[fakesnake]

What is the calculation used to determine which speedo teeth gear to use? I thought I recalled it having to do with rear gears and tire size. Rear end is stock but am running 18" tires in front and 20" in back.

 

[MauriSSio]

What is the calculation used to determine which speedo teeth gear to use? I thought I recalled it having to do with rear gears and tire size. Rear end is stock but am running 18" tires in front and 20" in back.

20" tires?! that's tiny. stock tires are maybe 26". if you're running 20" tire I'm guessing you'll need a speedo gear with roughly 20% more teeth. so count your gear teeth and multiply by 1.2 and order that.

if you have 20" wheels but overall have taller tires (diameter) you'll need a gear with a smaller tooth count doing the same basic math.....find out your tire height or post your new tire size and old tire size and we can go from there.

 

[fakesnake]

DOH! Yes, sorry 18" and 20" wheels. The problem is I haven't had the original tire/wheels for 3+ years so I don't know what stock height is.

 

[puttster]

Saw a few days ago here someone posted one tooth per 5 mph. Forgot which way, though!!

 

[Scott66GTA]

it was me who posted that, It is 1 tooth/5mph. Less teeth on the driven gear will make your speedo read more, and vice-versa...

on the Drive gear on the output shaft, the opposite holds true..

 

[fakesnake]

I am thinking that if my new tire combo was taller then I would need smaller teeth to spin faster to match old set up.

 

[KULTULZ]

Ford Ranger/BroncoII speedometer gear change/calibration