I had the ring and pinion replaced from stockers to 3:73. I am trying to figure out how to get the speedometer to read the coorect speed. The retards @ the ford dealer apparently can't figure it out. Question is, on a 99 Cobra (with IRS) how is the speed reading picked up? Is it via a "small gear" or magnetic? Any help would be appreciated.

 

you will need a chip to correct this

 

or a speedcal