Scale to GramsHow to Read Tire Size: What the Numbers on Your Tire Mean
Quick Answer
A tire marked P225/45R17 91V means passenger tire, 225mm wide, sidewall 45% of width (101mm tall), Radial construction, 17-inch rim, 91 load index (1,356 lbs / 615 kg per tire), V speed rating (149 mph max).
Try the Tire Size ToolExample tire
P225/45R17 91V
common sport sedan
Width
225 mm
8.86 in across
Rim diameter
17 in
must match your wheel
Tire Size Decoded Piece by Piece
Every character on the sidewall means something specific. Use this as a decoder for your own tire.
| Part | Means | In our example |
|---|---|---|
| P | Tire type | P = Passenger, LT = Light truck, ST = trailer |
| 225 | Width in millimeters | 225 mm = 8.86 in across |
| 45 | Aspect ratio (% of width) | Sidewall = 225 x 0.45 = 101 mm tall |
| R | Construction | R = Radial (modern standard) |
| 17 | Rim diameter (inches) | Must match your wheel exactly |
| 91 | Load index | 91 = 1,356 lbs (615 kg) per tire |
| V | Speed rating | V = 149 mph (240 km/h) max |
Speed Rating Reference
The letter at the end caps the safe sustained speed of the tire. Always match or exceed your vehicle's original rating.
| Code | Max speed | Typical use |
|---|---|---|
| S | 112 mph (180 km/h) | Family sedans, SUVs |
| T | 118 mph (190 km/h) | Standard touring |
| H | 130 mph (210 km/h) | Sport sedans |
| V | 149 mph (240 km/h) | Sport, performance |
| W | 168 mph (270 km/h) | High-performance |
| Y | 186 mph (300 km/h) | Supercars |
| Z | 149+ mph (240+ km/h) | Older performance code |
Width and Aspect Ratio
Width is sidewall-to-sidewall in millimeters. Wider = more grip but lower MPG and worse in snow. Aspect ratio is sidewall height as a percentage of width. Lower (35-45) is sportier and firmer, higher (55-70) is more comfortable. Changing aspect ratio without rim change throws off speedometer.
Load Index and Rim
Load index 91 = 1,356 lbs per tire. Multiply by 4 for total. Never go below your vehicle's required load index (check the door jamb sticker). Rim diameter must exactly match your wheel.
Where to Find Your Tire Size
Three places: sidewall of the tire (raised lettering), driver's door jamb sticker (original equipment size), or owner's manual. For dirty or worn embossing, photograph the sidewall and use an AI tire size reader.
When Sizing Goes Wrong
Incorrect tire size affects speedometer reading, ride height, braking distance, fuel economy, and ABS/traction control. AWD vehicles with mismatched front/rear sizes can suffer drivetrain damage. Stay within ±3% overall diameter when plus-sizing.
Frequently Asked Questions
What does 225/45R17 mean on a tire?+
225 = width in millimeters. 45 = sidewall height as a percentage of width (so 101 mm tall). R = radial construction. 17 = rim diameter in inches. So this tire is 225 mm wide, 101 mm sidewall, radial, fits a 17-inch wheel.
What is the load index on a tire?+
A two- or three-digit number indicating max load per tire. 91 = 1,356 lbs (615 kg). 95 = 1,521 lbs (690 kg). Multiply by 4 for total vehicle capacity. Never go below your vehicle's spec.
What does the V or H mean on a tire?+
It is the speed rating. H = 130 mph (210 km/h), V = 149 mph (240 km/h), W = 168 mph (270 km/h), Y = 186 mph (300 km/h). Match or exceed your original tire's rating.
Can I put wider tires on the same rim?+
Up to about 10-20 mm wider is usually safe on the same rim. Bigger jumps may cause wheel-well rub, change handling, and affect speedometer accuracy. Check a tire fitment calculator first.
How do I know what tire size my car needs?+
Look at the sticker on the driver's door jamb (lists factory-recommended sizes), or check your owner's manual. The current tires will also have the size on the sidewall, but those may have been changed from factory.
Are bigger tires better?+
Wider tires improve dry grip and look but cost MPG, road noise, and snow performance. Larger diameter (plus-sized) gives sharper handling but harsher ride. Stay within ±3% of original overall diameter to avoid issues.
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