Legal car modifications in California include those that meet the state's safety, noise, and emissions standards. For instance:
Engine modifications are legal if they use EPA-certified or CARB-exempted parts that do not negatively impact emissions.
Exhaust modifications are allowed if they do not amplify the sound beyond factory levels and meet decibel limits.
Suspension and body modifications can be done within specified height limits and should not compromise vehicle safety.
Window tints are legal, provided they adhere to the specific VLT (Visible Light Transmission) requirements the state sets.
Lighting modifications, such as aftermarket headlights or taillights, must comply with brightness and color regulations.