I have a Tremec 600 and a 3:31 rear. When I got the car it had a 17 tooth driven speedo gear and the speedo consistently read about 6mph lower than actual speed. So I thought I needed to go with less teeth to make it read faster and installed a 16 tooth driven speedo gear and it was slow by more like 10mph. So I thought I had gone the wrong direction and installed a 19 tooth gear and it seems to still be slow by about 10mph. I am using a GPS for actual speed and it might not be perfect, but it does seem to be fairly consistently 10mph slow. How is the above even possible?
Is there something else going on here that I don't understand?
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