1. What is a Tire Size Speed Calculator?

Definition: This calculator estimates vehicle speed based on engine RPM and tire diameter.

Purpose: It helps automotive professionals and enthusiasts determine speed when changing tire sizes or gear ratios.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( S \) — Speed (miles per hour)
• \( RPM \) — Engine revolutions per minute
• \( \pi \) — Pi (approximately 3.1416)
• \( TD \) — Tire diameter (inches)
• 1056 — Conversion factor (combines unit conversions)

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

3. Importance of Speed Calculation

Details: Accurate speed calculation is crucial for proper gear ratio selection, speedometer calibration, and performance tuning.

4. Using the Calculator

Tips: Enter the engine RPM and tire diameter in inches. Both values must be > 0. The result shows the theoretical speed at that RPM.

5. Frequently Asked Questions (FAQ)

Q1: What affects the accuracy of this calculation?
A: Transmission gear ratio, torque converter slip, and tire growth at high speeds can affect actual speed.

Q2: How do I measure tire diameter?
A: Measure from ground to top of tire under load, or calculate from tire size markings (e.g., 275/60R15).

Q3: Why is the conversion factor 1056?
A: It combines conversions from inches to miles (63360) and minutes to hours (60): 63360/60 = 1056.

Q4: Does this work for any vehicle?
A: Yes, but you must know the RPM at the wheels (account for transmission and differential ratios if measuring engine RPM).

Q5: How does changing tire size affect speed?
A: Larger tires increase speed at same RPM, smaller tires decrease speed. This calculator helps quantify that change.