A steering wheel makes a passable easel, though movement is somewhat limited inside a car and that does effect the sketch because it's pretty much impossible to make marks from your shoulder, at best marks were made from the elbow but even that wasn't easy. Having to sketch from inside the car also limits the subjects available but this wasn't about making a polished piece of art, it was about practice from life, any subject would do as long as it had interesting and challenging shapes. Obviously I'm more used to sketching classic cars.
Here's the finished sketch, if you can call any sketch finished. I used charcoal then added some touches of color using pastel. I'd rather not sketch from inside a car, but in a pinch it will do.