OceanCalc

Tire Size Calculator

Compare tire sizes and calculate speedometer error.

Original Tire Size
mm
%
in

225/45R17

New Tire Size
mm
%
in

235/40R18

Understanding Tire Sizes

225/45R17

  • 225 - Tire width in millimeters
  • 45 - Aspect ratio (sidewall height as % of width)
  • R - Radial construction
  • 17 - Rim diameter in inches

Keep tire diameter within 3% of original to avoid speedometer errors and potential clearance issues.

Comparison
Diameter Difference+0.43" (+1.7%)
Speedometer Error-1.7%
Tire Specifications
Original
New
Diameter
24.97"
25.4"
Circumference
78.45"
79.8"
Rev/Mile
808
794
Sidewall
101.3mm
94mm