Rusty Trucks Starting Point
A one color, primer if you will, to start weathering trucks for your freight cars.
I often prime my trucks and wheels with one, or two colors, depending on where I'm going with the model. Here's how I accomplish it quickly and easily. Learn more about the colors here: Basic Weathering Colors
These trucks were primed with Rustoleum Ruddy Brown primer. As you can see the wheels treads are still clean. I did a side-by-side comparison of wheel masks for HO scale. HO Scale 33” & 36” Wheel Painting Mask Side-by-Side Comparison
I often use a dark grey automotive primer for my trucks, unless they need a significant brown like these ones required. Newer wheels start with this color, and older grimy wheels I'll use Camo Brown.
Images © 2010, Article © 2020, Josh Baakko, https://www.modelrailroadtips.com