Superformance Speedo Issues

[Bannon]

Hydramada,

Talked to Dennis a week or so ago(bought my first car from Bob and Dennis back in 2003 and trust Olthoff Racing above all others) He said that the car may have either a 21 or a 19 tooth gear from the factory. I pulled it today and it had a 21. I am guessing the original dealership maybe went the wrong way when they changed the tires and put in the new gear. According to other threads, a 19 is correct for the 265/60/15 tires.
From what I read today there is a formula that you can use to find the right gear based on your current gear: New Teeth = (Current Teeth x Speedo Reading)/Actual Speed)
Strangely from using this formula. I need a 15th tooth gear and the smallest one ford makes is a 16 tooth. I ordered one today so we will see how it goes. I also found a great Ford Speedo gear part number/color reference. The parts folks at the local dealer were able to find these from the part numbers I gave them.
Manual Transmissions:

16-teeth-wine (C0DZ-A)

17-teeth-white (C3DZ-C)

18-teeth-yellow (C0DD-B)

19-teeth-pink (C0DZ-B)

20-teeth-black (C1DZ-A)

21-teeth-red (C4OZ-A)

Auto Transmissions:

16-teeth-blue (D0AZ-A)

17-teeth-green (C7SZ-A)

18-teeth-gray (C7SZ-B)

19-teeth-tan (C7VY-A)

20-teeth-orange (C8SZ-B)

21-teeth-purple (D0OZ-B)