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The Guide to Legal Car Modifications in Washington

The Guide to Legal Car Modifications in Washington ARENA Creative /

If you have a modified vehicle and live in Washington or plan to do so in the near future, you need to know the laws that govern the changes that you can make. The following information will help you understand the modifications you can make while still keeping your car or truck street legal on Washington roads.

Sounds and noise

Washington has laws that cover the noise that your vehicle can emit.

Sound systems

  • Sound systems cannot be heard clearly from a distance of 50 feet or over from the vehicle when in parks or near residential areas, commercial establishments and human service facilities.


  • All vehicles must have mufflers that prevent unusual or excessive noise.

  • Vehicles weighing 10,000 pounds or less cannot exceed 72 decibels when traveling 35 MPH or under when measured from a distance of 50 feet from the lane they are driving in.

  • Vehicles weighing 10,000 pounds or less cannot exceed 78 decibels when traveling more than 35 MPH at 50 feet from the lane in which they are driving.

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

Frame and suspension

Washington has a variety of laws that cover suspension and lift height on vehicles that determine whether it is street legal. Washington also has regulations for bumper height based on the Gross Vehicle Weight Rating (GVWR).

  • Less than 4,501 GVWR – Maximum front bumper height is 24 inches, rear is 26 inches

  • 4,501-7,500 GVWR – Maximum front bumper height is 27 inches, rear is 29 inches

  • 7,501 and higher GVWR – Maximum front bumper height is 28 inches, rear is 30 inches

  • Cars and SUVs – Maximum front and rear bumper height is 22 inches

  • Frame height cannot be lower than the sidewall of the vehicle’s tires.

  • Aftermarket and replacement frames have to be Federal Motor Vehicle Safety Standards certified.

  • Vehicles can be no taller than 14 feet

  • Body lifts are permitted but must have anti-sway bars and cannot be homemade.


Washington does not have any limitations listed for engine modifications or swaps. However, five counties and certain vehicles do require emissions testing. Check the Washington State Vehicle Emission Check Program website for more information.

Lighting and windows


  • Two fog lamps are permitted

  • Two auxiliary lamps are permitted

  • No more than four lights can be lit at one time

  • Blue lamps are only permitted for law enforcement vehicles

  • Red emergency lights are prohibited on passenger vehicles

  • White flashing lights are not permitted on passenger vehicles

  • Neon lights are not permitted to be lit while on roadways

  • Scrolling signs are permitted providing that they are not lit up and do not contain messages that scroll while on the roadways.

Window tinting

  • Non-reflective tint is permitted on the top six inches of the windshield

  • Front side, back side and rear window tint must allow over 24% of light to pass through

  • Front side and back side window tint cannot be over 35% reflective

  • Side mirrors are required with rear window tint

  • Red tint is not legal for use

  • Sticker certifying that tint levels are legal is required on the driver’s window between the glass and film

Antique/classic car modifications

Washington has the following requirements for Collector Vehicle Plates:

  • Must be over 30 years old
  • Must be able to be driven safely on the highway
  • Can be driven for the purposes of shows, parades, exhibitions, and club meetings
  • Cannot be used for daily transportation or commercial purposes

If you want to make sure the modifications on your vehicle are legal in Washington, 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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