digi dash speedo reading wrong...

[broody]

i know there are two types, i got one that says AX or AK on it, and when i flick the switch on top of dash it reads half the speed one settings, and only about 8MPH over on the other setting, could the setting which is reading over 8mph be because of my 17's?
Or do u need the other tpe of transducor?

[Big Box]

r u sure thats not the switch to change it between mph and km/h??