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Tools / Automotive / Tire Size Calculator
🚗 Automotive Calculator

Tire Size Calculator

Never guess if your new tires fit. Calculate exact dimensions.

Overall Diameter:

Revs per km:

/ 25

How to Use This Tool

  1. Enter tire section width in mm.
  2. Enter aspect ratio percentage.
  3. Enter rim diameter in inches.
  4. Get overall diameter and circumference.

The Formula

Diameter = 2 × (Width × Aspect Ratio / 100) + (Rim × 25.4mm).

Why It Matters

Your car came with 225/45R18 tires (25.5-inch diameter). Considering 235/40R19 (25.8 inches) — a 1.2% increase. Your speedometer will read slightly slow. This small change also affects your ABS calibration.
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