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New Tyres Throw Off Speedo 

 

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 Post subject: New Tyres Throw Off Speedo
Posted: Tue Aug 25, 2009 10:51 pm 
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Age: 26

Posts: 676

Joined: 7th Jun 2009

Ride: Ford EB II Falcon

Location: Morphett Vale
SA, Australia

Ok so i got some new tyres fitted some time ago to my EB II and i got done for speeding the other day and i know my car is going slower than what the speedo is saying how do i find out how much slower it is going with the new tyres compared to stock?

This is a program i use to help me

http://www.miata.net/garage/tirecalc

My new tyres are 215/65 or 60/ R14 something like that, all i know is they are on the Door Card of my EBII

 

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 Post subject: Re: New Tyres Throw Off Speedo
Posted: Tue Aug 25, 2009 11:36 pm 
Getting Side Ways
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Age: 49

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Joined: 18th Dec 2006

Ride: 93 ED sedan

Power: 161 rwkw

Location: Rockhampton
QLD, Australia

I use an actual one........tyre diatmeter in inches X rpm ( ie 2,600rpm becomes 2.6 ) X 3 ( constant)
___________________________________________________________
Diff ratio X Gerabox ratio.

Equals.......speed in MPH........times this by 1.61...= KMH.

26.1" X 1.8 X 3 = 140.94.

Diff of 3.08 and 3rd on 4sp auto is 1:1.
so 140.94 divided by 3.08 = 45.759 MPH X 1.61 = 73.673Kmh.

 

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 Post subject: Re: New Tyres Throw Off Speedo
Posted: Wed Aug 26, 2009 1:08 am 
Getting Side Ways
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Age: 50

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Joined: 2nd Dec 2006

Ride: EF wagoon

Location: perth
WA, Australia

i use a gps. This is the best method i have found

 

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 Post subject: Re: New Tyres Throw Off Speedo
Posted: Sun Aug 30, 2009 11:53 pm 
Getting Side Ways
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Age: 30

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Joined: 15th Apr 2009

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Ride: 2013 Ford Focus ST

Power: 175 rwkw

Location: North West Sydney
NSW, Australia

awesome little program, just tried it out, my speedo will say im going faster than i really am with my new rims and tyres (0.4% to fast )which is always a good thing.

 

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 Post subject: Re: New Tyres Throw Off Speedo
Posted: Mon Aug 31, 2009 2:09 pm 
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Age: 30

Posts: 1870

Joined: 14th Apr 2006

Ride: 1993 EBll xr6, 2003 ba xt

Power: 150 rwkw

Location: Whyalla
SA, Australia

http://www.miata.net/garage/tirecalc


if going by this


my speedo is 0.6% to fast so when my speedo is sitting on 100 kph i am actually doing 99.4 kph

 

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