The best way to make tires look muddy bro is to go outside after it rains. I have two dogs and Ill go to were they bark and chase people next to the fence and ill take a slab of the mudd that was created by the earth and apply it to the tires. If you want the super special way you ca either take some brown muddy acrylic and mix it with dirt or take a tan/brown chalk pastel and shave some of the chalk off of it and add it to some bits of water. you can also add it to some odorless mineral spirits and it works best just dont over do it since most of the toys are plastic.

Hope this helps my favorite way is with actual mudd but when winter hits the other ways work as well or sometimes better.

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