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ZBUM's Speed and RPM Calculator This page will calculate the actual speed or RPM given the other Change any one of the "Initial Information" (bolded) parameters to see the affects. Initial Information Section width (millimeters): 185 195 205 215 225 235 245 255 265 275 285 295 305   Tire aspect ratio: 20 25 30 35 40 45 50 55 60 65 70 75   Wheel diameter (inches): 14 15 16 17 18 19 Tire height (inches):   RPM: MPH: Tire rollout (inches):   differential gear: 3.36 3.54 3.70 3.90 4.08 4.45   Speed RPM transmission: FS5W71C - NA FS5R90A - 84-86T FS5R30A - 87T FS5R30A - 88-89T 4N71B - Automatic First gear transmission gear ratio: 1st Second gear transmission gear ratio: 2nd Third gear transmission gear ratio: 3rd Fourth gear transmission gear ratio: 4th Fifth gear transmission gear ratio: 5th Reverse gear transmission gear ratio: Rev Calculations used: Tire Width (mm) x Aspect Ratio Tire Height (inches) = Wheel Diameter (inches) + 2 x ------------------------------ 2540 Rollout (inches) = Tire Height x PI Engine RPM x Rollout Speed (MPH) = ----------------------------------------- 1056 x Diff Gear Ratio x Trans Gear Ratio 1056 x Speed (MPH) x Diff Gear Ratio x Trans Gear Ratio Engine RPM = ------------------------------------------------------- Rollout