Montana Truck Mud Flap Law
Montana requires fenders, splash aprons, or flaps on the rearmost wheels of nearly every vehicle except bikes and farm tractors (61-9-407). Trucks over 8,000 pounds keep the flap within 10 inches of the road when empty; lighter rigs get 20 inches. The flap spans the full tire width, singles or duals. Street rods and vehicles never factory-equipped are exempt. A trooper checks the empty-truck gap and coverage. A short flap is a correctable equipment ticket, not out-of-service.
What Montana makes you run
Montana requires fenders, splash aprons, or flaps on the rearmost wheels of nearly every vehicle except bikes and farm tractors (61-9-407). Trucks over 8,000 pounds keep the flap within 10 inches of the road when empty; lighter rigs get 20 inches. The flap spans the full tire width, singles or duals. Street rods and vehicles never factory-equipped are exempt. A trooper checks the empty-truck gap and coverage. A short flap is a correctable equipment ticket, not out-of-service.
Coverage and clearance
- Required: Yes
- Coverage: At least the full width of the tire, or the combined width of dual or multiple tires.
- Ground clearance: Trucks over 8,000 lb GVW: within 10 inches of the road when empty. 8,000 lb or less: within 20 inches (61-9-407).
- Fine: Equipment violation. A small fix-it fine; a state trooper can warn or cite.
Montana Mud Flap FAQ
Are mud flaps required on trucks in Montana?
How low can mud flaps hang in Montana?
What is the mud-flap fine in Montana?
Reference information for planning, not legal advice. Traffic laws change and this can be out of date, so always confirm the current statute and obey posted signs before you rely on it. Last reviewed July 2026. Source: https://mca.legmt.gov/bills/mca/title_0610/chapter_0090/part_0040/section_0070/0610-0090-0040-0070.html. See our Terms & Disclaimer.
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