Updated October 19, 2026
What the figures are
Diameter and sidewall are in millimetres. Circumference is the distance one rotation covers. Revolutions per kilometre follow from that length. The speed line assumes the speedometer was accurate on the current size: if it shows 60 km/h, the figure is how fast you are actually moving on the new size.
The diameter difference is shown in millimetres and as a percentage. It is a measurement, not a pass or fail. Read it next to the size guide and the load index on the tire you plan to buy. Start from the size on the driver's door placard.
A smaller winter wheel with a taller sidewall is a common Kanata setup. Compare that pair here before you order, then set cold pressure to the placard once the tires are mounted.
Questions
What does the speedometer line mean?
It is the actual speed when the speedometer shows 60 km/h, if the speedometer was correct on the current size. A taller tire makes the true speed higher than the needle.
Which size should I enter as current?
The size on the car now, or the original size from the door placard if you want to compare against the factory tire.
Does the calculator check load index or speed rating?
No. It compares geometry only. The replacement tire still needs a load index and speed rating that meet the placard.
Are the results a recommendation to buy?
No. They are the measured difference between two sizes. Clearance, load, and the vehicle maker's approved sizes still decide whether a tire fits.