Vehicle Mod Laws in Idaho

Replacing the exhaust system is legal in Idaho, but a muffler in good working order is required and cutouts or bypasses are prohibited. Modifications that make the exhaust louder than the originally installed muffler are prohibited.

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Idaho sets no statewide decibel limit for passenger cars. A muffler in good working order is required, exhaust may not produce excessive or unusual noise, and cutouts or bypasses are prohibited.

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Smoked or tinted film on headlights and taillights is illegal in Idaho. Headlights must emit white light and taillights must show red at the required visibility distance, and tint that dims or discolors them violates those requirements.

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License plate frames are legal in Idaho as long as nothing required stays hidden. The plate must be clearly visible, clearly legible, and free from foreign materials.

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Idaho requires bumpers at least 4.5 inches tall and caps their height at 22 inches front and rear on passenger cars, rising by weight class for trucks and multipurpose vehicles to as much as 30 inches front and 31 inches rear.

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Idaho requires no cover and no switching off. The limits are four front lamps lit at one time where any exceed 300 candlepower, aimed so no part of the high-intensity beam strikes the roadway beyond 75 feet.

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Idaho applies a rim-line test: no part of the vehicle other than the wheels may sit lower than the lowest point of any wheel rim.

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Underglow is legal in Idaho, including while driving, subject to color and flashing limits: No flashing, no red visible from the front, and no blue (police only); white or amber to the front is the safe choice.

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Idaho requires fenders or covers over all wheels on all motor vehicles, extending the full width from a point above and forward of the tire center over and behind the wheel, reaching within 20 inches of the road (10 inches for trucks, buses, and trailers).

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Non-reflective tint or sunscreening may not extend below the AS-1 line, or below 6 inches from the top on windshields with no AS-1 line. Because the material must be transparent, a printed or opaque banner is not legal in Idaho — only a clear tint band.

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Front side windows: minimum 35% VLT. Rear side windows: minimum 20% VLT. Back window: minimum 35% VLT.

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