What size tires do I use?

Your tire size should match the vehicle manufacturer’s specification. In most cases you’ll use the size printed on the door jamb placard or in your owner's manual, and the same size is usually stamped on your current tires. If you’re replacing with a different size, you must choose one that preserves proper clearance, load capacity, and overall diameter.

Where to Find Your Tire Size

Use these sources to locate the exact tire size for your vehicle. The information is typically printed in several places for quick reference.

• Door jamb placard (driver’s door pillar) that lists the OEM tire size and recommended cold tire pressures.


• Your vehicle’s owner’s manual or the official specification sheet for your model.


• The sidewall of the current tires (a common format is something like P215/65R15).


• The spare tire or inflator kit may have a size listed as a quick reference.

Having the exact size is essential before buying tires or rims, because using an unsupported size can affect safety systems, handling, and accuracy of the speedometer.

Understanding Tire Sizing Nomenclature

Most passenger tires use a standard format like P215/65R15. Here’s how to read it:

Breaking down the size code

• P indicates a passenger vehicle; LT indicates a light-truck or larger vehicle; ST is for special trailer tires.


• 215 is the tire width in millimeters from sidewall to sidewall.


• 65 is the aspect ratio (the height of the sidewall as a percentage of the width).


• R denotes radial construction.


• 15 is the wheel diameter in inches that the tire is designed to fit.


• Additional digits/letters after the size (e.g., 95H) indicate load index and speed rating, and sometimes extra markings like XL (extra load) or T (temporary spare).

Understanding these codes helps you compare options and ensure the tires will fit your wheels and meet your performance needs.

Choosing a Size When Upgrading or Replacing

If you’re considering a different size for performance, aesthetics, or off-road use, keep these guidelines in mind:

• Try to stay as close as possible to the OE (original equipment) size. The manufacturer designs the suspension, brakes, and drivetrain around that size.


• Limit changes to about a 3% difference in overall diameter to avoid speedometer error, gearing shifts, and clearance problems.


• Ensure the tire width is compatible with your wheel width and fender clearance to avoid rubbing.


• Check load index and speed rating to meet or exceed the vehicle’s requirements with passengers and cargo.


• For AWD/4WD systems, maintain the same size (and ideally the same brand/model) on all wheels to prevent drivetrain issues.

When in doubt, consult a tire professional or your vehicle manufacturer to confirm that a non-OE size is appropriate for your ride and local regulations.

Practical Tips for Buying and Installation

Before purchasing or mounting tires, consider the following practical steps to ensure safety and performance:

• Match tread type to your typical conditions (all-season, summer performance, snow, etc.).


• Verify that the new tires’ load index and speed rating meet or exceed the OE specifications.


• Have the tires installed on the correct wheel size and ensure proper balancing and alignment.


• Recalibrate or recheck your speedometer if you change overall tire diameter significantly.

After installation, monitor tire pressures regularly (cold readings) and rotate tires according to your vehicle’s recommended schedule to maximize longevity and performance.

Summary

In most cases, you should use the tire size listed by your vehicle’s manufacturer, found on the door placard or in the owner's manual, and imprinted on your current tires. If you change size, keep the overall diameter within a small tolerance, ensure compatibility with wheels and suspension, and consider the impact on speedometer accuracy and safety systems. When in doubt, seek professional guidance to select the right size for your vehicle and driving needs.

What is the 3 percent rule for tire size?

The tire size "3 percent rule" is a guideline that recommends replacement tires should not have a diameter that differs by more than 3% from the original equipment (OE) tires. Sticking to this rule helps ensure the speedometer is accurate, safety systems like ABS and traction control function correctly, and there are no fitment issues with wheel wells or the vehicle's drivetrain. While the rule applies to most passenger vehicles, trucks and SUVs may be able to accommodate a larger tire diameter change of up to 15% due to their more robust design. 
Why the 3% rule is important

• Speedometer and odometer accuracy: A change in tire diameter affects how many times the tire rotates to cover a certain distance, which can make your speedometer and odometer inaccurate. 
• ABS and traction control: These systems rely on sensors that are calibrated to the OE tire size. An incorrect size can cause these systems to malfunction or engage improperly. 
• Drivetrain stress: Larger or smaller tires can change the gear ratio, putting extra stress on your transmission, differential, and other drivetrain components. 
• Fitment and clearance: Going too large can cause the tire to rub against the fender or suspension components, especially when turning. 

How to check compatibility

• Use a tire size calculator: Online tools can help you compare your OE tire size with a potential new size and calculate the percentage difference in diameter. 
• Consult your owner's manual: This is the best source for official information on the correct tire sizes for your vehicle. 
• Seek professional advice: If you are considering a significant change, it's best to consult a tire professional to ensure the new tires will be safe and compatible with your vehicle. 

Is a 275 tire the same as a 33?

No, a "275 tire" is not the same as a "33-inch tire" because the numbers represent different measurements in a tire's size. However, a specific metric size, such as a 275/60R20, can be nearly equivalent to a 33-inch diameter tire. The term "33" is a common, non-metric measurement for a tire's approximate overall diameter. 
Tire size explained

• Metric size (e.g., 275/60R20): This is a precise measurement with three parts: 
  • 275: The width of the tire in millimeters. 
  • 60: The aspect ratio, which is the height of the sidewall as a percentage of the width (60% of 275mm). 
  • R20: The radial construction and the diameter of the wheel in inches. 
• Non-metric size (e.g., 33x12.5R20): This is a common, more direct way to refer to a tire's approximate overall diameter: 
  • 33: The approximate total height of the tire in inches. 
  • 12.5: The width of the tire in inches. 
  • R20: The radial construction and the diameter of the wheel in inches. 

When they are similar

• A 275/60R20 tire is a close equivalent to a 33-inch tire, with a total diameter of approximately 33 inches. 
• Other metric sizes, like a 285/75R16, also result in a diameter close to 33 inches. 

Why it matters

• Compatibility: Always check the exact metric size of a tire to ensure it will fit your vehicle and is compatible with your suspension and wheel size.
• Speedometer accuracy: Changing your tire diameter significantly can cause your speedometer to be inaccurate. For example, larger tires will make you appear to be driving faster than you actually are. 

How do I figure out what size tires I need?

Find the information in your vehicle owner's manual in the glove compartment or on the tire information sticker on your driver's side door. Usually those elements contain all the information related to your tire size and specifications as well as the appropriate tire pressure.

What is the 7 7 rule for tires?

If you leave them on too late, your winter tires will degrade quickly. So, when is the right time to swap? The rule of thumb is 7-for-7: wait until there are seven consistent days at 7 degrees Celsius. The reverse is also true for transitioning to winter.