Calchy.
Automotive - tire size

What is the difference between 255/40R18 and 275/35R18 tires?

Answer
-11.5
mm overall diameter
649.7 mm − 661.2 mm = -11.5 mm (-1.74%)
How we got there
  1. 01255/40R18: sidewall 102.0 mm, total diameter 661.2 mm
  2. 02275/35R18: sidewall 96.3 mm, total diameter 649.7 mm
  3. 03Difference: -11.5 mm (-1.74% — speedometer error in same direction)
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