Tire Size accuracy

[jayman]

The spec for my tire diameter is 34.1" from the manufacturer, but measuring using the level method recommended in the DS manual I get 32.75" which is more accurate? Thanks.

[MagsTuning]

I use the true measurement of the tire as it sits on the vehicle. I've never had a speedometer be right when using the side wall sizing or manufacturer sizing.

[mikel]

Honestly, the value thats most accurate is the one that gets the speedo dead on

It seems like it should be an exact science, but its far from it in most cases