Thứ Hai, 28 tháng 11, 2016

Double Clutch-Heel Toe Downshifts... part 2

LastResort 11-15-2006 09:18 AM

I wouldn't bother with double clutching an STI around town, as it's a significantly better gear box than mine, I would work on rev matching though.


Thanks Gary.
waktasz 11-15-2006 09:23 AM

^^ Best explaination I've read yet. I mostly only double clutch once in the morning when the trans is still cold and I have to shift down to first to get up a giant hill, and I've been doing it forever, but thinking about it in Gary's way still helped :)
Mykl 11-15-2006 09:23 AM

I'm looking for an applause smiley, but I can't find one... thanks Gary.
MaxSTi05 11-15-2006 09:33 AM

So, Gary and all, back to my question posted earlier. Do you really need to 'sequentially' move down the gears to the gear desired, double-clutching each with that 'clutch pumping', or is it just as quick to wait long enough while braking, to bring the revs low enough, then select the gear wanted with one double-clutch? I see that with the parallel process should take the same amt of time, but what about the mechanics of it? Ok for the gearbox? This is what I've been using at the track.
waktasz 11-15-2006 09:40 AM

It's ok to skip gears, lots of racers go through each one because it's a timing thing...each downshift is a timed move that takes the same amount of time...skipping a gear adds another element to that timing.
GarySheehan 11-15-2006 10:31 AM

[QUOTE=MaxSTi05;15996456]So, Gary and all, back to my question posted earlier. Do you really need to 'sequentially' move down the gears to the gear desired, double-clutching each with that 'clutch pumping', or is it just as quick to wait long enough while braking, to bring the revs low enough, then select the gear wanted with one double-clutch? I see that with the parallel process should take the same amt of time, but what about the mechanics of it? Ok for the gearbox? This is what I've been using at the track.[/QUOTE]
Skipping gears is fine. I do it sometimes and not others. It depends on how busy the approach to the corner is as well as how much speed there is to shed.

The "risk" you run with skipping gears is that you have less reference for your timing and speed of the blip for your final gear. It's easier to over or under-blip or downshift into the gear too early with skipping gears. Rowing down through the gearbox gives an additional reference to road speed throughout the downshifting process.

It comes down to what you are comfortable with. If you are skipping gears and not over-reving or jerking the car, you're all set. If you are, go back to rowing down through the gears. Ultimately, it all takes the same amount of time because the limiting factor is the duration of the braking zone.

Gary
Sheehan Motor Racing
[url]www.garysheehan.com[/url]
Hyper 11-15-2006 10:41 AM

great thread, I started to learn today

I heel-toe, and sometimes don't use clutch (just rev match) when in city or lazy, and I am getting the hang of it! However, the background fear is that I won't syncro the second clutch in + gear in as I am trying to do is fast:lol:
pete_falcone 11-15-2006 11:13 AM

There are actually consumer-level shoes specially designed for driving. My basketball shoes are too fat for consistent HTDC-ing, but since I bought these blue suede Reebok Driving Shoes for $35, I no longer need to be barefoot to perform HTDC's consistently. Plus these shoes match the color of WR Blue Imprezas.

[QUOTE=shemoves;15971748]I've been working on it for a while now. I never thought I'd get it, but I kept at it, and I can do it with fair success. Though I am not quick/natural enough to do it in a fast-paced/high-stress environment yet. Something I have noticed though, is that the shape of the shoes makes a big difference. There are certain shoes that it just don't work in, and some it does. Strange as it is, my rainbow sandals are actually pretty good for it :rolleyes:[/QUOTE]
Pavlo 11-15-2006 05:01 PM

Wrong.

I regularly use double declutching on upshifts with my dogbox when I feel like I don't want to hammer it into every gear. All I do is lift the clutch pedal as I go past neutral, then back down again as I engage the gear, there is no blipping of the throttle. With this method you can do a nice, quiet, smooth upshift in a relaxed manner.

A dog box is not like a synchro box at all. If it was you would never be able to change gear, just like a worn baulk ring, just constant crunching. A dog box will have widely spaced dogs that mean you can get about 30degrees of backlash, enough to engage the gear before the you go "dog to dog". With a synchro box, the engagement teeth have say a 6mm pitch, and there is no backlash. This means that any difference in speed means no engagement, whereas a dogbox changes easiest with a slight difference in speed.

[QUOTE=SubaruCO;15974364]Sorry to burst your bubble, but I think you need to brush up on your concepts. Double clutching is ONLY for downshifting, and dogboxes are exactly like a synchronized transmission just without the synchronizer cones.[/QUOTE]
Subaru_555 11-15-2006 05:38 PM

What a funny thread! At least Gary cleared some things up.
SubaruCO 11-15-2006 06:03 PM

[QUOTE=Pavlo;16003089]Wrong.

I regularly use double declutching on upshifts with my dogbox when I feel like I don't want to hammer it into every gear. All I do is lift the clutch pedal as I go past neutral, then back down again as I engage the gear, there is no blipping of the throttle. With this method you can do a nice, quiet, smooth upshift in a relaxed manner.

A dog box is not like a synchro box at all. If it was you would never be able to change gear, just like a worn baulk ring, just constant crunching. A dog box will have widely spaced dogs that mean you can get about 30degrees of backlash, enough to engage the gear before the you go "dog to dog". With a synchro box, the engagement teeth have say a 6mm pitch, and there is no backlash. This means that any difference in speed means no engagement, whereas a dogbox changes easiest with a slight difference in speed.[/QUOTE]

Well, strictly speaking your technique isn't needed though it sounds like a good method for synchronizing RPM's between upshifts. I wonder if this would help in the "hanging rev" issue I dislike so much especially between first and second. It certainly wouldn't hurt as the shift times are pretty long now waiting for the engine to come back down.
davis10 11-16-2006 03:12 AM

^^^ No hes right Dogboxes need to be shifted fast of they will grind so if you happen to be lucky enough to drive one on the street the best way to casually shift it without wearing out your tranny is to double clutch and when you are ready for the next gear after being in neutral stab the clutch and slab it into gear.
PC tuner 11-16-2006 04:40 AM

Double clutching on an upshift would only be needed if you took too long to shift and the gears weren't spinning fast enough. You need to shift quickly with a dog box but double clutching isn't going to help with an up shift at all. Just put in the clutch and make a strong deliberate shift then let out the clutch.

The gears are all spinning at the same speed so when you up shift the gear you are shifting into (n+1) is going faster than it needs to be. Drag will naturally cause the gears to slow down, eventually reaching the exact speed that gear n+1 needs to be spinning at for the particular speed.

Double clutching may cause the gears to slow down more quickly (I'm just guessing here) so that you can shift faster but it would be almost undetectable.
Calamity Jesus 11-16-2006 08:08 AM

[QUOTE=PC tuner;16009690]Drag will naturally cause the gears to slow down, eventually reaching the exact speed that gear n+1 needs to be spinning at for the particular speed.

Double clutching may cause the gears to slow down more quickly (I'm just guessing here) so that you can shift faster but it would be almost undetectable.[/QUOTE]Consider an upshift. The input shaft and any directly attached gears are spinning freely in neutral, so they're just floating in some bearings and there's a little gear oil clinging to them... the engine is slowing down quickly due to the vacuum & compression in the cylinders. Since I would wager that 90% of dogbox users have a lightweight flywheel, the crank is slowing down very quickly by comparison to the input shaft.

This may be different for the 6 speed since it has an integral oil pump... but the 5 speeds do not.

The only reason it's not a big deal is because the dogs can handle the shock to the input shaft of being forced into the next gear.
Pavlo 11-16-2006 10:48 AM

Some very nice theories there. How many of you regularly drive with a dog box?

I know it's not necessary, but for normal driving, it is preferrable for me to double declutch. I am not worried about shock loads, I am worried about dog wear. For drag and circuit use I do clutchless upshifts anyway, but I am not always wanting to race to the shops or wherever, the car is more than quick enough for me to be able to shift slowly.
SubaruCO 11-16-2006 11:27 AM

[QUOTE=Pavlo;16011786]Some very nice theories there. How many of you regularly drive with a dog box?

I know it's not necessary, but for normal driving, it is preferrable for me to double declutch. I am not worried about shock loads, I am worried about dog wear. For drag and circuit use I do clutchless upshifts anyway, but I am not always wanting to race to the shops or wherever, the car is more than quick enough for me to be able to shift slowly.[/QUOTE]

Hey, I think we are trying to keep it friendly here. I have practiced many of these techniques for years on regular gearboxes. I'm sure though we may argue the particular mechanical dynamics for the techniques we all probably do it the same way in practice because that's just the way it works.

Seriously though, I've never had the chance to drive a dogbox only sequential transmissions. I would love to if given the chance. Hey any volunteers out there? :)
Mykl 11-16-2006 11:49 AM

[QUOTE=SubaruCO;16012366]Seriously though, I've never had the chance to drive a dogbox only sequential transmissions. I would love to if given the chance. Hey any volunteers out there? :)[/QUOTE]

Ever ridden a motorcycle before? I've never been on a bike that didn't have a dog box.
Pavlo 11-16-2006 12:10 PM

[QUOTE=Mykl;16012691]Ever ridden a motorcycle before? I've never been on a bike that didn't have a dog box.[/QUOTE]

THey have a sequential shifter mechanism which makes it almost impossible to do a slow change. With the the increased throw and different detents the H-pattern dog box is not the same experience.

SubaruCO

Have you driven a car with a dog box?
Mykl 11-16-2006 12:13 PM

[QUOTE=Pavlo;16012992]THey have a sequential shifter mechanism which makes it almost impossible to do a slow change. With the the increased throw and different detents the H-pattern dog box is not the same experience.
[/QUOTE]

Yes, however... if you're lazy with the shifter you can hit a false neutral. Some bikes are worse about this than others. I can tell you the first time you hit a false neutral shifting from fourth to fifth gear at over 130 mph it gets your attention.
Pavlo 11-16-2006 01:36 PM

I guess that would be a situation where you were "between" gears.

I certianly don't mind a single "clonk" as it goes into gear, but the big c-c-c-c-crunch through the gearset when you're too slow on a mismatched shift sounds quite literally like the $$$$ being shaved off your dogs!
chimchimm5 11-16-2006 02:02 PM

I'm a noob to novice motosports but I've been practicing double clutch downshifting and here are a few points I learned the hard way that NO ONE seems to provide details to when they talk about this subject:

- [B]The RPM's you need to blip to depend on which two gears you are switching between because the gear ratios of each gear is different. [/B]This is where "familiarity with the car" is important. You can become familiar with the gear ratios by paying attention to the RPM difference when upshifting

- [B]The RPM's you need to blip to also depend on what RPM you are starting from.[/B] As the scale of the RPMs go up, so to does the scale of the blip. So, blipping between 3rd->2nd @5000 RPM is different than at @2000 RPM. Plus, it seems that the engine has more resistance at higher RPM and thus slows itself down faster at high RPM than low RPM.

- [B]The RPM's you need to blip to also depend on the rate at which you are slowing the car down. [/B]The harder you brake, the faster the wheels will slow down. So the fast but finite amount of tme you take to downshift means that the engine needs less RPMs for the slowing wheel rate.

- [B]Your foot action depends on how much you are pressing the brake pedal.[/B] Since you are using one right foot to do both brake and gas, then the amount you are pressing the brake determines the foot's startng height, which affects the motion you take to blip the throttle. It's way easier if you consistantly brake hard to do a controlled blip.

- [B]The blip in double clutch heel-toe downshifts has a different purpose than the blip of a heel-toe downshift.[/B] In the former, you are blipping to match the intermediate shaft speed with the gear being selected (either to help the synchro, or because you don't have a synchro); engaging the clutch comes soon after but is matched because the car is under braking (slowing) and thus lower RPMs are needed (exactly what the engine is doing since you engaged the gear). On the other hand, non double clutching heel-toe downshift is for rev matching the driveshaft (which is the already engaged gear/wheels) with the engine speed. However, for the driver, both things "feel" the pretty much the same.

- [B]Both double clutch and non-double clutch downshifts are harder in street applications because of the constantly varying braking rate. [/B]Usually on the street, you aren't always braking hard. Thus double clutch downshifts only seem necessary when you are at high RPMs and/or braking consistently hard; usually both come hand in hand, ie performance driving. (Don't get me wrong, there's a lot more OTHER things in motorsports that are harder than street driving.)

- [B]On the street, below say 4k RPMs, you usually have the time to gently engage a gear using the synchros at the end of your braking zone and don't really need to row the gears downshifting.[/B] IE, if I'm in 5th coming off a freeway exit to an offramp red light, I stay in 5th and just brake. If by chance the light turns green and 2nd is the appropriate gear, I clutch in, *gently* shift to 2nd (applying light pressure and wait for the synchro to do it's job), get off the brake at the end of the brake zone, and blip the throttle to rev match and engage the gear.
SubaruCO 11-16-2006 05:41 PM

[QUOTE=Pavlo;16012992]THey have a sequential shifter mechanism which makes it almost impossible to do a slow change. With the the increased throw and different detents the H-pattern dog box is not the same experience.

SubaruCO

Have you driven a car with a dog box?[/QUOTE]

No, though I really would like to try one someday. I've been in some sequential shift carts but that's kind of a different animal.

(I know, I know this renders all previous posts in this thread moot, but hey I'm an expert on anything on the internet, right? :))
epoth 02-26-2007 07:03 AM

[QUOTE=chimchimm5;16014487]I'm a noob to novice motosports but I've been practicing double clutch downshifting and here are a few points I learned the hard way that NO ONE seems to provide details to when they talk about this subject:
...[/QUOTE]

Your observations are pretty much right on, although I double-clutch almost every shift on the street or not. It's really kind of unnatural now to brake at any level without doing it.

After about six months or so of practice I think all of it comes naturally. I don't even have to think about it now (after a couple of years of doing it), but mostly because my brain has learned what is needed in what situations. I did drive my buddy's Acura RSX and it revs much faster than the Suby (no lightwheight flywheel on my car). Took a little getting used to very small throttle blips.

On the other hand my wife's Pontiac Vibe revs *extremely* slowly, so it needs big ole' throttle blips to get anything to happen. It isn't nearly as natural to double-clutch as the suby.
Butt Dyno 02-26-2007 07:19 PM

I very very occasionally double clutch upshifts. I have some "happier in warm weather" transmission fluid in the Miata (one of the Redlines) and the first couple 1-2 shifts in the morning are usually quite meh. So for the first minute or two I usually double clutch the 1-2 upshift and everything's peachy. That (and getting into 1st on the WRX) are the only spots I've really found it useful for upshifts.

john
subi_2.5rs 02-26-2007 10:20 PM

i learn heal-toe down shift within 3 month and added in double clutch within a month later. learn from reading and apply. practice makes perfecto. now its a natural, always in gear in cornering.
scoobydrew06 02-27-2007 10:55 AM

is the WRX pedal setup naturally hard to learn heal toe on? I double clutch almost every down shift, it is very natural to me now. But every time I try heal toe it seems like the pedals aren't the ideal shape and or in ideal positions for heal toe.

I'm assuming that some good driving shoes will make a little bit of a difference, but my new balance running shoes have a great feel.
Mykl 02-27-2007 11:02 AM

[QUOTE=scoobydrew06;17194294]is the WRX pedal setup naturally hard to learn heal toe on? I double clutch almost every down shift, it is very natural to me now. But every time I try heal toe it seems like the pedals are the ideal shape and or in ideal positions for heal toe.

I'm assuming that some good driving shoes will make a little bit of a difference, but my new balance running shoes have a great feel.[/QUOTE]


The problem with "good" driving shoes is that they tend to be very narrow and basically made for proper race cars. I like the STi's pedal setup, but even still I'm more comfortable with a wide pair of regular sneakers. Basically because I don't have to twist my heel around as much with wider shoes.

One of these days I'll buy a better set of pedals to install so I can get more use out of my Puma Speedcats.
epoth 03-02-2007 09:40 AM

[QUOTE=scoobydrew06;17194294]is the WRX pedal setup naturally hard to learn heal toe on? I double clutch almost every down shift, it is very natural to me now. But every time I try heal toe it seems like the pedals aren't the ideal shape and or in ideal positions for heal toe.

I'm assuming that some good driving shoes will make a little bit of a difference, but my new balance running shoes have a great feel.[/QUOTE]

I very rarely double-clutch without heel-toe. If you can't heel-toe then anytime you are braking and downshifting you aren't properly double-clutching the downshift.

The only time you don't use heel-toe with double-clutched downshifts is when you are just moving down a gear without wanting to actually slow the car down. Normally when you downshift though you are in the process of slowing the car with the brakes, so that necessitates the use of heel-toe with the double-clutch.

Make sense? At any rate, I wear new balance running shoes every day, and I seem to make do just fine with them on the pedals. As you get more practice you will pick up the proper feel/positioning on the pedals for heel-toe.

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