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Tire Size Chart: How to Read Tire Sizes

Quick answer

In 225/45R17, 225 is the width in mm, 45 is the sidewall height as a percent of width, R means radial and 17 is the rim diameter in inches. Overall diameter is rim x 25.4 plus two sidewalls.

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Common tire sizes

Overall diameter is calculated.

Common tire sizes
SizeWidthSidewallRimOverall diameter
205/55R16205 mm113 mm16 in24.9 in / 632 mm
215/60R16215 mm129 mm16 in26.2 in / 664 mm
225/45R17225 mm101 mm17 in25.0 in / 634 mm
225/65R17225 mm146 mm17 in28.5 in / 724 mm
235/55R18235 mm129 mm18 in28.2 in / 716 mm
245/45R18245 mm110 mm18 in26.7 in / 678 mm
265/70R17265 mm186 mm17 in31.6 in / 803 mm
275/55R20275 mm151 mm20 in31.9 in / 810 mm

Speed ratings

Maximum sustained speed.

Speed ratings
LetterMax speed (km/h)
Q160
S180
T190
H210
V240
W270
Y300

How to read a tire size

The size is molded on the sidewall. The load index follows the rim number, then the speed letter, e.g. 94V.

Frequently asked questions

What does 225/45R17 mean?
225 mm wide, 45% sidewall, radial, 17 in rim.
Can I fit a different size?
Keep overall diameter within about 3% of stock.
Where is my tire size?
On the sidewall and the driver door jamb placard.

Related guides

Sources and further reading