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.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.