How tire size is calculated
In 205/55 R16, 205 is section width in millimeters, 55 is sidewall height as a percentage of width, and 16 is wheel diameter in inches.
Sidewall = width × aspect ratio ÷ 100
Diameter = wheel × 25.4 + sidewall × 2
How a tire-size change affects the vehicle
A larger tire raises ground clearance by half the diameter difference and makes actual road speed higher than the speedometer reading. Width changes inner and outer space, but wheel offset, rim width and vehicle geometry still determine real fitment.
What tire diameter difference is acceptable?
The common ±3% guideline is useful for an initial comparison, not universal approval. Check the owner’s manual, load and speed ratings, approved wheel widths, fender space and suspension clearance.
Preliminary wheel-width reference
This table gives a broad reference envelope for groups of nominal passenger-tire widths. It is only an initial proportion check: aspect ratio and the construction of a specific tire can require a narrower approved range.
| Nominal tire width | General wheel-width reference |
|---|---|
| 135–155 mm | 3.5–5.5 in |
| 165–185 mm | 4.5–6.5 in |
| 195–215 mm | 5.5–8 in |
| 225–245 mm | 6–9.5 in |
| 255–275 mm | 7–10.5 in |
| 285–305 mm | 8–11.5 in |
| 315–335 mm | 8.5–12.5 in |
| 345–355 mm | 9.5–13 in |
Not a fitment or compatibility approval
Even a result inside the table does not confirm that the tire, wheel and vehicle are compatible. Find the approved wheel-width range in the specification for the exact tire model and size, then verify the size against the vehicle placard, owner’s manual and manufacturer requirements.
Bead-seat diameter must match exactly: an R17 tire fits only a 17-inch-diameter wheel.
Why the exact tire must be checked: Michelin · Toyo Tires