Published by Rims & Tires
Compiled & checked by the site's publisher from manufacturer, NHTSA & USTMA data · Updated 2026-08-01
In a size like P235/65R17 102H, every character means something specific. P is a passenger tire, 235 is the section width in millimeters, 65 is the aspect ratio, R means radial construction, 17 is the wheel diameter in inches, 102 is the load index, and H is the speed rating. Your vehicle’s correct size is printed on the sticker inside the driver’s door jamb.
What does 235/65R17 actually mean?
P (or LT): the type. “P” is passenger; “LT” is light truck (heavier-duty, for towing and hauling). No letter usually means metric passenger.
235: the section width in millimeters — the tire’s width from sidewall to sidewall.
65: the aspect ratio — the sidewall height as a percentage of the width. Lower number = shorter, sportier sidewall; higher = taller, more cushion.
R: radial construction (almost all modern tires).
17: the wheel diameter in inches the tire is built to fit.
What do the load index and speed rating mean?
After the size you’ll see something like 102H. The number (102) is the load index: how much weight the tire can carry. The letter (H) is the speed rating: the max safe speed the tire is built for. The U.S. Tire Manufacturers Association is explicit about this one — replacement tires should carry the same size, load index, and speed rating designation the vehicle or tire manufacturer recommends. Match or exceed. Never go under.
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What do the other sidewall markings mean?
The size string is only part of what’s molded into the rubber. DOT: the U.S. Department of Transportation code, ending in four digits that give the week and year the tire was built (3223 = week 32 of 2023). UTQG: the Uniform Tire Quality Grading numbers for treadwear, traction, and temperature.
M+S means mud and snow, a self-certified tread-pattern designation with no test behind it. The three-peak mountain snowflake (3PMSF) is the one that means something. It requires passing a standardized snow-traction test, which is why 3PMSF-rated all-terrains like the BFGoodrich KO2 and Falken Wildpeak A/T3W handle a Georgia ice morning better than a plain all-season does.
Small triangles or the letters TWI around the shoulder point to the tread wear indicator bars sitting down in the grooves at 2/32". MAX PRESS is the tire’s structural pressure ceiling, not your target. That number comes from the door jamb.
Where do you find your correct tire size?
The easiest place is the sticker inside the driver’s door jamb (also in your owner’s manual) — that’s the manufacturer’s recommended size. The size on your current tires works too, unless someone sized up or down before you.
Changing wheel diameter or width? Then your tire size has to change to match, and getting offset and overall diameter right matters — a local shop can spec it so your speedometer stays accurate and nothing rubs.
Frequently asked
Can I put a different size tire on my car?
You can change sizes, but the overall diameter should stay close to stock to keep your speedometer accurate and avoid rubbing. Plus-sizing (bigger wheel, shorter sidewall) keeps diameter the same. A shop can confirm what fits.
What does the letter before the size mean?
“P” means passenger tire; “LT” means light truck — built tougher for towing and heavier loads. Use the type your vehicle calls for.
What if the tires on my car don’t match the door-jamb sticker?
It usually means a previous owner sized up or down. The door sticker is the factory recommendation, so it’s the safe default when you replace. If you like how the current size drives and nothing rubs, a shop can confirm it’s a sound setup before you buy another set.
What does the R in 235/65R17 stand for?
Radial construction: the body plies run radially, from bead to bead across the tire. Essentially every modern passenger and light-truck tire is a radial. If you ever see a D instead, that’s a diagonal (bias-ply) tire, still found on some trailers and vintage vehicles.
What does the 65 in a tire size actually change?
It’s the aspect ratio: sidewall height as a percentage of section width. On a 235/65R17, the sidewall is 65% of 235mm, roughly 153mm tall. Drop that number and you get a shorter, stiffer sidewall — sharper steering, harsher ride, more vulnerability to pothole damage. Raise it and you get more cushion and more sidewall flex.
Do all four tires need to be the same size?
On most cars, yes. Mismatched sizes can confuse the ABS, and on all-wheel drive they can damage the drivetrain. Some sports cars run wider rears on purpose — that’s a staggered setup, and it’s intentional. When you’re not sure, match what the door sticker lists.
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Last updated 2026-08-01. General guidance only — confirm specifics with a local shop for your exact vehicle.