Tire Size Calculator

Tire Size – Quick Cheat Sheet

Inputs: Section width in mm, aspect ratio in %, rim in inches.
Sidewall height (mm) = width_mm × (aspect% / 100) → inches ÷ 25.4.
Overall diameter (in) = 2 × sidewall_in + rim_in.
Circumference (in) = π × diameter_in.
Revs per mile ≈ 63360 ÷ circumference_in (since 1 mile = 63360 in).
Speedometer: Actual speed = Indicated × new_diameter ÷ stock_diameter.
Clearance change ≈ half the diameter difference (ride height).

Notes & limits

Results are geometric; real-world loaded radius can vary with brand, load, and pressure.
Keep overall diameter within manufacturer tolerances; large changes may affect ABS, gearing, and fitment.
Aspect ratio and width must be realistic (bounds enforced here to avoid obvious entry errors).

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