Engine Speed vs Vehicle Speed for 6MT

[DetroitJake]

Engine Speed vs Vehicle Speed for 6MT

Maybe I'm crazy, but I did the math and thought this would be a helpful graphic for understanding when to shift and how to rev match. Its helpful for me anyway to think about it.

You could easily change the ratios for the 6AT, but since it rev matches for you, it might only be for academic interest.

PDF and XLS (as ZIP) files are attached.

[mashal]

8000 rpm and 40 mph 1st gear? What?? Do you want to blow up that engine ?

[jedibow]

Originally Posted by mashal

8000 rpm and 40 mph 1st gear? What?? Do you want to blow up that engine ?

He extended the graph to show what is possible, no you do not want to shift at 8000RPM in first, but if you do, you will be at 4950 RPM in second, that is why he posted this....

[DetroitJake]

Originally Posted by jedibow

He extended the graph to show what is possible, no you do not want to shift at 8000RPM in first, but if you do, you will be at 4950 RPM in second, that is why he posted this....

Ya. I thought it would be helpful to think about shift timing so you'll know how much to blip the throttle when downshifting into lower gears or what RPM your engine will synchronize the trans with when shifting to higher gears.
I'm thinking it would be a bad idea to pull past red line very often (if at all).
But if you are keeping the tac around 3-4k for regular driving vs revving it up to 6-7k for fun driving, you can see the spacing to match revs is a little different. I'm sure this becomes natural with practice, but it seemed a useful tool to help visualize how the ratios sync together.

[OrbitalEllipses]

Much appreciated.

[Bonburner]

from my driving experience this sounds pretty darn accurate!

[ahausheer]

Shift everything right just slightly. My reasoning is that none of the car mags that I know of got to 60 at the top of second. There is something with the tire size and resulting gearing that make the car need to shift to 3rd to get to 60 even though It was apparently designed to hit 60 at the top of second.

[atledreier]

And here you can see the reason it's "slow" to 60. Shifting from 1st to 2nd @ 7k lands you squarely in the torque dip.

[Symbiont]

You should actually land at about 5k from a 7200 rpm shift.

The thing is, the MT only hits 57mph at redline in 2nd, so most people shift to 3rd before hitting the barrier.

[xjohnx]

Originally Posted by Symbiont

You should actually land at about 5k from a 7200 rpm shift.

Judging by that chart, it looks like it should be around 4400 in second after a 7200 RPM shift from first.

[Symbiont]

I'm just going by what I experience on the road. I can definitely avoid that dip by shifting hard at close to redline.

I do it pretty much every day, and you can basically hit right around 5k with a fast shift.

[DetroitJake]

Originally Posted by jedibow

He extended the graph to show what is possible, no you do not want to shift at 8000RPM in first, but if you do, you will be at 4950 RPM in second, that is why he posted this....

Originally Posted by Symbiont

I'm just going by what I experience on the road. I can definitely avoid that dip by shifting hard at close to redline.

I do it pretty much every day, and you can basically hit right around 5k with a fast shift.

The calculation was based on gear ratios stated in the BRZ service guide and the tire diameter. I checked the tire diameter by three methods and choose the smallest value because it seemed the most conservative. The three methods include tire sidewall ratio calculation (tire code), manufacturer stated diameter, and manufacturer stated revolutions per mile (which was the least value and probably accounts for tire deformation when loaded and rolling).

If you changed your tires, this stuff would need to be re calculated. There could also be some other deformation affects I'm not aware off (non belted tires grow in diameter at high speed, but I would guess this affect is small or non existent due to the radial belting, etc). Its also possible I made some kind of units conversion mistake, but I'm pretty sure all that stuff is good. At least the graph seems to follow what I see when I drive.

[Symbiont]

Originally Posted by DetroitJake

The calculation was based on gear ratios stated in the BRZ service guide and the tire diameter. I checked the tire diameter by three methods and choose the smallest value because it seemed the most conservative. The three methods include tire sidewall ratio calculation (tire code), manufacturer stated diameter, and manufacturer stated revolutions per mile (which was the least value and probably accounts for tire deformation when loaded and rolling).

If you changed your tires, this stuff would need to be re calculated. There could also be some other deformation affects I'm not aware off (non belted tires grow in diameter at high speed, but I would guess this affect is small or non existent due to the radial belting, etc). Its also possible I made some kind of units conversion mistake, but I'm pretty sure all that stuff is good. At least the graph seems to follow what I see when I drive.

Definitely haven't changed my tires (or any other drivetrain parts). All I know is that I'm definitely not landing in that dip under hard acceleration. Maybe I'm just hitting the gas too soon as I'm letting out the clutch.

/shrug

EDIT: I suppose it's also possible that I land right at 4500 (which is out of the torque dip) and at WOT I'm past 5k so fast I don't even notice. I can try to hook up a go-pro to analyze that when I get my car back.

[DetroitJake]

I flipped the axes as I have realized its easier to think about it this way.