How to read a tyre size?
In 225/45 R17, 225 is the width in millimetres, 45 the sidewall height as a percentage of the width, R means radial construction and 17 is the rim diameter in inches. The original tyre sizes for each vehicle are shown on its vehicle page (search by make).
Frequently asked questions
How do I calculate a tyre's diameter?
For a 225/45 R17 tyre: sidewall height = 225 × 45% = 101.25 mm; rim diameter = 17 × 25.4 = 431.8 mm; overall diameter = 431.8 + 2 × 101.25 = 634.3 mm.
What diameter difference is allowed between two tyre sizes?
Common practice is to stay within 3% of the original size, and to prefer a size approved for the vehicle (registration document, certificate of conformity). Beyond that, the speedometer, ABS and ESP may be affected.
Does the speedometer change with larger tyres?
Yes: with a larger-diameter tyre, the wheel covers more distance per revolution. When the speedometer shows 100 km/h, your actual speed is slightly higher.