A Guide to Legal Vehicle Modifications in Missouri

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If you live in Missouri and want to modify your vehicle, or if you are moving into the state with a car or truck that you have modified, it is important that you know the laws to make sure your vehicle is legal for use on public roads. Below are the most important rules for keeping your vehicle compliant with Missouri laws.

Sounds and noise

Below are the laws regarding car sound systems and mufflers in the state of Missouri.

Audio system

Missouri has no specific sound system guidelines, except that vehicle noise cannot be considered unpleasant or harmful to the well-being or health of people who live within city limits or within half a mile of city limits.

Muffler

• Silencers are required on all vehicles to function properly and prevent unusual or excessive noise.

• Muffler cutouts are not permitted.

• Any existing muffler openings must be secured in such a way that they cannot be turned on or opened while the vehicle is in motion.

Functions: Also check your local Missouri County laws to make sure you comply with any municipal noise ordinances that may be stricter than state laws.

Frame and suspension

Missouri has no frame height or suspension lift restrictions, but there are bumper height restrictions.

• GVW below 4,501 - Maximum front bumper height - 24 inches, rear - 26 inches.
• Gross Weight Rs 4,501-7,500 - Maximum front bumper height - 27 inches, rear - 29 inches.
• Gross Weight Rs 7,501-9,000 - Maximum front bumper height - 28 inches, rear - 30 inches.
• Gross Weight Rs 9,002-11,500 - Maximum front bumper height - 29 inches, rear - 31 inches.

ENGINES

Missouri does not currently list engine modification or replacement rules. However, St. Charles, St. Louis, Franklin, and Jefferson counties require emission testing.

Lighting and windows

Lanterns

• Three auxiliary lights are allowed at the front, spaced 12 to 42 inches apart.

• White lights are required to illuminate license plates.

• Two lights on fenders or side fairings emitting yellow or white light are permitted.

• One footrest lamp emitting yellow or white light is allowed.

• One spotlight is allowed that does not dazzle or dazzle another person.

Window tinting

• Non-reflective tinting above the AS-1 line provided by the manufacturer is allowed.
• Front side windows must let in more than 35% of the light.
• The back side and back glass can have any darkening.
• Reflective tinted front and rear side windows cannot reflect more than 35%.
• Side mirrors are required if the rear window is tinted.

Vintage/classic car modifications

Missouri vehicles may be listed as historic if they are 25 years old or older. Vehicles with historical numbers:

• Have no mileage restrictions when traveling to and from educational or exhibition events.
• Available for repair shops within 100 miles.
• Have a limit of 1,000 miles per year for personal use.

If you want to make sure your modifications are within Missouri laws, AvtoTachki can provide mobile mechanics to help you install new parts. You can also ask our mechanics what modifications are best for your vehicle using our free online Ask a Mechanic Q&A system.