Understanding tire sizes is essential when buying new tires or rims. Every tire has a series of numbers and letters on its sidewall (example: 205/55 R16 91V). Here’s what they mean:

📌 Example: 205/55 R16 91V

205 → Tire Width

• The width of the tread in millimeters.
  
• Example: 205 mm wide tire.
  

55 → Aspect Ratio (Profile Height)

• The height of the sidewall, expressed as a percentage of the width.
  
• Example: 55 = sidewall height is 55% of 205 mm.
  

R → Construction Type

• R = Radial (the most common construction today).
  
• Other types (bias or diagonal) are rare in modern cars.
  

16 → Rim Diameter

• The wheel diameter in inches.
  
• Example: 16-inch wheel.
  

91 → Load Index

• A numeric code that indicates the maximum load capacity per tire.
  
• Example: 91 = supports 615 kg.
  

V → Speed Rating

• A letter showing the maximum speed capability of the tire.
  
• Example: V = up to 240 km/h.
  

🔎 Other Important Markings

• XL / Reinforced → Extra load capacity for heavier vehicles.
  
• M+S (Mud & Snow) → Certified for use in mud and snow conditions.
  
• 3PMSF (Three Peak Mountain Snowflake) → Meets EU standards for severe snow use.
  
• DOT Code → Shows the manufacture date (week + year, e.g., 3522 = 35th week of 2022).
  

✅ Quick Tips for Choosing the Right Tire Size

• Always check your vehicle registration (libretto di circolazione) for approved tire sizes.
  
• The load index and speed rating must be equal or higher than the original specification.
  
• Using the wrong size can affect safety, fuel efficiency, and performance.
  
• For upgrades (wider or larger rims), ensure compliance with Italian road regulations.