With the aid of a GPS, I managed to detect my 2005 RAM has a +15% speedometer error due to the bigger tires (37" Goodrich). Those 5" extra diameter against the 32" stock make that speed difference. I assume speedo takes a signal from some shaft inside the transmission
and has a conversion factor set for standard 32" wheels.
Do you have an idea about what could I do to correct this? I know some Jeep user change a teethed-cog that directly couples the speedo cable, I don't know if there's an equivalent in our machines
Any advice welcome...