Vehicle Mod Laws in Wisconsin

Replacing the exhaust system is legal in Wisconsin, but a muffler in good working order is required and cutouts or bypasses are prohibited. Modifications that make the exhaust louder than the originally installed muffler are specifically prohibited.

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Wisconsin sets no statewide decibel limit for passenger cars. A muffler in good working order is required, exhaust may not produce excessive or unusual noise, and cutouts or bypasses are prohibited.

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Smoked or tinted film on headlights and taillights is illegal in Wisconsin. Headlights must emit white light and taillights must show red at the required visibility distance, and tint that dims or discolors them violates those requirements.

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Frames are legal if nothing is obscured. Plates must be maintained in a legible condition and displayed so they can be readily and distinctly seen and read — which covers the whole plate face, not just the numbers and stickers.

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Wisconsin allows a lift of up to 4 inches above the manufacturer's specified height (5 inches for qualifying strengthening or handling modifications on 4WD vehicles up to 8,000 lb).

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Wisconsin requires no cover; no more than four adverse-weather, spot, auxiliary, or other front lamps over 300 candlepower may be lit at any one time on a highway.

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Wisconsin's floor is the rim-line test: after suspension, axle, chassis, or exhaust modifications, no part of the vehicle except the tires may extend below lines drawn from the bottom of each wheel rim to the opposite tires' points of road contact.

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Underglow may not be used on public roads in Wisconsin. Only white or amber light may show to the front and only red to the rear, and flashing is banned — which makes most colored underglow unlawful while the vehicle is in motion.

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Wisconsin's fender and mudguard statute does not cover passenger cars.

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Tinting film or other non-transparent material may be applied to the inside of the windshield only where it is both outside the windshield critical area and above the AS-1 mark. If the windshield bears no AS-1 mark, no film may be attached at all. A printed banner can be legal in Wisconsin if it stays within the strip described above.

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Front side windows: minimum 50% VLT. Rear side and back windows: minimum 35% VLT.

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