Missouri Truck Mud Flap Law

What Missouri makes you run

Trucks, trailers, and semitrailers without rear fenders need mud flaps when the power unit is a commercial vehicle registered over 24,000 lb (RSMo 307.015). Flaps must cover the full tread width and hang within 8 inches of the ground, 12 inches for dump trucks. Farm implements, unregistered vehicles, and in-transit rigs with temporary flaps are exempt. It's an infraction with a fix-it fine. Roadside, a trooper checks for a present, full-width flap.

Coverage and clearance

• Required: Yes
• Coverage: Wide enough to cover the full tread width of the tire or tires being protected. Applies to trucks, semitrailers, and trailers (except utility trailers) that lack rear fenders.
• Ground clearance: Fixed-number rule: flaps must hang within 8 inches of the ground for most trucks, and within 12 inches for dump trucks. Measured behind the rear wheels in a vertical plane.
• Fine: Infraction under RSMo 307.015, a correctable equipment violation. The statute sets no dollar amount; it's handled as a fix-it ticket on the local fine schedule, not an out-of-service order.

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