Your stock tire size is the Original Equipment (OEM) size chosen by the manufacturer for your exact make, model, year, and trim. The quickest way to confirm it is to check the door jamb placard on the driver’s door, or consult the owner's manual or the manufacturer’s official specifications. If you’re inspecting tires you already own, read the markings on the sidewall—those show the tires you’re using, not necessarily the factory recommendation.
Where to look for the Original Equipment size
Use these sources to locate the official OEM tire size for your car. They are the most reliable way to ensure your wheels and tires meet safety and performance standards.
- Door jamb placard on the driver’s side (often near the latch or door frame) listing the recommended tire size, inflation pressures, and load limits.
- Owner’s manual or maintenance guide, which includes the original equipment tire spec for your year and trim.
- Vehicle Identification Number (VIN) and model-year databases provided by the manufacturer or a dealership; you can also use trusted data sources like the manufacturer’s site or certified service centers.
- Official manufacturer-approved spec sheets or product brochures for your exact model/trim; these may be found on the automaker’s website or through a dealership’s parts department.
- Original window sticker (Monroney label) for new cars or any dealer documentation for a used car; it lists the factory-specified tire size at the time of sale.
Knowing the OEM size helps ensure you replace tires with the right width, height, and diameter so the car performs correctly and remains within safety and warranty guidelines.
How to read the tire size code
The size printed on a tire’s sidewall encodes the width, height, construction, and wheel diameter, plus the load and speed ratings. Here is what to look for and how to interpret it.
- Tire type prefix: P = passenger car, LT = light truck, or no prefix for some regional tires; indicates intended vehicle class.
- Section width in millimeters: the first number after the prefix (e.g., 215) describes the cross-section width of the tire.
- Aspect ratio: the two digits after the slash (e.g., 60) express the sidewall height as a percentage of the width.
- Construction: the letter following the aspect ratio (R = radial construction is standard today).
- Wheel diameter: the number after the construction (e.g., 16) indicates the rim diameter in inches that the tire fits.
- Load index and speed rating: the final pair of numbers/letter (e.g., 94T) signify how much weight the tire can carry and the maximum speed it’s built to handle.
- Example: P215/60R16 94T demonstrates all parts: type, width 215 mm, aspect ratio 60%, radial construction, fits 16-inch wheel, load 94 and speed rating T.
Understanding these codes helps you compare OEM sizes to alternatives and ensure any replacement matches performance and safety requirements.
What to do if your current tires differ from the stock size
If you already have tires or wheels that aren’t OEM, you still want to verify compatibility and safety before driving. Use these guidelines to decide whether to keep, adjust, or revert to stock sizing.
- Keep the overall diameter within a small deviation (often within 2-3%) of the OEM specification to avoid speedometer error and traction differences.
- Match or exceed the OEM load index and stay within the vehicle’s recommended speed rating and performance envelope.
- Check clearance for fenders, brake calipers, and suspension components, and ensure the wheel width and offset suit your car’s design.
- Consider wheel and tire weight, rolling resistance, and potential impact on ABS/traction control systems; consult a tire/wheel professional if in doubt.
- When in doubt, consult the dealer or a trusted tire shop to confirm compatibility and obtain OEM-recommended replacements.
Sticking to OEM-recommended sizes helps preserve handling, fuel efficiency, warranty coverage, and safety on the road.
Regional and trim variations
Stock sizes can vary by market and by trim level. What’s listed as standard on one version of the same model might be different in another country or for a higher-spec variant with different wheels. Always verify for your exact vehicle configuration.
US and Canada variations
In North America, the placard on the door jamb and the owner’s manual are the most reliable sources, as manufacturers publish a sole OEM size per trim for a given model year.
Europe and other markets
European and other regional specs may differ due to tire labeling systems (TYRE pressure in kPa, E-mark approvals) and regional wheel options; consult the dealer or the official manufacturer site for your exact VIN and region.
Summary
To determine your stock tire size, start with the door placard on the driver’s door frame and verify with the owner's manual or the manufacturer's specifications. If you’re reading a tire size code, know how to decode it: width, aspect ratio, construction, wheel diameter, and load/speed ratings. When replacing tires, aim to match the OEM size or consult a professional to choose a compatible alternative that maintains safety, performance, and proper vehicle electronics function.
What is the 3 tire rule?
The 3% tire rule is a widely used guideline in the automotive world. It says that the overall diameter of your new tires should not differ by more than 3% from the diameter of your original, factory-spec tires.
Is a 285 the same as a 33?
A 285/70R17 tire measures 32.71 inches in diameter, not quite a true 33-inch tire but close enough for similar performance characteristics. The key difference between 285/70R17 and 33x12. 50R17 is width: 11.2 inches versus 12.5 inches, affecting traction and vehicle stance.
Is a 265 tire a 31?
Yes, 265/75R15 matches 31x10. 5R15 dimensions. Both deliver nearly identical measurements: 30.6 inches overall diameter, 10.4 inches width, and 7.8 inches sidewall height.
How do I find out my stock tire size?
Simply check the tire placard on the front driver's side door sill or in the glove box, the Owner's Manual, or the sidewalls of your tires for a series of numbers and symbols that should look like this: P215/60 R17. The wheel diameter will be the last number in the series.