265/70R17 vs 285/70R17: What Changes?

Moving from 265/70R17 to 285/70R17 increases overall diameter by a calculated 1.10 in (28.0 mm) and width by a calculated 20 mm. This change produces a calculated 3.49% increase in diameter.

Because the rolling diameter is larger, your speedometer and odometer will register slightly lower values than your actual speed and travel distance.

What do the numbers in each tire size mean?

BFGoodrich explains that metric tire sizing defines three primary dimensions on the sidewall.

The first number indicates nominal section width in millimeters. Therefore, 265/70R17 has a nominal width of 265 mm, whereas 285/70R17 measures 285 mm. The difference is a calculated +20 mm increase in section width.

The second number, aspect ratio, describes sidewall height as a percentage of width, according to BFGoodrich. Both sizes share a 70 aspect ratio. Because 285 mm is wider, 70% of 285 mm produces a taller sidewall.

The final number specifies wheel rim diameter in inches. Both tires mount on a 17-inch wheel rim. Overall diameter grows while wheel rim diameter stays unchanged.

How do you calculate the diameter difference step by step?

Tire diameter uses a nominal formula: rim times 25.4 plus two times width times aspect ratio divided by 100.

1. Original diameter (265/70R17): The formula yields a calculated 802.8 mm (31.61 in).
2. New diameter (285/70R17): The formula yields a calculated 830.8 mm (32.71 in).
3. Height difference: Subtracting 802.8 mm from 830.8 mm yields a calculated +28.0 mm (+1.10 in).
4. Percentage difference: Dividing +28.0 mm by 802.8 mm yields a calculated +3.49%.
5. Width difference: Subtracting 265 mm from 285 mm yields a calculated +20 mm.

Industry guidelines suggest staying within about 3% of original diameter. The calculated change here is +3.49%. This 3% guideline is a comparison benchmark, not a safety limit or law.

Compare dimensions using our tire size calculator.

How do calculated dimensions compare to published specs?

Formulas give nominal dimensions, but physical tires vary. The table below contrasts calculated nominal figures with published specifications for one real tire.

Tire Rack published specs for the BFGoodrich KO2 LT285/70R17 list a 32.8 in diameter and an 11.5 in width on an 8.5 in measuring rim. Tire Rack also lists 635 revs/mile for this real tire, a published figure that differs from the calculated nominal 616.6 revs/mile. The calculations on this page use the nominal figures. Always check published manufacturer specifications.

How do speedometer and odometer readings change?

Because the 285/70R17 tire is taller, each complete rotation covers more distance on the road.

Nominal circumference increases from 2,522 mm to 2,610 mm (calculated). Therefore, the tire rotates fewer times over each mile traveled.

Calculated nominal revolutions drop from 638.1 to 616.6 revs/mile.

With fewer rotations per mile, the speedometer reads lower than your actual speed.

At an indicated 60 mph on your speedometer, your calculated actual speed is 62.1 mph.

When the odometer records 10,000 miles, the vehicle has traveled a calculated 10,349 actual miles.

To evaluate alternative sizes and their impact on readings, check our guide to tire size alternatives.

What should you check regarding fitment and clearance?

Moving to 285/70R17 requires careful fitment checks.

NHTSA states that the recommended tire size appears on the Tire and Loading Information placard on the driver's door frame or in the owner's manual.

A tire with a calculated +20 mm wider section and +28.0 mm taller diameter may not fit every vehicle. Have a tire shop check clearance before you buy.

This guide provides geometry calculations only and makes no vehicle fitment claims or safety verdicts. Consult your owner's manual, verify the tire maker's approved rim width range, and have a tire professional inspect clearance.

For details on sidewall markings, see our guide on how to read a tire sidewall or our used tire check page.

Frequently asked questions

Is 285/70R17 considered a 33-inch tire?

It is close. The calculated nominal diameter is 32.71 in, and the Tire Rack spec for the KO2 LT285/70R17 is 32.8 in. Both are just under 33 inches.

Does 285/70R17 require a wider wheel rim?

The Tire Rack spec in the table above lists an 8.5 in measuring rim width for the KO2 LT285/70R17. Check the tire maker's approved rim width range and your wheel specifications before mounting.

Do I need to recalibrate my speedometer for 285/70R17?

At an indicated 60 mph, actual speed is a calculated 62.1 mph. Consult your vehicle manufacturer or a professional technician regarding speedometer programming.

Sources

• Tire Rack: BFGoodrich All-Terrain T/A KO2 LT285/70R17 Specs
• BFGoodrich: Reading a Tire Sidewall
• NHTSA: Tire Safety