Easy Ordering for Custom Products
Since 1979, SCS Gearbox has specialized in interchangeable gearing solutions for truck and tractor pullers.
Utilize SCS Gearbox calculators designed to simplify gear selection, ratio calculations, and performance planning. Our intuitive tools help you find the right components for your specific needs, whether you're optimizing torque, speed, or efficiency.
Select your Lower Gear Set (Bull Gear) to compare available quick-change gearing. The chart updates automatically to show combined transfer case ratios. Use the calculator to determine your transfer case ratio, estimated vehicle speed, and overall driveline ratio.
| Upper Ratio | Teeth | Underdrive | Overdrive |
|---|
Select an available Underdrive or Overdrive cell to update the calculator. Blacked-out cells cannot be selected. The 1.462 Overdrive option is unavailable.
Underdrive: Lower Gear Ratio × Upper Gear Ratio. Overdrive: Lower Gear Ratio ÷ Upper Gear Ratio.
Overall Driveline Ratio: Transmission Ratio × Transfer Case Ratio × Rear Axle / Differential Ratio.
MPH estimates assume direct mechanical gearing without accounting for tire growth, drivetrain slip, or other losses. Confirm gear compatibility with SCS Gearbox before ordering.
Select your lower gear set and quick-change gearing to calculate your transfer case ratio, overall drivetrain ratio, and estimated vehicle speed. You can also select ratios directly from the interactive gear chart.
| Quick Change Ratio | Teeth | Under Drive | Over Drive |
|---|
Select an Under Drive or Over Drive value to apply that quick-change gear set to the calculator. The chart updates automatically when you change the lower gear set.
Transfer Case Ratio: Lower Gear Set Ratio × Quick Change Gear Set Ratio, with each selected Over Drive configuration using the reciprocal of its listed ratio. Overall Drivetrain Ratio: Transfer Case Ratio × Rear End Ratio × Transmission Ratio. Estimated MPH: Engine RPM × Tire Diameter ÷ (Overall Drivetrain Ratio × 336). MPH estimates do not account for tire growth, drivetrain slip, or other mechanical losses. Verify gear compatibility and calculation conventions with SCS Gearbox before ordering.
Calculate overall drivetrain gear ratios for SCS Gearbox 20, 30, and 40 Series and Twin Countershaft Transmissions. Enter your planetary and rear-end ratios, then select your headset and quick-change gear sets to determine your overall two-wheel-drive gear ratio.
Select a gear ratio in either column to apply it to the calculator. Underdrive and Overdrive are controlled by the configuration selectors.
| Ratio | Teeth | Gear IDs | Underdrive O.A. | Overdrive O.A. |
|---|
O.A. ratios update with the calculator inputs. Select an underdrive or overdrive value to update the selected gear set and its configuration.
2-Wheel Drive Formula: Planetary Ratio × Rear-End Ratio × Effective Headset Ratio × Effective Quick-Change Ratio = Overall Gear Ratio.
For overdrive gearing, the selected ratio is applied as its reciprocal. Gear set tooth counts and ID numbers are based on the supplied SCS Gearbox quick-change spur gear charts. Some gear models may have limited availability. Verify gear compatibility with SCS Gearbox before ordering.
Small adjustments can go a long way, make sure you have your Straight Thru Transfer Case optimized perfectly for what you need to get out of your machine!
New to the Drop Transfer Case systems or trying to figure out a new ratio? The Drop Transfer Case Calculator will be helpful for you!
If you are unsure of the gear system you need for your use case our Twin & Single Countershaft Calculator will help you!
We have a page dedicated solely to all of our Monster Truck Case Prouduct Lineup! Not sure if you see what you need? Be sure to contact our staff here at SCS Gearbox today!
