1. What is a MPH to RPM Calculator for Bikes?

Definition: This calculator estimates the revolutions per minute (RPM) of a bike's crankset based on speed, gear ratio, and tire diameter.

Purpose: It helps cyclists and mechanics understand pedaling cadence at different speeds and gear combinations.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( RPM \) — Revolutions per minute (crank rotations)
• \( S \) — Speed in miles per hour
• \( GR \) — Gear ratio (chainring teeth ÷ cog teeth)
• \( TD \) — Tire diameter in inches
• \( 336 \) — Conversion constant (combining unit conversions)

Explanation: The formula converts speed to wheel rotations, then applies gear ratio to determine crank rotations.

3. Importance of RPM Calculation

Details: Knowing your RPM helps maintain efficient pedaling cadence (typically 80-100 RPM for road cycling) and select appropriate gears.

4. Using the Calculator

Tips: Enter your speed in mph, gear ratio (e.g., 2.5 for 50T chainring and 20T cog), and tire diameter (e.g., 27.5" for many mountain bikes). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Where does the 336 constant come from?
A: It combines conversions for hours to minutes (60) and miles to inches (63360) with π (3.1416) in the calculation: (60 × 63360)/(π × 60 × 60) ≈ 336.

Q2: How do I find my gear ratio?
A: Divide the number of teeth on your chainring by the number of teeth on your rear cog (e.g., 50T front ÷ 20T rear = 2.5 ratio).

Q3: What's a typical tire diameter?
A: Common sizes are 26" (MTB), 27.5" (650B), 29" (700C MTB), or 27" (road bike). Check your tire sidewall for exact size.

Q4: Why is RPM important for cycling?
A: Maintaining optimal RPM improves efficiency, reduces fatigue, and prevents knee strain. Most cyclists target 80-100 RPM.

Q5: Does this work for fixed-gear bikes?
A: Yes, but on fixed-gear bikes your pedaling RPM is directly tied to wheel speed - you can't coast.