Permitted Car Modifications in California

Humble Eagle
Jan 13, 2020 2:24:00 PM

In America, we certainly love our cars and nowhere is this more evident than in California, where car culture is king. 

Every month it seems there’s another show for every type of car: low-riders, hot rods, classics, etc. Our cars are an expression of who we are and boy do we love to modify them to show off. But do you know which modifications are allowed and which are not?

 If you want to know what modifications are allowed to keep your ride street-legal then keep reading, otherwise, watch out for those tickets and fines you won’t be able to drive away from those.


Mufflers are a particular favorite of drivers when it comes to California car modifications. Unfortunately, the main issue with them is noise. California laws state that exhaust systems can’t be modified in a way that increases or amplifies the amount of sound that the vehicle makes beyond that produced by factory equipment. Vehicles with a gross vehicle weight under 6,000 pounds must produce a sound that is 95 decibels or less. This does not apply, however, to motorcycles.  So basically, if you want to upgrade your exhaust, it’s ok as long as it doesn’t make any more noise.


If you are the kind of person who wants to drive a monster truck to work, you might not be happy. California law has limitations on the frame and suspension heights of cars and breaks them up into three categories: less than 4,500 lbs Gross Vehicle Weight Rating (GVWR), 4501 to 7,500 GVWR, and 7,501 to 10,000 GVWR. 

Each category can have a frame height of no more than 27”, 30”, and 31” respectively. Additionally, body lifts can’t exceed five inches, and the tallest part of your vehicle can’t be higher than 14 feet. This is to keep you safe and so that you don’t drive right into a bridge. That’s not a modification you want to make.


Engines are the heart of the car and we all want our hearts to be strong and fierce, but do you know which modifications you can make to them? It turns out that there’s not much you’re allowed to do to your engines of modified cars in the Golden State. For one thing, the engine has to be certified by the state for use on the road. That means that 49-state or EPA-certified engines are not permitted. 

You also need to have the EPA or the ARB certify all of the cams, pistons, intakes, and other parts that you use with the exact engine in your car. While some parts are exempted by the ARB to work with any engine, this still means you can’t completely customize it to your liking.

Additionally, you need to pass a smog check provided by the Bureau of Automotive Repair Referee Station and make sure the emission control systems must be certified as for the same or newer model year vehicle to ensure compliance with emissions certification standards. 

Sound System

For some people, the sound system is a huge part of the car. You want to be able to listen to your favorite tunes and share that music with the world around you. Luckily, there are not many limitations on sound systems. 

While you’re on a highway though, your sound system can’t be audible from 50 feet away. So, you can’t blast your tunes while cruising down the 405 as you want. You can, however, get whatever kind of sound system you want and any type of speakers as well, all you gotta do is keep it down while driving. Nobody likes to turn it down but nobody likes to be pulled over either.


If you are not a fan of super bright headlights when you’re driving on the highway, California laws have got your back when it comes to modifying them.  So you won’t go blind while driving, the law limits you to two lights with “white” lamps and at a maximum of 32 candlepower. Also, the lights can’t light up more than 300 feet of the road. There are a few other laws that state how many lights you can have on your car. You can only have two fog lights and only four lamps can be turned on at once.  It’s dangerous to drive in the dark but it’s also dangerous to blind other drivers.


You can tint your windows in California but there are some restrictions. For example, you can’t black out all of your windows. Only the rear windows and back windshield can be dark. The front windows have to let at least 70% of light in. Only the top four inches of the front windows are allowed to be tinted, which lets you block out some sun rays while you drive. You can’t have any super reflective tint, either. If you want to drive around with mirrors, you’re gonna have a bad time. Best to use common sense when it comes to tinting your windows.


Anything obscene painted on your car might cause issues. Plate frames that cover the letters would also get you pulled over. Rolling coal in your car or having nitrous will also get you in some trouble. If you have a kit car you have to register it by completing an application for title and registration,  undergo a vehicle verification through California Highway Patrol, have a completed statement of construction form, complete a smog check, and get your light and brake adjustment certificates from a brake and light station.

The Bottom Line

You can’t go too crazy but you can fall within the limits of modifying your ride. Just make sure it’s not too loud, too dark, too bright, too big, too small, or too pollutive. It’s basically just being mindful of other drivers so that there are fewer accidents and traffic can stink a little less.

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