Myth
“17 means the tire is 17 inches tall.”
Reality
17 is wheel diameter. Overall diameter for 225/65R17 is 28.52 in.
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Tire size guide
How to Read Tire Sizes: What the Numbers Mean
A tire size such as 225/65R17 describes nominal section width, sidewall ratio, construction type and required wheel diameter. Extra marks such as 102H are the load index and speed rating.
225 Width 225 mm
65 Aspect 65%
R Radial Construction
17 Wheel 17 in
102 Load Index
H Speed Rating
- 225 Tire width — nominal section width in millimetres
- 65 Aspect ratio — sidewall height as a percent of width
- R Radial construction
- 17 Wheel diameter — bead-seat diameter in inches
- 102 Load index — maximum load per tire under specified conditions
- H Speed rating — tested speed capability symbol
What does the first number mean?
225 is nominal section width in millimetres: the designed distance from outer sidewall to outer sidewall. It is not tread width. Tread is the contact patch on the road and is typically narrower than section width.
A mounted tire on a given wheel width, at a given pressure, may not measure exactly 225 mm. Treat the label as a size code, not a caliper reading.
Key point 225 does not mean tread width. It is nominal section width, sidewall to sidewall.
What does the second number mean?
65 is the aspect ratio: sidewall height as a percentage of nominal section width.
225 × 0.65 = 146.25 mm
Nominal sidewall height (5.76 in). Overall diameter then adds two sidewalls to the 17-inch wheel.
Key point Sidewall height = section width × aspect ratio ÷ 100.
What does R mean?
R means radial construction. Body cords run from bead to bead. Nearly all modern passenger, SUV, and light-truck tires in this catalog are radial. The letter is a construction mark, not a speed symbol.
Key point R is a construction mark, not a speed symbol.
What does the wheel number mean?
17 is the bead-seat wheel diameter in inches. A 17-inch tire must mount on a compatible 17-inch wheel. It is not the overall tire diameter — 225/65R17 calculates to 28.52 in overall.
Key point 17 is bead-seat wheel diameter — not total tire diameter. 225/65R17 calculates to 28.52 in overall.
What do 102H mean?
After the size, 102 is the load index (850 kg / 1874 lb per tire in the TireReference mapping) and H is the speed rating (210 km/h (130 mph)).
The full charts live on those guides. Replacement still has to match the vehicle placard and tire manufacturer specifications.
Key point 102H is the service description. Geometry can match while load and speed markings differ.
P, LT, ST and other prefixes
TireReference parses metric sizes with an optional P or LT prefix, unmarked metric sizes such as 225/65R17, and flotation sizes such as 33x12.50R15.
- No prefix — metric size as commonly moulded in many markets.
- P — P-metric passenger marking. The parser accepts it; geometry still uses the millimetre width, aspect ratio, and wheel diameter.
- LT — light-truck metric size. Often paired with a dual load index and a load range letter. Example: LT265/75R16.
ST (Special Trailer) is an industry designation this catalog does not currently parse as a first-class prefix. Do not treat an ST trailer tire as interchangeable with a P-metric or LT tire of similar numbers.
Real tire examples
Indexed TireReference sizes with calculated overall diameter. Each size links to its hub page.
Try your own size
Common misconceptions
Myth
“225 is the tread width.”
Reality
225 mm is nominal section width. Tread width is a different measurement.
Myth
“Any 225/65R17 has the same load and speed rating.”
Reality
Geometry can match while service descriptions differ. Check 102H versus other markings on the actual tire.
FAQ
What do the three tire-size numbers mean?
In a metric size such as 225/65R17, 225 is nominal section width in millimetres, 65 is the aspect ratio (sidewall height as a percent of width), and 17 is the bead-seat wheel diameter in inches.
What does R mean on a tire?
R means radial construction: the body cords run radially from bead to bead. It is the construction type in the size code, not a speed rating.
What is the number after R?
The number after R is the wheel diameter the tire is made to mount on, in inches. A 17-inch tire mounts on a compatible 17-inch wheel. It is not the tire’s overall diameter.
What does 102H mean?
102 is the load index and H is the speed rating. Together they are the service description. See the load index and speed rating guides for the mapped capacities.
Does tire width mean tread width?
No. The first number is nominal section width, sidewall to sidewall, not tread width. A mounted tire also may not measure exactly the labelled millimetre width.
Can I change one number in my tire size?
Changing width, aspect ratio, or wheel diameter changes sidewall height and usually overall diameter. Use the tire size calculator and comparison calculator, and follow the vehicle tire placard.
Continue learning
Related tools
Sidewall height, overall diameter, circumference and revs per mile on this page are produced by the same TireReference geometry helpers used in the calculators. Load index and speed rating use the production rating resolver. See TireReference Data & Calculation Standards.