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Discussion Starter · #1 ·
this will probably be locked because its a stupid question but i never got a clear-cut answer from all the syncro talk. is it bad to downshift without matching revs? how bad is it for my tranny and engine. and i mean 1 gear at a time, i'm not that stupid to downshift from 6 to 2. thanks. :D
 

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The primary reason to match revs is to minimize the weight shift that would occur due to sudden, rapid engine braking if you didn't match revs. Sure, it's little more stressful to downshift without rev matching, but if you're careful it should be a problem. Of course, you could always wait to downshift until the car has slowed down due to braking.

Are you having trouble with rev matching? Are you double clutching? Learning heel/toe?
 

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Compustar failsafes

I'm too tired to think clearly right now, but that hasn't stopped me before, so...

Even when you rev-match while downshifting, you're using your synchros. If you rev-match using the double clutch method, you don't use your synchros. Without double clutching, it's more of a smoothness thing.
 

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madSTI said:
...i'm not that stupid to downshift from 6 to 2. thanks. :D
who says it's stupid to downshift from 6 to 2?? if you rev match, this can be done quite nicely. i sometimes skip gears when rev-matching; just for the practice sake. never done 6->2, but it could be done.
 

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Fhqwhgads said:
Even when you rev-match while downshifting, you're using your synchros. If you rev-match using the double clutch method, you don't use your synchros. Without double clutching, it's more of a smoothness thing.
you're right on the mark for being tired. ;) since we have synchros, there's really no reason to double clutch, unless you wanna baby the synchros. some cars have no synchro on 1st gear to prevent you from getting it in there if you're going too fast; the only solutions are to grind or double-clutch.
 

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madSTI said:
this will probably be locked because its a stupid question but i never got a clear-cut answer from all the syncro talk. is it bad to downshift without matching revs? how bad is it for my tranny and engine. and i mean 1 gear at a time, i'm not that stupid to downshift from 6 to 2. thanks. :D
Always rev match when downshifting. Don't worry about double clutching, there is absolutely zero point on this tranny. Don't downshift to brake, downshift because you have already slowed down and you want to stay in the meat of the torque band. Brake pads are cheaper than clutches and other associated bits : )

-st
 

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Blizzaks MZ01??

4MLA1FN said:
you're right on the mark for being tired. ;) since we have synchros, there's really no reason to double clutch, unless you wanna baby the synchros. some cars have no synchro on 1st gear to prevent you from getting it in there if you're going too fast; the only solutions are to grind or double-clutch.
Yeah, that's what I was trying to get out... it's kinda useless to double clutch. Funny thing is that's the way I learned first (was doing it even while heel-toeing). My dad taught me how as he was used to driving little Italian cars without synchros. Then I went to Bondurant and re-learned the more modern method (they told me that it was the old man method and called me gramps even though I was only 19 :D ). Now I don't think I'll be able to double clutch heel-toe anymore... and I used to be quick at it too.
 

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resontator

I'm not exactly sure what the purpose of double clutching is....

Just to lock the tranny and get the engine speed to match the speed of the tranny parts?
 

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in one of the test that pitted the STi against the EVO one tester made the comment that most sports cars like to be rev-matched when down shifting but that the STi did'nt seem to care one way or the other.
i have a great deal of interest in posts about shifting and am reading a talking to everyone i know about shifting tips and tricks. i had never driven stick before i bought the STi.
i have read that the main purpose of rev-matching and using the heel toe method to maintain the proper rpm while downshifting is to reduce/eliminate the upset in balance that can be caused when downshifting. with the exception of using engine braking to slow down.i believe it was in Car Craft magazine and they were interviewing Bob Bondurant from the racing school of the same name.
 

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bitabur said:
I'm not exactly sure what the purpose of double clutching is....Just to lock the tranny and get the engine speed to match the speed of the tranny parts?
just to be clear, double-clutching is how rev-matching is done on a tranny *without* synchronizers. it goes kinda like this:

- push in the clutch (engage? disengage? i could never figure out which.)
- move the shifter to neutral
- release the clutch
- blip the gas
- push in the clutch
- shift to desired gear
- release the clutch.

the blipping of the gas with the clutch released and the tranny in neutral spins up the *input* side of the tranny to the same speed (hopefully) of the gear on the *output* side that you've moving to.

however, since we have synchornizers, we do the following to rev-match:

- push in the clutch (engage? disengage? i could never figure out which.)
- move the shifter to neutral
- blip the gas
- shift to desired gear
- release the clutch.

much fewer steps, thanks to synchronizers.

also, note that although rev-matching is usually spoken of when heel-toeing (i.e. when braking), you can also do it when you want to accelerate by downshifting. say you're in 6th and want a quick squirt to pass a car. you can jam it in 4th and get that clumsy lurch, or you can rev-match and get a wonderful seamless acceleration. whendone right rev-matching (when accelerating or braking) is a beautiful thing. :oops:

mandatory reading; test on friday. :)
http://auto.howstuffworks.com/transmission2.htm
http://auto.howstuffworks.com/transmission3.htm
http://auto.howstuffworks.com/transmission4.htm
http://www.brookwood1.com/samples/CB_Transmissions/transmission_shift.htm
http://users.erols.com/elans4/Transmission.htm
http://www.dansmc.com/gearbox.htm
although about motorcycles, this last one has some good info and a nice pic of the dogs.
 

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i can imagine that rev matching must be wicked important on a bike. since you only got two wheels that clumsy lurch could easily turn into a deadly slide.
 

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i don't *think* it's any more important on a bike. you could still slip the hell outa the clutch. but i dunno. my next thing to learn about is motorcycle trannys. i took bob bondurant's 6-speed shifter kart course and there was no clutch; just get off the gas and shift. the karts do have a clutch but it's only used for start from a stop. (oh, btw, karts use motorcycle enginges. ;) )
 

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can you explain to me the possiblity of locking up the wheels when downshifting in wet weather?? i read about it in the owner's manual. i assume it has to do with excessive engine braking but i don't really know. any ideas?
 

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crashsti said:
can you explain to me the possiblity of locking up the wheels when downshifting in wet weather??...i assume it has to do with excessive engine braking...
you're right on the mark. you'll sometimes see this in racing. i remember mika hakinnen at monza (??) in the late 90's; formula one. leading the race, approaching a chicane, he downs shifts and goes down one too many gears, the back end brakes loose and off he goes. he climbs out the car, pissed as hell, sits on the grassy bank at the side of the track...weeping.
 

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4MLA1FN said:
just to be clear, double-clutching is how rev-matching is done on a tranny *without* synchronizers. it goes kinda like this....<snip>
Maybe I wasn't quite clear.... I understood why you would double clutch, just not what the point is of letting out the clutch during the engine matching phase of the whole thing? As is my understanding, if you're not in gear, taking out the clutch doesn't do anything, so is the idea just so you can devote your attention to matching engine speed instead of working the clutch? Cause this really isn't a problem for me while I have the clutch in.....

I'm pretty good at matching my tranny speed and engine speed for whatever gear i'm in. Most of the time, especially upshifting, I can make completely smooth shifts without putting the clutch in at all (of course not while trying to accelerate hard or anything like that.... that would just be stupid...). I dont try it much when downshifting because the drop off in the flywheel (engine speed) works naturally to allow you to shift up, not down....


Ok, so anyway, back to my main question. What purpose does disengaging the clutch serve? (Just for future reference, when you press the clutch pedal down, you are engaging the clutch and disengaging the transmission. When you take your foot back off the clutch, you're disengaging the clutch and engaging the transmission.)
 

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bitabur said:
...if you're not in gear, taking out the clutch doesn't do anything...
*not* true, assuming "taking out the clutch" means "disengaging the clutch" (foot off the pedal). i did try to write a description, but ended up basically rewriting http://auto.howstuffworks.com/transmission2.htm. take a minute and study that page. the second bullet from the bottom of the page speaks directly to double-clutching, but you need to understand the other stuff on the page. *partricuarly* that the blue gears spin freely on the yellow output shaft when in neutral.



in a sentence, with the clutch disengaged (foot off the pedal) and the tranny in neutral, revving the engine spins up the green shaft, then the red shaft, then the free-spinning blue gears, and hopefully spinning up the desired blue gear to the *same* speed as the yellow output shaft, so the collar (which is spinning at the same speed as the output shaft) can easily mesh with the desired blue gear when you engage the clutch and downshift to that desired gear. trannys are *so freaking cool*!

bitabur said:
Just for future reference...
got it. that's the clearest description i've seen. thanks.
 

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Ok, I suppose that makes some sense. It also gives me a better idea of why there's really no reason to do that anymore, which makes me feel better about the whole process.

Understanding things always helps make me enjoy using something, and able to use it more efficiently.
 

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Discussion Starter · #20 ·
Rally Car versus Road Car

it not that i have a problem rev-macthing. i just wanted to know whether it was bad for when i was downshifting at slower speeds coming up to a stop sign in the neighborhood. maybe im just a little uneducated
 
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