📋 Quick Facts
Width
mm (e.g., 225)
Aspect
% of width (e.g., 65)
Diameter
Wheel inches (e.g., 17)
Speed rating
H = 130 mph
Tire sidewalls follow ISO/DOT standards. A typical size like P225/65R17 95H reads as: P (passenger tire), 225 (section width in millimeters), 65 (aspect ratio - sidewall is 65% of width), R (radial construction), 17 (wheel diameter in inches), 95 (load index = 1,521 lb per tire), H (speed rating = 130 mph). Always match the size and load/speed ratings printed on your driver-door jamb sticker, not just the previous tire.
🔎 Breaking Down the Numbers
REASON 01
P, LT, or no prefix
P = passenger car. LT = light truck (heavier load capacity, stiffer sidewalls). No letter = European metric (functionally similar to P).
REASON 02
Section width (e.g., 225)
Width in millimeters from sidewall to sidewall. A 225 tire is 225 mm (~8.85") wide at the widest point.
REASON 03
Aspect ratio (e.g., 65)
Percent: sidewall height = aspect × width. A 225/65 has sidewalls 146 mm tall. Lower numbers = shorter sidewalls = stiffer ride, better handling.
REASON 04
Construction (R or D)
R = radial (modern standard). D = bias-ply (old, mostly trailers). Almost every modern tire is R.
REASON 05
Wheel diameter (e.g., 17)
Inches of the wheel the tire fits. Must match your wheel exactly - a 17" tire won't mount on an 18" wheel.
REASON 06
Load index (e.g., 95)
Coded number = max load per tire. 95 = 1,521 lb, 100 = 1,764 lb, 105 = 2,039 lb. Multiply by 4 for total vehicle capacity.
REASON 07
Speed rating (e.g., H)
Letter = max sustained safe speed. S=112, T=118, H=130, V=149, W=168, Y=186 mph. Match or exceed the OEM rating.
⚠ Don't mix sizesAlways replace tires in pairs (per axle) or full sets, and never mix size, brand, or tread depth on the same axle. On AWD vehicles, all four tires must match within 2/32" of tread depth to avoid driveline binding and differential damage.
🔗 Related Guides
❓ Frequently Asked Questions
Where do I find my OEM tire size?
Driver-door jamb sticker, glove-box manual, or the inside of the fuel-filler door. This is the authoritative source - not just the existing tire (someone may have changed it).
Can I change tire size?
Plus/minus sizing is possible if the overall diameter stays within 3% of OEM. Going wider can affect speedometer accuracy and may rub at full lock.
What's the DOT date code?
The 4-digit number at the end of "DOT..." = week/year (e.g., 2421 = 24th week of 2021). Tires age out at 6–10 years regardless of tread.
What does the M+S marking mean?
Mud and Snow - standard on all-season tires. The 3PMSF (three-peak mountain snowflake) is a separate, stricter winter rating.
What if my tires have different sizes front and rear?
Some performance and sports cars use staggered sizing intentionally. Only do this if specified by the OEM. Rotation rules change - usually side-to-side instead of cross-rotation.
What's a "C" or "E" load range?
LT tires use letter load ranges (C=6-ply, D=8-ply, E=10-ply equivalent). Higher = heavier-duty for trucks and trailers.