Calchy.
Automotive - tire size

What is the difference between 245/45R18 and 255/40R19 tires?

Answer
+8.9
mm overall diameter
686.6 mm − 677.7 mm = 8.9 mm (1.31%)
How we got there
  1. 01245/45R18: sidewall 110.3 mm, total diameter 677.7 mm
  2. 02255/40R19: sidewall 102.0 mm, total diameter 686.6 mm
  3. 03Difference: 8.9 mm (1.31% — speedometer error in same direction)
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