[scoooby slayer]

put a gps in my r32 gtr and sat at 90 kph and gps showed 56 mph which is spot on.

on 18 inch rims 265/35 tyres.

ive read on here they massivly overread though ?

 

[mattysupra]

someone may have calibrated it. I have with mine and it reads spot on

 

[furrywoolyhatuk]

Iv heard the same, but the gps doesnt lie. Need to check mine too....

 

[G40tee]

speed will be more inaccurate the faster you go.

mine has never been too bad though, only seems to outread by about 10mph right round the end of the clocks.

wouldnt mind recalibrating soon though

 

[ru']

Most speedos are generally 5% to 10% out (over-reading). Seems you've got an odd accurate one!

 

[Cris]

Bigger wheels increase the rolling circumference. Generally when I've put bigger wheels on cars the speedo's become more accurate.

My previous Datsun was 1mph out at 70mph.