I used the stack sensor, calculated rolling radius of tyre and amount of pick ups per 1 rotation as shown in the stack book an used 1 pick up as that is all that's needed,

You can use anything metallic as a pick up, I glued a heavy duty magnet to the front driveshaft

Was within 0.5mph and tested with the fast ford timing gear at brunters during a mag thrash up to 150mph