215/40R18
Overall diameter 629.2 mm
215/40R18 — 629.2 mm tall, and what it swaps with
215/40R18 is 215 mm wide with a 40% sidewall on a 18-inch wheel. That sidewall is 86 mm, so the tyre stands 629.2 mm tall and turns 505.9 times per kilometre.
- Section width
- 215 mm
- Aspect ratio
- 40 %
- Wheel size
- 18 in (457.2 mm)
- Sidewall height
- 86 mm
- Overall diameter
- 629.2 mm (24.77 in)
- Circumference
- 1976.7 mm
- Turns per km
- 505.9
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.
195/70R14628.6 mm · -0.1% you go slower225/50R16631.4 mm · +0.35% you go faster205/60R15627 mm · -0.35% you go slower205/55R16631.9 mm · +0.43% you go faster215/45R17625.3 mm · -0.62% you go slower225/45R17634.3 mm · +0.81% you go faster195/65R15634.5 mm · +0.84% you go faster255/35R18635.7 mm · +1.03% you go faster205/50R17636.8 mm · +1.21% you go faster185/65R15621.5 mm · -1.22% you go slower225/40R18637.2 mm · +1.27% you go faster195/55R16620.9 mm · -1.32% you go slower
Same profile, different width
Other sizes for this wheel
18-inch wheels
215/40R18 629.2mm215/45R18 650.7mm215/50R18 672.2mm225/35R18 614.7mm225/40R18 637.2mm225/45R18 659.7mm225/50R18 682.2mm225/55R18 704.7mm225/60R18 727.2mm235/40R18 645.2mm235/45R18 668.7mm235/50R18 692.2mm235/55R18 715.7mm235/60R18 739.2mm235/65R18 762.7mm245/40R18 653.2mm245/45R18 677.7mm245/50R18 702.2mm245/60R18 751.2mm255/35R18 635.7mm255/40R18 661.2mm255/45R18 686.7mm255/55R18 737.7mm255/60R18 763.2mm265/60R18 775.2mm275/35R18 649.7mm275/40R18 677.2mm275/65R18 814.7mm
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 215/40R18?
629.2 mm — the 457.2 mm wheel plus the 86 mm sidewall at top and bottom.
Q. How many turns per kilometre does 215/40R18 make?
Its circumference is 1976.7 mm, so 505.9 turns.
Q. What can I swap it for?
12 sizes stay within 3% of its diameter — the closest is 195/70R14 at 628.6 mm.
Q. Why is the sidewall 86 mm?
Because it is 40% of the 215 mm width. The aspect ratio is a proportion of the width, not a length.