Checks whether alternative tire sizes fit a vehicle correctly.
The tire fitment checker compares a replacement tire size against the original size to determine if it is safe to use, checking differences in overall diameter, speedometer error, and load/speed rating compatibility.
Tire width (mm), aspect ratio (%), rim diameter (inches). Section height = Width × Aspect / 100 Overall diameter = Rim diameter × 25.4 + 2 × Section height (all in mm) Speedometer error % = (New OD − OEM OD) / OEM OD × 100
OEM: 205/55 R16. OD = 16×25.4 + 2×(205×0.55) = 406.4 + 225.5 = 631.9 mm. Replacement: 215/55 R16. OD = 406.4 + 236.5 = 642.9 mm. Difference = +1.7%. Speedometer reads 2% low — generally acceptable (within ±3% tolerance).
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