Yugo L4-1300cc 1.3L (1991)
Old Drive Gear divided by the New Drive Gear = Ratio
7 teeth divided by 8 teeth = 0.875
Old Driven Gear divided by Ratio = New Driven Gear
21 teeth divided by 0.875 = 24 teeth
A 24 tooth driven gear will correct the speedometer error.
Let's do one more speedometer change. This time the old drive is 9, and the new drive is 10. The old driven gear is still 21.
Old Drive Gear divided by New Drive Gear = Ratio
9 tooth divided by 10 tooth = 0.9
Old Driven Gear divided by Ratio = New Driven Gear
21 tooth divided by 0.9 = 23.33 teeth
We can't get a 23.3 tooth count so we round it off to 23 teeth. Now the speedometer will be close, but not exact, because we had to round off the number.
