Everything a manufacturer legally has to tell you about a tire is molded into its sidewall. Size, load capacity, speed capability, construction type, manufacture date, tread wear expectations, and cold-weather certification are all there — compressed into a series of codes that nobody ever explains to you. Once you can read them, you can verify that a shop sold you the right tire, spot a tire that's too old to trust, and know at a glance whether you're legal on a Colorado mountain highway in winter.
Here's the sidewall, decoded piece by piece, with the Denver-specific implications called out.
The Main Size Code — P225/60R17 98H
This is the big one, and it breaks into six separate pieces of information:
- P — Tire type. "P" means P-metric, a passenger vehicle tire. "LT" means Light Truck, built with heavier construction for higher loads — common on pickups and larger SUVs around Denver. No letter at all indicates a Euro-metric tire, which is functionally similar to P-metric but rated slightly differently for load.
- 225 — Section width. The width of the tire in millimeters, measured sidewall to sidewall at its widest point. A 225 is 225mm wide, roughly 8.9 inches.
- 60 — Aspect ratio. The sidewall height expressed as a percentage of the section width. A 60 means the sidewall height is 60% of 225mm, or about 135mm. Lower numbers mean shorter, stiffer sidewalls (sportier, harsher); higher numbers mean taller sidewalls (more cushion over Denver's pothole-scarred roads).
- R — Construction. "R" is radial, which is essentially every modern passenger tire. You may see "D" (diagonal/bias-ply) on trailer tires.
- 17 — Wheel diameter. The diameter of the wheel the tire fits, in inches. This one is absolute — a 17-inch tire does not go on an 18-inch wheel, ever.
- 98 — Load index. A coded number that maps to a maximum weight the tire can carry. 98 corresponds to 1,653 pounds per tire. Never go below your vehicle's specified load index — it's a safety limit, not a suggestion.
- H — Speed rating. A letter that maps to a maximum sustained speed. H is 130 mph. Common ratings you'll see: T (118), H (130), V (149), W (168). This is about sustained heat tolerance, not how fast you plan to drive.
Denver-Specific Note on Load Index: If you've added a roof box, run a loaded rig up I-70 for ski weekends, or tow anything, load index matters more than most drivers assume. A tire operating near its load limit generates more heat and wears faster — and Colorado's long sustained grades are exactly the condition that exposes an undersized tire.
The DOT Code — How Old Are Your Tires?
Somewhere on the sidewall you'll find "DOT" followed by a string of characters. Most of it is manufacturing plant and batch data that doesn't concern you. The part that matters is the last four digits.
Those four digits are the manufacture date. The first two are the week of the year; the last two are the year. So 3624 means the tire was built in the 36th week of 2024 — early September 2024.
This matters more in Denver than almost anywhere in the country. Rubber degrades from UV exposure and ozone regardless of how much you drive on it, and Denver's altitude means significantly more UV reaching your tires than at sea level. A tire with plenty of tread can still be structurally unsafe if it's aged out.
- Under 5 years: normal service, no age concern.
- 5 to 6 years: have them inspected annually. Look for fine cracking in the sidewall — "weather checking."
- 6+ years: most manufacturers recommend replacement regardless of tread depth. At Colorado altitude, take this seriously rather than treating it as conservative.
- 10 years: universally considered the absolute maximum, no exceptions.
This is also the number to check when buying tires. "New" tires that have sat in a warehouse for three years are still three years into their service life. Always ask, and verify on the sidewall.
Not Sure What's on Your Sidewall?
Bring it in — Denver CO Tire Shop will read your sidewall codes, check your date codes, and tell you exactly where your tires stand. No charge for the inspection.
M+S vs. 3PMSF — The Marking That Matters on I-70
This is the single most misunderstood thing on a sidewall, and in Colorado it has legal consequences.
M+S (sometimes M/S or M&S) stands for Mud and Snow. It is a self-certified marking based purely on tread pattern geometry — the manufacturer decides the tread has sufficiently large voids and applies the stamp. There is no performance test. Most all-season tires carry it, and most of them are mediocre in real snow.
3PMSF — the three-peak mountain snowflake symbol — is different. It requires the tire to pass an actual standardized snow traction test, demonstrating meaningfully better performance than a reference tire. It's an earned marking, not a claimed one.
Colorado's Traction Law, active on I-70 between Morrison and Dowd Junction during winter weather events, requires adequate traction equipment. A 3PMSF-rated tire with at least 3/16" of tread satisfies it. An M+S tire may satisfy it under some conditions, but when the Passenger Vehicle Traction Law escalates, 3PMSF is the safe answer — and violations carry fines that increase substantially if you block the roadway.
If you regularly drive to the mountains, look for the snowflake. Learn more about choosing tires for Colorado weather.
UTQG — Treadwear, Traction, and Temperature
You'll find three more ratings grouped together, part of the Uniform Tire Quality Grading system:
- Treadwear (a number like 400 or 600). A relative durability score — a 600 tire should theoretically last twice as long as a 300. The catch: it's self-reported by each manufacturer against their own reference tire, so it's only reliable for comparing tires within a single brand. Don't compare a Michelin 500 to a Goodyear 500 and assume they're equal.
- Traction (AA, A, B, or C). Wet-braking performance on asphalt and concrete. AA is best. Given Denver's afternoon thunderstorms and the wet-to-icy transitions in shoulder season, A or better is worth prioritizing.
- Temperature (A, B, or C). Heat resistance at sustained speed. A is best. Relevant for long highway runs, though less critical in Colorado's climate than it would be in, say, Phoenix.
Max Load and Max Pressure — Not Your Target Pressure
Near the rim edge you'll find something like "MAX LOAD 1653 LBS AT 44 PSI MAX PRESS." This is one of the most commonly misread markings on the tire.
That 44 PSI is the maximum pressure the tire can safely hold — it is not the pressure you should inflate to. Your correct inflation pressure comes from the placard in your driver's door jamb, which specifies what the vehicle manufacturer determined is right for your car. That number is usually somewhere between 30 and 36 PSI.
Inflating to the sidewall max gives you a harsh ride, a center-worn tire, and reduced contact patch. Always use the door jamb number. Denver drivers should also remember that Colorado's temperature swings move tire pressure roughly 1 PSI for every 10°F change — check monthly, always in the morning before driving. Learn more about how TPMS works and what triggers the warning light.
Directional Arrows and Rotation Markings
Some performance and winter tires have an arrow and the word "ROTATION" on the sidewall. These are directional tires — the tread is designed to work in one direction only, typically for water evacuation. They can only be rotated front-to-back on the same side of the vehicle, never crossed.
Others are marked "OUTSIDE" and "INSIDE" — asymmetric tires with different tread patterns across the face. These must be mounted with the correct face outward.
If you have either type, it changes your rotation pattern. A shop that rotates directional tires side-to-side has made a real mistake. Learn more about tire rotation schedules for Denver drivers.