Read the three numbers
A size marked 27 × 9–12 describes a nominal 27-inch outside diameter, a 9-inch section width, and a 12-inch wheel diameter. The final number is the wheel diameter, not the sidewall height. The wheel diameter must match the tire’s specified bead diameter. These numbers are dimensions in inches, not metric automotive tire notation.
Separate nominal size from measured size
Two tires carrying the same nominal size can have different mounted heights and widths. Published dimensions can depend on the test wheel, pressure, and load. Use the tire manufacturer’s measured dimensions and approved wheel widths when evaluating fit. Measure your existing setup so you know the real starting point.
Estimate clearance and gearing changes
An increase from 25 to 27 inches adds 2 inches to diameter. Since the axle rises by roughly half the diameter change, theoretical ground clearance increases about 1 inch. The diameter ratio is 27 ÷ 25 = 1.08, so theoretical travel per wheel revolution increases 8%. This can affect wheel-based speed readings and effective gearing. A GPS speed reading does not use that wheel-size calibration.
Check fit throughout suspension travel
A parked machine can have plenty of clearance yet rub under steering lock or suspension compression. Check the owner’s manual, tire and wheel specifications, wheel offset, and the available space around suspension, fenders, and brake components. Front and rear tire widths may differ. Compare each axle separately in the calculator.
Build a tire-change checklist
Record the current tire sizes, wheel diameters, wheel widths, and offset. Verify approved replacement combinations. Compare actual mounted dimensions and confirm full-travel clearance. Recheck inflation guidance, load ratings, handling, and speed indication after an approved change. A favorable calculator result cannot establish a safe fit.
Editorial method: formulas are disclosed on each tool page; examples are illustrative, not model specifications. See our editorial standards.
Continue the plan
30 vs 32 vs 35 Inch UTV Tires: Clearance, Speed and Gearing · ATV/UTV Tire Width, Wheel Diameter and Actual Measurements
Put the numbers to work
Use actual measurements and official ratings. Results are estimates; all inputs remain editable.