Decode any tyre size marking and calculate outer diameter, circumference, sidewall height, and revolutions per km. Compare two tyre sizes and see the speedometer difference.
205 = tyre width in mm. 55 = aspect ratio (sidewall height as % of width). R = radial construction. 16 = rim diameter in inches. Sidewall height = 205 × 55% = 112.75 mm.
Yes. If the new tyre has a larger circumference, your actual speed will be higher than the speedometer shows. If smaller, your actual speed will be lower. More than 3% difference can cause significant speedometer error.
Aspect ratio is the sidewall height expressed as a percentage of the tyre width. A 205/55 tyre has a sidewall of 205 × 55% = 112.75 mm. Lower aspect ratio = lower profile = sportier look but stiffer ride.
Equivalent sizes maintain nearly the same outer diameter (within 2-3%). Wider tyres need lower aspect ratio; narrower need higher aspect ratio. This calculator lets you compare two sizes to find the closest equivalent.
SUVs use larger tyres (e.g. 265/65 R17) for higher ground clearance, load capacity, and off-road performance. The larger diameter also reduces revolutions per km, which can improve highway fuel efficiency slightly.
Tubeless tyres seal directly to the rim and can be temporarily driven on after a puncture with sealant inside. Tube tyres require an inner tube and deflate immediately when punctured. Most modern cars use tubeless tyres.
Replace tyres when: tread depth is below 1.6mm (use the 20-paise coin test), sidewall cracks appear, age exceeds 5-6 years (even if tread looks good), or after any significant impact. Regular rotation every 8,000-10,000 km extends tyre life.