Complete Guide to Vehicle Modification Laws in Montana
Montana is known for having some of the more permissive vehicle modification laws in the country, but that doesn't mean "anything goes." Several mods are conditional on specific standards, and a few are outright illegal. The figures in this guide were verified against primary statute text (August 2026), so you can use it as a reliable starting point before you start wrenching. Below is a breakdown of the most common modifications and how Montana law treats each one.
Exhaust Noise
Status: Conditional
Montana caps exhaust noise at 95 dB for cars, measured under the SAE J1169 (May 1998) test standard. Motorcycles and quadricycles are exempt from this specific limit. Regardless of the decibel reading, a muffler in good working order is separately required, and exhaust cutouts are prohibited outright. Check the exhaust noise laws page for the full statutory language.
Statute: MCA §§ 61-9-435, 61-9-403
Headlight & Taillight Tint
Status: Illegal
Smoked or tinted film on headlights and taillights is not permitted in Montana. Headlights must emit white light, and taillights must show red at the required visibility distance. Montana law prohibits any material that reduces light transmission from these lights, so applying tint film — even light smoke — puts you in violation. See the headlight tint laws page for details.
Statute: MCA §§ 61-9-203, 61-9-204
Wheel & Tire Protrusion
Status: Conditional
Montana requires fenders, splash aprons, or flaps on the rearmost wheels of every vehicle, with exemptions for motorcycles, quadricycles, motor-driven cycles, and farm tractors. Spray control equipment must reach within 20 inches of the road, or within 10 inches for vehicles over 8,000 lb GVW. Notably, Montana sets no limit on how far a tire itself may protrude — there's no specific statute addressing protrusion limits. Full details are on the wheel protrusion laws page.
Statute: MCA § 61-9-407 (penalty: § 61-9-515)
Aftermarket Exhaust
Status: Conditional
Swapping your factory exhaust for an aftermarket system is legal in Montana. A muffler in good working order is required, and cutouts or bypasses are prohibited. There's no statutory "no louder than stock" requirement — instead, the standard is that the exhaust must not produce excessive or unusual noise. Keep in mind that catalytic converter removal is prohibited under federal law, and your setup still needs to avoid violating local noise ordinances. Learn more on the aftermarket exhaust laws page.
Statute: MCA §§ 61-9-403, 61-9-435
License Plate Frames
Status: Conditional
Frames are fine in Montana as long as the plate stays conspicuously displayed. Nothing may obstruct or obscure the plate — including the state name, county number, and any registration decal. There's no cover-specific statute, but any frame or cover that blocks part of the plate is prohibited. Details are available on the license plate frame laws page.
Statute: MCA § 61-3-301
Light Bars & LED Lighting
Status: Conditional
Montana doesn't require a cover on light bars, but placement and usage rules apply. Off-road lamps mounted above 42 inches may not be illuminated while operating or parked on a highway. No more than 4 front lamps over 300 candlepower may be lit at the same time. Additional lamp allowances include up to 2 spot lamps, 2 fog lamps, and 2 auxiliary driving lamps (mounted 16–42 in). Full specifics are on the light bar laws page.
Statute: MCA §§ 61-9-217, 61-9-225
Lift Kits
Status: Legal
Montana has no statewide lift, frame-height, or bumper-height limit for modified vehicles. The only real ceiling is the overall vehicle height limit of 14 feet. General equipment rules — like proper headlamp height and working lighting — still apply regardless of how high you go. See the lift kit laws page for more.
Statute: MCA §§ 61-9-430, 61-10-103
Lowering
Status: Legal
There's no statute in Montana limiting how low a vehicle can be set. As with lift kits, general equipment requirements still apply — headlamp height must remain functional, lighting must work properly, and nothing should be dragging on the road. More info is on the lowering laws page.
Statute: MCA § 61-9-430
Window Tint
Status: Conditional
Montana's window tint law sets minimum visible light transmission (VLT) requirements: front side windows require a minimum of 24% VLT, while rear side windows and the back window require a minimum of 14% VLT.
Differs by vehicle:
- SUVs, trucks, and vans follow the same 24% VLT minimum for front side windows, but MPV windows behind the driver are exempt from the rear/back window minimums.
Darker limits can apply behind the driver on some larger vehicles. Full breakdown on the window tint laws page.
Statute: MCA § 61-9-405
Underglow
Status: Conditional
Underglow lighting is legal in Montana, including while driving, but it comes with color and behavior restrictions. Blue is reserved for emergency vehicles only, red is prohibited facing the front, rotating or flashing lights are not allowed, and any beam over 300 candlepower must be aimed within 75 feet. Practically speaking, only white and amber auxiliary lighting is generally permitted, since red and blue are off-limits and flashing/strobing isn't allowed. See the underglow laws page for the complete rule set.
Statute: MCA §§ 61-9-219, 61-9-226
Window Banners
Status: Conditional
Montana prohibits any sign, poster, or non-transparent material that obstructs vision through the windshield. Sunscreening material must be clear and transparent below the AS-1 line, meaning any strip is confined to the area above that line. Because the material must remain transparent, a printed or opaque banner is not legal in Montana — only a clear tint band is allowed in that upper windshield area. Check the window banner laws page for more.
Statute: MCA § 61-9-405
Every modification above links to its full law page with exact limits, statute citations, and exceptions — or browse every Montana mod law in one place, free.
Disclaimer: This guide is for informational purposes only. Data is AI-extracted from public statutes and may contain errors. Always verify with local authorities.