Wisconsin Truck Mud Flap Law

What Wisconsin makes you run

Privately owned trucks and semitrailers in intercity travel need rear fenders or mudguards, unless the rig runs a dump body or the wheels are boxed in by the body (Wis. Stat. 347.46). The guard must be at least as wide as the tires, and its ground gap can't exceed one third of the distance from the rear axle center to the guard. Violation is a $10 to $200 forfeiture (347.50). Inspectors check width and rear coverage, not a set inch.

Coverage and clearance

• Required: Yes
• Coverage: At least as wide as the tire or tires it protects. No separate mudguards are needed if the rear wheels are already covered by the body or an enclosure meeting the same coverage.
• Ground clearance: Proportional rule: the ground gap can be no more than one third of the horizontal distance from the center of the rearmost axle to the fender or mudguard. Coverage starts at a vertical line through the axle center and runs rearward and downward.
• Fine: Forfeiture of $10 to $200 (Wis. Stat. 347.50(1)); a correctable equipment violation.

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