1. What is an RPM To Tire Size Calculator?

Definition: This calculator determines the effective tire diameter based on vehicle speed and engine RPM.

Purpose: It helps automotive enthusiasts and mechanics understand tire sizing requirements for proper gearing and speedometer calibration.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( TD \) — Tire diameter (inches)
• \( S \) — Vehicle speed (miles per hour)
• \( RPM \) — Engine revolutions per minute
• 1056 — Conversion factor (5280 feet/mile × 12 inches/foot ÷ 60 minutes/hour)

Explanation: The formula calculates how far the vehicle travels per engine revolution to determine effective tire diameter.

3. Importance of Tire Size Calculation

Details: Proper tire sizing ensures accurate speedometer readings, optimal gear ratios, and proper vehicle performance.

4. Using the Calculator

Tips: Enter the vehicle speed in MPH and engine RPM. For accurate results, measure RPM at steady speed in direct drive (no torque converter slip).

5. Frequently Asked Questions (FAQ)

Q1: Why is 1056 used in the formula?
A: It combines unit conversions: 5280 feet/mile × 12 inches/foot ÷ 60 minutes/hour = 1056.

Q2: Does this account for tire squish or slip?
A: No, this calculates theoretical diameter. Actual rolling diameter may be slightly less due to weight deformation.

Q3: How does transmission gear ratio affect this?
A: The formula assumes 1:1 final drive ratio. For other ratios, use transmission output shaft RPM instead of engine RPM.

Q4: Can I use this for metric units?
A: No, this version uses MPH and inches. A metric version would use km/h and meters with different constants.

Q5: What's the typical range for tire diameters?
A: Passenger cars: 24-28 inches, trucks/SUVs: 28-35 inches, commercial trucks: 35-42+ inches.