How to Read a Tire Size (225/65R17 Explained)
Every tire has its size printed on the sidewall in a format that looks like a serial number: 225/65R17 98H. It reads like jargon, but it's a simple code, and decoding it takes about two minutes. Once you can read it, you can shop for tires anywhere with confidence that what you're buying actually fits your car.
Let's break down 225/65R17 98H piece by piece.
225: the width
The first number is the tire's width in millimeters, measured sidewall to sidewall. A 225 tire is 225 millimeters wide, about 8.9 inches.
Width affects grip, fuel economy, and road noise. Wider tires put more rubber on the road; narrower tires roll with less resistance. For buying purposes, you don't need to weigh any of that. You need the width your vehicle was engineered for, which is the number already on your car.
65: the aspect ratio
The second number is the sidewall height expressed as a percentage of the width. In a 225/65 tire, the sidewall is 65 percent of 225 millimeters, roughly 146 millimeters tall.
Lower numbers mean a shorter sidewall: sportier handling, harsher ride. Higher numbers mean more cushion. This is why a 55-series tire looks low and aggressive while a 70-series looks tall and cushioned. Again, for buying: match what your vehicle specifies.
R: the construction
The letter R stands for radial construction, which describes how the internal plies are laid. Virtually every passenger tire sold today is a radial, so this letter rarely matters when shopping. If you ever see D (diagonal/bias-ply) it's likely a trailer or specialty tire.
17: the wheel diameter
The last number is the diameter of the wheel the tire mounts on, in inches. A 225/65R17 fits a 17-inch wheel. Yes, the code mixes millimeters and inches. Nobody claims it's elegant.
This number has zero flexibility. A 17-inch tire fits a 17-inch wheel, period. If any number in the size is wrong when ordering, this is the one that makes the tire physically unusable.
98H: load index and speed rating
After the size, most tires list two more characters that shoppers skip and shouldn't.
The load index (98 here) is a code for how much weight the tire can carry. A load index of 98 means 1,653 pounds per tire. Your vehicle's required load index accounts for the car's weight plus passengers and cargo. Never buy below it. Buying above it is fine.
The speed rating (H here) is the maximum sustained speed the tire is built for. H covers 130 mph, which is more than enough for most drivers, but the rating also correlates with how the tire is constructed and handles. Stick with your vehicle's specified rating or higher.
Some sizes also carry prefixes and suffixes: a P prefix means passenger tire, LT means light truck (built for heavier loads at higher pressures, common on work trucks), and XL after the size means extra load, a reinforced version of the same size. If your vehicle calls for LT or XL, that requirement matters as much as the size itself.
Where to find your size
The most reliable source is the tire placard, a sticker inside the driver's door jamb. It lists the sizes and pressures your vehicle came with from the factory. Your owner's manual has the same information.
You can also read the sidewall of your current tires, with one caution: it tells you what's on the car now, not necessarily what belongs there. If a previous owner or a shop installed an off-spec size, copying the sidewall repeats their mistake. When the sidewall and the door placard disagree, trust the placard.
Note that some vehicles are staggered, with different sizes front and rear. Performance cars do this often. Check both axles before ordering four of anything.
Common mistakes to avoid
The classic error is transposing digits: searching 235/65R17 when you need 225/65R17. The listing will look completely normal because that other size really exists, and the mistake only surfaces at the install shop. Double-check against the placard before you order.
The second mistake is treating "close" as "good enough." Neighboring sizes can differ enough in overall diameter to throw off your speedometer and confuse safety systems that read wheel speed. There are legitimate ways to change sizes, but they involve checking overall diameter math, not grabbing whatever's on sale.
The third is ignoring load index and speed rating to save money. A cheaper tire in your size that's below your specified load rating isn't a deal, it's the wrong tire.
Armed with your size
Once you have the full string from your door placard, width, ratio, diameter, load, and speed, you can shop anywhere and compare with confidence. Prices for the exact same size vary a lot between retailers, so the size code that felt like jargon ten minutes ago is now the key that lets you comparison shop. Enter it once on Treddur and we'll show you current prices from major online retailers, sorted cheapest first.