Vehicle Mod Laws in Missouri

Replacing the exhaust system is legal in Missouri, but a muffler in good working order is required and cutouts or bypasses are prohibited.

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Missouri 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 Missouri. 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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License plate frames are legal in Missouri as long as nothing required stays hidden. All parts of the plate must be plainly visible and reasonably clean with reflectivity unimpaired. Transparent covers are expressly permitted on those terms; tinted or smoked covers are effectively illegal.

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Missouri caps bumper height at 22 inches front and rear on non-commercial passenger vehicles, with weight-tiered limits for commercial vehicles.

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Missouri allows up to three auxiliary lamps mounted 12 to 42 inches on the front, with no cover requirement. When lit they must be substantially white, yellow, or amber.

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Missouri has no statute limiting how low a vehicle may be. General equipment rules — headlamp height, working lighting, nothing dragging on the road — still apply.

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Underglow is legal in Missouri, including while driving, subject to color and flashing limits: Red, blue, flashing, and rotating lights are reserved for permitted emergency and work vehicles (a Class A misdemeanor otherwise); steady amber, white, and other non-red/blue colors are fine.

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Missouri has no fender or protrusion rule for passenger cars.

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Missouri allows no aftermarket windshield strip — all sun-screening devices on the windshield are prohibited apart from the factory-tinted upper portion of the safety glass. A printed windshield banner is not legal in Missouri.

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

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