On the BIS wiki, on the tanks config guidelines page, it states that ground-contacting tank wheels must all be of the same radius, or else the tank will crawl at no more than about 6 mph (10 kph). This is a shame, because it is a large limitation on creativity. For example, I have already designed a tank, which happens to have five ground wheels on each track, sporting three different sizes. The three wheels in the middle are small, the front wheel is medium, and the rear wheel is large, and of course the same is true on the other track. The odd thing about this is that it appears one must specify the radius for EACH WHEEL in the memory LOD. If this must be done, then why couldn't it make a simple calculation to turn differently-sized wheels with appropriate rotations?
One of the main reasons I purchased ArmA3 was for creating my own personal vehicles and playing around with them in the editor. The game has so much potential, but it falls short of some seemingly simple measures. On the one hand, model artists should develop their vehicles (or other objects, in this case it's a tank) so as to operate within a normal realistic functional parameter. The Game Engine should accommodate realistic expectations (and some non-realistic, but conceivable functions), and wheel size variation is within a very reasonable range.
As it stands, I could theoretically create a tank chassis with four monster truck tires and have it operate smoothly. Although it would function, it sucks that such an unrealistic scenario is more functional in this engine than having a normal tread system which happens to sport different wheel radii. {F26862}