In a few minutes I'll post the part numbers for the speedometer gears, but first, Here's THE precise formula to getting it right:tire revolutions per mile, times number of teeth on speedometer driven gear, times axle ratio, divided by 1000. This will give you the number of teeth you need on your driven gear. Always round down to avoid a speeding ticket. For example. 18 tooth drive gear, 25.7" tires such as 245/50R16s, and 3.08:1 axle. 784.75 x 18 x 3.076923 = 43.463. Need 43 tooth. Try again with 17 tooth gives 41.05. That's 1 mph more accurate on the interstate, but more trouble to change the drive gear.