Paul_in_DC

Peace in our time.

rotor_man

could be keen on a track day at Pukekohe Brett let us know closer to the time

Brettus

iTrader: (2)

will pm you

Brettus

iTrader: (2)

This discussion started up again in another thread when Mysql challenged me to find a single occurence on the whole site where MM has been proven wrong . We all know MM is right most of the time but could it actually be possible for him to be wrong - just this once .......

Here is my last post from the other thread ......

Brettus

iTrader: (2)

here is the other thread if anyone wants to be bothered reading it - see pages 7&8
https://www.rx8club.com/newreply.php...eply&p=2568192

Kersh4w : my tyre size is 235/40/18

MazdaManiac

iTrader: (3)

No. I was simply pointing out that you can't use the post of that advert as a premise of your argument because it was data for the 2007 model.
The JDM parts guide of '08 (which has all previous models) doesn't have a different 3rd gear until '07. '09 has yet a different set of ratios.
The reference is spurious.


No.

The problem with the argument you are trying to raise here is that you are missing the fundamental difference between indicated speed and actual speed.
You jack stand model is particularly telling because it indicates a speedo error of 100%. Doesn't your own example make you understand why your argument doesn't work?
Probably not.
I'm not going to rehash all of this. I already laid it all out for you, but you are refusing to follow the logical conclusion from the facts.

paulmasoner

iTrader: (1)

first its important to note that all tires are NOT created equal. one tire brand or series' 225/45/18 may not have the exact same measurements as another brand/series of tires. we all know there are slight differences. we are also working with 92mph being the norm for 3rd gear peak, whereas you are seeing 103mph

per the calculator on www.1010tires.com your 235/40/18 will read 2.234% too fast on the speedo... or 94mph at 3rd gear peak. this obviously doesnt account for the difference you see.

BUT if you stop to think that perhaps that calculator doesnt take into effect total diameter lost due to a slighty more streched tire(as it doesnt factor rim width)***see my crappy artistry to explain this***, and then you also remember that your particular tire may be slightly smaller in diameter anyway compared to the indusrtry standard or whatever(remember that it's well known not all tire actually measure exactly what they state)... then you start to get into the realm of possibility.

per 1010tire your side wall height is 3.7in. if you say that perhaps its actually only 3.5, then you lose another .5in in radius due to a stretched tires...then your actual tire diameter is only 24in. this is an 8.21% difference in diameter which yeilds a 3rd gear peak speedo reading of 99.5mph.

if your speedo already has an error of 3.5% at that speed, then it will read 103mph. SOOO..... a couple mph off due to pure speedo miscalibration, a couple due to your tire size and the variance it may have to ACTUAL measured sizes, and a couple more due to losing total tire diameter/circumference with slightly stretched tires......



thank you, thank you very much. this thread can now be closed

Brettus

iTrader: (2)

Please locate these facts about 03 JDM 8s for us all to view - you seem to have intimate knowlege of the JDM specs so it wont take you a moment to dig them up .


uhhh no - how about you think about this test - you don't even have to do it - just think about it ......
tell me what speed do you think your speedo will indicate if your car is on jackstands and you rev up to 9000 in 3rd .
Now take the wheels off and put smaller ones on and tell me what speed you think your speedo will indicate now at 9000 in 3rd .
Is there going to be any change to the reading on the speedo - yes or no ?
I'm picking you wont answer this question .

you have not presented any facts yet just veiled insults and a whole lot of hot air.

Give me some facts .......

tajabaho1

top speed is retarded, there is no such thing.......top speed.......wtf is that?

that's like "the end of the universe" or " the inner walls of a *****'s vagina" or "The Logical and nice MM" or "The cheap Mazsport"

you guys are all idiots

Brettus

iTrader: (2)

Please think about the jackstand test I posted above and answer my question ......

MazdaManiac

iTrader: (3)

AAAAAAAHHHHHHHH!!!!!!!

It doesn't matter what your speedo says! Don't you get it? Indicated speed is not actual speed.
You speedo would read exactly the same in your example. But both times the error would be 100%!!

I think you might actually be hopeless and that depresses me.

tajabaho1

there's only one way to end this............

muskets, in the parking lot

after 7-11 closes

MazdaManiac

iTrader: (3)

Its ended. It was ended last year.
I had just really hoped that Brett had one of those "ah-ha" moments.

Brettus - At what indicated speed are you "topping out" 2nd?
How about 1st?
You understand that your ~10% error in 1st or 2nd would only be a couple of miles an hour, right?
Have you measured your actual vs. your indicated? How about for RPM?

If you stood on the gas pedal in 3rd gear until you hit the rev limiter and then did the same in 2nd, you understand that your RPMs would be different, right?

paulmasoner

iTrader: (1)

if your speedo shows ~103 on jackstands, then that should be proof that either you have a miscalibrated speedo, or a different gear ratio.... others can hash out which that may be.

i think me previous post might have been overkill to explain what most seem to understand about tire size and speedo variance

Brettus

iTrader: (2)

ahhhhhh haaaaaaa !!!!!!
so you admit that the speedo will read the same - we are finally getting somewhere .
BTW I never contended that smaller tyres didn't create an error in actual speed vs the speedo I,m not talking about actual speed here - I'm talking about what the speedo says i'm doing .

Now that we have that established :
Please explain to me why my speedo ,not f'ing actual speed, my SPEEDO says i'm doing over 100mph in 3rd .........

Brettus

iTrader: (2)

I posted this video earlier so you could see what is happening with my speedo - you obviously never took the time to look at it ....

http://www.youtube.com/watch?v=NzlvSC_8N-Y

From the video we see (taking into account that revcounter reads approx. 500rpm high)

64km/hr(40mph) @8600 rpm
113km/hr(70mph) @8900rpm
163km/hr(102mph)@8900rpm

MazdaManiac

iTrader: (3)

Who cares what the speedo says you are doing!?!?! Its not reality.
You are saying that one car tops out at one speed and yours at another, but you are not measuring them with the same method.
Have you topped out 4th (I know you can't)? Wanna take any guesses at what the indicated speed would be?

Better experiment for you -
Get a RADAR gun and measure your speed at the top of 3rd and the speed at another car at the top of 3rd.
That is the only measurement that matters.

Just to help you get away from your jackstand experiment in which you gave yourself your own red herring, consider the importance of the idea of error.

You put your car on jackstands. You put on OE tires. You spin it to the top of 3rd. The speedo says 100 MPH. What is the error?
100%. The car is actually standing still.
Now, put on mini wheels. Spin it to the top of 3rd. The speedo says 100 MPH. What is the error?
Well, its still 100% because the car is still standing still, regardless of what the speedo thinks.
Now, here is the rub - what is the relative error?
Well, you would say "Both error values were 100% so the relative error is zero".
Of course, you would be wrong because the wheel speeds were actually different, even though the absolute error was 100% in both cases.

Get away from thinking that what your speedo says has any relevance to what your vehicle is actually doing.
You don't know your effective gear ratio from your speedo.

Brettus

iTrader: (2)

care to explain why my speedo reads 100 and yours is around 90 - do you think Mazda really f'd it up with my car and not yours ?

Lets talk about actual speed now (I know it's not 100% acurate but it will be close enough )
see my g tech run in the below video and note the speed at the end of the run and the gear i'm in when i get there ....

http://www.youtube.com/watch?v=WF5axGDsCHs

Brettus

iTrader: (2)

Answer this question for me please :

Is approx. 70 mph the speedo reading you get at 9000 rpm in 2nd - yes or no ?

MazdaManiac

iTrader: (3)

Yours reads 100 and mine reads 90 when we are doing what actual speeds?
Are you suggesting that both of our motors will be spinning at the same RPM when our speedos read this way or that both of our vehicles will be traveling at the same speed? Or both?!?!

Please tell me you are starting to get this.

I don't know. I've never sat at 9000 in second gear long enough to care.
It wouldn't tell us anything because the speedo is wrong and the tach is wrong.

BTW - I hit the rev limit when my speedo reads about 96 MPH. How fast I am going and how fast the motor is actually spinning is anyone's guess.

Brettus

iTrader: (2)

correct - thankyou .
My contention is that it is the latter and I think I've proved it 99% beyond any doubt .

MazdaManiac

iTrader: (3)

Even if this were actually the case, you haven't even presented a cogent argument that it is possible, let alone plausible. You haven't proven a thing because you have yet to even offer a thesis.

Unfortunately for your purposes, the only way to actually prove what you are suggesting (aside from dismantling a JDM tranny, which I have done) is to run your jackstand experiment with two cars and roto-tach the wheels and log the RPM.
You could do it on a track as well.
The speedo is meaningless. The speedo is meaningless. The speedo is meaningless.
Just say that a bunch of times. Maybe it will help.

Brettus

iTrader: (2)

I'm trying to point out that my speedo reads the same speed at the same rpm as yours in 2nd gear but not in 3rd .
Thus , my contention that I have a different ratio in third than what you do .....

MazdaManiac

iTrader: (3)

Brettus

iTrader: (2)

wrong - If two RX8s read the same speed on the speedo when in 1st,2nd,4th,5th&6th but not 3rd , what conclusion could you draw about 3rd gear ?