jimbo01 0 Report post Posted September 3, 2007 My GPS radar detector is showing 109kph when the 740's speedo is showing 120kph indicated!. I thought that it was the tyres as currently it has a 245/35/20 (679mm diameter), however these are 1.29% smaller than original which doesn't account for a 10% speedo error. Is there some adjustment? Is the speed just optimisitc? I thought when i was cruising it felt slower than the indicated speed - and it wasn't the smoothness of the ride - it is slower! Any tips? Quote Share this post Link to post Share on other sites
cainchapman 0 Report post Posted September 3, 2007 Speedometers are generally optimistic. Have a look at NZ Autocar tests. The range from 97kph down to 91kph (actual) for an indicated 100kph. Sounds about right. Quote Share this post Link to post Share on other sites
my_e36 43 Report post Posted September 4, 2007 Just drive at a faster indicated speed to compensate for the slowness! But that doesn't explain why my speeding tickets are faster than my indicated speed on speedo. Do we have a defense if we have recorded the GPS reading at the time? Quote Share this post Link to post Share on other sites
cainchapman 0 Report post Posted September 4, 2007 No, is the short answer. However, I do know someone who used the GPS data in a truck to have the police drop a careless use charge. Quote Share this post Link to post Share on other sites
bravo 35 Report post Posted September 4, 2007 (edited) And the long answer: The onus would be on you to prove your GPS was accurate enough and calibrated (same as their guns have to be). GPS are not designed to give velocity (although they do and quite accurately too). It depends alot on the way in which the unit calculates velocity. Whether it is an averaged velocity calculated from your position change over time, whether it is calculated from the doppler shift in the satellite signal or the latter smoothed with the former. Each unit uses one of these methods, and there are varying accuracies associated with each. Edited September 4, 2007 by bravo Quote Share this post Link to post Share on other sites
jimbo01 0 Report post Posted September 5, 2007 (edited) The Mitsubishi Outlander when reading 100kph shows about 98kph on the 9500i - and this is about what the autocar magazine said the accuracy was so I'm pretty confident in the 9500i. Given the usual Germanic precision engineering a 10% speedo error is pretty expected. Anyway I've got new rubber for the carwhich should improve the speedo accuracy - 245/40ZR20 Dunlop 01A tyres - $830 each from Beaurepaires but I bought them from the closing South Pacific Tyre plant here in Upper Hutt via trademe - $755 for the 4. I'm happy - they have got to be better than the Nexen tyres. He's now has 4x 265/35ZR18 97Y XL Goodyear Eagle F1 GS-D3 New Tyres for sale for a buy now of $1300. Trader is Richdarr Edited September 5, 2007 by jimbo Quote Share this post Link to post Share on other sites
