Rev-matching while downshifting....
 

Hi guys,

I wanna know if you guys practice rev-matching while downshifting.

Assume your going 60 km/h on 4th gear and you want to drop it to 3rd gear:

1) Press the clutch in, downshift to third.
2) Blip the gas, and depress the clutch smoothly to avoid jerkign the engine.

My question is this:

1) Does this save your clutch/flywheel and extend it's lives?
2) If I release the clutch and miscalculate the blip of the gas to be under-revved, or over-revved - is that more harmful than performing the usual method of downshifting without rev-matching?

Thanks for you help guys.

God bless. :)

Ben.

You should really do it this way.

1) Press in clutch
2) Shift to neutral
3) Blip the throttle to rev match
4)Press in clutch
5) Shift to lower gear


What this does is take stress off of the syncros. If you shift into gear before blipping the throttle, it still puts stress on the Syncros. Blipping the throttle while in nuetral avoids that and makes the downshift even smoother.

This method is called double clutching.

HA!!!! my lucky day!!! i was gonna ask this too....^THANKS!

what about this:

disengauge the clutch
shift into nuetral
blip the throttle
shift into lower gear with matched revs
engauge the clutch


notice its NOT a double clutch routine....

If you don't disengage the clutch while in neutral, the Syncros do not get matched to the revs.

That would bethe same thing as what the OP said.

If you're down-shifting in order to increase the torque at the wheels to accelerate you pretty much have to rev-match with this car. If you're actually trying to slow down you don't have to, but you're putting a lot of unnecessary wear on your transmission.

Personally I rev-match on aggressive down-shifts, but I don't double clutch; I do clutch in, neutral, rev, down-shift, clutch out. Letting the clutch out while in neutral before revving the engine will further decrease wear on the synchros, but I'm too lazy/not coordinated enough to do it :)

To answer your other question, if you "miss" your target RPM when rev matching you will not do any more harm than you would have not doing it at all unless you miss your target BADLY :) The amount of RPM differential between the transmission and the engine will determine the amount of wear on the clutch and synchros, so as long as you get the engine RPM closer to where it needs to be you're going to be better off.

I had to learn to be very good at double clutching as my first vehicle was a 1991 Mazda b2600i 5 speed with bad Syncros. If I didn't double clutch I would grind gears :shocking:

Not quite; the OP implied he was performing the shift and THEN rev matching while in gear with the clutch depressed which is going to cause more wear and tear on the synchros. Like I said, this is the method I use... and yeah, it does cause more wear on the synchros than a true double-clutch, but just bringing the clutch assembly up to speed isn't going to be that hard on them. The synchros are there for a reason after all :)

What I was implying is that wether you rev match with the stick in the neutral position, or wether in one of the gear positions, the syncros do not get matched with the engine, so both methods do the same thing.

But like you said Syncros are there for a reason.


I double cutch because its a habit. If I don't double clutch it feels awkward to me.

cool, makes sense to me in a vague way. i need to learn about trannys and synchros and see an animation of how they work, then i'll really get it :)

just like rotary.enthusiast, i'm too uncoordinated to do a true double clutch... and prolly to lazy too. its not like i abuse my tranny anyway, just the motor

Wow, it's a toss-up between double-clutching and "half" double-clutching? lol So what do you guys suggest then? Honestly, to perform double-clutching would take more effort that it's probably worth, and synchros are there for a reason....while I am concerned about my synchros, I am more concerned about my clutch, so can I stick with my method (as I try and do that every downshift), or should I switch to one of the mentioned methods, or any new methods any one else? lol :)

Chris311's technique is the best way to shift if you can do it. But do whatever you're comfortable with :) Better to wear out the synchros slowly over a long period of time than to totally screw a shift trying to do it "right".

That being said, the synchros in this transmission do have to deal with some significant RPM differentials, and I honestly don't know how well they hold up in the long run. Maybe there's another thread out there somewhere that discusses that.

I guess it really depends on what you want to replace.

Clutches usually cost less to replace than Synchros, however, Synchros usually last longer than Clutches.


I have seen Synchros in a transmission go before a clutch (A la MR2 transmission explosions), and when the Synchros go bad, you need a transmission rebuild which can get into the $thousands. I do not know how much a rebuild would cost on our transmissions.


If you can get good with double clutching, that would put less stress on both the synchros and the clutch plate which is the best of both worlds.

However, it should be a long time before the Synchros go out. On my b2600i the truck had about 130K miles when my Synchros started to slowly die on me. I didn't want to pay the repair bill so I learned to double clutch and have been doing that ever since.

I would like to know this as well. I do know that the Synchros in my car tend to be loud. This could be from a lot of stress of having to deal with a big RPM band, or it could be that they are just loud.

I try to avoid making them make any sounds just to keep me assured.

my other issue with double clutching is its so slow.. unless you really hammer it....

oh btw, this thread is starting to remind me of NFS....:icon_tdow lol

Yeah, I know what you mean. A little mechanical empathy goes a long way here... if it doesn't "feel" right, chances are you're wearing something out. Right now my 8 is only getting used on the street, and I don't generally make many aggressive shifts, but I have had to fight with the synchros a couple of times in the past, and they do definitely complain loudly about it :)

At least it doesn't remind you of the fast and the furious yet :lol:

ehhh, ^^ what i meant

Granny shifting...not *FILL IN BLANK* like you should! LOL

weight transfer without heel-toe downshifts could make your car unstable coming into turns. also very hard on your synchros. then again this is in a road/race course enviorment. you'll see some race drivers who do not heel-toe at all into turns. it all depends on your driving style.

i don't see any reason to really double clutch on street. do it for practice, but i wouldn't make it a point to do it all the time. it's why your transmission has synchros.

In my old chipped 1.8T, I have 185,000 original kms on it and I always double clutch. It definitely helps ease the wear and tear.

I am doing the same in this car as well...

On the topic of missing your target rpm: It is better to over rev than under rev. If you over rev then the revs will just fall down to where the new gear needs them. If you under rev (miss low) then you will get some of that "engine breaking" or that slow, foward lunge feeling, when the revs have to rise up to what the new gear needs. Missing low causes wear on the clutch and flywheel pretty bad. It puts all the stress and weight on the clutch and flyW. This technique is used in racing some times. It is a helpfull way to slow the car down when you boil your brake fluid and your brakes don't respond well. You leave the clutch in till the revs fall to idle and then release the clutch. This uses the engine and tranny as the brakes "engine breaking". It also helps in slippery conditions by taking some stress off of the front tires during deceleration. The engine speed must match the drive wheel speed. That is what you're matching during the downshift. ALSO NOTE IF YOU ENGINE BRAKE: If you have alot of power you will lose traction of the drive wheels when the revs rise to the max power rpm. In FR cars this can be used to drift or just wreck your car. On a personal note I just: Clutch in, Shift, Rev, Clutch out. Heel Toe not rev matching.

Bah, I don't think its slow.



I even double clutch while doing a heel-toe. (actually, for me, its left side of foot-right side of foot) :lol:


And so that some people don't get comfused, I only double clutch while downshifting. I know that *some* people even double clutch while upshifting (I never really understood how this helped) unless you shift so slow that you let the rpms drop below the next gear you are upshifting to. :confused:

I find that double clutching makes for faster - as well as cleaner - downshifts. You've got an engine, not just a friction surface, spinning the gears up.

Yep - that's the cool part. Working three pedals with two feet, and getting it right.

Ken

If done right double-clutching can be faster and makes your arm less tired. And you are right about cleaner shifts. Sometimes I can get the revs match so perfectly that the gear stick seems to almost "fall" into gear with just the slightest pressure. I can sometimes even shift when double clutching by just tapping the stick, no need to grab and yank into gear. However, for me to get a perfect of a shift as this is rare. I sometimes rev match wrong and it makes me look bad to my passengers as the car jerks a lot:banghead:




Once you learn double clutching, heal-to double clutching is just one small learning step. Granted, that is if you can already heel-toe.