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Not all car mods are created equal. While some modifications will make your car perform much better, others will ruin it.
Owning a car is never quite as simple as it seems. While buying a new car can be stressful and expensive, maintaining an old car can be equally expensive and might even result in getting stuck on a mountain road late at night. But for those auto enthusiasts who love their cars and do everything to keep them running in tip top shape, a used car is usually the way to go. With plentiful aftermarket knowledge and parts availability thanks to massive online communities, learning every little detail about the car can become a hobby in itself.
Updated February 2022: If you're looking to modify your car, you'll be happy to know that we've updated this article with more tips and tricks to make it easier for you to decide which mods to perform and which to avoid.
But every true enthusiast knows that whether they own a truck, a commuter, or a sporty coupe, the way they use their car can always be improved. From bigger tires on a truck to bluetooth audio on a daily driver, there are infinite ways to customize a car so that it becomes the most enjoyable version of itself. That's especially true for performance oriented owners and their cars, with a whole world of potential upgrades available to improve power, handling, and efficiency. The world of aftermarket modifications can be overwhelming, as advice on a wide range of forums often clashes with the information available on parts websites, but the basics of where to start on a project are true for most cars. Keep scrolling for the first ten steps to take on a new build, and for the worst ten to avoid at all costs.
Tires are the single best upgrade for owners looking to improve the overall performance and reliability of their car. And while it might seem excessive to shell out a couple hundred bucks per tire, the benefits of high quality tires help to accentuate everything that a car does well while helping to minimize areas of weakness. Essentially, almost every single thing that makes a car a car must eventually be translated into the patch of rubber making contact with the ground. Want to accelerate? Better have good traction. Going into turns at high speed? Better have good traction. Want to slow down? Better have good traction. Whether the rest of the car will remain stock or not, tires are always the best first step.
And if the future potentially holds more modifications of any kind, tires become even more important. After all, there's no point in investing in a big brake kit if the brakes then become more powerful than the tires can handle. Suspension upgrades become useless if tires can't handle tight turns. And all the engine and exhaust mods in the world, no matter how expensive and powerful they may be, are totally in vain if the engine is putting power to the ground through tires that spin out with the first punch of the accelerator pedal.
Most badly thought out car modifications are silly and impractical details like fake vents or oversized shifters. Some even detract from the utility of a car, like aggressively enormous rims and lowering springs so low the sidewalls scrape. But a few are so bad that they pass from matters of mere taste and style into a realm of being borderline dangerous and potentially illegal.
In every driving school, students are taught when to turn on their cars' headlights, when to use the high beams, when hazard lights are appropriate, and how early to use turn indicators. These are matters of safety that affect all drivers on the road, helping to make a driver's intentions clear to all the cars around them. But adding underglow lights to a car, no matter how sweet it may look when parked, can be a confusing source of information when driving on the highway. Is that a police car signaling from behind me? Is there a car heading towards me from the other side that's causing that car to glow underneath? Uniform auto design between all manufacturers helps to keep things simple in what can be a hazardous driving environment, and sometimes changes that are too radical can lead to dangerous confusion.
The second step for car owners looking to boost performance is almost always an ECU tune (also known as a map or flash). Reprogramming the car's computer affects the fuel-to-air ratio going into the engine cylinders, allowing for more power - some tunes even allow for users to continually refine the programming to try and squeeze out every last bit of possible improvement or to maintain a wide power band and flat torque curve for better city driving rather than going for peak output at high RPMs. ECU tunes are especially effective for cars that use forced induction in the form of a supercharger or turbocharger.
Often referred to as a Stage 1 upgrade, a variety of tunes from companies like Revotechnik, APR, and Cobb, are available that do not require, or minimally require, upgrades to mechanical components of the car. However, it is important to make sure that all aspects of the car, especially its engine, intake, and exhaust system, are in good condition before flashing an ECU, as any problems will be exponentially enhanced. And as with any modification to a car, with cost often comes quality, so a higher end tune will help to reduce any potentially negative effects on vehicle reliability and longevity.
Related: These Japanese Cars Look Insane With Some Cheap Mods (And 5 You Should Never Modify)
Race cars use a variety of engineering feats to maintain enough downforce at high speeds to stay connected to the ground - spoilers just happen to be the most prominent. In reality, rear spoilers work in conjunction with front lips, rear diffusers, side skirts, and overall finely tuned aerodynamic profiles to keep high performance cars planted. In the world of supercars, active aero can include raising and lowering ailerons, dropping ride height at speed, and the use of adaptive air channels under the car.
And yet because the wing is the first thing many amateur automotive enthusiasts see, they think that their car would undoubtedly look better, and perform better, with a race car type wing bolted on the rear. This misconception has only been accentuated by movies like The Fast and the Furious and its sequels, but in reality, 99% of wing actually increase drag, slowing the car down, while they stick up high in the rear, blocking the driver's vision and generally looking silly. Not to mention the holes people drill in their trunk lids. Chances are, if there's any chance your car was going to need a spoiler, the manufacturer would have included it, so this is one popular mod almost everyone should avoid.
When it comes to performance modifications on a car, the goal is usually to improve either power or handling. Often times, owners will focus too much on overall power, trying to get huge horsepower figures or big boost numbers, so that when the accelerator pedal gets pushed to the floor, drivers and passengers alike are pushed back into their seats. But handling upgrades have to go alongside increased horsepower and torque, otherwise overall performance will suffer. High quality shocks, struts, and springs can do so much more than just keep a car riding low and smooth.
In fact, many modders lower their cars excessively, figuring that just being lower means better handling. But in reality, an excessively lowered car can actually have worse traction, thanks to losses in spring compression and too much detrimental change to proper steering geometry. Instead, springs and shocks should be used in conjunction with each other to maximize grip. Many companies offer adjustable coilovers, the ultimate package for maintaining the perfect ride height, while offering adjustable damping and optimal compression ratios. High quality spring and shock packages can do it all without even lowering a car an inch, though higher priced coilovers allow owners another degree of customization.
Related: These Japanese Sleepers Are Insane With Some Under-The-Hood Mods
One of the first steps many owners take when starting out on a modification project is to shell out thousands of dollars for big, flashy rims. Nothing is sillier than enormous rims and low profile tires on a Jeep Wrangler, but on any car they stand out as useless and in fact detrimental to car and driver in many ways. Whether in town, on the highway, or off road, big rims lead to a harsh, uncomfortably bumpy ride while reducing lateral traction, and potentially rubbing the interior of wheel wells. Big rims can also greatly increase the chances of getting flat tires when going over tiny bumps, as the metal of the wheel and concrete tarmac can pinch the rubber to the point of creating a hole.
Performance suffers as well, since the stiff low profile tires are actually less pliable where the contact the ground, resulting in decreased traction during acceleration and braking on top of quicker skids and burnouts. Even if style is the only goal, as is the case with many more reasonable modifications, the potentially dangerous addition is something to avoid, much less dedicate money towards while neglecting other potentially much more effective modifications.
Sway bars, also known as anti-roll bars, can complement a set of springs and shocks or coilovers by transferring cornering forces from side to side as a car rolls during turns. Most cars have their engines located in front, and so will have a larger front sway bar, since the heavy duo of the engine and transmission leads to the front of the car shifting around more during turns. Keeping weight distributed more evenly balanced with a sway bar helps both tires maintain traction, while simultaneously reducing body roll.
An upgraded rear sway bar can be especially helpful for a car that suffers from understeer, a common problem in front-wheel drive and all-wheel drive cars that are nose heavy. These cars often come with narrower sway bars in the rear, since the front sway bar is responsible for much of the car's weight. A rear sway bar will help to reduce understeer by minimizing body roll over the rear axle, though a side effect is reduced traction for the rear tires. The rear sway bar presents a trade-off, though, as more predictable steering leads to more confidence in tight turns, though less power is actually being transmitted to the ground through the rear wheels.
With egregious lowering and the burgeoning popularity of bagging cars down to ridiculous levels, fender flares are making their way back into the world of aftermarket modding. Fender flares are becoming necessary because cars so low, and with such huge wheels, that their tires and rims scrape the inside of the wheel well when even going around soft curves on the highway. From bolt on additions that look pure 1980s to widebody kits reminiscent of 90s rally cars, fender flares seem to be making a comeback.
But if a car is riding so low that its tires and wheels rub at every turn and hit the top of the wheel well going over crosswalks, much less speed bumps, there's more wrong with the car than there is right. Engineers spend lifetimes and manufacturers spend billions of dollars designing cars that are meant to be driven, only for aftermarket modders to render all their efforts useless. Automotive style in all its successes has been a confluence of form following function, and if your mods are upping power to 600 horses and your rear wheels need sixteen inches of rubber, then fender flares might be necessary, but for most owners, fender flares are a warning sign that the rest of the build has probably gone wrong.
Related: These Affordable Sports Cars Shine With Power-Increasing Mods
Power and handling upgrades make up the majority of aftermarket modifications available for cars, but a short shift kit is one area that affects the car in neither of those ways. For cars with manual transmissions, though, a short shift kit can be a huge upgrade. Some short shift kits affect the actual shifter column and the angle it takes, while others change the point at which shifter cables attach to the actual transmission, but the whole point of either option is reduce the time it takes to change gears. Various kits can change either the side to side distance between gears or the front to back length.
Short shift kits help to compensate for what is often the weakest link in a sports car's performance: the driver. After all, when blasting around as fast as possible, it can be difficult to steer with one hand while shifting as quickly and accurately as possible. Minimizing the distance between gears can help to minimize the time when the engine is not actually putting its power to the wheels and the ground, and can also help optimize shifts by allowing for more purposeful rev matching. From upshifting while accelerating to downshifting during a heel-and-toe technique, a short shift kit is almost mandatory for manual transmission cars.
While spring and shock kits or coilovers made it high onto our list of best modifications, a surprisingly large amount of car owners go way too far and lower their cars to ridiculous ride heights. Whether inspired by style alone or mistakenly believing that being so low means the car goes faster, owners of excessively lowered cars all eventually learn to live with taking every driveway at a snail's pace and being prepared to replace bumpers, fenders, and side skirts on a regular basis.
Lowering springs can be done well, as a drop of an inch or two can help to improve suspension geometry, but they're on the list of mods to avoid just because they are so commonly done badly. When dropping so low, not only do the springs have to be installed, but custom control arms, end links, tie rod ends, sway bars, and more are required to make sure the car can actually drive. And to accommodate the wheels and tires riding high up into the wheel wells, often owners will be forced to undertake a fender rolling project or risk causing damage or suffering through life with a dangerously wide turning radius. Despite much popular belief, in the case of most lowering springs, form doesn't quite follow function.
Engines require fuel and air in specific mixtures to combust and create power. A good ECU tune can allow for a higher optimization of the ratio between fuel and air, but in order to increase overall engine output, more air and more fuel become necessary. And while upgraded fuel injectors are a modification many owners choose to make, a much easier and typically much more affordable route first step is to allow the engine to breathe a little easier.
Intake upgrades can be as simple as a high flow air filter or as complex as a cold air filter paired to a larger mass air flow sensor, a bigger turbo, and larger intercoolers. The amount of possible upgrades depends on the engine, but air intake improvements can be effective for engines of all size and type. For cars with an ECU tune, upgrades like a cold air intake or high flow MAF may actually be required, and Stage 2 tunes often require larger intercoolers that sometimes need to be moved depending on the size of the engine bay. These can be costly steps to take, but at the very least most owners of cars that aren't even tuned should try to find at least an affordable high flow dry air filter.
Aftermarket body kits can improve aerodynamics and a car's overall efficiency, but for the most part gluing or bolting cheap plastic to the front and sides of a car results in more pieces that are likely to fall off when going over speed bumps or entering parking garages. While factory performance upgrades often include fascia and cladding that allows for all the benefits of a body kit, aftermarket options don't actually increase space for wheels, don't reroute air flow either outside or under the car, and even add unnecessary weight.
Once again, the topic turns to style versus function, as body kits that originated in race-derived sports cars are now being added to daily commuters like they will ever make a difference. Adding even a tasteful body kit to an older car also presents the challenge of paint matching, since factory painted surfaces will have faded in a relatively uniform fashion, while new cladding will have brand-new paint that hasn't seen the light of day and won't match the correct color of the car's body panels. Another common side effect of aftermarket body kits is moisture retention, leading to rust patterns like those seen on the ridiculous car above.
Exhaust modifications might seem low on the list here, but the truth is that most exhaust systems exist only to increase rumble, rather than performance. Not that there's anything wrong with driving a louder car - after all, who doesn't love the wonderful sound of a Ferrari V8 or Aston Martin V12 as it roars along? But an obnoxiously loud Honda Civic that can't outrace a tricycle is about as silly as it gets. The fact of the matter is that performance exhaust systems rarely allow for power improvements much more than an increase in the 3-5% range.
From cat-back to turbo-back or even headers, the purpose of an upgraded exhaust is to allow the engine to eject gas faster. (Yes, the highest end aftermarket exhausts may also weigh slightly less, it's true.) But the biggest hold up for most exhaust systems is the bottleneck created by catalytic converters, which help to reduce emissions. High-flow cats are an option, though local laws must be consulted to determine legality. Still, with the combination of a slight increase in performance and the joy of a deeper rumble, an exhaust system is often a great choice, though not the first step for most car owners.
Increasingly popular in certain circles is the use of giant shift knobs and shifter extensions, in the style of Gymkhana racers and rally drivers. From pistol grips to ten inch bars, the option to increase the height of the shifter can be alluring after watching Ken Block burn rubber the whole way up Pike's Peak. And with all the smoky twisting and turning he is able to coax out of his monstrous drift cars, Ken Block needs a huge shift knob and emergency brake grip so that he doesn't have to reach down too low to select gears.
But for the rest of us mortals, adding a taller shift knob is fairly pointless - and even against the point of adding a short shift kit like so many enthusiasts wisely do, all the more so on cars that require the driver to push down or use a reverse lockout. Add in the longer throw distance necessary for selecting gears, and the silliness only multiplies. In the end, the choice is based almost entirely on style alone, and in reality this recent fad is truly harmless to anyone or even the car (keep your stock shift knob for resale values!). Unless your friends start laughing too hard as your shifts become clunky and slow, that is.
After coilovers or a shocks and springs kit, and after sway bars, another way to increase body rigidity is to add strut tower braces to both the front and rear axle of the car. A strut tower brace is essentially a sway bar that connects to the top of either shocks or struts, typically stretching from one side of the car to the other above the engine or in the trunk. Strut tower braces can also be incorporated into full roll cages, and paired with rear seat deletes and subframe braces, as well. Some will even help to reinforce strut and shock mounts, a notorious weak point in many vehicles thanks to the unavoidable wear and tear of daily driving.
However, they are connected to a vehicle, they allow for more predictable body roll, as well as a more stable chassis under bumpy or uneven conditions. But don't immediately go online and purchase the most expensive strut tower brace available - there are many aftermarket options out there for most makes and models, and a fair amount of cars actually came with strut tower braces from the factory. Still, strut tower braces are often a low-cost part and unless major dismantling of the trunk is required, they are typically fairly easy to install, too.
One of the most harmless but silliest additions that many people make to their car is the addition of fake vents and scoops all over the hood and side panels. Hopefully, these owners recognize the humor in the addition of what are essentially stickers to their car, often in ridiculous places like the lower edge of a rear door. Regardless of whether they are placed in correct locations, like for brake cooling ducts or intercooler intakes that are increasingly utilized on high end sports cars these days, the vent decals just serve to distract from the lines of a well-done project build. Where is that air going from the vent? Into the door's custom, one-of-a-kind door handle air conditioning system?
Of course, the practice of adding fake vents is fairly harmless, serving only to make it easier to identify a badly modified car from a distance. But those little pieces of plastic are also liable to unstick and fly off at freeway speeds, making them occasionally dangerous, on top of being completely ridiculous. While a seriously built car might actually need to have real vents added to allow for engine cooling, fake vents should be avoided unless their purpose is pure comedy.
One of the least subtle ways to modify a car is to just bolt an enormous rear wing onto the trunk. And while true race cars use spoilers to increase downforce at high speeds (counteracting the Bernoulli effect caused by a car's overall aerodynamic profile), most cars simply do not need a spoiler, and most spoilers increase drag so much as to render themselves useless. A better, and much more subtle, improvement for both the exterior look and overall performance of a car is to add a diffuser below the rear bumper.
Rear diffusers help to increase downforce by creating air patterns that pull the rear of the car down, rather than a spoiler which pushes the rear down by sticking up into untouched air while creating resistance. And unless the diffuser is unnecessarily huge, most average people on the road won't even notice the upgrade - only real enthusiasts will know what that thing even is under there. For most drivers a diffuser wouldn't even improve actual performance in daily life, since it takes high speeds for the air flow to create downforce. But like a lip spoiler on the front, without the increased likelihood of being torn off by curbs, a rear diffuser can improve overall aerodynamics and efficiency.
Where spoilers and body kits grew out of the performance enhancements that allowed high end sports cars and race cars to stay glued to asphalt at high speeds, the phenomenon of fake blue headlights grew out of attempts to mimic the higher cost halogen, xenon, and HID bulbs used by luxury manufacturers to increase nighttime visibility. The real high quality bulbs themselves are wonderful when driving a car that features them, but everyone knows that they add to the strain of nighttime driving due to their somewhat blue tint and high intensity beams.
Fake versions try to mimic that blue of the real deal by adding a color tint to the headlights, but they lack the high intensity of the real deal. In fact, because the bulb is essentially now shielded by the color shift, they can be less bright than a normal headlight or may overcompensate and be far too bright, making them more dangerous both for their owner and for other drivers. Fake blue headlights are now illegal in most states and countries for just this reason, a fact that most potential users of the backwards technology will hopefully find out before adding the feature to their own cars.
The only time tires might not be the very first upgrade on a new project car are if new wheels might be required. Surprisingly for many would-be modders, though, big wheels are down at the bottom of the list, close to mods to avoid, because wheel upgrades can be both beneficial and detrimental to a car's performance depending on cost and type. True, wider wheels can allow for wider tires, which may be necessary if modding up a car that did not come from the factory in a sporty configuration. And it is certainly true that some car owners just have to have big wheels for the looks alone.
But bigger wheels often weigh more, negatively affecting acceleration and fuel economy. They also can cause a rough ride in areas with lots of potholes or bumpy roads. And in order to make up for the increase in size, lightweight (and expensive) materials become necessary. Some drivers might find this worthwhile, and some may not. In general, most sports cars come with wheels that are plenty wide enough to support the powertrain - given the use of proper tires. Overall, if better performance is the goal, increasing width is more important than increasing overall wheel diameter.
One of the most popular conversations on any car forum is the argument between polyurethane and rubber bushings. Cars come from the factory with rubber bushings, seen above in a metal sleeve, that allow for suspension parts to bend and twist without breaking or causing sharp bumps. The malleable rubber is what results in a smooth ride. From inner and outer control arm bushings to subframe and trailing arm bushings, these suspension bits are critical to both handling and vehicle longevity.
Bushings eventually wear out over time, leading to clunking and bumping that can become unpleasant and with enough neglect can lead to dangerously unpredictable steering or lurching. One aftermarket option is to replace rubber bushings with polyurethane bushings, which come in street and race densities that are firmer, resulting in a stiffer ride. And many responses on forums will advocate poly bushings, but those users often forget that they are replacing worn rubber bushings rather than fresh ones. While considering the pros of poly bushings, it is important to remember that their stiffness causes more wear on the rest of the car. And for most daily drivers, poly bushings will be harsh on any bumpy or uneven city streets.
Sources: wikipedia.org, bringatrailer.com, and howdoesacarwork.com.
Michael Van Runkle grew up surrounded by Los Angeles car culture, going to small enthusiast meets and enormous industry shows. He learned to drive stick shift in a 1948 Chevy pickup with no first gear and currently dailies his 1998 Mitsubishi Montero while daydreaming about one day finishing up that Porsche 914 project. He's written in various media since graduating from UC Berkeley in 2010 and started at HotCars in February 2018.