1QWIK7

iTrader: (1)

Good.

And i could hit 101 in 3rd gear @ only 8000rpm.

Now we're even.

swoope

iTrader: (5)

all the ecu in the usa knows is the dia of the tires is supposed to be 25.9"

it does not care if it is a 14" rim or 22" rim. or the aspect ratio of the tire is 30 or 70.

the magic # is 25.9.

beers

RojoOcho

*patiently waits for next posts*

mmats69

I have nothing better to do so I will dig up my 2 year old thread and bitch about nothing

Brettus

iTrader: (2)

Cough ......

MazdaManiac

iTrader: (3)

What do you mean? Go get a data log with RPM and speed through as wide an RPM range as you can.
Then, we can correct your true speed from your tire diameter and we will know the effective gear ratio for each gear.
That is what you want to know, right? Your effective gear ratio?
Go do it!

Brettus

iTrader: (2)

I will , but that's like seeing what colour underpants the conductor has on to work out how fast the train is going .....

Is it OK if I take my wheels off & do the datalog on jackstands rather than on the road ? If not OK please explain why ....

MazdaManiac

iTrader: (3)

OMG. That's it. I'm done. Have fun.

Brettus

iTrader: (2)

well I would think you could answer that .
How will the information gained from a datalog of rpm and speed be any different on jackstand than it would be on the road ? It's a simple question .
I'm pretty sure the front wheels don't need to be turning to get a speed reading on the speedo .


I think MM realises that if he can't satisfactorily answer the question it blows his assertions about trye size out the window ......

alexisthemovie

sounds like you have the 3rd gear from a 5 speed. (1.484 vs 1.645)...

do the calculations. It adds up... sort of.

neXib

LOL. You really aren't listening are you? :P

He's not saying anything about your 3rd gear, he's trying to help you by giving you a method that actually works for figuring out any possible differences in gear ratio or other things. You are arguing a dead point.

Brettus

iTrader: (2)

yes i know



I'm just struggling to see why he couldn't answer my question .....

rotary.enthusiast

I believe what Brettus has been trying to ask is this: Assuming the speedo accurately measures revolutions of the wheels, then why in 1st/2nd gear is he seeing the same reading as other RX8's, but in 3rd he is seeing a higher reading at a given RPM? It has nothing to do with tire size or actual vehicle speed, just the gear ratios in his transmission (and differential).

I'm making the assumption that the 8 uses the ABS wheel speed sensors to report speed to the ECU and speedo, if that assumption is incorrect could somebody please enlighten me?

Delmeister

Hallelujah! And you call yourself the local idiot.

Brettus

iTrader: (2)

Yes - well put .


Yes again .

Brettus

iTrader: (2)

BTW - I changed my avatar in honour of this thread .
MM is the crane - trying to eat me . I am the frog with my hands around his neck .And I wont give up !!!!!

Brettus

iTrader: (2)

here they are - not much of 5th and none of 6th but enough to give us an answer

PerSmitt

Just for further understanding the argument: In what way does the rolling diameter matter?

If measure the speed at 9000 rpm (using a high performance GPS or any other device that is accurate) in all the gears on my car we would approximately get:
1st: 65 km/h
2nd: 120 km/h
3rd: 145 km/h
4th: 210 km/h

Then if we were to repeat it on Brettus car the values would all differ because of rolling distance etc. However, IF the gear ratios are the same there would be a linear difference between all the gears. Brettus would for example be 4% slower in all the gears. If he were to be 7% fast in 3rd and 4% slower in all the others it would clearly indicate that there is a difference in the gear ratio between his and my car.

So I don't understand why rolling distance is needed considering that fault will always be linear and thus we can calculate it.

Brettus

iTrader: (2)

I averaged all the readings for 3rd gear which gave me a ratio RPM/speed of 55.52
if we take 9000rpm/55.52 = 162.1 km/hr per the speedo

Speedo speed = 162.1 km/hr = 162.1x1000/3600 = 45.03 m/s

revs = 9000/60 = 150 revs/s

diff ratio = 4.444

Tyre circumference = 2.042 - but the ECU does not know this so we should use the figure in the ECU - if swoope 25.9" is correct it would make this 2.068m

(150r/s / 4.444xgear ratio) x 2.068m = 45.03 m/s

33.78/gear ratio x2.068 = 45.03

so my 3rd gear ratio = 1.55

Delmeister

Should read 33.78/gear ratio x 2.068 = 45.03

Speed indication at 9000 rpm from PerSmitt and Brettus:
...............PerSmitt..........Brettus (speed at 4500 x 2)
1st:. . . . .65 km/h. . . . . . 66 km/h
2nd:. . . .120 km/h. . . . .109 km/h
3rd:. . . . 145 km/h. . . . .162 km/h
4th:. . . . 210 km/h. . . . .211 km/h

Looks like you might have a second gear issue as well Brettus

rotary.enthusiast, you must be doing this now . Look, you guys don't need no stinkin spreadsheet, GPS, tire size etc. Just read your spedo when your tack reads 9000 (or 4500 if the former is too fast for you). The gear ratios for the NA cars are know, Brettus's will just be some correction based on the difference of the above table.

Brettus

iTrader: (2)

corrected

Per smitts' 120 in 2nd is 75mph - is that what others get as well ?



Yes - I tried to explain it this way several times but MM insisted i needed more information - he is rather a hard person to argue with .......

rotary.enthusiast

Wow, this thread is really all over the place. GPSes to measure speed now?

Here is what you should see (in MPH) on the speedo@9000 RPM with stock US 6 speed and stock differential:

1st: 42
2nd: 68
3rd: 95
4th: 132
5th: 157
6th: 186

It doesn't matter what tire sizes you have as the speedo and PCM don't adjust for that. We don't care about actual vehicle speed, we're just interested in gear ratios. If you aren't seeing numbers within 2-3% of these, then you have an oddball. If you are seeing different numbers on your speedo, I would also datalog RPM vs. MPH (the numbers reported by the PCM will probably be slightly different than what the speedo says even if the speedo is working correctly).

rotary.enthusiast

I believe MM was trying to calculate your effective gear ratio by taking into account your smaller than stock diameter tires, but I don't think that's what you're interested in knowing. You just want to know how the gear ratios in your box compare to everybody else's all other things being equal, right?

Brettus

iTrader: (2)

Yes

Brettus

iTrader: (2)

Anyway I have calculated all the ratios and they are all within a 1% of the chart Dynamho posted 2 years ago . The post that should have been enough to end this thread.
I took the average error over the whole lot and applied this to each figure gained from the datalogs to get these figures

JDM Spec RX8.......................MY RX8
1st......3.760.........................3.789
2nd.....2.269.........................2.271
3rd......1.539.........................1.534
4th.......1.187.........................1.184
5th.......1.000..........................0.997
6th.......0.843..........................no numbers


As you can see the numbers are almost identical . You would have to have a name like "maniac" to dispute that the posted spec is not the same as my car .

Is this enough proof for you MM ?