As racers, we are all familiar with the famous quote from Lotus founder Colin Chapman, “Simplify, then add lightness.” In racing we are always trying to “add lightness” because less mass makes cars faster, easier to stop, handle better, and get better fuel mileage.

However, making a car weigh less is often easier said than done. Sure, there are the easy things to remove from a racing car that was once a passenger vehicle like seats, carpeting and glass windows. But after that, things get a bit more challenging to “add lightness.” The further you go, things also get exponentially more expensive. Have you priced a set of forged wheels lately? Be prepared to get both of your wallets out. We covered an aspect of this, which was expensive, in an earlier Toolshed Engineer article Weight Savings Using Different Hardware. This month we will show you how to “add lightness” by building your own carbon fiber body panels.

Prior to using our metal door as a mold for a carbon fiber door, we prepped the surface by wet sanding it with 400 grit sandpaper.

If you want to use the “easy button,” what I call the “money button,” and purchase a carbon fiber part for your car, oftentimes you can do that. But for reference to this specific project, a carbon fiber door panel for an SN95 Mustang will set you back between $2,500 to $3,000 per door — and you need two. I told you adding lightness is expensive. I know people who race in NASA that have purchased complete race cars for less than $6,000 and won a race. I will show you a method where you can have two carbon fiber doors and a carbon fiber trunk lid for less than $1,000. Let’s get to work.

We used products from Composite Envisions to ensure our carbon fiber door skin would pop off the mold without any grief.

To begin our carbon fiber do-it-yourself project, we enlisted the products and tech support of the folks at Composite Envisions. We used its specific carbon fiber, resin and mold release to make sure everything would gel together nicely. There are multiple techniques to make carbon fiber parts. You can make a female mold of a part — time consuming and expensive — and use vacuum forming — also expensive and requires more tools and consumables, bags, media, etc. to create carbon fiber parts. Or, you can go with the less expensive method we used for the Service Motorsports NorCal NASA Time Trial SN95 Mustang. Our method is essentially using an OEM part, in our case, a metal door skin from a Mustang, prepping it, turning it into a male mold, then laying carbon fiber over the top of it and adding resin into the layers of fiber until you have a completed part.

We added outer flanges to the edges of the stock metal door skin using simple outdoor sign stock, a hot glue gun, and caulk from Home Depot.

Just like getting a car ready for paint, the more work you do on the prep, the better the final product. It is the same when making a mold for carbon fiber. Once we repaired any dings and dents in the door skin and filled in the door handle bubble and spot primed the Bondo with Duratec Primer, we wet sanded the door with 400 grit paper.

Then once the door was looking sharp, we added flanges around the door’s outer edges to create a space for the carbon fiber material to land without folding over onto itself during the epoxy processing. We created the flanges by simply hot-gluing corrugated plastic sign board material from Home Depot to the back of the door and then used urethane caulking seal between the door and the flanges. Foil tape was added to any seams or holes we needed to cover.

To seal the sign board flanges to the side of the metal door we used urethane caulk.

Once we had a clean door and created our DIY Home Depot flanges, we then set up the door mold to release by applying three coats of Partall Paste No. 2, like waxing a car door. This was followed by spraying three coats of the Partall PVA Release Film. This would ensure that our carbon fiber door would separate from the metal door after we applied coats of epoxy into the carbon fiber. Two-part epoxy is extremely sticky, so if we didn’t have the mold-release film on the metal door, then we would never be able to separate the carbon fiber door from the metal door.

We used Partall Paste No. 2 and Partall PVA Release Film to coat the OEM Mustang metal door skin with it to ensure the carbon fiber door panel would release once the epoxy had cured.

The idea of using the OEM metal door — a male mold — to create our carbon fiber door means that the final product will be 1.5 to 2 millimeters larger than the original door. For us building a racecar part, this wasn’t an issue. The clearances on a Ford Mustang just aren’t that critical. We used a Harbor Freight sprayer to shoot the door with four coats of Duratec Surfacing Primer prior to adding fiber. This surfacing primer will become the inside layer of our carbon fiber door. The primer forms the base layer (shell) against the PVA film to prevent us breaking though when working the epoxy into the cloth layers.

To assist with the mold release process, we shot the metal door with four coats of Duratec Surfacing Primer using an inexpensive Harbor Freight airless sprayer.

We were finally getting to the exciting part: laying down some lightweight carbon fiber. But the actual layers of carbon fiber are the interesting part of the recipe. By just using carbon fiber cloth, the part will be strong, yet extremely brittle. By just using fiberglass cloth, the part will not be as strong and too heavy. By just using Kevlar cloth, the part will be less brittle but extremely flexible. The trick is to use a hybrid of different cloths mixed together in a certain order to make the part strong and light, which is what NASCAR and F1 teams do.

Since we were on a budget, we did not use Kevlar for this part, but we will consider using it when we mold a new nose/bumper for the Mustang. Our layers of cloth on top of the metal door were as follows: one carbon, one glass, one carbon, one glass, and one carbon. Five layers total.

Eli Cronbach, team principle for Service Motorsports, made the final decision on the order of fiber layers, using a hybrid of carbon fiber and fiberglass for five total layers.

The next step, and the most crucial, is to use a two-part, high-strength epoxy and squeegee it into the layers of fiberglass and carbon fiber, getting out all of the air bubbles. The key in this step is to use the correct epoxy and really force the air bubbles out of the epoxy. The correct amount of epoxy is the key, too little and the part isn’t strong, too much and the part will be heavier than necessary. The point of this project is to add lightness.

We used Premium Resin Tech’s High Impact Epoxy Resin (RD 3212) mixed with its Hardener (RDH-9386). The choice of epoxy is crucial because the less expensive epoxy has a lower heat resistance, known as glass transition temperature. As the panel gets warm, like the hood of a racecar over a hot engine, the panel will begin to soften and then start to flap all over the place — this is a bad thing, folks. An airbox is another example that would require a high temperature epoxy to remain stable in the engine compartment. This is where the tech team at Composite Envisions can really help you choose the correct product for your project.

With a lot of attention to detail, and working the epoxy before it hardened, we were able to get all of the air bubbles out between the five layers of cloth. Adding the layers of glass cloth between the carbon also helps ensure you have fully wetted out the fiber before adding the next layer of carbon. Take your time, keep working the cloth while adding small amounts of epoxy as needed.

Once the epoxy dried, we popped it off of the metal door skin without any problems and then trimmed the edges (removing the flanges). The big question is: How much weight did we save? The original metal partially gutted door weighed 35.5 pounds. The metal door skin by itself weighed 15.5 pounds. Our carbon fiber door skin weighed in at a svelte 4.5 pounds. That is 31 pounds per door totaling 62 pounds taken off the car just with the passenger doors.

Here we can see our bargain carbon fiber door in place on the Service Motorsports’ Mustang.

Using the same materials and methods, we also made a rear decklid for the Mustang to save even more weight. In the end, for less than $1,000 we had three carbon fiber body parts created in our own garage. For those of you who are curious how much lighter our 4.5 pound doors would be if we had made a female mold and used vacuum forming, the estimated answer would be a half a pound less, 4 pounds total weight. Yes, we could have gone a touch lighter, but our budget wasn’t allowing us to go full F1 Team Red Bull on this project. However, we have run the car around Sonoma Raceway and the doors have held up great. So, if you are looking to add lightness, order up some carbon fiber and epoxy and get to work!


Rob Krider is a four-time NASA Honda Challenge 4 National Champion, the author of the memoir, “Cadet Blues,” and is the host of the “Stories and Cocktails” podcast.

Image courtesy of Eli Cronbach


  1. Unless my math is wrong, you saved 11 pounds per door with the carbon door skin versus the metal door skin if you compare apples to apples. For 22 pounds I think I’d just keep the metal door skin and leave it at that. We’re not talking a 2,000LB car here. Even then I don’t think it’s worth the hassle.

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