275/65R18 — 814.7 mm tall, and what it swaps with

275/65R18 is 275 mm wide with a 65% sidewall on a 18-inch wheel. That sidewall is 178.75 mm, so the tyre stands 814.7 mm tall and turns 390.7 times per kilometre.

Section width: 275 mm
Aspect ratio: 65 %
Wheel size: 18 in (457.2 mm)
Sidewall height: 178.75 mm
Overall diameter: 814.7 mm (32.07 in)
Circumference: 2559.5 mm
Turns per km: 390.7

Sizes you can swap to

Only sizes whose overall diameter stays within 3% are listed. A different diameter covers a different distance per turn, and that gap becomes speedometer error.

285/45R22815.3 mm · +0.07% you go faster 275/55R20810.5 mm · -0.52% you go slower 275/45R22806.3 mm · -1.03% you go slower 265/75R16803.9 mm · -1.33% you go slower 265/70R17802.8 mm · -1.46% you go slower 305/40R22802.8 mm · -1.46% you go slower 285/50R20793 mm · -2.66% you go slower

Same profile, different width

235/65R18 · 762.7mm

How the code reads

The 205 is millimetres, the 55 is a percentage of that width, and only the 16 is inches. The R stands for radial construction.

How to read this

The first three digits are the width in mm, the middle two are the aspect ratio in percent, the last two the wheel in inches.
Sidewall height = width × aspect ÷ 100. For 205/55 that is 112.75 mm.
Overall diameter = wheel diameter + twice the sidewall. A 16-inch wheel is 406.4 mm.
Once the diameter shifts by more than 3%, the speedometer and odometer drift by the same amount.

Frequently asked questions

Q. What is the overall diameter of 275/65R18?

814.7 mm — the 457.2 mm wheel plus the 178.75 mm sidewall at top and bottom.

Q. How many turns per kilometre does 275/65R18 make?

Its circumference is 2559.5 mm, so 390.7 turns.

Q. What can I swap it for?

7 sizes stay within 3% of its diameter — the closest is 285/45R22 at 815.3 mm.

Q. Why is the sidewall 178.75 mm?

Because it is 65% of the 275 mm width. The aspect ratio is a proportion of the width, not a length.