Speedometer Accuracy

[Panners]

Does anyone know how accurate/inaccurate the speedometers are on these motors?

I was driving down the M6 last Sunday, doing a steady 80mph and thought I'd reset the trip on the dash display which read 76mph. Also, I've been past these radars which display your speed on passing, in a 40mph area and it flashed up 37mph.

Judging by the amount of folks wanting in my back seat when driving through built up areas, the evidence so far does suggest the the clock is over reading...

What's the consensus on which of the two instruments are telling the truth?

[Jones~32]

The dials are supposed to read fast ;)

upto 10% out

[PaulT]

Against my Tomtom satnav (which should be accurate on level ground) the dial seems to over-read by about 5% or so. Maybe slightly more, but I don't think it is 10% out.

Paul.

[Bero]

Road angel2 shows 4mph less than on the speedo all the way through the range (not a %) Manufacturers always (well nearly always b4 any1 gets smart, i know the Mac F1's was calibrated) err on the side of caution especially when tyre pressures and even tread depth would alter the spedo speed.

Bero