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Many car modifications that break the law can be fairly tough to spot and therefore difficult to enforce.

Modifying vehicles, whether the mods are legal or not, has always been popular among gear heads. Many people may assume if they can buy a part from an aftermarket shop, it's legal to put on a car for road use. However, more often than not, it turns out that this new toy is actually not legal for street use. Companies get away with it by printing “for off-road use only” somewhere usually very small and inconspicuous spot on the packaging. A lot of laws vary from state to state, with California and New York being known to be notoriously tough on their emission laws.

Updated January 2022: If you're planning to modify your vehicle, you need to make sure that the modifications are actually legal for road use. However, that being said, there are some illegal mods people seem to get away with more often than not.

The oil shortage in the early 70s brought on the “Clean Air Act”, that's when muscle cars saw their power drop massively thanks to catalytic convertors and detuned engines that were mandated to help reduce smog and improve the air quality. Any sort of tampering with a vehicles catalytic convertor, including removing or tampering is protected under federal law. A lot of heavily modified vehicles have removed their cats without any issues, and here are 19 other mods that are illegal but most drivers likely got away with. We don't recommend making illegal car mods to use on the roads, and instead implore everyone to check their local, state and federal regulations to ensure compliance.

Electric cutouts are installed by cutting out a section of your exhaust system and welding the cutouts in.

The cutouts are controlled by a switch either installed in the vehicle or by a wireless remote, allowing to be opened or closed.

According to Hot Rod cutouts are more of a fun noise maker, but there was some gain when dyno-tested increasing the horsepower and torque by less than 10 each when tested on a '67 GTO. Regardless, they are illegal due to the increased noise that your exhaust system will be making.

A straight pipe is just that, a pipe that is straight with no restrictions unlike stock exhaust systems. There are a few reasons as the why this is illegal. The first being the obvious for noise ordinance. The second being emissions, which in some states is tougher to get around as its required to be checked annually in order to pass inspection and register or insure your vehicle. According to New York Car Laws, a vehicle must have an adequate muffler and exhaust system, making any straight pipes illegal.

Related: These Trucks And SUVs Were Modified To Perfection

Why do some cars shoot flames out of their exhaust, and better yet how?

Flames shoot out of a vehicles exhaust when unburned fuel is dumped into the exhaust system.

It is ignited by the hot pipes the result is flames shooting out of the cars exhaust. How does fuel manage to get into the exhaust system? According to Car Throttle this is usually due to the removal of the catalytic convertor and adding straight pipes, making it you guessed it; illegal. Other ways to create a flame-shooting exhaust is by fitting a spark plug in the exhaust, buy a flamethrower kit, install anti-lag, mess with the air/fuel ratio, or simply ECU tuning.

A particularly tasteless modifying trend that’s been popping up on the tuner car scene is negative cambered wheels. Camber is the angel in which the wheels and tire stand relative to the road. Running too much negative camber will cause the wheels to angle in. Ocean City, Maryland has gone to the extreme of having tools made to measure camber, giving the ability to impound a vehicle with too much camber according to Jalopnik, and apparently, that has caused car shows to be canceled.

Headers aren’t illegal, however, long tube headers on the other hand are a bit of a different story. Not only will they make your vehicle louder, but it is also considered tampering with your vehicles emissions, which according to the EPA is illegal under federal law.

Drivers will most likely get away with it as long as your catalytic convertor and O2 sensors are still intact.

If your state has an annual emissions and inspection for vehicles, you may need some help from a tuner to ensure you pass.

Nowadays you can still find or better yet hear an old hot rod at a car show running open headers. What are "open headers?" It's simply when there is no pipe attached after the header, hence no exhaust system; hence illegal. In addition to messing with the vehicles emissions, the exhaust is going to be ridiculously loud, not to mention the smell won’t be great either, as your vehicle will be dumping out the exhaust fumes closer to where the driver is sitting.

Related: These Cheap New Cars Look Insane Modified

Strobing brake lights are very commonly seen on motorcycles used for more of a safety mechanism, but are popping up more and more on the tuner scene as a vanity mod. A strobing brake light is achieved when a module is wired into the vehicles brake light system making the brake strobe several times before tuning into a solid brake light. According to Popular Mechanics, it illegal to have flashing or strobing lights on your vehicles, other than your signals.

After market race seats and harnesses are becoming a popular mod in the car scene. The bottom line is; they’re illegal. There’s a few reasons why as well.

First, the seats were not used when the car passed a crash test, and are not recommended by Corbeau to install in a vehicle with a factory air bag system.

With a warning like that it means not only is it illegal, but it means you have voided the vehicles warranty. That's a lose-lose situation.

Tinted windows are a common mod on cars, that most of the time a cop won’t bother you for, but it’s always a reason to pull you over if you’re not doing anything else wrong. Tinted windows are achieved when a darker coloured film is bonded onto your windows, creating a dark coloured glass. Each state has different tint laws, some being more strict than others. Recently according to DMV, a New York State vehicle will not pass their annual inspection if their side windows are tinted past the legal limit.

Related: These Boring Japanese Cars Can Be Modified Into The Coolest Show Cars

A new fad among Jeeps and Trucks are LED lightbars, and if you’ve been blinded on the road by one of them then you know exactly what we’re talking about. Laws varies from state to state, but more states are starting to crack down passing specific laws to require them to have covers when on public roads. According to Pirate4x4, West Virginia passed a law banning them all together.

Nitrous is used in cars as a power booster. While it is not illegal to have nitrous oxide in your vehicle, it is illegal to use it on the street, and is sold with the intention to be used for off-road purposes only. State laws vary, some being more clear than others. According to Super Chevy, in Maryland there’s an exception protecting drivers that are driving their vehicles with NOS to and from the track.

Engine tuning is more like hacking into your cars computer. All new cars these days have computers, and according to the Wired.com each vehicle's software has a copyright and will always belong to the vehicle manufactures. Modern day tuners can hack into just about any car. Once in the vehicles ECU, they can change a number of thing, making the car faster and more powerful. Hacking your ECU will not only void your vehicles warranty, it can also be considered illegal, depending on where you live.

A trend that has been around forever is having decals across or down your windshield. Each state has different laws on how they regulate this.

In addition, most states will add non-transparent material to the list of things you can’t have on your windshield, which would make tint strips of any darkness illegal.

According to AAA, there may be a few states that you may be able to get away with it, Iowa, Michigan and Tennessee allow it as long as it doesn’t interfere with the drivers visibility.

When it comes to modifying your suspensions, whether you’re lifting or lowering, there is a limit to how high or low you can go. Each state has their own laws that cap both of these, but most have other laws restricting bumper and headlight height restrictions that would make extreme cases of both of these illegal. According to Lift Laws, NJ restricts the amount you can lift your vehicle by the weight and requires all lifted vehicles to get an “elevated vehicle approval certificate.” The state of Georgia allows you to legally lift your vehicle a whole two inches.

Packing crazy sound systems into car has always been a trend among car enthusiasts, but just like anything there are limits to how extreme you can go. Each states noise ordinance laws are different, but most will put restrictions on the distance or decibels heard outside the vehicle. According to Car Audio, in California a sound system is illegal if it can be heard from fifty or more feet, and doesn't need to use a decibel meter in order to write you a ticket.

Related: 10 Cheap Classic American Cars That Look Incredible Modified

Adding coloured lights to vehicles was made wildly popular after the movie “The Fast And The Furious.” According to Find Law, it is legal to have under-glow lights in some states as long as they’re not visible or strobing. While state laws vary, according to Extreme Tactical Dynamics, vehicles other than emergency personnel are not allowed to have flashing red or blue lights. Some state laws prohibit any coloured lights anywhere on a vehicle.

When it comes to the legality of tires, it again varies from state to state. According to It Still Runs, in 49 states, with Kentucky being the exception, it is illegal to have tires that stick out further than your vehicle's fenders. Hard to believe with the newest trend of stance trucks?

In Ohio, the size of tires allowed on a vehicle is decided by the vehicles weight.

In most state the vehicles tires size is dictated by other laws like restrictions on bumper or headlight height or the ability to fit under bridges and overpasses.

Radar detectors aren’t technically always illegal. Federal law does make it illegal in all 50 states for any commercial vehicle to use a radar detector, but according to Motor1 the only state laws that ban radar detectors are Virginia and Washington DC. It also states that 28 out of 50 states ban items from being mounted to the windshield. Radar jammers are a completely different technology that messes with a radar guns ability to read a vehicles speed, and are becoming illegal in more and more states

Rolling coal is when black smoke pours out of a diesel's exhaust system. Rolling coal is achieved when a diesel vehicle has a defeat mechanism installed to trick the emissions test. According to the EPA it is super illegal and is a huge penalty if you get caught.

Volkswagen was recently caught and fined after using defeat devices on their diesels in order to comply with the EPA laws specifically regulating diesels.

According to Car and Driver, Volkswagen was ordered to pay over 4 millions dollars in fines on top of having to buy back every single dirty diesel.

Catalytic convertors were made back in the 70s to help reduce the amount of smog that vehicles were producing, but. According to How Stuff Works, the catalytic convertor was designed to convert fumes into a harmless product. Removing a vehicles catalytic convertor is one of the of the easiest ways to gain horsepower and better exhaust sound, but it is also super illegal, as under federal law it is illegal to remove or tamper with. A vehicle that requires an annual emission check would not be able to pass if its cats have been tampered with or removed.

Sources: HowStuffWorks.com, EPA.com, LiftLaws.com, AAA.com