1. What is a Tire Size Calculator?

Definition: This calculator estimates vehicle speed based on tire revolutions per minute (RPM) and tire diameter.

Purpose: It helps automotive enthusiasts and professionals understand how tire size affects speed calculations.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( S \) — Speed (miles per hour)
• \( RPM \) — Revolutions per minute
• \( \pi \) — Pi (approximately 3.1416)
• \( TD \) — Tire diameter (inches)
• 1056 — Conversion factor (12 inches/foot × 5280 feet/mile ÷ 60 minutes/hour)

Explanation: The formula converts tire rotations into linear distance traveled per minute, then converts to miles per hour.

3. Importance of Tire Size Calculations

Details: Proper tire size calculations ensure accurate speedometer readings, proper gearing, and optimal vehicle performance.

4. Using the Calculator

Tips: Enter the RPM (from your tachometer or engine specs) and tire diameter (measured or from manufacturer specs). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure tire diameter?
A: Measure from the ground to the top of the tire (loaded) or use the formula: (wheel diameter) + (tire width × aspect ratio × 2 ÷ 25.4).

Q2: Why does tire size affect speed?
A: Larger tires cover more distance per revolution, while smaller tires cover less, affecting the speed at any given RPM.

Q3: What's a typical RPM range?
A: Most vehicles cruise at 1500-3000 RPM, but this varies by vehicle and driving conditions.

Q4: How accurate is this calculator?
A: It provides theoretical speed. Actual speed may vary due to tire slippage, inflation, and other factors.

Q5: Can I use this for gear ratio calculations?
A: Yes, this is fundamental to gear ratio and final drive calculations.