Tire and Rim Size Calculator

How to use

1. Enter your current tire specifications (e.g. 205/55 R16).
2. Input the proposed new tire size (e.g. 225/45 R17).
3. Review outer rolling diameter and circumference differences.
4. Check theoretical ground clearance change in millimeters.
5. Assess speedometer variance across different vehicle speeds.
6. Verify rim dimensions: width, ET offset, PCD bolt pattern, and center bore DIA.

What the Tire Size Calculator Shows

The overall wheel diameter is calculated from rim diameter plus two sidewall heights: D = d × 25.4 + 2 × (W × H / 100). Changing overall tire diameter alters ride height, gear ratios, and speedometer accuracy.

• Tire width — section width in millimeters
• Aspect ratio — sidewall height expressed as a percentage of tire width
• Rim diameter — wheel rim seat diameter in inches
• Rolling diameter — total wheel assembly height in millimeters

Ride Height and Ground Clearance Impact

Because the axle sits at the center of the wheel, vehicle ride height changes by exactly half of the rolling diameter difference: ΔClearance = (D₂ − D₁) / 2.

Speedometer Variance

Larger tires cover more distance per revolution, causing the speedometer to read lower than actual vehicle speed: V_actual ≈ V_indicated × D₂ / D₁.

Wheel Rim Specifications: ET, PCD, DIA

• ET (Offset) — distance from mounting hub face to wheel centerline in mm
• PCD — bolt circle diameter and lug hole count (e.g. 5×112)
• DIA — center bore diameter matching the vehicle wheel hub
• Rim width — distance between bead seats in inches