I am a huge fan of Dürer and became obsessed with his lines and cross-hatching. I went through a phase of trying to mimic that classic style and watched an episode of Cosmos about light and began looking at things in the way that light wraps a surface.
The best way I can explain it is if you could wrap any surface in string, how would it look? It's essentially the same pattern I see of light wrapping objects and you can notice it with the parallel lines of these illustrations.
'34 Ford Speedster
'72 Nissan Skyline GTR