I often have assemblies with a roller running in a C-channel rail.  The roller can contact the front, side, or rear of the rail.  Usually I have a good idea which will or will not make contact, depending on the loading, but have found that they all possible directions need to be defined to get a solution.  As I watch the solver pick through all the possible combinations I suspect that I coould help it along byt being more explicit and putting in everything I already know for sure.

What is the best way to set up the contact pairs, for speed?  [see example screencaps]

I could put all the surfaces in one set, the cylindrical and flat face of the roller and the three flat faces of the rail.

The side-thrust and rolling motions could be separated, so the flat face of the roller is in one set and the cylinder in the other.

All could be set up separately.

But how about the cylinder?  Does the solver have to do anything special to deal with this shape that comes around on itself?

In some cases I have split the cylindrical face and then had three separate contact sets with nothing in common.

Another question not illustrated here - Since the rails are usually very long compared to the roller size, and I know generally where the roller might contact, does it help any to split them up so that the entire length is not considered?