Car Gearing Calculator For Speed

Speed Formula:

\[ S = \frac{RPM \times \pi \times TD}{GR \times AR \times 1056} \]

Engine RPM:

RPM

Tire Diameter:

inches

Gear Ratio:

Axle Ratio:

Speed (mph):

Unit Converter ▲

Unit Converter ▼

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1. What is a Car Gearing Calculator For Speed?

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

Purpose: It helps automotive enthusiasts and professionals determine speed at specific RPMs for gear selection and performance tuning.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ S = \frac{RPM \times \pi \times TD}{GR \times AR \times 1056} \]

Where:

\( S \) — Speed (mph)
\( RPM \) — Engine revolutions per minute
\( TD \) — Tire diameter (inches)
\( GR \) — Transmission gear ratio (unitless)
\( AR \) — Axle ratio (unitless)
1056 — Conversion factor (combines unit conversions)

Explanation: The formula calculates how far the vehicle travels per minute based on wheel rotation, then converts to miles per hour.

3. Importance of Gearing Calculations

Details: Proper gearing calculations ensure optimal performance, fuel efficiency, and engine operation within its power band.

4. Using the Calculator

Tips: Enter engine RPM, measured tire diameter, current gear ratio, and axle ratio. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure tire diameter?
A: Measure from ground to top of tire (loaded) or calculate using tire size markings: (width*aspect ratio/100)*2/25.4 + wheel diameter.

Q2: Where can I find my gear ratios?
A: Check your vehicle's service manual or manufacturer specifications for transmission and axle ratios.

Q3: Why does the result seem high/low?
A: Verify all inputs, especially tire diameter (use loaded measurement) and that you're using the correct gear ratio for the selected gear.

Q4: Does this account for tire slip or torque converter slip?
A: No, this calculates theoretical speed. Actual speed may be slightly lower due to these factors.

Q5: Can I use this for different gear selections?
A: Yes, change the gear ratio value to compare different transmission gears or axle ratios.