How to read a tire size code
P225/65R17 98H broken down piece by piece, LT and flotation formats explained, and why a size search has to fold three customer formats into one.
What the customer is actually asking for
A guy walks up to the counter and says he needs "the seventeens." Another one texts a photo of his sidewall with his thumb covering half the numbers. A third reads it off his phone, slow and careful: "two-two-five, sixty-five, seventeen." All three want the same tire. None of them said it the same way twice, and none of them are wrong to say it their way.
That's why any decent inventory search has to fold 225/65R17, 225/65/17, and 2256517 into one query. If it doesn't, you're retyping the same size three different ways before you find what's actually on the shelf.
Reading the code itself
Take P225/65R17 98H. Every piece of it means something specific.
- P: passenger tire. LT means light truck, and it usually carries a load range letter like C, D, or E.
- 225: section width in millimeters, measured sidewall to sidewall at the widest point.
- 65: aspect ratio. The sidewall's height is 65 percent of that 225 mm width.
- R: radial construction, which is nearly everything on the road today.
- 17: rim diameter in inches, the wheel this tire is built to fit.
- 98: load index. It converts to a weight rating per tire, 1,653 pounds in this case.
- H: speed rating, good for 130 mph under ideal conditions.
Eight characters, seven pieces of information. Once you've read a few hundred of these, it stops feeling like code.
Why the load index matters more than the number suggests
Two tires can look identical on the shelf and carry very different weight ratings. A 98 load index means 1,653 pounds per tire; drop to a 94 and that same size only carries 1,477 pounds. On a heavier SUV or a loaded pickup, that gap matters. Sell a customer a lower load index than what's stamped on their door jamb and you've put them in a tire that isn't rated for their vehicle, even if the size on the sidewall matches perfectly.
Check the door jamb sticker, not just the old tire coming off. Sometimes a previous owner already downgraded the size, and matching what's currently mounted just repeats someone else's mistake.
LT and flotation sizes read differently
Light-truck tires often carry a load range on top of the load index, and that range changes how much weight the tire's rated to carry at a given pressure. Flotation sizes drop the metric format entirely. A tire marked 33x12.50R20 reads as overall diameter, then width, then rim, all in inches: 33 inches tall, 12.5 inches wide, on a 20-inch rim. No aspect ratio percentage in sight, and no section width in millimeters either.
Doing the diameter math
Overall diameter comes from the rim plus twice the sidewall height. Take our P225/65R17 example. Section width 225 mm times aspect ratio 65 percent gives a sidewall height of about 146 mm. Double that, add the 17-inch rim converted to millimeters (17 × 25.4 = 432 mm), and you land around 724 mm total, or about 28.5 inches overall.
The math isn't hard. Two tires sharing the same rim size can still sit noticeably taller or shorter depending on aspect ratio, and that's exactly what matters when a customer's asking whether a different size will rub against the fender.
This comes up most with plus-sizing, where a customer wants a bigger rim but doesn't want the speedometer thrown off or the ride height changed. Keep overall diameter close to the original and both stay roughly correct. Drift too far from it in either direction and the odometer reads wrong, the ABS system can act strangely, and the car sits noticeably higher or lower than it did before. Small drift is fine. None of that is a size the shop should talk a customer into without walking through the diameter math first, especially on a vehicle where the owner cares about ride height or speedometer accuracy more than most people do.
Search has to do the folding, not the customer
None of this works if a shop's system expects one exact format typed one exact way. A size search that only matches "225/65R17" misses the customer who wrote "225 65 17" on a sticky note, and it misses the tech who just typed seven digits with no slashes at all.
DuroBay's size search folds those formats together automatically, so 225/65R17, 225/65/17, and 2256517 all pull up the same tire. For how the DOT date on the same sidewall works once you know the pattern, see how to read a DOT date code, and for what the tread depth on that tire is worth, see our tread depth chart.
Common questions
What does the 65 mean in 225/65R17?
That's the aspect ratio. The tire's sidewall height is 65 percent of its 225 mm section width, so a lower number means a shorter sidewall.
Why do LT tires have letters like C, D, or E?
That's the load range. It tells you how much weight and pressure the tire is built to handle beyond what the load index number alone shows.
How is a flotation size like 33x12.50R20 different from a metric size?
It skips the aspect ratio percentage. The numbers read straight through as overall diameter, section width, and rim diameter, all in inches.
Why does inventory search need to handle three ways of typing the same size?
Because customers and techs never type it the same way twice. Folding 225/65R17, 225/65/17, and 2256517 into one query saves everyone from retyping the size by hand.