KHoffman

This is for the truck in my sig. I ran the tire size and gear ratio though a gear ratio calculator because I thought my speedo was off. Acording to that I should be around 2000 at 65mph. But my tach is reading more like 2250 @ 65. Next I checked my speedo with gps and it appears to be reading correctly. So my question is it possible my tach is that far off?

Lil Dog

The tach isn't that close, but I would be surprised at 250 Rpm out. I set my idle using a phototach and the needle didn't move on the dash as I moved the idle up 100 Rpm.