Dimensions only need to be precise enough to distuinguish one tyre part from another - so rounding is OK. We are not looking for engineering precision here - just enough to be descriptive.
The diagram/file that Markus provided is correct - the rim diameter should be that of the outer edge of the wheel hub and the profile is the measurement from there to the tread.
The diagram/file that Markus provided is correct - the rim diameter should be that of the outer edge of the wheel hub and the profile is the measurement from there to the tread.
Chris (LDraw Parts Library Admin)