How to Read Your Tire’s Sidewall Numbers
The string of letters and numbers on your tire’s sidewall — something like P215/65R16 98H — tells you the size, load capacity, and speed rating in one line. Once you know the pattern, reading tire sidewall numbers takes about ten seconds and saves you from buying the wrong replacement.
Breaking down the code
Start from the left. The letter prefix (P for passenger, LT for light truck, or none for a Euro-metric tire) tells you the vehicle class it’s built for. The three-digit number after that is the tire’s width in millimeters, measured sidewall to sidewall. The two-digit number after the slash is the aspect ratio — the sidewall’s height as a percentage of that width. A lower number means a shorter, stiffer sidewall.
- R — radial construction, standard on nearly every tire sold today
- 16 — wheel diameter in inches the tire is built to fit
- 98 — load index, a code for maximum weight per tire
- H — speed rating, a code for maximum sustained speed
Load index and speed rating matter more than people think
The load index isn’t a marketing number — it’s a hard limit. A tire coded 98 carries up to 1,653 pounds; drop to a 91 and you’re down to 1,356 pounds per tire. Load up a truck or trailer with tires rated below the vehicle’s placard number and you’re running overloaded rubber, which shows up as heat buildup and, eventually, a blowout under load.
Speed ratings work the same way: they’re tested limits, not suggestions. An H-rated tire is built for sustained speeds up to 130 mph, a T for 118 mph. Downgrading the rating on a replacement set — even if the size matches — can change how the car handles at highway speed and may affect insurance in the event of a claim.
Where to find the numbers that apply to your car
Ignore what’s currently mounted if the tires were swapped by a previous owner. The manufacturer’s specified size and ratings are on a sticker inside the driver’s door jamb, and that’s the number to match, not whatever happens to be on the car now. If you’re not sure what a marking means, a tire shop can read it in seconds — there’s no penalty for asking, and the U.S. Tire Manufacturers Association’s safety guidance covers the same basics in more detail.
One more marking worth knowing: a four-digit DOT date code near the size, like 2324, means the tire was made in the 23rd week of 2024. Tires degrade with age even if the tread looks fine, so a “new” tire that’s actually five years old off the shelf is worth asking about before you buy.
Check this code before your next replacement, not while you’re standing in a parking lot with a flat. It’s also worth checking tread depth against your rotation schedule and folding it into a pre-road-trip check — a five-minute read of the door jamb sticker now means you order the right tire the first time.
