Speedo / GPS

[si.w]

Did a very unscientific test at the weekend comparing speed as shown on speedo to GPS on phone. GPS showed 70mph when car indicated 75mph. How do I know which is right!?

Has anyone else compared theirs!?

Cheers

[Jon8710]

It will run about 10% out mate,
My speed limiter comes in at 180mph on the speedo but showing 155mph on GPS

[mattCSLnut]

Did a very unscientific test at the weekend comparing speed as shown on speedo to GPS on phone. GPS showed 70mph when car indicated 75mph. How do I know which is right!?

Has anyone else compared theirs!?

Cheers
As far as I know GPS never lies... the analogue speedometers often do.
On an AUTOBAHN my Cecil showed a GPS reading of 174 MPH while the needle was off the clock way past the 180 MPH mark.

[outnumbered]

I think the M3 speedo is calibrated for the standard 18" wheel setup with 225/45/18 and 255/40/18. Mine was quite accurate when it had 18" winter tyres fitted, but is a long way under with the 19s on.

[estoril]

Trust the GPS not the speedo!

[Bounce]

Trust the GPS not the speedo!+1

[si.w]

Maybe BMW looking out for my licence then... Got surprised by a mobile speed gun on the A13 recently and worried didn't slow down in time but probably not an issue!

[nw99]

GPS always reliable

[Mike R]

It will run about 10% out mate,
My speed limiter comes in at 180mph on the speedo but showing 155mph on GPS

That's a long way out - mine is on the speed limiter at an indicated 168mph and that equates to a GPS 161mph. Standard CSL 19" wheels and correct rolling radius tyres.