1. What is a Gear Ratio RPM Speed Calculator?

Definition: This calculator estimates vehicle speed based on engine RPM, tire diameter, gear ratio, and axle ratio.

Purpose: It helps automotive enthusiasts, mechanics, and engineers determine vehicle speed at specific RPMs for gear selection and performance tuning.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( S \) — Vehicle speed (mph)
• \( RPM \) — Engine revolutions per minute
• \( TD \) — Tire diameter (inches)
• \( GR \) — Transmission gear ratio
• \( AR \) — Axle ratio
• 1056 — Conversion constant (combines unit conversions)

Explanation: The formula calculates how many miles the vehicle travels per hour based on wheel rotations derived from engine RPM and gear reductions.

3. Importance of Speed Calculation

Details: Accurate speed calculations help in gear selection, performance optimization, fuel efficiency tuning, and verifying speedometer accuracy.

4. Using the Calculator

Tips: Enter engine RPM, tire diameter in inches, current gear ratio, and axle ratio (default 3.73). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure tire diameter accurately?
A: Measure from ground to top of tire under load, or calculate using tire size markings (e.g., 275/60R15 = ~28" diameter).

Q2: What's a typical axle ratio?
A: Common ratios range from 3.08 (highway) to 4.10 (performance), with 3.23-3.73 being common for street vehicles.

Q3: Why does gear ratio affect speed?
A: Higher gear ratios (numerically lower) allow higher speeds at lower RPMs, while lower ratios (numerically higher) provide more torque but lower top speed.

Q4: How accurate is this calculation?
A: It's theoretical - actual speed may vary due to tire slippage, load, and transmission efficiency (typically 95-98% accurate).

Q5: Can I use this for motorcycle or bicycle calculations?
A: Yes, but omit the axle ratio (set to 1) for single-speed applications.