You can read the largest code on a tire without knowing every mark molded into the rubber. The useful question is whether the tire on the car matches the vehicle's specification and whether a replacement would. Start at the driver's door label or owner's manual, then look at the sidewall. The sidewall alone cannot tell you what the car needs.
Decode one size, then compare it with the car
Take P205/55R16 91V as an example, not a recommendation for your vehicle. “P” identifies a passenger tire in this US style of marking; some tires have no prefix. “205” is nominal width in millimeters. “55” means the sidewall height is 55% of that width, not 55 millimeters. “R” identifies radial construction, and “16” is the wheel diameter in inches. A 16-inch tire is not interchangeable with a 17-inch wheel.
The following “91” is a load index, a code that must be looked up for its load capacity; “V” is a speed category. Neither tells you what speed to drive or how much cargo your car may carry. Compare both with the vehicle's required specification before buying. A tire shop can confirm any permitted alternative size, especially where front and rear tires differ or the vehicle has all-wheel drive. NHTSA points owners to the manual or Tire and Loading Information label for the correct size.
Take a clear photo of the vehicle label and all markings on the current tire before calling a shop. If the current tire does not match the label, do not assume the label is wrong; ask a qualified tire professional what sizes the manufacturer permits for the exact vehicle and wheel. Load and speed ratings should be checked as part of that conversation. A tire with the same width but a different aspect ratio or wheel diameter is not a casual substitute.
Some vehicles use different sizes on the front and rear. Others may have instructions about matching tire circumference or type across an all-wheel-drive system. State the axle position when requesting a quote and ask whether replacing one tire is appropriate under the vehicle instructions. The sidewall is information for a specific tire; the car's design determines the full replacement decision.
Find the date without turning it into an expiry date
The last four digits of the full DOT Tire Identification Number give the production week and year. For example, “2422” means week 24 of 2022. NHTSA notes that the full number may appear on only one side; do not crawl under a vehicle to find the inward-facing code. Ask a shop to show it to you if needed.
There is no single age at which every tire suddenly fails. Age, storage, heat, tread and damage all matter. Some tire or vehicle makers recommend replacement between six and ten years regardless of remaining tread, according to NHTSA. Check the vehicle and tire makers' instructions and have an older or questionable tire inspected; a date code is a prompt for a decision, not the decision itself.
Inspect the spare if the vehicle has one; it may be older than the road tires despite unused tread. A date code can be hard to reach on the inward side. Have a shop read it during regular service instead of crawling beneath a parked vehicle. Keep the date with your tire records so the next age check does not depend on another search.
Keep the maximum marking separate from inflation
“Max pressure” on the sidewall is a tire limit. It is not the normal cold pressure for your car. Use the vehicle placard for routine inflation, including any front/rear difference; the pressure guide walks through the gauge reading. Likewise, “max load” belongs to the tire and does not replace the car's payload rating.
While you are close enough to read the marks, look for a bulge, exposed cord or deep cut. If you see one, the next task is a tire inspection, not a size comparison. For a replacement quote, photograph the entire size and service description, the vehicle label and the date code. That gives the shop something more precise than “the same tire as before.”
Take the specification to the tire shop
Photograph the vehicle placard and write down the current tire’s full sidewall description while the car is parked safely. Add the vehicle year, model, version and whether the owner’s manual gives special instructions for the spare or an all-wheel-drive system.
Ask the shop to explain how the proposed tire matches the required size, load capacity, speed specification and vehicle use. Keep the explanation with the receipt. A shared diameter or familiar brand name is not enough information to establish compatibility.
Ask the quote to identify the complete tire model, size, load and speed rating, installation charges and any disposal or warranty terms. If a shop proposes an alternative, ask why it is compatible with the vehicle and the other tires. The reason should be more specific than "it fits the wheel." After installation, confirm the correct positions and the vehicle's cold-pressure targets. A replacement purchase is complete only when the tires match the car's requirements and are mounted and inflated properly.
