Speed Calculator

[shaneth]

There is always questions about the accuracy of the speedo so I wanted to do this for a long time. this may not be 100% accurate but is just a guide to see how far out the speedo is. I have done a bit of research for this formula and this was about the easiest i could find.

Speed Calculator

Equation :- (0.00006) * (RPM * r) / (R1 * R2) = vehicle speed in km/hour

Where :-
RPM = engine speed, in revolutions/minute
r = loaded tire radius (wheel center to pavement), in mm
R1 = Gear Ratio
R2 = Diff Ratio

Polo Tire Radius
299.95

Polo Gear Ratios
1st – 3.30
2nd - 1.94
3rd - 1.36
4th - 1.03
5th - 0.82

Polo Diff Ratio
3.65


Now I have done one going off the Motor Mags Figures Which is 1km/hr out compared to the equation I found which is above. So either one is close enough for me. I will be testing this out later this week and see.




Disclaimer :- This is not ment to replace your speedo. It is a guide only. Testing this is at your own risk and neither I or VWW.org.au takes any responsibility

Now before everyone asks no im not back yet I have wanted to do this for a long time and when Motor Mag published the Gear Ratios I could finish it. If anyone has any questions or queries I suggest you email it to me as I can only check it when I go over to my parents place. I will be back in the new year.

[Eddy]

Hoyhoy.
SSSSSSSSHHHAANE we miss ya.
P.S. Speaking for myself that is.

[PeterHBne]

Welcome back! (kind of....)

[Timbo]

Welcome back, Shaneth....but now my head hurts!

[jasn78]

geez shane talk bout way too much maths

good to have u back mate

so wheres the next group buy? lmao

[95vr6]

Why dont you plug in a GPS nav unit and it will till you your exact speed in any gear.

[VWindahouse]

He Lives!!!!!

[Wand Weaver]

Nice work Shaneth.

For those complaining about 'too much maths' - I've knocked up a JavaScript calculator for in-gear speeds.

At the moment, only the Polo's there, but the script's modular enough for me to add more cars if I find out their tyre size, diff ratios and gear ratios.

If you're wondering how a different sized tyre might affect your speedo (not that the Polo's speedo's particularly accurate) - just change the tyre size at the top.

As with my post in the 'Top Speed' thread, the assumption of a perfectly round tyre is made, so the values are probably marginally high.

http://home.people.net.au/~kenny-f/home/miscellaneous/calculator/

All thanks goes to Shaneth for providing the gear ratios.
Edited to add: Found the ratios for the Golf

[Timbo]

Good work! but some of us with 17" wheels use 40 profile tyres and I guess some of the Golf guys do, too

[Wand Weaver]

Good work! but some of us with 17" wheels use 40 profile tyres and I guess some of the Golf guys do, too

Thanks

Point taken on the profile - I've added a few extra options to the form. I think all tyre widths end with '5'?

or at least I hope so!

[Timbo]

Ya gotta love modern life's instant revision capability

[Funkdancer]

Ya gotta love modern life's instant revision capability

Funny, I was just reading the following! (alt tabbing between the pages!).

Act V: The act of remembering

Another possible change: with connected books, the tether between the author and the book is still active after purchase. Errata can be corrected instantly. Updates, no problem.

Newsweek, The Future of Reading

Day by day and almost minute by minute the past was brought up to date. In this way every prediction made by the Party could be shown by documentary evidence to have been correct; nor was any item of news, or any expression of opinion, which conflicted with the needs of the moment, ever allowed to remain on record. All history was a palimpsest, scraped clean and reinscribed exactly as often as was necessary.

George Orwell, “1984″, Book One, Chapter 3

Great work on the speed calculations Shaneth, very useful information! (As you know I'm quite into this thing via my Scangauge hehe).

[Timbo]

Bit like Fed Govt websites, after the change of government

[GT3]

"Day by day and almost minute by minute the past was brought up to date. In this way every prediction made by the Party could be shown by documentary evidence to have been correct; nor was any item of news, or any expression of opinion, which conflicted with the needs of the moment, ever allowed to remain on record. All history was a palimpsest, scraped clean and reinscribed exactly as often as was necessary.

George Orwell, “1984″, Book One, Chapter 3"

This has happened to my comments in many threads too lol ..and it's implemented by editors of Aust motoring mags the moment they encounter comments remotely in favour of the VW Polo GTI .."oh dear, must get rid of that, what would our 'sponsors' say?...

..and all of this is highly relevant to speed calculations too I may add

[PeterHBne]

I love '1984'.

I particularly liked the concept of advanced versions of Newspeak which involved whittiling the language and dictionary down to basic concepts so that the ability to think about and then express anything that The Powers That Be don't want is simply not possible.