Our last video spurred a few questions about what went into making our DIY rear wing. Between picking the right profile, choosing the right materials, and forming the required shapes accurately by hand, there's a lot of work involved in making your own wing. The skills and materials are often so specialized that it isn't possible for your average DIY mechanic to build his or her own rear wing.
Fortunately for the budget-constrained of us, there is a big market for cheap, appearance-oriented aero add-ons. And some of those huge ricer wings can be made to work on your track or race car. Here's how:
Find the Right Cheap Wing
The first thing to do is to find the right wing to work off of. Not all cheap wings produce usable downforce. In fact, some cheap wings have so many problems that it isn't worth trying to modify them.
Look for wings that are:
Single element
Have a simple profile (or bear a strong resemblance to the APR 3D wing profile)
Have no holes in the endplates
Are as wide as possible
Include tall struts that bring your wing up to roof height (or higher)
Here are some examples of wings that could be easily modified to produce downforce:
Avoid wings that look like this. They have so many fundamental problems that they aren't worth fixing:
Add Internal Reinforcement
One common attribute among cheap wings is that they are more flexible than their more expensive counterparts. While it is ok for an automotive wing to be flexible, they do need to be rigid in a few key places. Those key places are the areas where the wing connects to the wing supports, and the trailing edge of the wing.
Most of the cheaper plastic and aluminum wings out there have no internal ribbing to support these key points. So the first modification you will want to do is to add some reinforcement to these points. The "right" way to do this would be to cut the wing open, add in internal ribs, glue them into position, and glue the wing back together. But there is a much cheaper, much easier way to accomplish this. And that involves using our old friend, 2-part expanding urethane foam.
Most of you who subscribed to car tuning magazines through the 90's and early 2000's will recognize this stuff. It's the same foam that enthusiasts used to pour into the side sills of cars to make their chassis stiffer. When mixed together in a 1:1 ratio, this two part foam quickly expands and hardens into a stiff, lightweight structure with properties similar to a light wood.
We drilled a few extra holes near the mounting points of our plastic wing, and poured in a small amount of the 16 lb/cu ft density. We first poured in a bit of foam and stood the wing up on its trailing edge to make sure that it would fill the tall gurney flap on our plastic wing. After allowing it to set for 10-15 minutes, we laid the wing down poured a small amount of foam into the holes to reinforce the mounting points for the wing uprights. This will ensure that the wing wouldn't collapse when faced with a 100 mph headwind like you would see on a racetrack.
Work slowly and pour the foam in small portions. You don't need much foam to fill the open cavities inside the wing. We used 1 oz shot glasses as measuring cups to make sure that we didn't overfill the wing. Sand off the excess and paint to match the rest of the wing.
Why go through the trouble of doing all this? The picture below shows what can happen if you run a hollow wing without the appropriate reinforcements in place.
A functional rear wing can generate hundreds of pounds of downforce at high speeds. These forces are easily high enough to crack the skin on these cheap wings. This wing had big cracks around their mounting holes from years of hard racing. If left alone, this could have resulted in the whole wing breaking off of the car mid-corner which, needless to say, would have been an extremely dangerous situation.
Fortunately, this is easy to fix if you catch it early enough. If this happens, drill small holes at the ends of the cracks to prevent them from getting worse. Then fill the cracks with a structural epoxy to ensure that no new cracks appear.
Choose Endplates that Don't Suck
Most budget friendly wings tend to come with very sharp, angular endplates that are trimmed into thin teardrop shapes. While these designs do look good, they actually don't work very well.
Why? It's because the main purpose of endplates are to keep the fast moving airflow from spilling over the edges of the wing. The most effective endplate designs tend to be simple squared-off designs that are large enough to cover the full chord of the wing. Very few cheap wings come with great endplates, but you can avoid the worst offenders by knowing what to look for.
Try to find a wing that comes with large, flat endplates. The closer they are to a simple rectangle or square, the better they will work. Stay away from endplates with big slots or holes in them. These endplates are basically guaranteed to not do anything for performance:
If you want to get the maximum benefit from your rear wing, you will need to make your own endplates. Fortunately this is quite simple. Drill a few holes into a piece of sheet metal or a 1/4" thick flat polycarbonate sheet and bolt them onto your wing in place of the endplates that came with your cheap wing.
Bolster your Trunk Mounted Supports
In an ideal situation, you would want your wing supports to bolt through your trunk and into your chassis. This ensures that all of the downforce generated by the wing is transmitted to the chassis and wheels. However, all of the cheap wings available on the market are designed to be mounted to the trunk or hatch panel, rather than the chassis. Fortunately, most car trunks and hatches are capable of handling the downforce produced by bolt on rear wings. The key is to spread the load as much as possible, and there are a few tricks you can use to do this.
The first is to make sure that the wing is mounted as close to the rearward edge of the trunk (or hatch) as possible. The edges of the trunk panel are significantly stronger than the middle, and it will go a long way towards reducing unwanted flexing and bending.
The second is to reinforce the underside of the trunk where the uprights bolt through the chassis. Most of the wing uprights that come with cheap wings tend to extend very far forward and are slanted rearwards at a fairly shallow angle. In most cases, this puts the center of pressure of the wing behind the rear feet of the wing supports. When a wing like this produces downforce, it will actually try to pivot around the rear feet of the wing uprights, pushing the rear feet down while pulling the front feet upwards. If the trunk is not strong enough to resist this motion, the wing will tilt upwards at higher speeds, resulting in a loss of downforce as you go faster.
Adding a few fender washers on the underside of the wing uprights will help reduce trunk flexing and will help transmit all of that hard earned downforce to the chassis.
Do You Need an Expensive Wing at All?
With a few careful modifications, an inexpensive wing will get you very close to the performance of a more expensive aftermarket wing. So why would you spend the extra money for an expensive purpose-built racing wing? There are a few good reasons:
Higher efficiency from newer wing profiles The profiles of cheap aftermarket wings are either copies of a popular wing or are modeled after a common NACA airfoil profile. While these profiles do work, they are older designs and tend to generate more drag relative to the amount of downforce they produce. The current generation of aftermarket racing wings are extremely efficient, and even the simplest looking of aftermarket wings boast a much higher downforce to drag ratio than the most elaborate looking "3D" wing profiles of yesteryear. With a cheaper wing, you will always give up a bit of efficiency compared to a well-designed modern racing wing.
Better variety in profile and width options Need a dual element wing for your powerful hillclimb car? How about an extra wide wing for your unlimited class time attack car? You'll need to shell out for a proper racing wing. Unfortunately there are almost no workable cheap wing kits that fit the bill for these niche applications.
Slightly lower weight As you might expect, purpose-built racing wings do tend to be lighter than these DIY wings. While the wing elements themselves are only fractionally lighter than a foam filled DIY wing, the wing uprights tend to be much lighter than the heavy steel pieces that come with cheap kits. If weight is a big concern for your car, going with a dedicated racing wing can mean saving 5-8 lbs off of the rear end.
Conclusion and Recommendations
With a bit of time and a few small modifications, you can make an affordable, functional wing that actually produces downforce. It might be a little more draggy and weigh a bit more than a high-dollar carbon fiber racing wing, but it will make your car much more stable through high-speed corners. It's a worthwhile modification for many track cars, as well as on club racing cars in classes which allow add-on aero.
If your aero budget is closer to $100 than the $500-$700 that many racing wing kits cost, give this option a serious look. You'll appreciate the added stability as well as the low impact it will have on your wallet.
See you at the track.
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