Use our free Tire Gear Ratio Calculator to determine the optimal final drive gear ratio for your vehicle. Whether you’re upgrading tire size, towing heavy loads, or tuning your off-road rig, getting the right gear ratio ensures optimal power, torque, and fuel efficiency.
Tire Gear Ratio Calculator
What Is Gear Ratio?
The gear ratio is the ratio between the number of teeth on two meshing gears. In vehicles, it’s most commonly discussed as the final drive gear ratio, which determines how many times the driveshaft rotates for every turn of the wheels.
For example, a 4.10 gear ratio means the driveshaft turns 4.1 times for each full wheel rotation.
Why Gear Ratio Matters
Your gear ratio directly impacts:
- Engine RPM at cruising speeds
- Torque output to the wheels
- Fuel economy
- Acceleration vs. top speed balance
If you increase your tire diameter without changing the gear ratio, you may lose torque and reduce acceleration. That’s why recalculating your gear ratio when switching tires is critical.
Gear Ratio Formula
We use the following formula:
Ratio = (Tire Diameter × RPM × 336) ÷ Vehicle Speed (MPH)
Where:
- RPM = Engine RPM at cruising speed
- 336 = Constant that accounts for time and distance units
- Tire Diameter = In inches
- Speed = In miles per hour
How to Use the Calculator
- Enter your tire diameter in inches
- Enter your target cruising RPM (e.g., 2,500)
- Enter your vehicle speed in MPH (e.g., 65)
You’ll get the optimal gear ratio to maintain that RPM at that speed with your current tires.
Real-World Example
If your tire diameter is 33″, cruising RPM is 2500, and speed is 65 MPH:
Ratio = (33 × 2500 × 336) ÷ 65 = 427384.62 ÷ 65 ≈ 6.57
This means a 6.57 gear ratio would keep you at ~2500 RPM while cruising at 65 MPH.
FAQs
Q. What is a good gear ratio for highway driving?
For better fuel economy, a lower gear ratio (like 3.55 or 3.73) is preferred. It keeps RPMs low at cruising speeds.
Q. What’s the best gear ratio for off-roading?
Off-road vehicles often use higher gear ratios like 4.88 or 5.13 for better torque at lower speeds.
Q. Will bigger tires affect my gear ratio?
Yes. Larger tires reduce engine RPM at a given speed, which can strain your drivetrain if not re-geared accordingly.
Check tire chain size of your winter tire for aggressive winter terreain drive.