Rev Matching
 

Like a lot of you, I'm fairly new to driving stick, so I have a few questions regarding rev matching.

Quick Questions:
1. Is it true that double clutching isn't really necessary in modern cars?
2. Is heel-and-toe for slowing down (i.e., for an upcoming turn)?
3. Is both double clutch and single clutch for accelerating (i.e., merging onto highway)?

Also, for single clutch rev matching which method is correct or are both correct or neither?

A) Clutch in, shift down and simultaneously rev engine to desired RPM, then clutch out while my foot is still on the gas

OR

B) Clutch in, shift down and simultaneously rev engine to desired RPM, release gas, clutch out, then get back on gas to accelerate

Thanks in advance!

You rev match to make the change smoother. You want to blip it so revs will be where they will be when you let the clutch back out.

Example:
Youre in 6th gear on the freeway at 3000rpm. If you want to down shift into 5th to pass a semi more quickly, clutch in, blip to ~4500rpm, as revs get there let the clutch out. If done correctly, you won't feel any shock from the down change and the change will be totally seamless. On the freeway it doesn't matter too much, but if youre going into a fast corner you don't want the down change to upset the car and send you spinning.

1) it is true, double clutching isnt necessary for modern cars. Syncro's allow the car to sense the speed of the engine and the drive train and get them matched up.
2) heel-and-toe is for high speed deceleration, when you need a smooth transition into gear before or at the very start of a turn. Without it, going too fast, the car can lose traction and cause a spin. Look it up on the web to get a better idea of its exact uses, but thats it in a nutshell.
3) I only single clutch. It just isnt necessary with modern transmissions to double-clutch.

And your final question, kinda hard to say, depends on what your desired effect is. If you are still slowing down, B is fine. But you want to release the clutch while your rpm's still match. If you are not prepping to slow down, then by all means A works (such as shifting to pass someone on a 2-lane road).

Double clutching saves the synchros, it's a good habit. As your transmission gets older and wears out, you might find that the transmission refuses to go into some gears without double clutching. Also when the transmission is cold downshifts without double clutching can be difficult. Get into the habit, and all downshifts will be really smooth and there will be no nasty surprises coming from a gear refusing to engage.

Not necessary, sure, you can still drive without double clutching, but it's not the best way to do it.

in normal driving you shouldn't need to double clutch unless your clutch is worn right out. i only really clutch 1st and second up during normal driving, and i just rev match without a clutch 6-3 down, before you say it will wear out syncros faster i put 145,000km on my s2k in 4 years and never had any problems not to mention the last 2 years had turbo torque and power to contend with. it shifted the same from the day i got it till i sold it. with over 220k on it in the end. and that's with a ton of auto-x and canyon carving. :burnrubber:

Uh, rev matching saves the clutch, double clutching doesn't do anything for the clutch. It just reduces the work the synchros need to do. Turbo doesn't change anything either, the synchros only bring the rotational speeds together when not under load.

Perhaps my transmission just needs a flush or something but double clutching makes it go into gear much much easier, so I prefer to do that.

probably a good flush and some good fluid with do the trick. i only ever used redline lightweight shockproof its great stuff, a little pricey though

Thanks akuhei. I was afraid I was somehow damaging the clutch if I'm revving while releasing the clutch (Method A). Because I'm riding the clutch...?? I'm not sure...?

Double clutching is fun. I've hit a few corners at MMP where I didn't use the clutch at all. Imagine dropping from 120+mph to 55mph downshifting from 4th to 3rd to 2nd with a perfect rev match without touching the clutch, and not hearing the gearbox grenading itself. Doing some double clutch practice and you can get more tuned-in with the gearing of the car and where you need to be for a perfect rev match.

The FRS has near perfect placement for heel-toe action too. These techniques aren't necessary, but they do help you make your commute entertaining, in the very least.

You only "damage" the clutch if you let it slip too much. Too much means you'll be smelling it. Technically the clutch is a wear item, it's lined with a sort-of brake pad material for smooth friction when it's engaged or released. If however, you upshift cleanly and downshift rev match cleanly, you put very little wear on it, but more importantly, you maintain the car's balance by avoiding herky-jerky clutch engagements.

The clutch is only the interface between the engine and transmission. It's kind of an on/off switch. The engine can rev smoothly anywhere you want, but the transmission will always spin at six specific ratios to the drive wheels. If those wheels are turning, so is the tranny.

Keep in mind that the transmission uses six fixed ratios. These ratios are fixed to the drive wheels at all times and will ALWAYS spin with the rear wheels, (even when you're in "neutral"). When you clutch up any one of these gears, the engine will be forced to spin at one of these six ratios. Rev matching is your analog input (when the clutch is disengaged) to get the engine speed correct for the gear you want. That's all. With some experience, you get the hang of how much rpm change is necessary between gears. The RPM spread between gears is wider at high RPM, and narrower at low RPM.

The synchros are like little clutches for each gear. When you shift, it's the *bump* that you feel in the throw. The transmission has two shafts, input and output with mated gears on each. The clutch is connected to the input shaft, the drive shaft to the output. The six gear pairs are always engaged to each other, but one spins freely on the input shaft. Between each group of gears (for instance, between 1st and 2nd) there's a collar that can engage either gear to the input shaft, depending on which way you push the lever. When the selector mechanism pushes the synchro collar toward a gear, The synchro for that gear will apply friction to the input shaft (imagine setting a can of soda on the center of a spinning record player). Once the shaft is spinning at the same speed as the gear, then *click* the synchro's splines can engage that gear to the shaft and you feel the stick finish the throw. Now you can apply power (or use engine braking) since the engine is now locked to the rear wheels at the ratio you've chosen.

Just like rev matching helps match the engine's speed to the transmission for the clutch, double clutching is a similar service for the synchros. When you rev match the engine while double clutching, you're in "neutral", but the clutch is engaged. This spins up the input shaft with the engine. Then, when you select the gear, the shaft is already spinning at the proper speed, and you feel little-or-no *bump* in the stick's throw because the synchro's job is already done.

Double clutching will not necessarily make a difference on the track or in canyons, but it is fun, improves your connection to the car, and does reduce synchro wear. The effect on wear may be minimal, but its the truth and the technique can prove to be a handy tool in your driver skill set. For most motorsports, double clutching and rev matching are really only used for downshifting. Some commercial vehicles equipped with dog box transmissions require double clutched upshifts because of the inertia of the big heavy parts and the lack of synchros. Rev matching on the other hand, is critical for motorsports for maintaining vehicle balance, especially when you're using your tires near their limits. The idea here is to be in the correct gear to exit a given turn. It has it's merits on the street too, you can be better prepared to accelerate out of harm's way, or simply take turns more efficiently, and simply be a better, more focused driver overall.

edit- wow that was a wall of text, lol... sorry I get a little "typey" at night...

The act of “riding the clutch" is to keep the clutch partially engaged...halfway between the floor and released. Releasing the clutch smoothly is good..but if you let off the clutch and you are at 6k-7k when you started at 3k...you just rode the clutch.

Dave
2011 Kawasaki Z1000

Hi Dave.
I too ride bikes Z9s. Z1000s, now a Suzuki GSX. The thought of changing down without matching scares me as it should anybody that rides. It amazes me that you see riders around that dont match. They've obviously worked out a way of getting all their ham fisted changing over before the lean in in the wet, Otherwise they'd be all but gone!
And of course the same goes for cars if your into driving well that is. You can forget about going fast if you can't match your revs.
I've often wondered if your saving your synchros by 'double declutching' I often do it in older cars if I think the synchros are on the way out.
Do you think changing is easier (goes into gear easier) if you match but don't double declutch? I guess no as the engine isn't conected to the gear box when the cog swap is going on.

wheelhaus >> thanks for sharing your info... How will I know how much RPM should I blip the accelerator pedal while downshifting per gear? It's their a table for correct RPM per gear while downshifting?

A table? What are you, an engineer? :bellyroll:

You blip according to the difference between the gears. For example, 5th is 1.000, 6th is 0.767, if you're in 6th, that means to shift down to 5 you want to blip to 1/0.767=1.303 times your current rpm. Start memorizing the "gaps" between the gears. Obviously, because it takes time to engage the clutch and stuff, you want to blip a little over so when the rpms come down a little they'll be correct. If you're slowing down at the same time, or coasting up a hill, then you blip less since you'll be going slower by the time your lower gear engages. It's okay to be off by a little, as the clutch will match the speeds up, but they'll just be a little jerkier. For smoothness you'd rather rev a little over than under, since your clutch won't be working against the decelerating engine. Might be useful to take some time playing with the gas in neutral just to get a feel for how the engine revs.