What are standard tire sizes?
Standard tire sizes are the codes printed on the sidewall that identify a tire's width, profile, and wheel diameter, most commonly formatted as P205/60R16 or LT245/75R16. These sizes must match your vehicle's wheel size and load requirements.
How standard tire size codes are structured
Tire sizes follow a few common formats that reveal width, aspect ratio, construction, and wheel diameter. The most widespread formats are P-metric for passenger cars and LT for light trucks; temporary spares use a T prefix, and some European sizes omit the prefix.
Key components of a size code
Below is what each part of a typical size code describes, using P205/60R16 as an example:
- Prefix: P indicates a passenger-car tire; LT indicates light-truck; T indicates a temporary spare. Some European sizes omit the prefix.
- Width: 205 mm — the tire's cross-section width from sidewall to sidewall.
- Aspect ratio: 60 — the height of the sidewall as a percentage of the width.
- Construction: R — radial construction is standard; other options exist but are rare in modern tires.
- Wheel diameter: 16 inches — the diameter of the wheel (rim) the tire fits.
Understanding these elements helps you compare sizes and ensures you choose a tire that fits your vehicle's wheels and clearance.
Common size formats you will encounter
Most tires and official vehicle documentation use one of several standard formats. The ones you'll see most often are listed here to help you recognize them at a glance.
- P-metric sizes for passenger cars, such as P205/60R16. These ship with a 'P' prefix and are widely used in North America.
- LT-metric sizes for light trucks and larger vans, such as LT245/75R16. These have higher load ratings and wider cross-sections for heavier vehicles.
- European or metric-only sizes, such as 205/55R16, which may appear without a 'P' prefix on some markets but convey the same width/ratio/dia format.
- Temporary spare sizes, typically starting with a T, such as T125/70R16, which are lighter duty and intended for short-term use only.
Choosing the right format is essential for compatibility with the vehicle’s wheel, load requirements, and safety guidelines.
Typical sizes by vehicle type
While there is wide variation across models, certain ranges are common for everyday vehicles. The sizes you see on the sidewall when you buy tires generally fall into these ranges.
- Compact and subcompact cars: often 165-205 mm width, diameters around 14-16 inches, e.g., 195/65R15 or 205/55R16.
- Mid-size cars and crossovers: commonly 205-245 mm width, 15-18 inch wheels, e.g., 225/60R17 or 235/55R18.
- SUVs and trucks: wider tires with larger diameters, such as 265/70R17 or 275/65R18; light-truck tires may be 245/75R16 or similar.
When replacing tires, always verify the exact size recommended by your vehicle’s manufacturer and consider the overall diameter to maintain accurate speedometer calibration and proper clearance.
Other size considerations
Besides the basic code, several practical factors affect sizing decisions, including load index, speed rating, overall diameter, and compatibility with suspension and braking systems. If you deviate from the recommended sizes, you may need to adjust with wheel offset or consider a different tire type to maintain safety and performance.
Where to find your standard tire size
Your tire size is printed on the tire sidewall and in the vehicle’s owner’s manual and door jamb placard. The size code may appear as P205/60R16 or 205/60R16 or similar, depending on market. Always confirm the exact size before purchasing replacements.
Summary
Standard tire sizes follow a few well-established formats that describe width, aspect ratio, construction, and wheel diameter. The most common are P-metric and LT formats for passenger cars and light trucks, respectively, with European metric-only formats also in use. Always match size, load index, and speed rating to your vehicle, and consider the impact on speedometer accuracy and clearance when changing sizes.
