[J Tyler]

Originally Posted by 94JZA80

i'm not sure i understand what you're trying to say...perhaps i'm confused, but hear me out.

...if you're heel-toeing (and thus rev-matching) on downshifts in the first place, then the clutch and the flywheel are engaging at identical (or near identical) rpms. if the clutch and the flywheel are engaging at essentially the same rpm, then you're already putting minimal stress/wear on your synchro b/c it isn't having to "sync" anything - you already accomplished that with rev-matching.

^Part in bold is not true.

When you single-clutch downshift, you only spin up the engine speed; the new gear is still spinning at too low of a speed. This is where the syncromesh comes in: it pushes up against the side of the new gear, spinning it up to speed. Although this is what the syncromesh was designed to do, this is also how it is worn down. When you double-clutch downshift, you spin up the gear assembly to match the speed of the syncromesh so that it essentially is not used.

Here, this picture may help. The output shaft is only connected to a gear when the syncromesh ('dog gear' as they call it in the picture, but for our purposes think of them as the same thing) is pushed onto the side of a gear by the selector fork (which is what you move with your right hand when you shift). Otherwise, the whole gear assembly spins freely (i.e., when you are in neutral with the clutch disengaged). The dog/syncro gear is connected to the output shaft; gears 1/2/3/4/5 are not:



When you single-clutch downshift, you do not spin the gear assembly up to the correct speed to match with the syncro/dog gear.



Now, my personal philosophy on downshifting with H-patter syncromesh 'boxes: I only double-clutch when I am skipping gears (i.e., going quickly from 5th to 3rd). In this case, the difference between gear speeds is great enough that the syncros actually get used pretty hard and require quite a bit of effort to pop onto the side of the gear. To me it is easier to double-clutch than to wait for the gear to engage; the new gear engages quite easily with a double-clutch. However, if I'm only going down one gear (like 4th to 3rd) I single-clutch because the difference in gear speed is pretty small and the syncros only have to work a little bit; and the gear usually pops right in with little effort.

[94JZA80]

Originally Posted by J Tyler

^Part in bold is not true...

...the whole gear assembly spins freely (i.e., when you are in neutral with the clutch disengaged). The dog/syncro gear is connected to the output shaft; gears 1/2/3/4/5 are not...

thanks for clearing that up. i forgot that the gears spin freely with respect to the synchros and the output shaft...i knew i was forgetting something lol. and while i haven't tried double-clutching as an alternative to waiting it out, i can attest to the significantly greater difference in gear speeds while skipping gears on a downshift by bad experience myself...you see, i got impatient once while waiting for 3rd gear to engage after a downshift from 5th. upon forcing the selector into gear, i got a bit of a crunch due to the synchro not being able to spin up the gear as quickly as i would have liked it to.

so i suppose that, while rev-matching alone (single-clutch rev-matching) minimizes wear on the clutch and flywheel, it doesn't minimize wear on the synchros b/c it doesn't spin up the gear assembly, only the ouput shaft and synchros. so the synchro still gets worn when the selector slots into place and the synchro makes contact with the gear. but i still don't quite understand how double-clutching makes a 5th -> 3rd or 4th -> 2nd downshift easier and quicker. i understand that double-clutching spins up the gear assembly to the same rpm of the output shaft (thus allowing minimal wear on the synchros), but i'm having trouble visualizing how double-clutching spins up the gears. could you elaborate on that a bit?



TIA,
Eric

[Jeff@TopGearSolutions]

Originally Posted by I335

The clutch stop is excellent, but it did take me a couple of days to get used to it and at first I wasn't even sure if I liked it. I've had it installed for a month or so now and don't even notice it anymore unless I'm thinking about it but when I do think about it, it is clearly an improvement. It makes a substantial change in clutch feel/engagement - especially for such a simple little thing and it really helps with heal/toe shifting because after you blip the throttle there's now less time for the revs to fall back down between gears. The tune helps with heal/toe because it's much easier to blip the throttle with a smaller tap now so it's a great combination. I'm amazed at the difference that inch makes as it eliminates a lot of the unnecessary clutch pedal travel which is just wasteful. I didn't get it with racing in mind at all - just to eliminate the wasted travel and that it did. It's much better now and I highly recommend it. That said, it now makes me want a short shifter to go along with it - I think that would be a great combination. I have my eyes on the UUC model and I just might spring for it in the spring.

Interesting, I was just afraid it would some how be detrimental to the clutch disc. Wasnt sure if it was effecting its engagement and/or allowing it to slip a little.

[Jeff@TopGearSolutions]

Originally Posted by J Tyler

^Part in bold is not true.

When you single-clutch downshift, you only spin up the engine speed; the new gear is still spinning at too low of a speed. This is where the syncromesh comes in: it pushes up against the side of the new gear, spinning it up to speed. Although this is what the syncromesh was designed to do, this is also how it is worn down. When you double-clutch downshift, you spin up the gear assembly to match the speed of the syncromesh so that it essentially is not used.

Here, this picture may help. The output shaft is only connected to a gear when the syncromesh ('dog gear' as they call it in the picture, but for our purposes think of them as the same thing) is pushed onto the side of a gear by the selector fork (which is what you move with your right hand when you shift). Otherwise, the whole gear assembly spins freely (i.e., when you are in neutral with the clutch disengaged). The dog/syncro gear is connected to the output shaft; gears 1/2/3/4/5 are not:



When you single-clutch downshift, you do not spin the gear assembly up to the correct speed to match with the syncro/dog gear.



Now, my personal philosophy on downshifting with H-patter syncromesh 'boxes: I only double-clutch when I am skipping gears (i.e., going quickly from 5th to 3rd). In this case, the difference between gear speeds is great enough that the syncros actually get used pretty hard and require quite a bit of effort to pop onto the side of the gear. To me it is easier to double-clutch than to wait for the gear to engage; the new gear engages quite easily with a double-clutch. However, if I'm only going down one gear (like 4th to 3rd) I single-clutch because the difference in gear speed is pretty small and the syncros only have to work a little bit; and the gear usually pops right in with little effort.

Originally Posted by 94JZA80

thanks for clearing that up. i forgot that the gears spin freely with respect to the synchros and the output shaft...i knew i was forgetting something lol. and while i haven't tried double-clutching as an alternative to waiting it out, i can attest to the significantly greater difference in gear speeds while skipping gears on a downshift by bad experience myself...you see, i got impatient once while waiting for 3rd gear to engage after a downshift from 5th. upon forcing the selector into gear, i got a bit of a crunch due to the synchro not being able to spin up the gear as quickly as i would have liked it to.

so i suppose that, while rev-matching alone (single-clutch rev-matching) minimizes wear on the clutch and flywheel, it doesn't minimize wear on the synchros b/c it doesn't spin up the gear assembly, only the ouput shaft and synchros. so the synchro still gets worn when the selector slots into place and the synchro makes contact with the gear. but i still don't quite understand how double-clutching makes a 5th -> 3rd or 4th -> 2nd downshift easier and quicker. i understand that double-clutching spins up the gear assembly to the same rpm of the output shaft (thus allowing minimal wear on the synchros), but i'm having trouble visualizing how double-clutching spins up the gears. could you elaborate on that a bit?



TIA,
Eric

Wow glad you guys cleared that up. My bigger concerns were usually clutch wear and not so much transmission wear, as you all know wearing out the trans is going to take a little more effort and time over clutch disc wearing out.

I noticed the Double clutch was always a cleaner rev match, i normally double as J-Tyler said from a large gear change as he mentioned... 5th to 3rd or even 2nd just depending on how the situation pans out.

Now I know why its so much cleaner, thanks to everything being matched up.

[J Tyler]

Originally Posted by 94JZA80

so i suppose that, while rev-matching alone (single-clutch rev-matching) minimizes wear on the clutch and flywheel, it doesn't minimize wear on the synchros b/c it doesn't spin up the gear assembly, only the ouput shaft and synchros. so the synchro still gets worn when the selector slots into place and the synchro makes contact with the gear. but i still don't quite understand how double-clutching makes a 5th -> 3rd or 4th -> 2nd downshift easier and quicker. i understand that double-clutching spins up the gear assembly to the same rpm of the output shaft (thus allowing minimal wear on the synchros), but i'm having trouble visualizing how double-clutching spins up the gears. could you elaborate on that a bit?



TIA,
Eric

Well, the output shaft & syncros spin at the driveshaft speed (i.e. rear wheel speed x final drive ratio)..... But you are correct about everything else


So, when you double-clutch, you engage the clutch during the throttle blip. Engaging the clutch (connecting it to the engine) means that when you blip the throttle, you spin up the engine speed and the gear assembly; with a single-clutch downshift (clutch disengaged during the throttle blip) you only spin up the engine speed, not the gear assembly, because the assembly isn't connected to the engine via the clutch.

I hope that makes sense, I don't feel like I worded it very well...lol. Double-clutching is very awkward at first, but once your brain & muscles get trained to doing it, it becomes second nature just like a single-clutch. In the 335i video in my sig, I'm double-clutching from 5th to 3rd at the end of the front straight and at the end of the back straight. It happens faster than two single-clutch shifts (5th > 4th, 4th > 3rd) and I know for sure the gear will pop right in.

[94JZA80]

Originally Posted by J Tyler

Well, the output shaft & syncros spin at the driveshaft speed (i.e. rear wheel speed x final drive ratio)..... But you are correct about everything else


So, when you double-clutch, you engage the clutch during the throttle blip. Engaging the clutch (connecting it to the engine) means that when you blip the throttle, you spin up the engine speed and the gear assembly; with a single-clutch downshift (clutch disengaged during the throttle blip) you only spin up the engine speed, not the gear assembly, because the assembly isn't connected to the engine via the clutch.

I hope that makes sense, I don't feel like I worded it very well...

actually you explained it perfectly. it all "clicked" the instant i read the bold sentence. how silly of me to not put 2 and 2 together. after all, double-clutching is disengaging the clutch twice, and it therefore must be engaged in between those two prods of the clutch pedal. now it makes complete sense to me how double-clutching can bring the gear assembly up to speed. thanks again Jeff.

[J Tyler]

Originally Posted by 94JZA80

actually you explained it perfectly. it all "clicked" the instant i read the bold sentence. how silly of me to not put 2 and 2 together. after all, double-clutching is disengaging the clutch twice, and it therefore must be engaged in between those two prods of the clutch pedal. now it makes complete sense to me how double-clutching can bring the gear assembly up to speed. thanks again Jeff.

Cool!

[HRC]

One of the great pleasures driving a manual tranny. This my first ownership of a german car and compared to all my previous cars, this by far the most natural pedal placement (and having the accelerator pivoting from the floor) I have Owned. Porsche is the best I have experienced.

On my other cars, sometimes I felt like I was spraining my right ankle.

Here is old pic I posted years ago:



The thread is HERE.

Danny

[fleetfoot]

I've had my e92 for 8 years now, and I've struggled to consistently heel-toe the entire time. I can get it sometimes, but other times my foot slips off the accelerator. And I'm not really comfortable uncovering more of the brake pedal.

I had my first track day recently, and my downshifting was total garbage. In an effort to remedy this before my next time out, I finally went and bought some Bimmerworld aluminum pedals with an extended accelerator along with some Piloti Pistone X driving shoes. I went for my first test drive tonight...very happy! I didn't miss a single downshift. Just having that extra half inch of pedal and purpose-made shoes did the trick! Can't wait to be properly downshifting next time I'm on track.