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.

Funny. Because I don't see why you all are separating Heel-toing and Double clutching. They are to be used at the same time. If you are double clutching and then braking for the turn you are not gonna be fast. The two techniques are not to be separated. You use the double clutch while you are heel-toing to consolidate your braking distance and your shifting distance before the turn. But I guess I do see how we can just double clutch while on the street during easy driving. But if you wanna learn how to go faster which should be the basis for this thread then one must learn what these techniques are truely for. There is a lot of confusion being dealt out here. The reason I beat half the super cars I race against is purely because these asses who buy supercars don't even know how to drive. By learning the simple Heel-Toe (which includes the use of double clutch) technique you can out brake most possers on the street. It is braking and corner prep that this technique is for. Go download or buy a book on basic high performance driving and instantly wow your friends and destroy Doctors and the like on the street.

There are lots of times when you downshift without being on the brakes. Back before disc brakes, racers used to slow down on compression, not brakes. Heel-toe is the answer to the question "How the hell do I do that when I'm on the brakes?"

Jack Brabham, who did come from the disc brake, heel-toe era, said that he never heel-toed when driving on the street. He said that it was associated with a level of violence that wasn't appropriate off the track.

I suspect we have a different concept of violence than Sir Jack. :)

Piero Taruffi's book, "The Technique of Motor Racing," is excellent. It's definitely dated for racing, but it's great for the fundamentals if you just want to know what you're doing on the street. Best "how-to" on double clutching and heel-toe that I've seen.

I've seen newer books that pooh-pooh the whole idea of double clutching. They say to just shove it in, let the synchros do the work. I presume those authors were not car owners or engineers.

Ken

I usually double clutch. It just feels more natural to me.

I've been trying to learn to incorporate heel-toe into it, but it's still scary and new to me, and I end up missing my rev match target because my speed is constantly decreasing. Theres also the fact that when I'm driving, I'm never entering corners at the kinds of speeds that would require a heel toe downshift. I'm totally cool with doing my downshft 100 yards away from the corner entrance, and I'm fine with only being at 5-6k RPM after doing so. If I was using heel toe in situations where I feel it's really required, I think I'd be far to close to loosing control of the car to be safe on the streets.

People who say "just let the syncro's do their job" are not worried about needing to replace them at some point. Good for them to be making that kind of money.

Exactly what this guys says... Heel-toe and and double clutching are complimentary techniques to be used together. Individually, they're a skill. Together, it's more like a dance step. Do it right and you can be perfectly prepared for a corner transition, and achieve a level of "smoothness" that would be impossible to pull off without it.

You aren't always on the brake when you down shift.


For instance, you are on the highway in 6th and need to pass. Do you step on your brakes and do a double clutch heel-toe to downshift to pass someone? Of course not. You just do a double clutch down shift.


And, not everyone can double clutch while doing a heel-toe. Watch some BMI races and you will see that many drivers who heel-toe don't even double clutch. Hell, sometimes the drivers don't even heel-toe. And the drivers on BMI are professional race car drivers.

It is best to learn to heel-toe without double clutching first. Trying to incorporate double-clutching while learning to do heel-toe is going to over welm you.


Since you already know how to double clutch, just learn how to heel-toe with just single clutch. Once you can learn to single clutch heal toe, then try to incorporate the double clutch into the heal-toe.

Thanks for the advice, I'll give it a shot and see if my muscle memory gets in the way or not.

Thats what I ment by easy driving, the highway downshift and stuff. But I never double clutch in a street car. Just like the BMI guys. In battle there is no time for the double clutch to me or the BMI guys it seems (and they don't have to fix them). The only time I or any one NEEDS to double is if you are driving a car with an H pattern box containing straight cut gears. I had to do those painfull shifts in a Formula Dodge car. And, if you happen to get in a car with a sequential box then you don't need it there either because Neutral can only be found under 1st gear. I miss that gearbox. It's like firing off rounds from a cannon.

First off. The magic is all in your pedals! If you don't have upgraded pedal pads then it will be Much harder for you to get it right. That's why it's easier for some than others. The key is to have the gas pedal and the brake pedal as close to each other as safely possible. Some cars come this way for this very topic. Other like my Accord do not. The first mod I do on any car is pedals. I like RAZO but thats just me. The easiest way to close the gap between the pedals is to simply take a piece of 1/8 or 1/4 inch piece of sheet metal and drill that sucker over the gas pedal. Instant race pedals! But check ALL the clearances before and after.

Now on practice. You don't have to be going fast to play with the transmission. Don't be affraid of messing up. Just make sure you practice on familiar roads in LOW to NO traffic.
When it comes to the Heel toe there IS a big difference to me in having the modded pedal and not.
A) With OUT the modded pedal you must usually use the definative HEEL and TOE. Like the BMI guys testing stock cars, you twist your ankle and use your Toes on the brake and your Heel to hit the gas. I have a hard time maintaining consistant brake pressure like this. As I stab the gas with the heel, my toes natually rise off the brake.
B) WITH the MOD pedal. (Practice this while PARKED first!) Keep your foot Vertical, place the BALL of your foot on the Right most EDGE of the Brake. (this will take time to find consitantly). As you press the brake down you will hit the gas due to the new closer pedals. SO, with the ball of your foot in place on the edge of the Brake, you will need to move, your RIGHT, KNEE, to the Left. This rolls your foot to the side letting the GAS pedal pass by as you brake. Now, while we are hard on the brakes our KNEE is still to the Left and the GAS pedal is now just under the right side of our foot waiting to be smashed. The clutch goes in, grab the proper gear, Now quickly swing your KNEE (NOT YOUR FOOT) to the Right! This will naturally roll your foot over on to the GAS pedal, reving the motor. Release the clutch, then the brakes and make your turn and power out like a Champ.
To make sure you get enough Revs for the selected gear, hold your foot on gas and grab A LOT of Revs. Go up to the red each time untill you memorize your ratios. But remember, you are BLIPING the throttle. It's a quick on / off motion. It may be a long Blip at times but it is just a Blip! After the blip let that clutch out. After the clutch is out there should only be pressure on the Brakes!
If you are in say 5th then you should heel-toe down through each gear as you are slowing until you reach the gear you want for the turn. You will find other detail that will become your personal style within all of this.

Don't Be Dead. Be Careful with this.

What size shoes do you wear? The only car I've ever been able to do that way was a '53 Chevrolet. The pedals on that (linkage coming up through the floor) were very different from modern hanging pedals. Except for the Chevy, I've always "heeled" with the side of my foot.

The 8 is the first car where I've had to move the ball of my foot to the edge of the brake the way you describe. I think that's because the center console prevents me from moving my knee over to the right.

There's a DIY on moving the 8's gas pedal over. Very simple - just unscrew the plate and re-attach using the next set of holes. I was on the verge of doing that until I hit upon putting my foot on the edge.

Ken

I recommend double clutching in a street car on the street. Since normal driving does not require lightning fast shifts, double clutching will help extend the life of your tranny.

I think the OP was referring to street driving, not thrashing the car around the track like on BMI.

And from what I have read on these forums, the synchros in the RX8 gear box are extremely fragile, so I would highley recommend double clutching for street use to prolong the life of your Synchros as it is a costly repair.


And heel-toe double clutching is still good for track use. Not everyone who takes their car to the track is going to do full throttle upshifts and slaming downshifts like on BMI as most people want to be able to drive home after track day :spank:

THis is how I have always done it (see my previous post about right side and left side of foot), and never with modded pedals, always stock. I had to learn this method as I have had arthritis in my hip since I was a kid and I can't even twist my leg to do a real heel-toe, so I had to learn the method above about using one side of the foot for the brake and the other for the gas.


But then again, I wear 17 size shoes so I don't need the pedals to be close together. :lol:

wow, great info here! Thanks for this.

Hehe yeah, I was merely talking about rev-matching on regular street driving to save clutch and synchro wear. But thanks for some great info. guys! :)

God bless.