Hi, i have run into a problem i can't easily describe (again ;))

Think about this car wheel. You can't use the self-mesh because it is too complex.



So you either have the option to use a sphere, which is not physically correct for a wheel.



It works. Because it has clean and even surface for physics simulation. However, not correct. The car will drift to the sides.
If you use the convex hull, there will be a problem.
The convex hull only works as long as you don't set a pivot for it. This is a bug. Here an example with an actual physics prop from the iClone stock content.
It has physics already enabled and shape set to convex hull. Looks good, right?



Setting the pivot to center causes this:



Now what is left is the idea of using a dummy wheel, which will be just a prop that you attach the real wheel to.
But that dummy prop has the same issue. Self-mesh doesn't produce a clean surface (still there are edges).



And the convex hull doesn't do it right from the start, since the pivot is already set.

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The cylinder in the create menu has beveled edges. Use the one in the 3d object folder. It should work better. Dummies are the best way that I have found. See this video:

I should add as well that the convex shape has to fully enclose the cylinder. Since it does it with fewer polys, the facets require is to enlarge to fit over the cylinder. Basically its fewer polys to cover the same curve. A good solution is to make your dummy wheel just a bit smaller than the prop wheel you attach to it, so the physics shape will match you prop wheel in diameter.

Thank you @Rampa for the comprehensive tutorial video and the additional hints.

With a basic test set-up, using the non-beveled cylinder as you mentioned, there is no issue.
The convex hull works well and the 'car' runs without a glitch.

The problem might be the weight and compexity that my truck has.
It has a very realistic suspension, which seems to make it more sensitive to the wheel shape.
Truck has 6 accelerated wheels and the trailer additional 6 passive wheels (i did my tests without the trailer).
In any case, as soon as i use a convex hull (or self mesh) for the wheel dummies, the whole thing gets unstable.
But a sphere shape obviously has much less 'edges' and the truck actually runs.
Only problem is that it lacks side-stability.

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I actually found spheres work best as well. Set the friction as high as possible to increase stability. I just type in 9's until I can't anymore. ;)