Complete Guide to Vehicle Modification Laws in Missouri
Missouri offers vehicle enthusiasts a fair amount of freedom when it comes to customizing their rides, but there are still rules to follow to keep your build street-legal. The figures, statutes, and exceptions in this guide were verified against primary statute text (August 2026), so you can rely on them when planning your next project. Below, we break down the most common modifications — from exhaust to window tint — and what Missouri law actually says about each one.
Exhaust Noise
Status: Conditional
Missouri does not impose a statewide decibel limit for passenger cars — there's no specific number to hit or stay under. That said, the law still requires a muffler in good working order, prohibits exhaust that produces excessive or unusual noise, and bans cutouts or bypasses outright. In other words, you have flexibility on tone and setup, but you can't run straight pipes or a system designed to bypass the muffler. This is governed under Mo. Rev. Stat. § 307.170. For full details, see the exhaust noise laws page.
Lowering
Status: Legal
Missouri has no statute dictating how low you can drop your vehicle — there's no minimum ground clearance rule on the books. However, general equipment requirements still apply: headlamp height must remain compliant, all lighting must continue to function properly, and nothing on the vehicle can drag on the road. The only related statute, Mo. Rev. Stat. § 307.172, addresses maximum height limits rather than minimums. Check out the lowering laws page for more.
Lift Kits
Status: Conditional
If you're lifting your truck or SUV, bumper height is the key number to watch. Missouri caps bumper height at 22 inches in front and 22 inches in the rear for non-commercial passenger vehicles. Commercial vehicles get weight-tiered allowances instead: 24/26 inches for vehicles up to 4,500 lb, 27/29 inches for 4,501–7,500 lb, 28/30 inches for 7,501–9,000 lb, and 29/31 inches for 9,001–11,500 lb. These limits are set out in Mo. Rev. Stat. § 307.172. Visit the lift kits laws page for the complete breakdown.
Aftermarket Exhaust
Status: Conditional
Swapping your factory exhaust for an aftermarket system is legal in Missouri, but the same baseline rules apply as with stock setups: a muffler in good working order is required, and cutouts or bypasses are prohibited. Catalytic converter removal remains prohibited under federal law regardless of state statute. Exceptions and exemptions boil down to this: don't exceed noise limits, keep a functioning muffler installed, don't tamper with the catalytic converter, and skip the cutouts/bypasses entirely. This falls under Mo. Rev. Stat. § 307.170.2. Learn more on the aftermarket exhaust laws page.
Headlight & Taillight Tint
Status: Illegal
Smoked or tinted film on headlights and taillights is not permitted in Missouri. No film is allowed on these lights at all. Headlights must emit white light, and taillights must show red light at the required visibility distance. Any tint, covering, or alteration that reduces light output or changes these required colors violates the law — there are no exceptions carved out for cosmetic tint jobs. This is governed by Mo. Rev. Stat. §§ 307.040, 307.045, and 307.075. See the headlight & taillight tint laws page for specifics.
Wheel & Tire Protrusion
Status: Legal
Missouri doesn't have a fender or protrusion rule for passenger cars — there's no protrusion limit specified in state law. This gives some flexibility for wider wheel and tire setups. The relevant statute is Mo. Rev. Stat. § 307.015. More information is available on the wheel & tire protrusion laws page.
Underglow
Status: Conditional
Underglow lighting is legal in Missouri, including while driving, but color matters. Red, blue, flashing, and rotating lights are reserved for permitted emergency and work vehicles — running these as underglow is a Class A misdemeanor. Steady amber, white, and other non-red/blue colors, however, are fine. Additional exceptions specify that underglow lights must not display red or blue (reserved for emergency vehicles), must remain steady and non-flashing, and must not impair driver vision or distract other drivers. This is covered under Mo. Rev. Stat. § 307.175. Check the underglow laws page for the full rundown.
License Plate Frames
Status: Conditional
License plate frames are legal in Missouri as long as they don't obscure anything required on the plate — all parts of the plate must remain plainly visible and reasonably clean, with reflectivity unimpaired. Clear/transparent covers are expressly permitted, but tinted or smoked covers are effectively illegal since they interfere with visibility. The exceptions here are straightforward: frames and covers must not obscure the plate number, letters, or registration validation stickers. This falls under Mo. Rev. Stat. § 301.130(5). See the license plate frames laws page for more.
Light Bars & LED Lighting
Status: Conditional
Missouri permits up to 3 auxiliary lamps mounted 12 to 42 inches on the front of the vehicle, and there's no cover requirement for these lamps. When lit, they must produce light that is substantially white, yellow, or amber. Note that the general 300 candlepower / 75 ft aiming cap in Missouri law expressly excludes headlamps, spotlamps, and auxiliary lamps, so those are governed by their own rules rather than that cap. This area is covered by Mo. Rev. Stat. §§ 307.080, 307.095, and 307.100. Full details are on the light bars & LED lighting laws page.
Window Banners
Status: Illegal
Missouri does not allow aftermarket windshield strips or banners of any kind. All sun-screening devices on the windshield are prohibited, with the sole exception being the factory-tinted upper portion of the safety glass that comes with the vehicle. A printed windshield banner is not legal to add — printed banners are not allowed, and aftermarket windshield strips are not allowed. This is set out in Mo. Rev. Stat. § 307.173.1. See the window banners laws page for more.
Window Tint
Status: Conditional
Missouri's tint rules differ by window position. Front side windows require a minimum of 35% VLT. Rear side windows and the back window may be tinted to any darkness, with no minimum VLT requirement. This tiered approach gives you a lot of freedom in the back while keeping front visibility standards in place. The relevant statute is Mo. Rev. Stat. § 307.173. Visit the window tint laws page for the complete rules.
Every modification above links to its full law page with exact limits, statute citations, and exceptions — or browse every Missouri mod law in one place, free.
This guide is for informational purposes only. Data is AI-extracted from public statutes and may contain errors. Always verify with local authorities.