What Size Tire Is 255/70R17? 255/70R17 Tire Size Explained

That string of numbers on a tire sidewall is not decoration — it is the exact recipe for the tire’s physical size, and misreading it is how people end up with rubber that rubs a fender or sits wrong on a rim. The 255/70R17 code breaks into four parts, and once you can read it, you can compare any tire on any shelf.

Here is the full breakdown, the real-world dimensions, and the fitment checks that matter before you buy.

What Each Number In 255/70R17 Actually Means

The 255 is the section width in millimeters, the 70 is the aspect ratio, the R stands for radial construction, and the 17 is the wheel diameter in inches. That is the entire code, read left to right.

• 255 — section width, measured in millimeters from sidewall to sidewall at the widest point.
• 70 — aspect ratio, meaning the sidewall height is 70% of the section width.
• R — radial construction, the standard build for passenger and light-truck tires today.
• 17 — the wheel (rim) diameter in inches that this tire mounts on.

One trap here: section width is not the same as tread width. The 255 mm figure describes the tire at its widest point, which includes the sidewall bulge — the part actually touching the road can measure narrower. Tire-size reference charts list the tread face separately for exactly this reason.

The Real Dimensions: How Tall And Wide Is A 255/70R17?

Working the math confirms it. Sidewall height is 70% of 255 mm, which is about 178.5 mm, or roughly 7.0 inches. Double that for both sidewalls (14.0 inches) and add the 17-inch wheel, and you land at about 31.1 inches of overall diameter. That revs-per-mile figure matters if you are correcting a speedometer or programming a tuner.

Will 255/70R17 Fit Your Wheels And Vehicle?

Tire-size reference data from the 255/70R17 size chart lists that 6.5–8.5 inch window as the working fit range.

Width is only one gate. The tire code alone never guarantees fitment — you still need to confirm vehicle clearance, the load rating your vehicle requires, and any OEM approval for your specific model. A tire can match the wheel perfectly and still rub a control arm at full lock.

Service descriptions vary across tires in this size too. But not every 255/70R17 is built the same — a P-metric version, written P255/70R17, can carry a different service description and load index than the plain metric size.

If you are weighing specific models rather than just sizing, our breakdown of the best 255/70R17 tires compares the real options side by side.

Mistakes That Cost People Money

Three assumptions cause most of the trouble with this size, and each one is easy to avoid once you know it is coming.

• Treating section width as tread width. The 255 mm number measures the widest point, not the contact patch.
• Assuming all 255/70R17 tires match. Load index, speed rating, weight, tread depth, and max pressure all shift between models in the same size.
• Assuming any 17-inch tire fits any 17-inch wheel. Width and clearance decide fitment, not the diameter alone.