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help with working out correct speed 

 

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 Post subject: help with working out correct speed
Posted: Wed May 23, 2007 12:48 am 
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just bought an ef xr8.

the diff has been changed to a 3.45 lsd

the gearbox is that from an el (if this makes any difference)

and it has 18" wheels

will this affect my speedo reading at all or will i be safe to be sitting on or just below the limit.

any help is much appreciated
cheers

 

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Posted: Wed May 23, 2007 12:57 am 
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I know the speed checker at Geelong on the Princes Freeway
and at Beveridge on the Hume Highway have been fixed and recalibrated so they read correctly now.
If your heading in any of them directions you'll be able to check your speedo
for correctness and if it is out, you then can get it recalibrated so it reads correctly.
There should be other speed checkers around the eastern side of the city also.
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Posted: Wed May 23, 2007 1:02 am 
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gearbox won't make a difference.
wheels will make slight difference (fractions of a percent, rolling diameter dependent on tyre size should be very close to stock)

diff will make big difference, IF the speedo gear hasn't been changed.
is the car auto or manual?

 

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Posted: Wed May 23, 2007 1:04 am 
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Steady ED wrote:
gearbox won't make a difference.
wheels will make slight difference (fractions of a percent, rolling diameter dependent on tyre size should be very close to stock)

diff will make big difference, IF the speedo gear hasn't been changed.
is the car auto or manual?


tyres are 235/40/18

car is manual

and no the speedo gear hasnt been changed

 

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Posted: Wed May 23, 2007 1:16 am 
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According to speedo calc you'll have -7.16% error, when you are doing 100 on the speedo, actual speed will be 92 clicks.
Can change the gear and have no ill effects, being manual.

edit: thats assuming original light green speedo gear and 3.23 diff.

 

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Posted: Thu May 24, 2007 1:36 am 
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Steady ED wrote:
According to speedo calc you'll have -7.16% error, when you are doing 100 on the speedo, actual speed will be 92 clicks.
Can change the gear and have no ill effects, being manual.

edit: thats assuming original light green speedo gear and 3.23 diff.


so i should be able to sit on the limit according to the speedo and not actually be going faster than that. that was my main concern as i didnt want to start racking up all of these speeding fines

 

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Posted: Thu May 24, 2007 1:42 am 
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nannas_ed wrote:
Steady ED wrote:
According to speedo calc you'll have -7.16% error, when you are doing 100 on the speedo, actual speed will be 92 clicks.
Can change the gear and have no ill effects, being manual.

edit: thats assuming original light green speedo gear and 3.23 diff.


so i should be able to sit on the limit according to the speedo and not actually be going faster than that. that was my main concern as i didnt want to start racking up all of these speeding fines

Thats the theory, yep :D

 

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Posted: Thu May 24, 2007 2:03 pm 
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What if you drive with the diagnostic mode running?
Doesnt that give you the actual speed you are travelling?
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Posted: Thu May 24, 2007 2:43 pm 
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One old fashion way is final drive x top gear x tyre rotation per k and then divide into 60000. I have a RTV, its has final drive of 3.45 x top gear .68 x tyre rotation 476rpk = 1116.696. Then 60000/1116.696= 53.72kph per 1000rpm.This means at 2000rpm I will be doing about 107kph.
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