1. What is a Speed Calculator for Gear Ratio and Tire Size?

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 with given drivetrain components.

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 for units

Explanation: The formula calculates how much distance the vehicle covers per minute based on tire circumference and drivetrain ratios, then converts to miles per hour.

3. Importance of Speed Calculation

Details: Accurate speed calculations help in gear selection, performance tuning, and ensuring speedometer accuracy after drivetrain or tire modifications.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

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

Q2: Where do I find my gear ratios?
A: Check vehicle manual, manufacturer specs, or online databases for your transmission model.

Q3: Why is axle ratio important?
A: The axle ratio is the final gear reduction that affects how many times the driveshaft turns per wheel revolution.

Q4: Does this account for tire slippage?
A: No, this calculates theoretical speed. Actual speed may vary due to traction conditions, tire wear, and other factors.

Q5: What's the 1056 constant?
A: It converts inches per minute to miles per hour (12 in/ft × 5280 ft/mile ÷ 60 min/hour = 1056).