Speedometer gear

K my speedometer is off and i want to fix it. it says i'm going 80 with big rigs are passing me by.

This is what i know: The car is stock, so i'm assuming the rear diff. is stock. Its a V8 auto transmission, C4. I'm going to put 17s on the car.
 
You won't know that until you get the new tires and wheels. Just saying you're going to put 17's on it doesn't tell us anything. It's the tire's outer diameter that determines what speedo gear you'll need, plus the rearend gear ratio. The C-4 has 7 drive teeth on the output shaft.
 
Sorry for the lack of info, i'm replacing my cable for the second time, and i don't want to pull it out again to replace it when i get my new rims, so i thought it could be just put in now, calculate how much it will be off until i get the rims. So i'm not sure what size rims i'm getting yet.
Thanks for the calculator tho.

What would i input for the axle ratio?

The one i pulled out was white if that helps...
my current tire is 195/70R14
 
Two things you need:

1.) Differential Gear Ratio! If you've got a 3.73 rear gear ratio; the number a teeth on the "driven gear" on the tranny end of the speedometer cable will be more than if you've got a 3.00 rear gear.

2.) Tire outside diameter! A 26" diameter tire will require less teeth than a 24" diameter tire.

Once you have those numbers; you can use THIS calculator.

I stole it all from THIS thread on mercurycougar.net - pretty handy! :nice: