does anyone know what would cause a speedometer to be off by 12mph? I have larger tires (195 pro comps)

I forgot to plug in my radar detector this morning, an started to head to work.
I had my cruise set on 70mph exactly (thats the speed limit on the highway were i live) an i got pulled over for doing 82mph. I got a warning. What does ford charge to have it adjusted and would would cause it to change?

 

on the tail housing you should have a speedometer gear, pull the one you have and count the teeth. maybe someone else will come along and give u an idea as to which one u need after that?

 

Well, the speedo is reading about 15% too low, so you need a speedo gear that is about 15% smaller than what you have now, or as close as you can get to that.

Now, I have no idea what speedo gear you have in there now, but for example, let's say you have a 32-tooth gear now. 32-(32x0.15) =27.2, so get a 27-tooth speedo gear. If you have a 39-tooth gear, 39-(39x0.15)=33.15, so get a 33-tooth gear. And so on and so on...

Hope that helps....

 

Umm, I think you just answered your own question right there...

You need a speedo gear with fewer teeth on it. That'll correct your speedometer.

-Joe