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4th January 2016, 06:50 PM
#1
Tyres affect on speedo
Hey guys,
Hope this is in the right place! I've just driven my new car back from QLD and have found that my speedo is out a bit, through trial and error and following other car's speeds I've got a good idea, just wondering if anyone can shed some light on different size tyres affecting the speedo as a constant or percentage... let me make that a bit clearer.
When I drive at 100kph my speedo reads 90, so 10kph difference, or 10%
When I drive at 60kph will my speedo read 50 (10kph) or 54 (10%)
I'm assuming 10% is the way to go but I have nothing to base that on.
Thanks all.
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4th January 2016 06:50 PM
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4th January 2016, 07:47 PM
#2
I am he, fear me
The tyre effect in % will be linear IE 10 at 100, 5 at 50, 1.7 at 17 etc
BUT
that doesn't mean your Speedo indication error IE the speedo itself is linear as it may have differing errors % wise at differing speeds unrelated to tyres or diff ratios
Dolphins are so smart that within a few weeks of captivity, they can train people to stand on the very edge of the pool and throw them fish.
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The Following 2 Users Say Thank You to the evil twin For This Useful Post:
ForgeCreekFerals4x4 (5th January 2016), michaelgreeny (5th January 2016)
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5th January 2016, 08:22 AM
#3
Cheers mate. Appreciate it.
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9th January 2016, 04:25 PM
#4
You can install one of these speedo correctors.
https://www.youtube.com/watch?v=bMs7w72QTVM
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9th January 2016, 04:30 PM
#5
Patrol God
For hwy driving I would rely on a GPS of some description, The Aust Gov gives car companies a 10% error in speedo readings
The Victorian Police allow you only 5% if that, do the math lol
I run 285s and find the speedo near enough to correct,
when I fit my 315s its out same as when I had 265s on it
For hwy driving @ 110kph Ill set the CC to 105kph Im in no rush
and my ETA in marginal over 2.5 hrs
04 ST 3lt auto, not enough Mods to keep me happy, but getting there
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9th January 2016, 11:32 PM
#6
Originally Posted by
threedogs
For hwy driving I would rely on a GPS of some description, The Aust Gov gives car companies a 10% error in speedo readings
The Victorian Police allow you only 5% if that, do the math lol
I run 285s and find the speedo near enough to correct,
when I fit my 315s its out same as when I had 265s on it
For hwy driving @ 110kph Ill set the CC to 105kph Im in no rush
and my ETA in marginal over 2.5 hrs
The ADRs allow the speedo to over read up to 10% error, but the speedo must never under read, so the speedo will nearly always indicate a higher speed that actual, so if you sit on the speed limit according to the speedo you will never by speeding (assuming standard size tyres fitted).
GPS is the best way to check, but there is no calibration traceability so not really suitable for evidence in court.
To answer the original question, tyre size changes the ratio, so it tyre size changes indication as a percentage.
Graham
Last edited by GeeYou8; 9th January 2016 at 11:36 PM.
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10th January 2016, 12:12 AM
#7
I am he, fear me
Originally Posted by
GeeYou8
snip...
The ADRs allow the speedo to over read up to 10% error, but the speedo must never under read, so the speedo will nearly always indicate a higher speed that actual, so if you sit on the speed limit according to the speedo you will never by speeding (assuming standard size tyres fitted).
Yes and No...
The ADR (ADR 18) was amended in 2006 effective from Jul of that year
The requirement you have mentioned is only for vehicles manufactured after 2006.
Vehicles manuf prior to 2006 are allowed a Speedo error of +/- 10% of the actual speed when travelling above 40KPH
For our beloved Patrols that means...
All Y60's and Y61's up to GU series III and the earlier series IV can have Speedo errors up to +/- 10%
IE at 100 KPH actual, the indication can be 90 to 110 KPH
Late series IV Y61 and up and Y62 that are post ADR 18 amendment and must only have an error faster than actual
IE at 100 KPH actual, the indication can be 100 to 114 KPH
Dolphins are so smart that within a few weeks of captivity, they can train people to stand on the very edge of the pool and throw them fish.
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The Following User Says Thank You to the evil twin For This Useful Post:
taslucas (21st April 2016)
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10th January 2016, 10:30 PM
#8
Thanks guys, loving the assistance on here!
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20th April 2016, 09:49 PM
#9
Does anyone know someone that's fitted the corrector or similar ?
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28th April 2016, 09:52 AM
#10
Jay77
i fitted a Marks Adapter speedo correction unit not long after i bought the car (previous owner gave it to me on test drive when we got to post office when picking up his mail)
was simple to install, hardest part was hooking up the power feed. Also had to drill a hole in trans tunnel, grommet came with kit & i sealed up with sixaflex. The plugs plug straight into existing nissan harness.Has 2 settings for different size tyres.
Calibrated against a Hema HN7, which was a simple process.
I have a 2005 GU IV with 33 tyres on it.
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