1. What is a Tire Size and Speed Calculator?

Definition: This calculator determines how changing your tire size affects your actual vehicle speed compared to what your speedometer shows.

Purpose: It helps vehicle owners and mechanics understand speedometer inaccuracies after tire size modifications.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( S_{new} \) — Actual speed with new tires (mph)
• \( S_{old} \) — Speedometer reading (mph)
• \( TD_{new} \) — New tire diameter (inches)
• \( TD_{old} \) — Original tire diameter (inches)

Explanation: The formula calculates the proportional speed change based on the ratio of new tire diameter to old tire diameter.

3. Importance of Speed Calculation

Details: Larger tires make your speedometer read slower than actual speed, while smaller tires make it read faster. This affects safety, fuel economy, and legal speed compliance.

4. Using the Calculator

Tips: Enter your speedometer reading, original tire diameter, and new tire diameter. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure my tire diameter?
A: Measure from the ground to the top of the tire or calculate using tire size markings (e.g., P225/60R16).

Q2: What if I only know the tire size code?
A: Use our Tire Size to Diameter Calculator to convert tire codes to diameter measurements.

Q3: How much difference is significant?
A: A 3% or more difference should be addressed with a speedometer recalibration.

Q4: Does this affect odometer readings?
A: Yes, the same ratio applies to distance measurements.

Q5: Where can I get my speedometer recalibrated?
A: Most dealerships and specialty automotive shops offer this service.