Your speedo accuracy

obi_waynne

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Deal, Kent UK
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A3 1.4 TFSI 150 COD
How accurate is your speedo?

Comparing mine with a sat nav I see an indicated 60mph when the sat nav shows I'm doing 59 - in my book that is pretty accurate.
 
Usually clocks are out by a bit . My caldina over reads by 8 to 9 %. The stagea however is spot on even correct at 170 mph confirmed by v box at Marham airfield runway during timed 30-130 runs.
 
I have a calibrated stack speedo. During Topspeed runs it was reading 3mph slow at 210mph.

 
Mine shows 32 when I'm doing 29 but 75 when I'm doing 70 so the error increases a bit with speed.

Do very modern cars have speedos that link to the GPS signal for the built-in satnav? That would make sense to me to use both gps and the internal road speed sensor to get a more correct reading.
 
Speedometers are often 'driven' from one or more ABS sensors. They're nearly all electronic now, the old days of a rotating Bowden cable into the back of the instument panel are long gone.
 
My 4x4 reads 107 kph @ a sat nav 100 on a flat straight highway and the Starion with a RX7 box speedo 100 = actual 105
 
How did you manage to verify it's accuracy at 170mph whilst carrying out 30-130 runs?
The event was for 30-130 using supplied v boxes.
The runway was over a mile long and the v box doesn't turn off at 130.
So everyone had their top speed recorded as well. The runway surface is said to be the best in the UK (very special ashfelt ) and it is about 80 metres wide . On a well set up stable car it is pretty easy to see the speedo.
The top speed on the flying mile was 239 in a seriously tuned GTR whichdid the 30-130 in an equally insane 4.6 seconds.
 
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