Composite Race Car Bodies

You Never Forget Your First One

My first car was a greenish-brown 1969 Buick LeSabre with a 123-inch wheel base and a 230-horsepower two-barrel V-8. That puppy weighed about 4200 lbs and taught me everything I know about Bondo and car repair. My parents got me that car because it was a tank. They figured, with that much steel, I would be safe from just about anything.

Back in the day, we equated the weight and bulk of steel with safety, but that’s not the case now. When you’re talking vehicles, weight means money because (as Newton taught us) you need more fuel to accelerate a bigger mass. The search was on for materials that were just as strong as steel, but lighter– like aluminum alloys, . Because those materials cost more, they’re used mostly in aerospace, where weight is much more critical than in cars. As the cost has decreased, we’re starting to see them in high-end cars and eventually they’ll be standard in the cars us normal people drive.

One of the big digs against NASCAR is that they’re stuck in the past, using old materials and old methods. Last week’s XFINITY race in Richmond was a step toward the future as NASCAR debuted its first composite body in its big three series.

Lower-level series like K&N and ARCA are already using composite bodies made by Twin Lakes, Wisconsin firm Five-Star Race Car Bodies. They were approved for tracks one mile and less in ARCA in 2015, for all tracks except superspeedways for the 2016 series. They’ve been testing the bodies at superspeedways and, in fact, have a test scheduled for November 7-8 at Talladega in anticipation of making them mandatory at all tracks for the 2018 season.

NASCAR has made composite bodies optional for XFINITY races at Richmond, Dover and Phoenix this year, optional at all tracks except superspeedways in 2018 and everyone expects NASCAR will make composite bodies mandatory at all tracks in 2019. I’ll have something to say about ‘optional’ later on.

What’s a Composite?

“Composite” is short for composition material, which is a material made from two (or more) materials with significantly different physical or chemical properties. When combined, the composite materials has properties that are significantly different from either material alone.

“But wait,” you say. “How’s that different than an alloy?” Alloys, like the different types of steel used now in NASCAR race car bodies, are atomic-level mixtures of different atoms. Composites are more of a macro-scale mixture, where each component retains its identity, but they must work together to be more than the sum of their parts.

Although composites can be made of more than two materials, we’re going to stick with two for the purposes of simplicity. Composites, then, are made up of a matrix and a reinforcement. The matrix is a material (like mud or cement or asphalt (for example), which has some desirable properties, but not quite desirable enough. We add to that a reinforcement that improves the properties of the matrix.

My favorite example is reinforced concrete (at right), where strong, ductile rebar (reinforcement) is used to improve the properties of the concrete matrix, which is relatively weak and brittle. You have to make sure there’s a good connection between the rebar and the concrete or the two don’t work as a single unit. Composites aren’t new and they aren’t all human-made.

The key, remember, is that you have to get a material with different (and hopefully better) properties that either material on its own. For example, bricks made of mud are not very strong, plus they crack because they don’t dry evenly. Some smart person figured out that if you add straw to the mix, the straw binds the mud together and also helps the bricks dry more evenly, so they don’t crack. Adobe is an incredibly durable building material for being, basically, dirt and straw. You can see from the table that we’ve been using composites in NASCAR for a very long time.



Given how many different types of matrices and binders there are, there are multiple types of composites, some of which are illustrated below.

Cement and asphalt are particle-type composites. We’re going to be interested in a variation on the fiber-based composites. When you’re talking about large pieces that will have to take force from different directions, you weave fibers (for example, carbon or kevlar or a combination) into a fabric.

You then mix the fabric with an epoxy resin that holds it all together. The key is to get really good connections between the fibers and the epoxy, so usually the process requires high temperatures, high pressures, or both. We’ve talked about this before when we’ve talked about the splitter, which is also a composite.

The photo below shows 100 sheets of (in this case) polypropylene oxide woven fabric put together. The top surface is what you get when you put those sheets together using heat and pressure. Any composite is made similarly: you start with a floppy fabric and you end up with a strong, rigid piece. Carbon fiber composites, increasingly used for seats and dashboards, are made the same way.

What is a Composite Laminate?

All the articles about the bodies use the phrase “composite laminate”, which is the terminology Five-Star uses on their website and promotional materials.

Remember when you were writing an essay in school about something and you didn’t actually understand it all, so you wrote down some words from your notes or the book verbatim without knowing what they mean? When the mainstream NASCAR press covers tech-y topics, you can always tell when they’re repeating what they were told: the same string of words keeps popping up. (hello “flange fit”! )

Here’s the issue: Carbon fiber has a very specific look. You see the fabric in the finished product. Carbon fiber is also very brittle: When it fails, you tend to get shards of material littering the track. Apparently, one of the reasons Apple hasn’t used a lot of carbon fiber to replace aluminum is that they don’t like the look. So a couple years ago, they filed a patent to sandwich (which is a fancy word for ‘laminate’ carbon fiber between other materials so that you get the benefits of carbon fiber without having to see it. The drawing below is from their patent application.

In the left figure, all of the first 7 sheets are carbon fiber. You’ll not that they alternate the weave direction, so that the composite material is strong in all directions. The last layer, however, is drawn differently. That’s the cosmetic layer, which is a different material. It gets bonded to the outside, so that’s what you end up seeing, not the seven (or however many) layers of carbon fiber.



My guess is that this is what Five-Star has done, in part because it gives you a smoother, nicer surface to work with and in part for security reasons (which we’ll get to in a moment).  it’s a combination of different materials. xSo I suspect they’ve put some other type of material on the top to give it a good smooth finish for painting or wrapping. Apparently Apple was delaying using carbon fiber in its cases because they didn’t like the way carbon fiber composites look, so they came up with a way to essentially make a sandwich with fiberglass on the outsides so that you didn’t see the carbon fiber layers.

But Why Composites? Why Now?

Metal has had an advantage in being readily available, easy to work with, and cheap. Usually, when we talk about advanced materials, we’re usually talking about how NASCAR bans them. In this case, though, it makes sense.


Composites are typically seen in high-end products (cars, aerospace, golf clubs, bike frames, etc.) because composites are more expensive than other materials.

What makes the difference for NASCAR is labor and logistics. The new bodies have 13 panels that snap together and bolt onto the chassis. (That’s what ‘flange fit’ means: you bolt them on.) Even if a team purchased the comparable steel pieces pre-made, they would have to rivet and weld to get them put together and onto the car. NASCAR says this move decreases the time to hang a body from weeks to days. More importantly, if you do damage the body, you can change out just the body part that’s been damaged.

If your driver wrecks in qualifying or practice, you’ll be able to fix the body right there at the track, something you can’t do now. This is especially important for the West Coast swing, where taking a car back to Charlotte is very expensive. (Of course, if your driver hits hard enough to mess up the chassis, you’re still stuck.) It will be interesting, however, to see how inspection goes the first time someone has to replace a body part without all the stuff at the shop like surface plates and jigs.

Theoretically, teams should be able to have fewer people hanging bodies because it goes much faster – which likely means fewer jobs.

The panels are extremely uniform. If you get five side panels, they’re going to be the same shape and same weight. Anytime you have reproducibility on that level, life becomes easier.


Composites have a much larger strength-to-weight ratio than metals. If you compare a 1/2″ thick, 1 square foot piece of steel with a 1/2″ thick, 1 square foot piece of composite, the steel will be stronger — but also much heavier. You can replace that steel with a piece of composite much thinner, thus getting the same strength for less weight.

The new bodies are 150 lbs less than the current steel bodies. NASCAR is using that feature to encourage teams to switch because they don’t have to make up that weight with ballast. While using the new body is optional, running steel puts you at a pretty big weight disadvantage. If that’s not enough, NASCAR’s won’t let you use a radiator pan to help air pass more quickly under the car if you stay with the steel body. That’s why 90% of the teams used the composite body at Richmond: It was faster. The teams that didn’t are mostly lower-funded teams that didn’t have the capacity to implement a new body as quickly.


NASCAR says that the teams are all for the new bodies, but this is a true win-win. NASCAR’s had big issues policing the garage this year, with growing consternation over encumbered wins and rising calls for taking away wins if the winning car hasn’t followed the rules. It just looks bad. The new body greatly decreases opportunities for the teams to mess around with the car. No bondo is allowed, not even to close up the cracks where the panels meet. No sanding is allowed. The panels are rigid up to 200+ mph, which means no flexing at speed, not matter how much you switch around the bracing.

The composite panels are also rigid when standing still, which means a pit crew member “accidentally” bumping into the side of the car to adjust the aerodynamics is just going to end up sore. The panel won’t budge.

To make sure teams aren’t testing the limits of The Aerodynamic Box, NASCAR put some security features on the body. The pic below (as well as the full body one above) are from a NESN source.

Note the hexagonal pattern covering the aerodynamically sensitive area of this part. The pattern, which is found on the quarter panels and A-, B- and C-posts, is raised, so it shows through a wrap or paint. (In fact, that’s a condition of passing inspection. If the officials can’t see the pattern, you fail.) If an official sees that the pattern is distorted in any way, they’ll know they need to look more closely.

I like this approach because it’s simple. It gives you a first-level screen that doesn’t require lasers and such.

Why, you might ask, does everyone in racing use hexagons so much? If you watch the NBCSN graphics, they use a hexagonal pattern — as did Fox Sports 1. Hexagons are associated with carbon, which is so prevalent in advanced composites. Carbon forms a couple different crystal structures, but one of the most interesting is when it forms sheets. This phase is called graphite. Graphite is good for pencils  lead because the stacks of sheets don’t have strong bonding between them, so they flake off and leave themselves on the page.


5 thoughts on “Composite Race Car Bodies”

    1. I don’t believe so. I have requested an interview with someone from the company and haven’t gotten any response from them to confirm for sure; Looking at the finished product leads me to believe it’s not carbon fiber on the outsides. Thanks for reading!

  1. My question is about the shattering effect in a crash. It is strong enough to withstand 200 MPH speeds without bending, so what happens when it gets bent? Does it shatter into lots of little sharp pieces like carbon fiber? that would cause a cleanup mess or blown tires from running over sharp pieces.

    1. The beauty of the sandwich ‘composite laminate’ is that it mitigates the brittle failure mode of carbon fiber, so they don’t have the problem with shards of material that can puncture tires. Of course, it remains to be seen whether that works in practice, although ARCA has been using these bodies for three years now and if you’re going to crash test anything, that would seem to be the perfect place to do it.

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