If you spend any amount of time in social media car groups, you’ll come across tons of people looking to do performance modifications to their cars, or showing off the ones they’ve already done.  Sometimes, this can be cringingly bad, as a fundamental lack of understanding on how these systems work contributes to performance mods actually slowing their car down.  Since the number of people actually taking their freshly modded cars to the racetrack is extremely small, the placebo effect takes over at this point.

I want everyone to get the most out of their cars, so avoiding a few of the pitfalls can make a big difference.  Now, if aesthetics are the only thing you are interested in, then if your car looks good to you then you’ve achieved your goal and frankly that’s a win.  But if you are looking into actually making a fast tuner, don’t get caught up.  Here’s five of the most popular performance mods I see that will actually make your car slower.

Huge ‘Sport’ wheels

High trim level sports cars, as well as many race cars, have huge wheels.  This is mainly for two reasons.  The first is that large wheels and low profile tires will help with more responsive handling and minimal sidewall flex.  The other reason is to clear extra large brakes.

Because aesthetically, wheels have one of the largest impacts on how a car looks, usually the first upgrade people make is to put on large sport wheels with low profile tires.

There’s a catch though, large wheels are often very heavy or very expensive.  You only get to choose one.  Obviously, there are people that will spring for the 19lb magnesium racing wheel (and probably pay upwards of $900 per), but most will just get the big wheels that look cool.  For example, your BMW may come with some plain 17in Style 394’s which weigh a modest 22.5lbs.  Not exactly light to start.  Now go shopping for your new 19in wheels.

If you picked up these very stylish Model Six’s, you’d have added around 8.5lbs per wheel.  Take into account that the 19in tire is around 5lbs heavier than the 17 on average, you’ve added around 54lbs of unsprung weight to your car.  That’s a catastrophic amount.  I have a more in depth answer to why that is here, but for now just know that unsprung weight (weight before the springs, like the knuckle, brakes, hub, wheels, and tires) has a substantially higher negative effect than normal weight. So before you spring for 19’s, take into account the unsprung weight you may be adding and drop the coin on those spiffy OZ Alleggeritas to get a real performance gain.

Verdict: If you want to go fast, stick with smaller and wider wheels, and pick the lightest one you can.  That’s the true performance upgrade.

Straight Pipe Exhaust

Alright, now that your car looks the business, now it needs to sound like it.  Who wants a wheezy, quiet sports car?  Let’s take the mufflers off and add a large straight exhaust pipe because that’s how race cars do it, right?  Well…sort of.   Race cars generally have large straight pipes because they are specifically tuned to work with a pipe like that.  To get performance out of an exhaust, you have to take advantage of scavenging, which is a reverberating pressure wave in your exhaust that helps suck exhaust out of the cylinder.  Really fat books have been written on the fluid dynamics behind this, which I won’t get into.

Racing cars have exhaust headers and pipes meant to allow that pressure wave to scavenge at very high RPM, near redline.  In order for them to work right, they need to live in that range.  For the street however, the high RPM tuned exhaust will do nothing but hurt off the line performance, lowering your exhaust velocity and making your engine slow to gain rpm.  This applies mostly to Non-Turbo cars.  On turbo cars, a large diameter downpipe will help turbo spool up, and you aren’t going to be enjoying much scavenging effect through the turbine wheel.

If you have a ripping tune and plan on moving a ton of exhaust gas, then the better flowing pipe would go with that.  However, if you have a stock car, that fat straight pipe will only make your neighbors hate you.

Verdict: Specific street tuned exhaust’s flow great with proper diameter pipes in order to place the powerband in the zone you use most often.

Slammed Coilovers

Race cars and sports cars are low in order to maintain an exceptional center of gravity and also aid in aerodynamics, so its natural when you are sport tuning to want the car to be very low.  Generally when you slam a car, you have to make it very stiff in order to keep it from bottoming out and scraping over bumps, so coilovers are very appealing here.  The problem is that very few people can actually work an adjustable coilover style suspension.

When you have ride height settings for every individual corner, you are able to set it up through a process called corner-weighting.  By making small increments in ride height, you can effectively move the weight around and control how the car’s balance feels.  On top of it, many coilovers have bound and rebound adjustment as well, giving even more precise control.  Adjusting them all to the lowest setting is not how you tune a well handling sports car.

When you stiffen a car, you lower the total amount of travel the suspension can use for mechanical grip.  If you haven’t substantially lightened the car, then you are asking a lot of a little, and the car will be very susceptible to bump steer and other poor handling characteristics.  Since roads do conventionally have bumps, you’ll find a very uncomfortable ride paired with sloppy cornering.

Verdict:  For most street situations, sport springs and upgraded struts/shocks (Koni or Bilstein are both excellent choices) will give you a significant boost in handling over poorly setup coilovers.

Cold Air Intake

When it comes to the design of the engine bay in your production car, chances are that someone that knew what they were doing is responsible for your air intake.  That doesn’t stop people from assuming that their air intake system is restrictive and robbing precious horsepower.  Often referred to as a cold air intake to fool the casual viewer, stuffing a cone filter in your engine bay without any heat shielding might make your car sound a little better, but you will find your power levels tanking fast.

Engines hate hot air.  It’s less dense, so in order for it to achieve the proper air-fuel mixture the car injects less fuel.  Less air, less fuel, less power, easy.  The most restrictive part of your air intake will always be the filter (not the location or the piping), and K&N makes high flow drop in replacements to remove that restriction and let you focus your tuning elsewhere.

Verdict: If you want the throaty intake sound, make sure your open air intake is located somewhere far from the hot engine.  In the front fender well ahead of the front wheel is often a good place to find nice cool air for the engine to enjoy, just be careful about water.

Big aerodynamic mods

I see improperly understood aero so often I felt compelled to writing this blog to describe the difference between a Wing and a Spoiler, two things people often mix up.  The thing about Aero is that almost everything you put on to manipulate the direction of the air as it flows over the body, you’re going to increase drag.  Spoilers are added to very specific parts of the car to condition the air in order to reduce drag and lift, often in the form of a small lip.

However, small spoilers don’t look that cool and race cars have big aerodynamic elements all over to help them go faster around a race track.  Just keep in mind that all of those elements add considerable drag.  While they are able to corner faster, the different aerodynamic devices attached to the car actually slow the car down on the straight away.  So before you put that big spoiler or wing on your car, keep in mind that if it isn’t perfectly designed, the only result you will get is adding weight some drag.

Verdict:  A big wing is like bolting a parachute to the back of your ride.  If you are looking to improve MPGs slightly, try a small lip spoiler on the rear deck and see if it helps.  Otherwise, leave the Aero to the pros.