1. What is an RPM Speed Gear Ratio Calculator?

Definition: This calculator estimates vehicle speed based on engine RPM, gear ratio, and a constant that accounts for tire size and other factors.

Purpose: It helps automotive enthusiasts and mechanics determine vehicle speed at specific RPM points for gear ratio selection and performance tuning.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( S \) — Speed (mph)
• \( RPM \) — Engine revolutions per minute
• \( GR \) — Gear ratio (unitless)
• \( C \) — Constant (accounts for tire diameter and other factors)

Explanation: The engine RPM is divided by the gear ratio to get output shaft speed, then multiplied by a constant that converts to vehicle speed.

3. Importance of RPM/Speed Calculation

Details: Proper speed calculation helps optimize gear ratios for performance, fuel economy, and proper engine operation within its power band.

4. Using the Calculator

Tips: Enter the engine RPM, gear ratio (default 3.73), and constant (default 0.00595 for typical passenger vehicles). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What affects the constant value?
A: The constant is primarily affected by tire diameter - larger tires increase the constant while smaller tires decrease it.

Q2: What's a typical gear ratio?
A: Common final drive ratios range from 2.73 (highway economy) to 4.10 (performance/towing).

Q3: How do I find the correct constant for my vehicle?
A: Calculate it by (Tire Diameter in inches × π) / (1056 × Axle Ratio × Transmission Ratio).

Q4: Does this account for torque converter slip in automatics?
A: No, automatic transmissions may show slightly lower actual speeds due to converter slip, especially at higher RPM.

Q5: Can I use this for motorcycles?
A: Yes, but you'll need to adjust the constant based on the motorcycle's final drive ratio and wheel size.