How It Works

When you enter a metric tire size like 225/65R17, we break it into three parts:

• Width (225) — the tire section width in millimeters.
• Aspect ratio (65) — the sidewall height as a percentage of the width.
• Rim diameter (17) — the wheel diameter in inches.

From these we derive:

• Sidewall height — width × (aspect ratio ÷ 100). We show both millimeters and inches.
• Overall diameter — rim diameter plus two sidewalls (top and bottom).
• Circumference — π × overall diameter, used to estimate revolutions per mile.
• Revs per mile — how many times the tire rotates in one mile, useful for gearing and speedometer reference.

A widely used rule of thumb is that a replacement tire's overall diameter should stay within roughly ±3% of the original tire's diameter.

Staying within this range helps keep speedometer readings reasonably accurate and minimizes impact on handling and transmission shift points.

Larger differences may cause noticeable speedometer drift, altered gearing feel, or clearance issues. This is a general reference only — it is not a legal or vehicle-specific certification. Always consult your vehicle manual or a qualified tire shop.

When comparing two tire sizes, TireFlows treats Tire 1 as the calibration baseline — the tire your speedometer was originally set up for.

The speedometer table shows: if your dashboard reads a certain speed (based on Tire 1), what the approximate actual speed would be if you switched to Tire 2.

A positive difference means you are traveling slightly faster than the speedometer indicates; a negative difference means slightly slower.

TireFlows provides mathematical estimates only. It does not guarantee fitment, load capacity, or suitability for your specific vehicle.

It is not a substitute for professional advice, your vehicle owner's manual, or a qualified tire dealer. Always verify clearance, load ratings, and local regulations before changing tire sizes.

The "Alternate Tire Sizes" section on a single-tire result page shows sizes that are math-only matches: same rim diameter and within the 3% diameter range.

Tapping an alternate size takes you to a comparison page so you can see exactly how it differs from your current size — diameter difference, speedometer impact, and visual overlay.

These alternates are not recommendations. They are simply the closest mathematical matches for reference.

Results are geometric estimates from the size marking, not measured from a physical tire.