Question 1

What is the diameter of a 255/45 R18 tire?

Accepted Answer

A 255/45 R18 tire has a nominal overall diameter of 687 mm (27.0 inches), a sidewall height of 115 mm and a rolling circumference of 2157 mm. These are nominal figures calculated from the size marking; actual dimensions vary by manufacturer, load and wear.

Question 2

What do the numbers in 255/45 R18 mean?

Accepted Answer

255 is the nominal section width in millimetres. 45 is the sidewall height expressed as a percentage of that width, giving a 115 mm sidewall. R denotes radial construction, and 18 is the wheel bead-seat diameter in inches — which is not the overall tire diameter.

Question 3

Which vehicles use 255/45 R18 tires?

Accepted Answer

The catalogue records this size on 21 vehicle configurations, including 2018 Audi Q3 2 Petrol Turbo Automatic 6-speed AWD, 2018 Audi Q3 2 Petrol Turbo Automatic 6-speed FWD, 2017 Audi Q3 2 Petrol Turbo Automatic 6-speed AWD, 2017 Audi Q3 2 Petrol Turbo Automatic 6-speed FWD, 2016 Audi Q3 2 Petrol Turbo Automatic 8-speed AWD. Always confirm the size against the vehicle placard before fitting.

Nominal section width	255 mm
Sidewall-to-width ratio	45%
Sidewall height	115 mm
Construction	R — radial
Wheel bead-seat diameter	18 inches
Overall diameter	687 mm (27.0 in)
Rolling circumference	2157 mm

255/45 R18 tire dimensions

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What 255/45 R18 means

Vehicles with 255/45 R18 tires