I am curious about this as well. I just installed new gears andused speedo from another car. My odometer logs 108 miles for every 100 i drive. Today I went by one of those moble radar machines, sppedo was dead on 25 radar said 23.

I had a lengthly drive on same parkway. I calculated at the end that I need to subtract 8.35% to calcualte mpg. After looking at the radar, if I subtract 8.35% from 25mph indicated I would be 23mph

So what drives them both that could be off? is there something in the speedo that is particular to each model?

I have always wondered why the little shift point indicators were so far off from what my tranny shifts at, maybe i got a gas speedo I do not know

Stock tire sizes. I am big 4x4 guy so I know how tires effect, smaller tires would do it, but i run avery slightly bigger tire.

I do not know what the cluster is out of. I know i put 12 12-48 48-15 gear set in it

I been wanting wheels and tires, I guess i could go bigger to offset everything.