I though i'd post somthing i've notided with my fabia's speedo, is only accurate up to 70mph in comparison with my sat nav. I noticed this on the motor way and tried different speeds with cruise control on and it only matched the sat nav at speed up to 70 on the speedo. I'm not really sure what is correct!

speedo = sat nav

70mph = 70mph

80mph = 74-6mph

110mph = 100mph

Tend to find my speedo overeads by about 10% across the board, (check with Road Angel II) A lot of cars do this..... Belive the GPS system when speed contant (100% accurate but has a slight delay), when acelerating/decelerating use the speedo.

mmm I agree with andy, mine reads approx 10% fast throughout the speed range, (checked against the origin B2) and GPS tends to be more acurate, I believe its law that all car speedo's have to read a bit fast....

edit: as for which ones correct, always go with the car speedo, then you stand a better chance when faced with a camera van!

mmm I agree with andy' date=' mine reads approx 10% fast throughout the speed range, (checked against the origin B2) and GPS tends to be more acurate, I believe its law that all car speedo's have to read a bit fast....

edit: as for which ones correct, always go with the car speedo, then you stand a better chance when faced with a camera van![/quote']

The effect of the law is that a speedo must never read slow, so to be sure the calibrations are usually optimistic.

A GPS is more accurate in most circumstances, especially if your speed isn't varying much. However, as the pic shows, not all GPSes are created "equal".

Is it something to do with the scale change - jumps from 10 mph increments to 20 mph increments without them getting noticably further apart (something like that - I can't be bothered to go outside and look right now), so how well the internal workings handle the non-linear scale I don't know.

Is it something to do with the scale change - jumps from 10 mph increments to 20 mph increments without them getting noticably further apart (something like that - I can't be bothered to go outside and look right now), so how well the internal workings handle the non-linear scale I don't know.

I don't believe it's down to the change in increments, as the speedo needle shows a deacceleration at 90mph where as the car doesn't...

Get your average speed showing on your onboard computer display... hold a steady 70, 80, 90, 100, 110mph on the clock and reset your computer by holding the button on the bottom for a couple of seconds. After a few seconds you'll see what your car actually thinks it's doing!!

For me 63mph=60mph and 110mph=103mph

Try it!..

Chris

The effect of the law is that a speedo must never read slow' date=' so to be sure the calibrations are usually optimistic.

A GPS is more accurate in most circumstances, especially if your speed isn't varying much. However, as the pic shows, not all GPSes are created "equal".[/quote']

lol.... bryan, your car has to have the award for "most gadgets running at one go" or something like that (especially after hearing the "claxon" and watching the "instant playback" at the C&F )

As for how it handles it - the ECU sends a signal to the clocks - the map of speed & voltage/angle is programmed into it as a lookup table more than likely (or a calculation, but it's probably just a speed X -> voltage Y thing).

Have noticed this myself, but with 17" and 40 profile tyres i find that its now near spot on