Transmission Calculator
Calculate vehicle speed from transmission and differential gear ratios, engine RPM, and tire size
Calculate Vehicle Speed
Engine revolutions per minute (typical range: 1000-7000 RPM)
Overall tire diameter (typical passenger car: 24-28 inches)
Gear ratio for selected transmission gear (e.g., 1st: 3.5, 2nd: 2.1, 3rd: 1.4, 4th: 1.0, 5th: 0.8)
Ring and pinion gear ratio (typical range: 2.5-4.5:1)
Vehicle Speed Results
Formula: Speed = (RPM × Diameter × π × 60) / (Trans Ratio × Diff Ratio × 1,000,000)
Calculation: (0 × 0.0 × π × 60) / (0 × 0 × 1,000,000)
Tire circumference: 0.00 meters
Typical Gear Ratios
Example Calculation
Sports Car Example
Engine RPM: 6000
Tire Diameter: 26 inches
Transmission (5th gear): 0.8:1
Differential: 3.7:1
Calculation
Tire diameter: 26 × 25.4 = 660.4 mm
Speed = (6000 × 660.4 × π × 60) / (0.8 × 3.7 × 1,000,000)
Speed = 743,665,177 / 2,960,000
Speed = 251.2 km/h (156.1 mph)
Transmission Components
Engine
Generates rotational power measured in RPM
Transmission
Changes gear ratios to optimize power and speed
Differential
Final gear reduction and power distribution
Wheels
Convert rotational motion to vehicle movement
Gear Ratio Tips
Lower gear ratios provide more torque for acceleration
Higher gear ratios allow for higher top speeds
Smaller tires increase acceleration but reduce top speed
Total gear reduction = transmission ratio × differential ratio
Understanding Transmission Gear Ratios
What are Gear Ratios?
Gear ratios determine how engine power is transmitted to the wheels. They represent the relationship between the number of teeth on driving and driven gears, affecting both torque multiplication and speed reduction or increase.
Transmission Gear Ratio
The transmission gear ratio is the ratio between the input shaft (from engine) and output shaft (to differential) rotational speeds. Each gear provides a different ratio to optimize performance for different driving conditions.
Differential Gear Ratio
Also called the ring and pinion ratio, this is the final gear reduction between the transmission output and the wheels. It provides the final torque multiplication and speed reduction.
Speed Calculation Formula
Speed = (RPM × Diameter × π × 60) / (Trans × Diff × 1,000,000)
- RPM: Engine revolutions per minute
- Diameter: Tire diameter in millimeters
- π: Pi (3.14159...)
- 60: Converts to kilometers per hour
- Trans: Transmission gear ratio
- Diff: Differential gear ratio
- 1,000,000: Unit conversion factor
Note: This formula assumes no slippage and ideal conditions. Real-world speeds may vary due to tire pressure, load, and road conditions.
Low Gear Ratios (High Numbers)
- • More torque multiplication
- • Better acceleration
- • Lower top speed
- • Hill climbing ability
- • Higher fuel consumption at speed
High Gear Ratios (Low Numbers)
- • Less torque multiplication
- • Slower acceleration
- • Higher top speed
- • Better fuel economy
- • Overdrive capabilities
Tire Size Effects
- • Larger tires = higher top speed
- • Smaller tires = better acceleration
- • Affects speedometer accuracy
- • Changes effective gear ratios
- • Impacts fuel economy