Every tire on every car you've ever owned has the answers to the questions you actually want answered — size, age, load rating, speed rating, treadwear grade — printed right on the side. Five minutes with this guide and you'll never get talked into the wrong tire again.
Reading the size: P215/65R16 explained
Most passenger tires use a string like P215/65R16 95H. Each part means something specific:
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P — passenger car (sometimes "LT" for light truck, or no letter at all for European-spec).
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215 — section width in millimeters (sidewall to sidewall when mounted, unloaded).
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65 — aspect ratio (sidewall height as a percentage of width). 65% of 215mm = ~140mm sidewall.
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R — radial construction (almost everything is radial today).
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16 — wheel diameter in inches.
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95 — load index (95 = 1,521 lbs per tire max).
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H — speed rating (H = up to 130 mph).
Where to find it
Easiest place: open the driver's door and look at the door jamb sticker. That's the manufacturer's recommended size. The size on your current tire might be different if a previous owner plus-sized.
The DOT date code — the most important number
Every tire sold in the US since 2000 has a DOT serial that ends in a four-digit week/year code. "3221" means it was made the 32nd week of 2021. Before 2000 it was three digits and you should not be driving on those tires regardless.
Why date matters
Tire compounds oxidize as they age. Sidewall rubber gets brittle, belts can separate, and wet grip drops sharply. Most manufacturers and the entire used-tire industry agree on roughly 6 years from manufacture as the safe limit, regardless of how much tread is left.
How to find the code
It's on one sidewall only (often the inboard side, which is annoying — you may need to crawl under the car or have it on a lift). Look for "DOT" followed by a string of letters and numbers. The last 4 digits before the end of the line are the date.
Real-world example
A new tire sitting on a dealer's shelf since 2019 is technically "new" — never driven, full tread — but it's already 7 years old. That's a tire to refuse, even at full price. Always read the date before signing.
Load index decoded
Load index is a numerical code, not pounds. Common values:
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110 = 2,337 lbs (light truck territory)
Always meet or exceed the load index on your door-jamb sticker. Going below is a safety issue, especially if you ever load up the car with passengers or cargo.
Speed rating decoded
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S = 112 mph (older sedans, some trucks)
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T = 118 mph (most family cars)
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H = 130 mph (sport sedans, performance trims)
You can go up in speed rating, never down. The rating includes a margin, but it also reflects how the tire was engineered for heat dissipation at sustained speeds.
UTQG: treadwear, traction, temperature
On the sidewall you'll also see something like "500 A B":
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Treadwear — relative life vs. a reference tire. 500 lasts about 5x the reference. Higher = longer life. Anything 400+ is a long-life tire.
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Traction — wet braking grade. AA, A, B, C in descending order. Avoid C.
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Temperature — heat dissipation grade. A, B, C. A is best.
Why date matters more on used tires
On a new tire, you're going to wear it out before it ages out. Treadwear is the limiting factor. On a used tire, the rubber has already aged 2–4 years on the road plus however long the previous owner had it sitting. Now age is the limiting factor — which is why any used tire shop worth its name will tell you the DOT date out loud before you commit.
Common scams to watch for
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"New old stock" tires from a closing dealership at a too-good price. Check the DOT — if it\'s 6+ years old, walk away.
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Sidewall plugs covered with tire shine or paint. Run a fingernail across any suspicious black dot.
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Mismatched tread patterns or speed ratings within a "matched set" of used tires.
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Tires labeled "Grade A" with under 5/32" tread. There's no industry-wide grade-A standard; insist on a tread-depth measurement in front of you.
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Refusal to dismount and inspect the inner liner. The inside tells you more than the outside.
How Tire Brothers labels every used tire
Every used tire on our wall has a tag with: tread depth at 4 points, DOT date, brand, size, load and speed rating, and our pricing tier. You see what you're buying before you buy it. If a shop won't tell you these things up front, that's the sign — find another shop.
Print this
On any tire, before you commit, you should be able to read aloud: the size, the load index, the speed rating, the DOT week/year, and the tread depth. If you can't, you don't know enough yet to buy.