Comparison (0)

Tyres · size

Tyre size calculator

Choose your current and new tyre size. See how the diameter and sidewall height change and what the speedometer shows.

1Current size

/ R

2New size

/ R
205/55 R16225/45 R17Difference
Diameter631.9 mm634.3 mm+0.4 %
Sidewall height112.8 mm101.3 mm-11.5 mm
Circumference1,985 mm1,993 mm+8 mm
Revolutions per km504502-2

+0.4 %. A good fit: the diameter difference is small.

When the speedometer shows km/h, with the new size you are actually doing 90.3 km/h.

Sizes with the same diameter (±1,5 %)

Pick a size to see its tyres — each page ranks tyres by wet grip and tests.

225/50 R16 -0.1 %225/45 R17 +0.4 %195/65 R15 +0.4 %215/40 R18 -0.4 %245/35 R18 -0.5 %195/70 R14 -0.5 %185/60 R16 -0.6 %255/30 R19 +0.6 %175/80 R14 +0.6 %285/30 R18 -0.6 %255/35 R18 +0.6 %255/40 R17 +0.6 %

How much can a new tyre size differ?

The diameter of the new size should differ from the factory size by up to 1.5%, and never by more than 3%. With a bigger difference the speedometer is wrong and ABS and ESP may work worse. Approved sizes are in the registration certificate or the maker's data.

How do you calculate tyre diameter?

Sidewall height is width times profile: for a 205/55 tyre 205 × 0.55 = 112.75 mm. The diameter is the rim diameter in millimetres plus two sidewalls: 16 × 25.4 + 2 × 112.75 = 632 mm.

Does a bigger tyre change the speedometer reading?

Yes. If the new tyre has a 2% larger diameter, at an indicated 90 km/h you are actually doing about 91.8 km/h. With a smaller tyre you drive slower than the speedometer shows.