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Tire Size Guide
Truck tires are sold in two sizing languages. Flotation sizing states the height directly; metric sizing makes you calculate it. Both describe the same three things: height, width, and rim diameter.
Flotation sizing — 35x12.50R20
- 35 = overall tire diameter in inches.
- 12.50 = section width in inches.
- R = radial construction.
- 20 = wheel (rim) diameter in inches — must match your wheel exactly.
Flotation sizes are the easiest to shop because the height is printed on the tire: a 37" tire is a 37" tire regardless of rim diameter.
Metric sizing — 285/70R17
- 285 = section width in millimeters.
- 70 = aspect ratio: sidewall height is 70% of the section width.
- R = radial construction.
- 17 = wheel diameter in inches.
To get overall diameter: (285 × 0.70 × 2 ÷ 25.4) + 17 ≈ 32.7 inches. So 285/70R17 is roughly a 33" tire.
Common equivalents
- 33" ≈ 285/70R17, 275/65R20, 285/65R18
- 35" ≈ 315/70R17, 305/60R20 (approximately 34.5")
- 37" ≈ 315/75R17, 37x12.50R20 flotation
Rim diameter is locked
A tire only mounts on a wheel of matching diameter. In our package builder, once a wheel is selected the tire diameter is locked to that wheel so incompatible sizes never appear. Section width also has to fall inside the wheel's approved rim-width range.
Bigger tires change speedometer calibration, effective gearing, and clearance. Our size math is informational; it is not a fitment guarantee for your specific truck and suspension.