dmacleod

Suggestions for harmonious gear shifts

Whatever rpm you shift at, a smooth shift (with rev matching) calls for a specific factor of change in the engine speed, The manual 04-08 RX8 gear ratios are
3.7600 2.2690 1.6450 1.2570 1.0000 0.8430

Based on these numbers, if you make an upshift with precise rev matching, engine speed must drop to
60% of its previous value for a shift from 1st to 2nd
72% of its previous value for a shift from 2nd to 3rd
76% for a shift from 3rd to 4th
80% for a shift from 4th to 5th
84% for a shift from 5th to 6th

Conversely, downshifts can be smooth (perfect rev matching) if you go to the redline starting from the above fractions of redline speed in the initial higher gear: 84% in 6th, and so on down to 60% in 2nd. Similarly, for any target engine speed that you may want to reach after the downshift, you need to downshift from the higher gear at these fractions of your target engine speed.

The recommendation that you sometimes hear, to increase rpm by 1000 on downshifts and decrease it by 1000 on upshifts, is not too accurate, though it may be fine if you aren’t finicky. In fact to get precise rev matching using that prescription, you would have to change up at these speeds:
from 1st at 2500
from 2nd at 3600
from 3rd at 4200
from 4th at 5000
from 5th at 6000
…and of course nobody shifts like that.

Fortunately the RX8 engine helps us by producing music during smooth shifts. Rev matching occurs at a characteristic musical interval for each shift. Based on the numbers (which you can check by listening), between 1st and 2nd the engine note drops a major 6th (the interval from C to E-flat below C, or from A to the C below). Between 2nd and 3rd it drops just barely more than a major 4th (for instance, from C to G below). Between 3rd and 4th, another major 4th (strictly, a little less than that). Between 4th and 5th, a major 3rd (from C down to A-flat). Between 5th and 6th, a minor 3rd (from C down to A natural).

If you use a major 4th to tune the shift from 2nd to 3rd, the slight undercorrection is actually helpful if you are accelerating or decelerating through the gears, rather than just maintaining a constant speed, because the release of the clutch at the harmonious engine speed gets you the desired (relatively gentle) nudge of acceleration on upshifts or deceleration on downshifts. In that situation, the ideal correction for the 3 to 4 shift is in theory a tad less than a major 4th, but the major 4th still works well.

Surely many people use the engine pitch to cue their engine speed adjustments, but I haven’t found this discussed anywhere, and I would be interested in any reactions.



Theory and practice always agree…in theory, but not in practice

G3tR3DDY2GR3DDY

iTrader: (8)

Im gonna be the first to say you have way too much time on your hands.

velociti

iTrader: (1)

that may be. but that's still cool as hell. well played, sir.

Shinka_MJR

Sure, i use the music of my car to tell me when to shift.

VROOOOOOOMMMMMMM ♪♫BEEEEEP♪♫!!! VRROOOOOOOOOM ♪♫BEEEEEEEEP♪♫!!!! VRRROOOOOOOOMMMMMMMM ♪♫BEEEEEEEEEEEEEEEEEP♪♫!!!! VROOOOOOOOOOOOOM

We Be Jammin, Baby!!!

Socket7

Wow dude...

I just feel the shifts. If I tried to do all that math and music stuff I'd forget how to shift entirely.

1.3L

I prefer driving by ear when it comes to shifting. Gluing your eyeballs to the tach too much invites trouble with other objects such as cars, curbs, telephone poles, etc.

-1.3L

dynamho

More related info:
https://www.rx8club.com/rx-8-discussion-3/rev-matching-gear-ratios-rpms-94854/



Also note that I've read that proper rev matching is not just about matching RPMs. To be really good and minimize drivetrain shock, you need to be aware of positive and negative momentum of the flywheel with respect to the transmission's momentum.

For example, let's say downshift rev match RPM is 4000RPM. You blip the throttle. It hits 6000RPM and on it's way down, you engage clutch at 4000RPM. This will cause some drivetrain shock because the flywheel needs to reverse directions.

I believe the correct method is to engage clutch when the flywheel is on its way up the tach, not on its way down. Even if you engage clutch at 3500RPM, it will be smoother than the previous incorrectly rev-matched example.

Our synchros our pretty forgiving, so this information is really for the hardcore shift connoisseurs.

kersh4w

iTrader: (3)

great 3rd post dma.

1.3L

You guys have taken something that is so easy and made it sound overly complicated. Seriously, any proficient manual transmission driver should be able to match shift up or shift down without the benefit of a tachometer.

-1.3L

always.anthony

i just give it a bit of gas before i feed the clutch in, whether its upshift or down its smooth for me. (depending on how big of a down, i sometimes give more ofcourse)

edit:...i think, wow i never payed attention to my driving, its just second nature to me..

Marklar

Kudos for the effort, but I think you guys are overthinking things a bit.

It doesn't matter much for upshifts, and for downshifts just double-clutch and blip the throttle, you don't have to aim for a precise spot on the tach.

1.3L

Supreme manual transmission drivers can shift through all gears (except first-gear dead-stop starts) without even using the clutch. That's ultimate gear matching skills guys.

Get in touch with your ride. Quit looking at the tach and look where you're going.

-1.3L

Kafka

I did that in my friend's car all the time lol...its perfect when it works! :P

actually..the 4th to 3rd and vis versa is easiest in the rx8...from my experience in my OWN car...

Marklar

Yeah, in a friend's car, maybe, not in an 8. I'm sure I could learn to shift without a clutch if I really wanted to...but I'd rather not destroy my tranny learning it.

greg985

+1 I used to shitf without the clutch on my old truck but thats because I didnt care about it. I would never do clutchless shift on my 8. Its just not worth it

always.anthony

yeah plus i think somehow i'd get in the habit of that, and that would end up badly

TheBurkeMan

lol i've got a truck i don't care about...i should try out the clutchless shifting

04RX8man

good write up but I just learn how to drive this car and feel what needs to b done!

RealXen8

So perfect pitch = perfect shift then I guess.
I (play) my car by feel too.
That was a fascinating read though.