I used the formula to come up with this:
1990, f-150 E4OD 2wd with 300-6
drive gear: 8tooth?? what i was told
axle ratio: 3.73

Current tires: 235/75-R15 Uses a 21 tooth gear
New tires: 32.0x11.5-R15 Calculated to use 19 tooth gear

What I want to know is the part numbers and color codes especially for these gears, and maybe entire list of all the speedometer gears for my truck.

Thanks for all the help

 

I got that information from the parts guys at a Ford dealership once. Been a while though, and this was a pretty good old time dealership with people who actually knew what they were doing. But I still think it's probably the best place to look.

 

The 21T gear is D0OZ-B, it's purple.

The complete list is in the Ford Racing catalogue

 

Here's what you asked for.

speedo gear calc.

I take it, you put the 3.73 gears in there.

 

Yes I put the 3.73 gears in it as well as a limited slip. Factory gearing was 3.08 open.

 

Or you could wait for someone here to tell you. Dealership schmealership.