Tire Size Comparison: Two Sizes Side by Side

How to read the comparison

The table lists each dimension for both sizes and the change. Green means the new size is larger, red smaller; neither is good or bad in itself.

• Diameter is the most important figure. It determines how far the vehicle travels per wheel turn, so it sets speedometer and odometer accuracy.
• Width affects clearance to suspension parts and fenders, and which wheel widths the tire is approved for.
• Sidewall height changes ride and the look of the tire. Lower sidewalls are typical of plus-sizing to bigger wheels.
• Revolutions per mile is what the vehicle's computer effectively counts. Fewer revolutions per mile means a taller tire.

Worked example

Going from 265/70R17 to 285/70R17:

• Diameter: 31.61 in to 32.71 in, +1.10 in (+3.5%).
• Width: 10.43 in to 11.22 in, +0.79 in.
• Revs per mile: about 638 to 617.
• At an indicated 60 mph: about 62.1 mph actual.
• Axle height: about +0.55 in.

The change is just over 3%, so the calculator flags it. That does not mean it can't be done; it means the speedometer and other systems may need checking, and clearance must be confirmed on the vehicle.

The plus-sizing checklist

Continental's technical bulletin on plus sizing lists four things to consider in every size change:

1. Load capacity equal to or greater than the original equipment tire.
2. Inflation pressure never lower than the vehicle manufacturer's recommendation, keeping any front/rear difference.
3. Speed rating equal to or greater than the original.
4. Rolling circumference kept as close to the original as possible; under most circumstances within ±3% needs no system adjustments.

Our plus sizing guide explains each point. Use the load index and speed rating decoder to compare service descriptions.

What the comparison can't tell you

Whether a tire physically fits depends on the wheel width and offset, brake caliper clearance, suspension travel, steering lock and fender liners. None of that is in the size code. NHTSA advises buying the size on the vehicle placard or another size recommended by the vehicle manufacturer, and consulting a tire dealer if in doubt.

Common comparisons

Some size pairs people often compare (calculated diameters):

The second and fourth rows show classic plus-one sizing: a bigger wheel with a lower sidewall that keeps the overall diameter nearly the same. See the common sizes chart for more.

Common questions

Is 265/70R17 vs 285/70R17 a big difference?

285/70R17 is about 32.7 inches tall against 31.6 inches, 3.5% taller and 0.8 inches wider. At an indicated 60 mph you would be doing about 62.1 mph.

What does the 3% rule mean?

Continental's plus-sizing bulletin says that, under most circumstances, a change in rolling circumference within plus or minus 3% does not require adjustments to speedometer, ABS or stability systems. It is a guideline for size math, not a fitment approval.

Does a taller tire increase ground clearance?

At the axle, by half the diameter increase. A tire 1 inch taller raises the axle about 0.5 inches. Suspension and body parts stay at the same height relative to the axle.

Can I put different sizes front and rear?

Only if the vehicle came that way from the manufacturer. Continental recommends that all-wheel and four-wheel drive vehicles use the same size on all four corners unless they were originally fitted with a staggered setup.