Car Gear Ratio Speed Calculator
Car Gear Ratio Speed is evaluated from Engine RPM, Transmission Gear Ratio and Axle / Final Drive Ratio. The calculation reports Vehicle Speed, Overall Final Drive and Engine RPM at 60 MPH.
Results
About the Car Gear Ratio Speed Calculator
The calculator uses a multi formula configuration. Each reported value is read as a direct evaluation of the stored rules with the declared field formats and units.
Formula basis:
Speed (mph) = RPM x (pi x tire_diameter_in) / (gear_ratio x axle_ratio x 63,360 / 60)
RPM at speed = Speed x gear_ratio x axle_ratio x 63,360 / (tire_diameter_in x pi x 60)
1 mile = 5,280 ft = 63,360 inches
Interpret the outputs in the order shown by the result fields. Optional inputs affect only the outputs that depend on those variables.
Formula & How It Works
The calculation applies the following relations exactly as recorded in the metadata: Speed (mph) = RPM x (pi x tire_diameter_in) / (gear_ratio x axle_ratio x 63,360 / 60) RPM at speed = Speed x gear_ratio x axle_ratio x 63,360 / (tire_diameter_in x pi x 60) 1 mile = 5,280 ft = 63,360 inches Each output field is produced by substituting the supplied inputs into the relevant relation and then applying the declared rounding or text format.
Worked Examples
Example 1: Ford Mustang GT (2024): 6th gear 0.63, axle 3.55, tire 27.5", at 3,000 RPM
Inputs
With Engine RPM = 3,000, Transmission Gear Ratio = 0.63, Axle / Final Drive Ratio = 3.55 and Tire Diameter = 27.5 as the stated inputs, the result is Vehicle Speed = 109.7 mph, Overall Final Drive = 2.24:1 and Engine RPM at 60 MPH = 1,640 RPM. Each value corresponds to the declared output fields.
Example 2: Ram 1500 pickup: 8th gear 0.667, axle 3.21, tire 32", at 1,800 RPM cruising
Inputs
With Engine RPM = 1,800, Transmission Gear Ratio = 0.667, Axle / Final Drive Ratio = 3.21 and Tire Diameter = 32 as the stated inputs, the result is Vehicle Speed = 80 mph, Overall Final Drive = 2.14:1 and Engine RPM at 60 MPH = 1,349 RPM. Each value corresponds to the declared output fields.
Example 3: Jeep Wrangler Rubicon off-road in 4-Lo 1st gear: 4.71 trans × 4.10 axle × 4.0 transfer case, 35" tires, 1,500 RPM
Inputs
With Engine RPM = 1,500, Transmission Gear Ratio = 4.71, Axle / Final Drive Ratio = 4.1 and Tire Diameter = 35 as the stated inputs, the result is Vehicle Speed = 8.1 mph, Overall Final Drive = 19.31:1 and Engine RPM at 60 MPH = 11,128 RPM. Each value corresponds to the declared output fields.
Example 4: Honda Civic Type R 2024: 6th gear 0.666, axle 4.47, tire 25.7", at 4,000 RPM
Inputs
With Engine RPM = 4,000, Transmission Gear Ratio = 0.666, Axle / Final Drive Ratio = 4.47 and Tire Diameter = 25.7 as the stated inputs, the result is Vehicle Speed = 102.7 mph, Overall Final Drive = 2.98:1 and Engine RPM at 60 MPH = 2,336 RPM. Each value corresponds to the declared output fields.
Common Use Cases
- Calculate vehicle speed at a given RPM and gear
- Find optimal gear ratio for highway fuel economy
- Determine how axle ratio change affects speed and RPM