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The Guide to Legal Car Modifications in Montana

The Guide to Legal Car Modifications in Montana ARENA Creative /

Whether you currently live in Montana or plan to move there, you will need to know the regulations that govern modified vehicles. The following information will help ensure that the modifications you make to your car or truck are street legal when driving on the roads in Montana.

Sounds and noise

Montana has certain restrictions on the sound systems and mufflers that are used on vehicles on the roadways.

Sound system

Montana does not have specific guidelines regarding sound systems in vehicles.


  • Mufflers are required on all vehicles, must work properly, and must prevent unusual or excessive noise.

  • Muffler bypasses, cutouts, and similar devices that amplify sound are not permitted.

Tip: Also check with local county laws in Montana to make sure you are following any municipal noise ordinances that may be more stringent than state-level laws.

Frame and suspension

Montana does not have any restrictions as far as bumper height, frame height or suspension height limits. However, vehicles cannot be more than 14 feet in height.


Montana does not have performance modification regulations for engines or engine swap guidelines. The state also does not require emissions testing.

Lighting and windows


  • Reflectors and marker lamps on the front or near the front of the vehicle must be amber in color.

  • White lights are required for illuminating license plates.

  • Backup lamps must emit white light.

  • Red lamps are not permitted on the front of passenger vehicles.

  • Decorative license plate lighting and undercarriage lighting that flashes or rotates or is not amber or white cannot be illuminated when vehicle is in motion on streets or highways.

Window tinting

  • Non-reflective tint is permitted above the AS-1 line provided by the manufacturer.
  • Front side windows must allow over 24% of light through.
  • Back side and rear window must allow over 14% of light through.
  • Front side and back side window reflective tint cannot reflect more than 35%.
  • Stickers identifying legal tint are recommended by law but not required.

Antique/classic car modifications

If you want to make sure your modified car or truck is street legal in Montana, YourMechanic can provide the mobile mechanics to help you install the new parts. You can also ask our mechanics what modifications may be best suited to your car using our free online Q&A system, Ask a Mechanic.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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