1. What is a Tire Size Up Calculator?

Definition: This calculator determines your actual speed when changing tire sizes, as larger tires rotate fewer times per mile than smaller tires.

Purpose: It helps vehicle owners understand how tire size changes affect speedometer accuracy and vehicle performance.

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)
• \( TD_{new} \) — Diameter of new tires (inches)
• \( TD_{old} \) — Diameter of original tires (inches)

Explanation: The formula calculates the proportional speed difference based on the relative sizes of the old and new tires.

3. Importance of Tire Size Calculations

Details: Proper tire size calculations ensure accurate speedometer readings, correct gear ratios, and maintain vehicle safety systems functionality.

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: Why does tire size affect speed?
A: Larger tires cover more ground per rotation, causing the vehicle to move faster than the speedometer indicates.

Q2: How do I measure tire diameter?
A: Measure from the ground to the top of the tire or use the tire size code (e.g., 265/75R16 has ~31.6" diameter).

Q3: What if I change both width and aspect ratio?
A: The calculator still works as long as you know the overall diameters of both old and new tires.

Q4: Does this affect odometer readings?
A: Yes, larger tires will cause your odometer to underreport actual mileage.

Q5: How much difference is significant?
A: A 3% or greater difference may require speedometer recalibration for accuracy.