Quick Answer
- A comparison turns two tire sizes into diameter, width, sidewall, revs per mile and speedometer error. Going from 265/70R17 to 285/70R17 adds 1.10 in of diameter (+3.5%).
- The speedometer then reads about 3.5% low: an indicated 60 mph is 62.1 mph, and every 100 indicated miles are 103.5 actual miles (calculated).
- Continental says to keep rolling circumference within 3% of the original, and that a larger deviation can affect speedometer accuracy, ABS and stability control.
① Original Tire
→ 265/70R17
② Compare Tire
→ 285/70R17
Enter tire specs above and click Calculate to compare
Supports P-metric (225/65R17) and Imperial/flotation (31x10.5R15) formats
Tire Size Comparison Chart: Common Swaps
Calculated from the size codes. For a drawing of two sizes side by side use the side-by-side tire comparison.
| Original | New | Diameter in | Change | Change % | Width change | Revs per mile | True speed at 60 mph |
|---|---|---|---|---|---|---|---|
| 265/70R17 | 285/70R17 | 31.61 to 32.71 | +1.10 in | +3.5% | +20 mm | 638 to 617 | 62.1 mph |
| 265/70R17 | 285/75R17 | 31.61 to 33.83 | +2.22 in | +7.0% | +20 mm | 638 to 596 | 64.2 mph |
| 225/65R17 | 235/65R17 | 28.52 to 29.03 | +0.51 in | +1.8% | +10 mm | 707 to 695 | 61.1 mph |
| 275/65R18 | 295/65R18 | 32.07 to 33.10 | +1.02 in | +3.2% | +20 mm | 629 to 609 | 61.9 mph |
| 245/75R16 | 265/75R16 | 30.47 to 31.65 | +1.18 in | +3.9% | +20 mm | 662 to 637 | 62.3 mph |
| 255/70R18 | 275/65R18 | 32.06 to 32.07 | +0.02 in | +0.1% | +20 mm | 629 to 629 | 60.0 mph |
| 285/75R16 | 315/75R16 | 32.83 to 34.60 | +1.77 in | +5.4% | +30 mm | 614 to 583 | 63.2 mph |
| 225/45R18 | 235/45R18 | 25.97 to 26.33 | +0.35 in | +1.4% | +10 mm | 777 to 766 | 60.8 mph |
| 245/65R17 | 265/70R17 | 29.54 to 31.61 | +2.07 in | +7.0% | +20 mm | 683 to 638 | 64.2 mph |
| 31x10.50R15 | 33x12.50R15 | 31.00 to 33.00 | +2.00 in | +6.5% | n/a | 651 to 611 | 63.9 mph |
For the percentage only, see the tire size difference calculator; for Toyota trucks the Tacoma tire size calculator.
Comparison Formulas and Sources
Overall diameter
Rim + 2 x width x aspect / 100 / 25.4 for metric sizes. For inch sizes such as 33x12.50R15 the first number is the nominal diameter.
Difference
New diameter - original diameter, and divided by the original for percent. 265/70R17 to 285/70R17: 32.71 - 31.61 = 1.10 in (+3.49%).
Speedometer error
True speed = indicated speed x new diameter / original diameter. A taller tire makes the speedometer read low.
Odometer error
Actual distance = indicated distance x new diameter / original diameter. The percentage is the same as the speedometer error.
| Source | Statement (paraphrased) |
|---|---|
| Continental Tire, plus-sizing guidance | Match the original rolling circumference closely. A deviation above 3% can affect speedometer accuracy, ABS, stability control and other systems. |
| USTMA, Care and Service of Passenger and Light Truck Tires | Acceptable load capacity or overall diameter does not imply acceptable vehicle clearance. Check clearance at all four wheel positions through full suspension travel and steering lock. |
| USTMA | Lower aspect ratio tires typically aid performance and handling but may give a less comfortable ride, may wear more quickly and be noisier, and are more susceptible to pothole and curb damage. |
How to Compare Two Tire Sizes
- 1Choose metric or inch format for the original tire and enter its size, for example 265/70R17 or 31x10.50R15.
- 2Enter the second tire in the Compare panel.
- 3Click Calculate and Compare.
- 4Read the Stats tab for diameter, width, sidewall and revs per mile, the Speedometer tab for true speeds, and the Visual and Graphs tabs for a picture.