1. What is a Top Speed Calculator from Gear Ratio?

Definition: This calculator estimates a vehicle's top speed based on engine RPM, tire diameter, gear ratio, and axle ratio.

Purpose: It helps automotive enthusiasts and mechanics determine theoretical top speed for gear ratio selection and performance tuning.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( TS \) — Top speed (mph)
• \( MaxRPM \) — Maximum engine RPM
• \( TD \) — Tire diameter (inches)
• \( GR \) — Gear ratio (unitless)
• \( AR \) — Axle ratio (unitless)
• 1056 — Conversion constant (combining unit conversions)

Explanation: The formula calculates how fast the tires rotate at maximum RPM given the gear reduction through transmission and differential.

3. Importance of Top Speed Calculation

Details: Proper gear ratio selection ensures optimal performance, fuel efficiency, and prevents engine over-revving at desired speeds.

4. Using the Calculator

Tips: Enter your engine's maximum RPM, actual tire diameter (not wheel size), gear ratio in the selected gear, and final drive (axle) ratio.

5. Frequently Asked Questions (FAQ)

Q1: Why isn't my actual top speed matching this calculation?
A: Real-world factors like aerodynamics, weight, traction, and power limitations affect actual top speed.

Q2: How do I find my tire diameter?
A: Measure from ground to top of tire or use tire size calculators (e.g., 275/60R15 ≈ 28" diameter).

Q3: What's a typical axle ratio?
A: Common ratios range from 2.73 (highway) to 4.10 (performance), with trucks often 3.55-3.73.

Q4: Should I use redline RPM or peak power RPM?
A: For maximum speed calculation, use redline RPM. For optimal performance, use peak power RPM.

Q5: How does changing tire size affect speed?
A: Larger tires increase theoretical top speed but may reduce acceleration; smaller tires do the opposite.