Wallace Racing Gear Ratio Calculator

Gear Ratio Formula:

\[ GR = \frac{RPM \times TD}{MPH \times FD \times 336} \]

Engine RPM:

rev/min

Tire Diameter:

inches

Vehicle Speed:

mi/h

Final Drive Ratio:

Gear Ratio (factor):

Unit Converter ▲

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1. What is a Gear Ratio Calculator?

Definition: This calculator determines the optimal gear ratio for drag racing based on engine RPM, tire diameter, vehicle speed, and final drive ratio.

Purpose: It helps racers and performance enthusiasts optimize their vehicle's gear setup for maximum acceleration and performance.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ GR = \frac{RPM \times TD}{MPH \times FD \times 336} \]

Where:

\( GR \) — Gear ratio (dimensionless factor)
\( RPM \) — Engine revolutions per minute
\( TD \) — Tire diameter (inches)
\( MPH \) — Vehicle speed (miles per hour)
\( FD \) — Final drive ratio (dimensionless)
336 — Constant for unit conversion

Explanation: The formula calculates the gear ratio needed to achieve a specific speed at a given RPM with your current tire size and final drive ratio.

3. Importance of Gear Ratio Calculation

Details: Proper gear ratio selection ensures your engine operates in its optimal power band, improves acceleration, and maximizes performance at the track.

4. Using the Calculator

Tips: Enter your engine RPM at the finish line, tire diameter in inches, desired trap speed in MPH, and final drive ratio (default 1.0). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's the 336 constant in the formula?
A: This converts units from inches and miles to revolutions per hour (336 = (5280 ft/mile × 12 in/ft) / (60 min/hour × π)).

Q2: How do I measure tire diameter accurately?
A: Measure from the ground to the top of the tire with the vehicle's weight on it, or use manufacturer specs for unloaded diameter.

Q3: What's a typical final drive ratio?
A: Most vehicles have a final drive between 3.0 and 4.5, but this varies by vehicle type and purpose.

Q4: Should I use peak RPM or shift RPM?
A: Use the RPM you expect to be at when crossing the finish line, typically slightly past peak power.

Q5: How does this help with gear selection?
A: The calculated ratio helps determine if you need to change transmission gears, final drive ratio, or tire size to optimize performance.