2005 A8 SWB Speedo accuracy ...
11-02-2004, 09:04 AM
#1
AudiWorld Senior Member
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2005 A8 SWB Speedo accuracy ...
<center><img src="http://pictureposter.audiworld.com/70217/a8_speedo_calibration.jpg"></center><p>In an earlier post there was a question that the speedo accuracy for 05 models may have been improved over the 04 models.
I have tested my 05 SWB using Plano-4.2's instant average method - thank you - and a pocketpc GPS system with speed readout capability.
The GPS numbers are effectively identical to the instant average method so you will not be able to see all the data points.
You will see that the actual speed is about 97.2% of indicated better that the 95% reported for 04 vehicles.
Maybe the problem is solved ...
I have tested my 05 SWB using Plano-4.2's instant average method - thank you - and a pocketpc GPS system with speed readout capability.
The GPS numbers are effectively identical to the instant average method so you will not be able to see all the data points.
You will see that the actual speed is about 97.2% of indicated better that the 95% reported for 04 vehicles.
Maybe the problem is solved ...
11-02-2004, 10:28 AM
#3
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Are you sure? I thought that 04's were reported as ..
reading 5% high and my 05 is reading 2.7% high. They have just closed the gap a little. Or am I incorrect?
11-02-2004, 10:58 AM
#4
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That's the way I read the info.
It does appear that the difference from indicated to actual has been reduced. What tire / wheel combo do you have Geordie? I have the 19" wheels.
11-02-2004, 11:19 AM
#5
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The 18 inch 9 spoke style wheel with ...
all season 255/45 R18's factory fit.
I was wondering if the "improvement" could be due to a wheel / tyre combo where the circumference is a little smaller and hence the speedo would read higher.
On checking this out a new 255/45 18 has a circumference of 84.9342 inches and the 255/45 19 is 84.9218 inches. The difference is so small as to be insignificant.
Of course my tires only have 3000 miles on them so the difference between actual and displayed can only increase. By my calculations, 5mm tread wear would add 1.6% to the wheel rpm and hence increase the inaccuracy in my speedo to around 4.5%.
I was wondering if the "improvement" could be due to a wheel / tyre combo where the circumference is a little smaller and hence the speedo would read higher.
On checking this out a new 255/45 18 has a circumference of 84.9342 inches and the 255/45 19 is 84.9218 inches. The difference is so small as to be insignificant.
Of course my tires only have 3000 miles on them so the difference between actual and displayed can only increase. By my calculations, 5mm tread wear would add 1.6% to the wheel rpm and hence increase the inaccuracy in my speedo to around 4.5%.
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