[ODE] trimesh triangle size and stability

[Pancini, Ettore]

hi,
recently i had problems with stability. after some test i came to
conclusion that's because the trimesh was composed of big tiangles (ie:
every tris was 100 units, while vehicle wheels are 0.5 unit). i didn't
thought that the 'keep it around 1' rule was valid also to tris size.

if you can confirm that tris in a trimesh should not be too big, maybe
we can add this to wiky, under the 'how to make stable stuff' page.

cheers,
ekt