@Konzept3D: that’s not entirely true.
While there are issues with the fbx export from Cinema 4D to UE4, you can export shading just fine in most cases.
The Mesh and Tags have to be set up correctly and export options have to be right, though.
I’d also recomend VertexNormalTool plugin for having more control over the vertexnormals.
There’s a free Lite version, but also a “pay what you want” version of it.
For more details about the Mesh setup and export/import settings, look here: https://forums.unrealengine.com/showthread.php?44234-Cinema-4D-Workflow&p=239465&viewfull=1#post239465
One small addition of an issue i discovered just recently:
if you use two UV channels, the smoothing won’t import correctly into UE4, so any angle >0° will have a hard edge.
BUT, the issue you have isn’t related to smoothing groups at all.
It’s an issue with the UV layout or maybe the lack of one.
The Texture is stretched in the black marked areas, since the UVs there have no proper layout.
Use a checkerboard texture in C4D and you should get the same result, at least when the material is set to UVW mapping.
I’d also recomend to right click on the UV-Tag and choose “help” from the context menue.
It’ll bring up the part of the documentary that is about UV mapping.
Read it, follow the links and read that too. It can give you a good overview about the topic.
(this hint might also help you in a lot of other situations, since the C4D help is very good)