Strange shading for face of wheel? I have extruded a wheel that originally looked like this:



My modified wheel now looks like this:



As you can see, the shading looks incorrect, with strange dips instead of a flat surface. But the normals seem ok to me:



Is there a way I can fix this? Is there some sort of issue with my vertices causing problems with interpolation? 

Thank you!
You need to remove these vertices. They are creating n-gons. You should strive towards quad based topology (4 sides).