teamsmr.com/movies/Footbox%20Small.wmv
#34
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Originally Posted by 911pcars
Driving a piece of transportation, for most people, requires some restraint in the way pieces of a car (like a gearbox) are used. So in this environment, it's always better to not speedshift and to double-clutch so the equipment lasts longer. Or.... you take your racing or recreation budget and plug it into periodic synchro replacement.
My last two road cars before my BMW were a Sentra SE-R with a 200 bhp NA engine and just under 200k miles and a turbo G20 with just over 200k miles. Heel/toed both, single clutch, all the time. Never a problem with the synchros with either.
This is silly.
#35
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I think between me and the PO, we did nearly 10 years of track driving in my old 914/6 with a high HP 3.2 (and it was a 901 gearbox, which ain't exactly strong). Synchros will last plenty long even on the track, so long as you don't try to rush the engagement.
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I agree with 38D and George. Porsche syncros last a loooong time IF NOT ABUSED....and single clutching is not abuse! I have owned just about every 911 trans from the 901 forward, and many of each, with high mileage and heavily tracked cars. The syncros were the least/last of my concerns.
#37
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Originally Posted by Geza
The process I listed is double de-clutching (DDC). What you described is a conventional downshift where the syncros speed up the “input shaft” (while shifting into the lower gear) to allow for the smooth mating of the lower gear. In DDC, once in neutral with the clutch released, the “input shaft” is directly connected to the engine, allowing the driver to speed up the input shaft to the right RPM for the downshift with the first blip of the throttle. Now, the clutch can be depressed and the lower gear selected smoothly without using the syncros (to speed up the input shaft). The rest is just rev matching the engine speed to the drive wheel speed to make sure things are smooth once the clutch is released. Hope this helps.
http://www.teamsmr.com/movies/Footbox%20Small.wmv
http://www.teamsmr.com/movies/Footbox%20Small.wmv
When the input shaft is kept at motor speed during the brake phase (clutch engaged) you can select and shift to a lower gear by rev matching the motor as the output shaft is moving at relative wheel speed and the input shaft will be naturally matching up as the correct lower gear is selected. The delta will be in motor speed from the higher gear to the lower gear. (Why we shift in the first place) The delta is motor speed if done a the right time and the syncros are not stressed if the lower gear selected is in range. in fact as I am sure you know you can shift a syncro box via dog box method with rev matching alone, if done precisely. It is fun to learn interesting methods as there are many feet, many variables and many ways to do things!
#38
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"Oh please.
My last two road cars before my BMW were a Sentra SE-R with a 200 bhp NA engine and just under 200k miles and a turbo G20 with just over 200k miles. Heel/toed both, single clutch, all the time. Never a problem with the synchros with either.
This is silly."
Silly?
In the appropriate BMW/Nissan/944 forum, your observation maybe quite valid. However, I was referring to a 911 and specifically the 915 gearbox, not a G50 or Aisen or Getrag. Perhaps I should have qualified my previous statement. IMHO, you're attempting to compare apples and oranges.
"I think between me and the PO, we did nearly 10 years of track driving in my old 914/6 with a high HP 3.2 (and it was a 901 gearbox, which ain't exactly strong). Synchros will last plenty long even on the track, so long as you don't try to rush the engagement."
Based on your experience, synchro wear was of little consequence in your 10 year old track car. That's great, but how does that equate to street-driven cars that are around 30 years old and have >100k+ miles on the original drivetrain? How many more up and down shifts is that?
".....Porsche syncros last a loooong time IF NOT ABUSED....and single clutching is not abuse!..."
What is a loooong time? Would that be 20 years or 125k miles whichever comes first? You are shifting the gearbox as designed. I agree. Using it in this manner is not abuse. However, in the process of speed-matching, the synchro assembly is being worn (it is a wear item). The greater the speed differential before meshing, the greater the wear. The smaller the speed difference before meshing, the less wear. With a mixture of stop and go, cruising and banzai driving conditions, I fail to understand "no wear" using the single declutch method.
This is the race car forum and I wanted to separate that aspect of driving style with comments from non-track car owners. As with most things and especially with this thread, YMMV.
Sherwood
My last two road cars before my BMW were a Sentra SE-R with a 200 bhp NA engine and just under 200k miles and a turbo G20 with just over 200k miles. Heel/toed both, single clutch, all the time. Never a problem with the synchros with either.
This is silly."
Silly?
In the appropriate BMW/Nissan/944 forum, your observation maybe quite valid. However, I was referring to a 911 and specifically the 915 gearbox, not a G50 or Aisen or Getrag. Perhaps I should have qualified my previous statement. IMHO, you're attempting to compare apples and oranges.
"I think between me and the PO, we did nearly 10 years of track driving in my old 914/6 with a high HP 3.2 (and it was a 901 gearbox, which ain't exactly strong). Synchros will last plenty long even on the track, so long as you don't try to rush the engagement."
Based on your experience, synchro wear was of little consequence in your 10 year old track car. That's great, but how does that equate to street-driven cars that are around 30 years old and have >100k+ miles on the original drivetrain? How many more up and down shifts is that?
".....Porsche syncros last a loooong time IF NOT ABUSED....and single clutching is not abuse!..."
What is a loooong time? Would that be 20 years or 125k miles whichever comes first? You are shifting the gearbox as designed. I agree. Using it in this manner is not abuse. However, in the process of speed-matching, the synchro assembly is being worn (it is a wear item). The greater the speed differential before meshing, the greater the wear. The smaller the speed difference before meshing, the less wear. With a mixture of stop and go, cruising and banzai driving conditions, I fail to understand "no wear" using the single declutch method.
This is the race car forum and I wanted to separate that aspect of driving style with comments from non-track car owners. As with most things and especially with this thread, YMMV.
Sherwood
#39
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Originally Posted by kurt M
I understand the activities going on in the gear box and am not one to underestimate a pro driver.
When the input shaft is kept at motor speed during the brake phase (clutch engaged) you can select and shift to a lower gear by rev matching the motor as the output shaft is moving at relative wheel speed and the input shaft will be naturally matching up as the correct lower gear is selected. The delta will be in motor speed from the higher gear to the lower gear. (Why we shift in the first place) The delta is motor speed if done a the right time and the syncros are not stressed if the lower gear selected is in range. in fact as I am sure you know you can shift a syncro box via dog box method with rev matching alone, if done precisely. It is fun to learn interesting methods as there are many feet, many variables and many ways to do things!
When the input shaft is kept at motor speed during the brake phase (clutch engaged) you can select and shift to a lower gear by rev matching the motor as the output shaft is moving at relative wheel speed and the input shaft will be naturally matching up as the correct lower gear is selected. The delta will be in motor speed from the higher gear to the lower gear. (Why we shift in the first place) The delta is motor speed if done a the right time and the syncros are not stressed if the lower gear selected is in range. in fact as I am sure you know you can shift a syncro box via dog box method with rev matching alone, if done precisely. It is fun to learn interesting methods as there are many feet, many variables and many ways to do things!
Now, if you use (what I believe is) the method you described without the clutch and shift into neutral, blip the throttle to rev match and then shift from neutral into the lower gear, you've basically done a DDC without using the clutch. That'll work, but will probably lead to greater instability in the braking zone or at turn-in.
General comment:
Everytime this subject comes up, I find two types of people emerge. Those that want to learn it, because it is another skill set to learn to become a better driver, and those who argue that it is not necessary with modern gearboxes. True, it isn't really necessary, but, I'm with the first group. Sometimes I think the later group uses their argument to justify the fact that they haven't mastered the technique...just my GENERAL observation.
#40
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Originally Posted by 911pcars
Silly?
In the appropriate BMW/Nissan/944 forum, your observation maybe quite valid. However, I was referring to a 911 and specifically the 915 gearbox, not a G50 or Aisen or Getrag. Perhaps I should have qualified my previous statement. IMHO, you're attempting to compare apples and oranges.
In the appropriate BMW/Nissan/944 forum, your observation maybe quite valid. However, I was referring to a 911 and specifically the 915 gearbox, not a G50 or Aisen or Getrag. Perhaps I should have qualified my previous statement. IMHO, you're attempting to compare apples and oranges.
Originally Posted by 911pcars
Based on your experience, synchro wear was of little consequence in your 10 year old track car. That's great, but how does that equate to street-driven cars that are around 30 years old and have >100k+ miles on the original drivetrain? How many more up and down shifts is that?
Originally Posted by 911pcars
Driving a piece of transportation, for most people, requires some restraint in the way pieces of a car (like a gearbox) are used. So in this environment, it's always better to not speedshift and to double-clutch so the equipment lasts longer. Or.... you take your racing or recreation budget and plug it into periodic synchro replacement.
#41
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Geza, don't get me wrong! I am in the learn it, understand it camp 100%. I also like to spilt "This is the way to do it because we have always done it this way" from “This is the underlying reason for doing it" I like to take everything apart to see how it works. (This caused much distress to my parents when I was young. The family tube type TV all spread out in the living room was the low point. It going back together and working was the high point
) Mine was a genuine question without malice or subterfuge. Sometimes print does not convey intent well as there is no “tone” to it.
When you get to milking out the last ½ % or tenth of anything things get interesting and don’t always follow standard lines of thought or methods.
To me clutch engaged is in contact and being clamped by the pressure plate to the flywheel, not clutch pedal being pushed. Is this backwards from standard racespeak?
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When you get to milking out the last ½ % or tenth of anything things get interesting and don’t always follow standard lines of thought or methods.
To me clutch engaged is in contact and being clamped by the pressure plate to the flywheel, not clutch pedal being pushed. Is this backwards from standard racespeak?
#42
Race Director
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Originally Posted by Geza
Everytime this subject comes up, I find two types of people emerge. Those that want to learn it, because it is another skill set to learn to become a better driver, and those who argue that it is not necessary with modern gearboxes. True, it isn't really necessary, but, I'm with the first group. Sometimes I think the later group uses their argument to justify the fact that they haven't mastered the technique...just my GENERAL observation.
In my case I am in the second group, although I have mastered the technique and used to do it daily. I stopped because it is unnecessary. But it's useful to at least know how to do successfully.
#43
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Originally Posted by kurt M
Geza, don't get me wrong! I am in the learn it, understand it camp 100%. I also like to spilt "This is the way to do it because we have always done it this way" from “This is the underlying reason for doing it" I like to take everything apart to see how it works. (This caused much distress to my parents when I was young. The family tube type TV all spread out in the living room was the low point. It going back together and working was the high point
) Mine was a genuine question without malice or subterfuge. Sometimes print does not convey intent well as there is no “tone” to it.
When you get to milking out the last ½ % or tenth of anything things get interesting and don’t always follow standard lines of thought or methods.
To me clutch engaged is in contact and being clamped by the pressure plate to the flywheel, not clutch pedal being pushed. Is this backwards from standard racespeak?
![Wink](https://rennlist.com/forums/images/smilies/wink.gif)
When you get to milking out the last ½ % or tenth of anything things get interesting and don’t always follow standard lines of thought or methods.
To me clutch engaged is in contact and being clamped by the pressure plate to the flywheel, not clutch pedal being pushed. Is this backwards from standard racespeak?