Tire Size Explained: How to Read 265/70R17 (With Chart)

May 18, 2026·10 min read

Quick answer: In a tire size like 265/70R17, 265 is the tread width in millimeters, 70 is the aspect ratio (sidewall height as a percentage of width), R means radial construction, and 17 is the wheel diameter in inches. The overall diameter of a 265/70R17 is about 31.6 inches. Need to compare two sizes? Use the tire size calculator.

I spent two years driving on the wrong tire size because I trusted the guy at the shop who said "close enough." My speedometer was reading 3 mph slow at highway speed, and I burned through a set of brake pads 12,000 miles early because the larger diameter threw off the ABS calibration. Those three numbers on the sidewall matter more than most people think.

Breaking Down the Tire Size Format

Every passenger tire sold in the US follows the same format: Width / Aspect Ratio + Construction + Rim Diameter. Some tires add a prefix letter and most add a load/speed suffix, but the core number is always the same structure.

Let's dissect P265/70R17 115T piece by piece:

Position	Example	What It Means
Prefix	P	P = Passenger, LT = Light Truck, ST = Special Trailer
Width	265	Tread width in millimeters (10.43 inches)
Aspect Ratio	70	Sidewall height = 70% of width (185.5 mm / 7.3 in)
Construction	R	R = Radial (99%+ of modern tires)
Rim Diameter	17	Wheel diameter in inches
Load Index	115	Max load capacity per tire (2,679 lbs)
Speed Rating	T	Max sustained speed (118 mph)

The prefix is optional. If there's no letter before the width number, the tire follows European (ETRTO) standards instead of US (T&RA) standards. Functionally identical for daily driving — the load ratings differ slightly at maximum inflation.

Width: The First Number

The width — 265 in our example — is the measurement from sidewall to sidewall when the tire is mounted on the recommended rim width and inflated to spec. It's always in millimeters.

Common widths range from 155 mm (small economy cars) to 355 mm (high-performance sports cars). Here's what different widths look like in practice:

Width (mm)	Width (in)	Typical Vehicle
185	7.3	Compact sedans (Civic, Corolla)
215	8.5	Mid-size sedans (Camry, Accord)
245	9.6	SUVs, muscle cars (Mustang GT, RAV4)
265	10.4	Full-size trucks (F-150, Silverado)
285	11.2	Heavy-duty trucks, performance SUVs
315	12.4	Performance trucks, sports cars

Wider tires give more grip because there's more rubber on the road. The tradeoff: more rolling resistance, worse fuel economy, more road noise, and higher cost. A 265 mm tire costs 15-25% more than a 225 mm tire in the same brand and model.

Going wider than stock also affects your speedometer accuracy and can cause rubbing on the fender or suspension components. If you're thinking about upsizing, run the numbers through the tire size calculator first.

Aspect Ratio: The Second Number

The aspect ratio is the most misunderstood number. It's not a measurement — it's a percentage. An aspect ratio of 70 means the sidewall height is 70% of the tire's width.

For a 265/70R17: sidewall height = 265 mm x 0.70 = 185.5 mm (about 7.3 inches).

This matters because it directly determines ride quality, handling, and overall tire diameter:

Aspect Ratio	Sidewall Character	Common On
30-40	Very low profile, stiff ride, sharp handling	Sports cars, performance sedans
45-55	Moderate profile, balanced ride/handling	Most sedans and crossovers
60-70	Tall sidewall, comfortable ride, more flex	Trucks, SUVs, off-road vehicles
75-85	Very tall sidewall, maximum cushion	Vans, trailers, older trucks

Lower aspect ratios look aggressive and corner better because there's less sidewall flex. Higher aspect ratios absorb potholes better and survive rough roads. If you're on a truck doing actual truck things — gravel roads, job sites, towing — stay at 65 or above. The guys running 35-series tires on lifted trucks are replacing bent wheels every pothole season.

Construction Type: The Letter

The "R" stands for radial. In a radial tire, the internal cord plies run perpendicular to the direction of travel (radially from the center). This gives better heat dissipation, longer tread life, and more flexible sidewalls.

You'll occasionally see:

R — Radial (99% of tires sold today)
D or B — Diagonal/Bias-ply (trailers, some off-road, vintage vehicles)
F — Run-flat (BMW, some Mercedes)

Unless you're buying trailer tires or restoring a 1960s Mustang, every tire you encounter will be radial. Bias-ply tires are cheaper but wear faster, run hotter, and handle worse. They survive heavy loads better in low-speed applications, which is why trailer tires still use them.

Rim Diameter: The Last Number

The 17 in 265/70R17 means this tire fits a 17-inch wheel. This is the one number you cannot fudge — a 17-inch tire physically will not mount on a 16-inch or 18-inch wheel.

Common rim diameters for passenger vehicles:

Diameter	Typical Application
14-15"	Economy cars, older vehicles
16-17"	Standard sedans, base-model trucks/SUVs
18-19"	Mid-trim trucks/SUVs, sport sedans
20-22"	Premium trims, aftermarket upgrades

Larger wheels need lower-profile tires to maintain the same overall diameter. A truck that comes stock with 265/70R17 might use 275/55R20 as an upgrade — different wheel, different tire shape, but nearly identical overall diameter (31.6" vs 31.9"). That similarity is intentional. The speedometer correction calculator shows exactly how diameter changes affect your speedo reading.

How to Calculate Overall Tire Diameter

Overall diameter determines ground clearance, speedometer accuracy, gearing, and whether the tire fits your wheel well without rubbing. The formula:

Overall diameter = (2 x sidewall height) + rim diameter

For 265/70R17:

Sidewall height: 265 mm x 0.70 = 185.5 mm
Convert to inches: 185.5 / 25.4 = 7.30 inches
Both sidewalls: 7.30 x 2 = 14.60 inches
Add rim: 14.60 + 17 = 31.60 inches

Here's a quick reference for popular truck tire sizes:

Tire Size	Overall Diameter	Difference from 265/70R17
245/75R16	30.5"	-1.1"
265/70R17	31.6"	baseline
275/70R17	32.2"	+0.6"
285/70R17	32.7"	+1.1"
265/65R18	31.6"	0.0"
275/60R20	33.0"	+1.4"
33x12.5R17	33.0"	+1.4"

A difference of more than 3% from stock will noticeably affect your speedometer. At 1.1 inches larger (285/70R17), your speedo reads about 60 mph when you're actually doing 62. Not a huge deal on surface streets. On a long highway trip, your odometer accumulates the error — over 10,000 miles, you've actually driven 10,350. That affects lease mileage tracking, maintenance intervals, and fuel economy calculations.

Load Index and Speed Rating

After the rim diameter, you'll often see two more characters — like 115T. These are the load index and speed rating.

Load index is a code that maps to a maximum weight per tire:

Load Index	Max Weight (lbs)	Common On
91	1,356	Sedans
100	1,764	Crossovers
110	2,337	SUVs
115	2,679	Trucks
121	3,197	Heavy-duty trucks
126	3,748	HD trucks / commercial

Multiply by 4 for total vehicle capacity. A 115 load index supports 10,716 lbs across all four tires. That's well above most half-ton trucks' GVWR. If you're towing heavy loads, this number matters — check the towing capacity guide for how tire ratings factor into safe towing.

Speed rating is the maximum sustained speed the tire is engineered for:

Rating	Max Speed	Typical Use
S	112 mph	Family sedans, SUVs
T	118 mph	Trucks, SUVs, standard sedans
H	130 mph	Sport sedans, coupes
V	149 mph	Sports cars
W	168 mph	High-performance sports cars
Y	186 mph	Exotic / supercars

Never downgrade speed rating from what your vehicle manufacturer specifies. Upgrading is fine — putting H-rated tires on a T-rated vehicle is safe. Going the other direction risks tire failure at highway speeds.

Common Mistakes When Reading Tire Sizes

After a decade of watching people buy wrong tires (including myself), these are the mistakes I see most often:

Confusing width with diameter. A 265 tire is not 265 inches around. It's 265 mm wide — about 10.4 inches. The overall diameter depends on the aspect ratio and rim size.

Ignoring aspect ratio when upsizing width. Going from 265/70R17 to 285/70R17 doesn't just make the tire wider — it also makes it taller because 70% of 285 is more than 70% of 265. The overall diameter jumps from 31.6" to 32.7". If you want wider without taller, you need to drop the aspect ratio: 285/65R17 gives you 32.0" — much closer to stock.

Mixing metric and flotation sizes. Truck tires come in two naming conventions. 265/70R17 is metric. 33x12.5R17 is flotation (overall diameter x width x rim). They're not interchangeable labels — a 33x12.5R17 is roughly equivalent to a 318/76R17, not a 335/70R17.

Assuming LT and P tires are interchangeable. LT (Light Truck) tires have stiffer sidewalls and higher load ratings than P (Passenger) tires of the same size. If your truck came with LT tires, replacing with P-rated tires of the same dimensions reduces your load capacity significantly. This matters for towing and hauling.

FAQ

Can I put a different tire size on my car?

Yes, within limits. The general rule is to stay within 3% of your stock overall diameter to avoid speedometer errors, ABS issues, and transmission strain. You can go wider or narrower by one size (e.g., 255 to 265) if the wheel width supports it. The tire size calculator shows the exact diameter difference between any two sizes.

What does the "R" in tire size mean?

R stands for radial construction, meaning the internal cord plies run perpendicular to the tread. Virtually every modern passenger and light truck tire is radial. You'll only see D (diagonal/bias-ply) on trailer tires and some specialty off-road tires. The construction type affects ride quality, heat buildup, and tread life.

How do I know what tire size fits my vehicle?

Check three places: the sticker on the driver's door jamb, your owner's manual, or the sidewall of your current tires. The door jamb sticker is the most reliable because it lists the manufacturer-specified size, load rating, and recommended inflation pressure. Don't go by what's currently on the car — the previous owner may have swapped sizes.

What's the difference between 265/70R17 and 265/65R18?

Both have 265 mm width but differ in profile and rim size. The 265/70R17 has a taller sidewall (185.5 mm) on a smaller wheel, giving a softer ride and 31.6" overall diameter. The 265/65R18 has a shorter sidewall (172.3 mm) on a larger wheel, giving sharper handling and 31.6" overall diameter. Nearly identical outer size, different ride characteristics.

Does tire size affect gas mileage?

Yes. Wider tires increase rolling resistance, which reduces MPG by 1-3% per size increase. Taller tires (larger overall diameter) reduce engine RPM at highway speed, which can slightly improve economy — but the heavier weight usually cancels it out. The biggest fuel economy impact comes from tire pressure, not size. Check your MPG calculations before and after any tire change to see the real-world difference.

Next Steps

Compare any two tire sizes side-by-side with the tire size calculator — it shows diameter difference, speedometer correction, and whether the swap is safe.
Already changed tire sizes? Use the speedometer correction calculator to find out how far off your speedo reads.
Check the tire size comparison chart for a full table of popular sizes with dimensions, load ratings, and common vehicle fitments.