How To Get Into Cars: Aero Mods For More Grip

In 1960, Enzo Ferrari said “Aerodynamics are for people who can’t build engines”. It’s a quote that’s been proven laughably wrong in decades since. Aerodynamics are a key consideration for anyone serious about performance in almost any branch of motorsport. Today, we’ll take a look at how aero influences the performance of your car, and what modifications you might undertake to improve things.

Gains To Be Had

Improving the aerodynamics of your vehicle can mean wildly different things, depending on what your end goal is. Aerodynamics affects everything from top speed, to fuel economy, to grip, and optimizing for these different attributes can take wildly different routes. Often, it’s necessary to find a balance between several competing factors, as improvements in one area can often be detrimental in another.

To understand aerodynamics with regards to cars, we need to know about the forces of lift (or downforce), and drag. Drag is the force that acts against the direction of motion, slowing a vehicle down. Lift is the force generated perpendicular to the direction of motion. In the context of flight, the lift force is generated upwards with respect to gravity, lofting planes into the air. In an automotive context, we very much prefer to stay on the ground. Wings and aerodynamic surfaces on cars are created to create lift in the opposite direction, pushing the vehicle downwards and creating more grip. We refer to this “downwards lift” as downforce.

Drag consists of several components, and can quickly become very complex. However, a simplified understanding of the different types of drag is enough to make basic improvements to a vehicle. The most obvious element is the cross-section of an object moving through flow. The general shape of a vehicle has the biggest effect here. A vehicle like a bus, which has a nearly-flat rectangular cross section, will have a lot of form drag. Conversely, slimmer, more streamlined shapes have less. There’s also lift-induced drag to consider, which is drag created by surfaces which generate lift, or in this case, downforce. For this reason, Formula 1 cars and other vehicles that generate a lot of downforce experience this type of drag. There’s also skin-friction drag, generated as air moves along the body of the car. Typically this is not a major concern when exploring vehicle aerodynamics, however it’s worth noting that washing the bugs off your car will generally reduce this component of drag.

It’s also important to remember that aerodynamic forces are proportional to velocity squared. This means that as speed doubles, the aerodynamic forces of downforce and drag are quadrupled.  Aerodynamic modifications to your car have the most effect at high speeds. This means that if your primary motorsport activity is parking lot autocross under 60 MPH, you won’t find much gain from aerodynamics. If instead your main pursuit is high-speed track work with many corners over 150 MPH, you could shave seconds off of your lap times with the right setup.

Thus, improving your vehicle’s aerodynamics is about manipulating the forces of downforce and drag. Application is key here. If you’re looking for ultimate fuel economy, minimizing drag is a must while downforce is unimportant. Conversely, if you’re creating a time-attack car, you’ll need as much downforce as you can get to maintain high cornering speeds. With the lift-induced drag being a necessary trade-off, as you’ll overcome that with sheer horsepower. A salt-flats land speed racer will also aim to reduce drag to a minimum, while likely wishing to maintain just a touch of downforce to keep the wheels on the ground past the 200 MPH mark.

Like any engineering discipline, it’s all about making carefully considered trade-offs to get the best possible performance. For this article, we’re interested on mods to generate more grip, helping keep a track-focused car glued to the tarmac.

More Downforce Please, And Don’t Skimp On The Down

You’re building a track car, aiming to carve the corners and leave your competitors in the dust. You’ve already got sticky tires and top-notch dampers – you now need to make the air work for you. These mods will help you in your quest to cut that lap time to smithereens.

Rear Wing

Most GT Wings are made of carbon fibre for its high strength and light weight. Adjustment is usually achieved with Allan keys.

A great way to get the authentic race car look and increase downforce, a big wing on the back of your car is a common aero mod among serious track fiends. Stick-on ducktails can have some minor effects, but for real gains, you’ll want a GT-style wing.

These should come with adjustments, allowing the angle of attack to be changed; thus varying the amount of downforce generated. This is an important aspect of tuning, both to avoid excessive drag, as well as getting the aero balance right. Too much rear downforce can lead to understeer in high-speed corner, as the wing pressing down on the rear reduces traction at the front of the car.

Mounting the wing in the right place is important too, with different set ups better suited to different cars. The wing needs clear airflow, and to be able to transfer the downforce to the body of the car effectively. Attaching the wing securely is a must – if it falls off on track, you’ll be in big trouble.

Front Splitter

This rather extreme front splitter is fitted to a time attack car. Note the rods, which can be changed in length to alter the angle of attack. This allows the amount of downforce generated to be tuned to suit the car and track.

A front splitter is a common modification, essentially acting in the same way as a rear wing, just on the front. Due to packaging constraints and the need to see out of the front windshield, they tend to look a little different, and are mounted at the bottom of the front bumper.

Front splitters come in a huge range of designs, from mild to wild. They can be as simple as a molded lip that helps guide the airflow smoothly under the front of a car, to a giant carbon fiber wing with adjusters and many layers of strakes and winglets to get the ultimate downforce.

For the street driver, the former is common as both an aero mod and a styling choice. The latter is generally limited to all-out time attack builds, with the average track rat falling somewhere in between. These devices can make a huge difference to front-end grip at speed, as they help press the steering wheels into the road.

Undertrays and Diffusers

A front undertray can help by reducing turbulence and thus drag under the car.

A less obvious way to nonetheless have a major effect on a vehicle’s aerodynamics is to look underneath. By carefully managing the airflow in this area, it’s possible to create a large amount of downforce.

Not just limited to purpose-built single seaters, it’s possible to make improvements to even mass-produced street cars if one is adventurous enough with sheet metal and carbon fiber. Typically, the goal in this case is to smooth the flow under the hood area, allowing the front splitter to work better, before the flow reaches a diffuser in the rear. A diffuser helps create downforce by slowing down the flow under the car by allowing it to expand, creating a low pressure zone which sucks the car onto the track.

Undertrays are available for many popular sports cars. They can also be easily manufactured out of sheet metal for those eager to build their own. It’s generally hard to go wrong, with a flat undertray being better than none at all. The key is to make something easily removable for service, and not blocking off necessary flow for cooling purposes at the front of the car.

Diffusers are somewhat more complex, requiring some calculation and forethought in their design. It’s also important to either avoid placing components too near hot exhaust pipes, or to use materials that can withstand the heat. Due to their complexity and expense, they’re generally something used by the more hardcore racer rather than those just starting out.

Consider The System As A Whole

Unlike a more powerful engine or stickier tires, aerodynamic parts aren’t always a simple drop-in solution for speed. Often, it’s important to consider the vehicle as a whole when making changes to aerodynamics. For the amateur, aero mods are something best approached once one is familiar with the performance of their car on track. For example, if the car is squirrelly under brakes at the end of a fast straight, a front splitter may help. If you’re noticing a lot of understeer in high-speed corners since you fitted the new rear wing, dialing it down a couple notches might help. Considering how the parts will work with the car as a whole is key to getting the most of out any modifications made!

While this article won’t help the experienced track nut shave seconds off at Willow Springs, it should serve as a guide to the neophyte as to how various common aerodynamic mods affect performance. Knowing how and where to spend your money is a major part of building a fast car, and this series aims to help you on that quest. Good luck, and happy wrenching!

32 thoughts on “How To Get Into Cars: Aero Mods For More Grip

  1. What about side skirts -very effective in F1 before being banned. We have no such rules on our own cars – bring on the skirts. Also you ought to mention active wings, we are hackers, with servos, after all.

  2. Enzo Ferrari was wrong. But not about aerodynamics. The real problem in transportation is energy source. If we somehow finally find really powerful and reliable energy source ( say, something like ZPM :) ), who would really care about cars aerodynamics or even about cars at all? :)

    However, cars and their mods could give you a lot of fun if you are enthusiastic about them. Process is much more important that the result here. :)

      1. Yes, but its energy flux is very limited. ~1kW/m² is too low even for smartphone, it’s only ~10W for surface of average gadget, and that is when awful efficiency of conversion and storage even not taken into account.

        1. What other energy sources are there? Oil and gas and coal and nuclear are all just storage mechanisms for solar! Are you sure you are using the right phrase when you say “energy source” maybe you should say “energy storage”

          1. How is nuclear stored solar energy? Energy from a supernova, sure. But not exactly solar energy. Unless fusion becomes practical, solar is probably the way forward. At any rate, the difficulty in solar is really the difficulty in storing energy for a cloudy day. I am sorry for that pun, but not sorry enough to omit it.

          2. Incidentally, Wind and hydroelectric power are also solar. I’d say that geothermal is not solar as such, and neither is nuclear, unless you consider it solar because radioactive elements were generated in an exploding nova that possibly used to be a sun to its own planetary system.

    1. “who would really care about cars aerodynamics”

      Aerodynamics can also mean down force and grip. Take a look at Top fuel dragsters and Nitro funny cars. At 10k+ horsepower they have far more horsepower than they can put to the ground. At that point creating down force becomes vitally important. So, a car with unlimited energy and therefore unlimited power would likely need aerodynamics to be able to use all that power.

      Another example would be dirt late models way back in the 1980s. Dirt track racers discovered that aerodynamics could help them gain massive amounts of grip on the slippery surfaces they race on. With very little restrictions in terms of body rules, things quickly got out of handle and that era of dirt track racing became known as the “wedge car” era.

  3. This series of articles is sadly missing the most important point:

    If you want to get into cars. Start by going to track days, and events with whatever you have.

    If you want actual performance gains that will result in lower track times, buy seat time with a good instructor. A good instructor, in 20 minutes, will ensure you’re developing good driving habits, and killing off the bad ones. Even if you do something I would consider esoteric, like rock-crawling. There are schools, and classes for you.

    Next best place to spend money? Learn about suspension setup and theory. They have actual textbooks if you find yourself to be the GIANT NERD that I am:

    Race Car Vehicle Dynamics – ISBN: 978-1-56091-526-3

    Fundamentals of Vehicle Dynamics – ISBN: 978-1560911999

    Aero enhancements beyond what a stock production car provides, can look awesome, but it is only valuable after you’ve figured out everything else. It’s literally the bottom of the list for the average grassroots driver.


    Most production car racing classes, and the tracks they race on, don’t allow/enable drivers and their cars to reach speeds where “good aero” will make a significant difference in any real competitive sense to the amateur driver. The gains just aren’t effective.

    1. Not to negate what you say, but the “most important point” is typically that you enjoy what you’re doing (without harming others). Some car folks may be more builders/tinkerers than drivers.

  4. I need to figure out how to tweak the aerodynamics of my car so that the wind will stick to the rear window and clear the water off of it when it rains.

    Maybe I need to look into making some vortex generators to put on my car roof.

    1. I hope you’re not part of the crowd who deleted their rear wiper.
      Far too many times have i encountered people who did that because they considered it ugly, following with them complaining about poor rear visibility when it’s raining about a month later.

      1. Same as the front glass: clean it with a reputable glass cleaner. Clay bar it. Glass cleaner again. *thin* coat of carnauba wax – none of the ‘milk’ coating that certain aftermarket products build up with use. Cheap, safe and birdsh!t wipes right off LOL.

  5. That is a very generalised statement, and therefore incorrect.

    There are heaps of possible and legal aero modifications available in germany. We wouldn’t have such a massive (proper) tuning scene if there weren’t. See Wörthersee, Reisbrennen, Tuning World Bodensee and many more.

  6. Years ago, I read on the Internet about a metal scrapper who used corroplast on his old Ford pickup to streamline the undercarriage and fenders. He also removed a lot of “unnecessary” items to reduce the load on the engine, such as radio, heater, door panels, grill, floor mats, ash tray, bench seat…
    IIRC, he claimed an improvement from 15mpg to 30mpg.

  7. “If your primary motorsport activity is parking lot autocross under 60 MPH, you won’t find much gain from aerodynamics.”

    Or, alternatively, if your primary motorsport activity is parking lot autocross under 60 MPH, you need to go a lot more overboard with aerodynamics for them to have any effect. Top level autocross hasn’t quite caught up to sprint cars, where the aero elements are nearly as large as the car itself, but they’re getting there.

  8. Aerodynamics is the biggest scam perpetrated on the consumer. Every car has a big hole on the front of it leading to a flat block of metal. Radiators and cooling systems are designed on the cheap, so money is put into plastic paneling to try to overcome the aerodynamic deficiencies.

    1. My 2000 Nissan Quest has a small hole at the front leading to a metal grating, but this is a functional element not a source of inefficiency. In fact so little air flows through that part of the system that it needs a large fan to create airflow inside the engine compartment.

      Also, since the article is totally wrong about undertrays being for sports cars, my stock undertray limits the airflow through grill to just what is needed for cooling.

      Because of the way heat limits power, increasing the cooling through other means would be unlikely to increase efficiency.

      The plastic paneling in other places doesn’t have its effects limited by the existence of (needed) drag in the heat exchanger. Since the tail of the car is not used in the heat exchanger, for example, it can completely ignore the drag in that system, and it will still give you the exact same gains as you’d get from it in a design that did not have any heat exchanger at all.

  9. Body and drive train mods are VERY old school… What I want to know about is the head units in modern cars.

    They are pretty sophisticated, integrated computer systems and to date, I’ve been able to find nothing on them. My car, a Ford Fusion has a built in LTE modem and WiFi hotspot. The modem is locked to AT&T and I think it would be just peachy keen to be able to change the carrier of my choice. On my cell phone, I just swap the SIM card and go. It’s the same technology I think.

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