The code stamped on every tire's sidewall — something like P215/65R15 95H — looks cryptic, but every character is telling you something specific and useful. Once you know how to read it, checking whether a replacement tire is actually the right fit takes seconds.
Breaking down P215/65R15 95H, piece by piece
P — the tire's class. "P" means it's built for passenger vehicles (cars, minivans, smaller SUVs). You might also see "LT" for light trucks, built for heavier loads, or "ST" for trailer-specific tires. No letter at all typically indicates a Euro-metric passenger tire, which uses a slightly different, related sizing standard worth noting when comparing tires across brands.
215 — the tire's width in millimeters, measured sidewall to sidewall. Wider tires generally offer more grip but can affect fuel economy and ride feel.
65 — the aspect ratio, expressed as a percentage. This means the sidewall height is 65% of the tire's width. A lower number means a shorter, stiffer sidewall (common on sportier vehicles); a higher number means a taller sidewall with more cushioning.
R — construction type. "R" stands for radial, which is nearly universal on modern passenger vehicles; the internal belts run radially across the tire, which improves fuel efficiency and tread life compared to older bias-ply construction.
15 — the wheel diameter the tire is built for, in inches. This has to match your actual wheel size exactly; there's no flexibility here the way there sometimes is with width or aspect ratio.
95 — the load index, a coded number representing the maximum weight the tire can safely support. A load index of 95, for example, corresponds to roughly 1,609 pounds per tire. Higher numbers mean higher load capacity; load index charts (widely available online and often on tire shop walls) convert the number to an actual weight.
H — the speed rating, indicating the maximum sustained speed the tire is rated for under proper conditions and inflation — H, for instance, corresponds to speeds up to 130 mph. This isn't a suggestion to drive at that speed; it's a structural rating for how the tire is built to handle heat and stress at sustained high speed.
Why this actually matters when replacing tires
Matching width, aspect ratio, and wheel diameter exactly (or to a manufacturer-approved alternate size) keeps your speedometer accurate and your vehicle's handling and safety systems working as designed — mismatched tire sizes can throw off anti-lock brakes and stability control calibration in some vehicles. Load index and speed rating should meet or exceed your vehicle manufacturer's original specification, found in your owner's manual or on a sticker usually located on the driver's door jamb — going below the original spec on either number isn't recommended, even if the tire otherwise fits and looks like a reasonable, cheaper substitute at the shop.
Other useful info on the sidewall
Beyond the main size code, sidewalls also list the DOT code (which includes the tire's manufacture date, useful for checking tire age even on a tire with plenty of remaining tread), maximum load and pressure ratings in more detail, and the tire's UTQG rating (treadwear, traction, and temperature grades), which is useful for comparing durability and performance across different tire models. A tire's manufacture date matters more than most people assume — rubber degrades with age even if a tire has barely been driven on at all, so a tire older than six or seven years is genuinely worth having inspected regardless of how much tread depth still remains.
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