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Tip: Improve your speedometer accuracy (for metric countries)

1.6K views 6 replies 7 participants last post by  jmnav  
#1 ·
Just a tiny thing I have discovered while playing with Star C3.

Speedometer usually shows faster speed than reality – partly because manufacturers need to fufill requirements of Regulation 39 or similar, partly because it makes the car look faster. I don't like this.

Anyway, until 2006, Australia only required speedometer to be accurate to ± 10 %. And with more or less modern car with electronic speed readout, there is not really a reason not to make it better – there is no mechanical linkage, no wear and tear, no spinny magnetic magic happening inside the dial itself.

If you set your instrument cluster location to Australia (vs. Rest of the world), displayed speed becomes very accurate with no percievable downsides. It may show slightly slower speed than reality (which is a big no-no from R39 standpoint), but as far as I can tell, 100 km/h on the speedometer shows 99–100 on the GPS (vs. like 95 before). So you'll get everywhere a little bit quicker :)
 
#2 ·
I have a Tomtom sat-nav, that I use in 4 different vehicles. When using it in the SLK (here in the UK) it agrees within a mph or 2 with the speedo. This is closer than any of the other vehicles that I use it in. (2002 Ford Fiesta,2009 YamahaFZ6, 2000 Honda Firestorm). Which means that I have to be extra careful not to drive "a bit too fast" in the slk if I don't want to attract "big brother's" attention!
Experience with the Tomtom sat-nav speed readings has lead me to believe it is more accurate than any of the vehicle speedo's.
 
#6 ·
Hi Robbie, in a previous life I was involved with testing GPS based speed enforcement tech for police vehicles. These vehicles had traditional wheel rotation calibrated speed detection, gps based systems and it was all checked with a calibrated stop watch on measured miles.
They also had TomTom nav units hard wired.
No prizes for guessing but the TomTom was the most accurate. 😁
 
#3 ·
I am using android device and setting the speedo to 70MPH, it shows 67, when RPMS are settled and maintained on a flat road. But the needle/pointer of the speedo is a bit large and it never bothered me that much!
Anyways @rfl where is that setting you talking about?
 
#4 ·
Agree with @Robbie4T - Both My R171 & R172 SLK's are 1 to 2 mph slow in comparison to my TomTom, though does change very slightly depending whether the front tyres are new or down to the cords ..

My chief navigators Nissan on the other hand: 4 to 5mph out....!! Guess it help's Nissan customers to be less disappointed with the mpg claims ...!!
 
#5 ·
When using Waze I find it close to 171, a couple mph lower than Murano.

Cross checking with those digital roadside speed monitors 171 spot on, Murano 1 or 2 mph lower. These are 20 & 30 usually but those are the most important as +/- 10% is very little to play with.

As with tomtom having an audible for over limit is handy. That one beep is enough for me.
 
#7 ·
Came here to add a "me too". As per my tom-tom GPS and up to quite forbidden speeds, my speedometer is 2Km/h below GPS reading, which I find good enough and much better than reading faster than GPS (no difference between R170 and R171).

Another thing I've seen more precise than in other cars I drive is the cruise control: it doesn't go away more than 3 Km/h on strong slopes, usually no more than 1Km/h and zero on flats. Other cars I've seen "moving around" 5 Km/h up or down or even more. Quite a problem when the cruise control is set right 1~2 Km/h below radar-triggering speeds.
 
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