Tire Size Comparison
To compare tire sizes, put your current size and the new one side by side. The tool draws both to scale, from the side and from the front, and lists the change in diameter, width, sidewall and revolutions per mile. A diameter change in percent is the number that affects your speedometer most.
Side-by-side visualizer
The calculator needs JavaScript. The formulas and tables on this page work without it: sidewall = width × aspect ratio ÷ 100, and diameter = rim × 25.4 + 2 × sidewall (in mm).
Accepts 225/45R17, P225/45R17, LT285/75R16, 225/45ZR17 94W and 33x12.50R15.
Result
Next: speedometer error · diameter · plus sizing
What the drawing shows
The left shape of each pair is the tire seen from the side, with the rim in grey. The right shape is the tread seen from the front, with its width to the same scale. All tires use one scale, so a taller tire really is drawn taller.
Common comparisons
| From | To | Diameter change | Width change |
|---|---|---|---|
| 205/55R16 | 225/45R17 | +0.4% | +20 mm |
| 225/45R17 | 235/40R18 | +1.7% | +10 mm |
| 265/70R17 | 285/70R17 | +3.5% | +20 mm |
| 265/70R17 | 285/75R17 | +7.0% | +20 mm |
| 215/60R16 | 225/55R17 | +2.2% | +10 mm |
| 245/75R16 | 265/75R16 | +3.9% | +20 mm |
Calculated from the nominal size codes.
Things the numbers do not show
Whether a tire fits also depends on the wheel width and offset, suspension parts, brake calipers and how far the wheel turns and moves up and down. Always check your vehicle owner’s manual, the tire placard in the door jamb, or a tire shop before changing size.
Frequently asked questions
What does 265/70R17 mean?
265 is the section width in millimetres, 70 is the aspect ratio (the sidewall is 70% of the width, 185.5 mm), R means radial construction and 17 is the rim diameter in inches. The overall diameter works out at about 31.6 inches or 803 mm.
How much bigger is 285/70R17 than 265/70R17?
A 285/70R17 is about 831 mm (32.7 in) tall against 803 mm (31.6 in), so 3.5% larger in diameter. It is 20 mm wider and the ground clearance at the axle rises by about 14 mm.
Will bigger tires affect my speedometer?
Yes. A taller tire covers more ground per turn, so the speedometer shows less than your actual speed. With a 3.5% taller tire, 60 mph on the speedometer is about 62.1 mph. A dealer or a programmer can often recalibrate it.
What is the difference between 225/45R17 and 235/40R18?
A 235/40R18 is 10 mm wider and about 1.7% larger in overall diameter than a 225/45R17 (645 mm against 634 mm), with a sidewall about 7 mm lower. It needs an 18-inch rim instead of a 17-inch one.
Is a 3% difference a lot?
On the speedometer it means about 3 km/h at 100 km/h. Whether it is acceptable depends on your vehicle and local rules, not on a fixed percentage. The colours in the tool are our own guide to the size of the change.
Can I compare three sizes?
Yes. Fill in size C as well. All three tires are drawn to the same scale, and the tables compare sizes B and C with size A, including the speedometer difference for each.
Last updated: October 15, 2026