... so it flows nicely is...light to dark.
Paint the wheels first, no matter how sloppy and then correct everything with the black.
Except for bodywork, I'd say reverse process.
As in painting soldier/ figurines, work dark to light.
Lay down the shadow areas, then build up the lighter tones.
I can't see any detail to comment on the wheels, but I'd be painting dead black, then dry brushing a charcoal and finally layers of whatever light 'road colors' you desire. Lighten the tire tread area even more.
After comment about the wash bays- the 'weathering' effects of water on stainless are usually obvious, so tanks such as these will have a 'patina' (dulling) effect tideline about mid curve (when all washing is directed from the ground anyway).
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