Speedo correcting healp

[Sixes350]

I have just installed a 3.91 diff into my M6 (was 3.46)

Speedo was correct before the upgrade. I then changed the settings using the "Speedo correction" button and I cant get my dial to sit anywhere near what I am doing. At last calculation the speedo displayed 173km/h when I was doing 100km/h (GPS speed)

Any help would be much appreciated on what I have done wrong.

Current parameters below (Speedo shows 140km/h when doing 80km/h)

H0101 - 19290
H0102 - 10.0
H0103 - 3.91
H0104 - 1929.0013
H0105 - 6226
H0106 - 79535
H0107 - 0.04

Tyre size is 235/40/18

Would using the Speedo fine tuning function help?

[gmperformancecentre]

try these's

H0101 32793
H0102 17.0000
H0103 3.910
H0104 1929.0013
H0105 6226
H0106 79535
H0107 0.04

[Sixes350]

Thanks for the help. I see what my main problem was, H0102

Cheers again! :)