With simple materials from your local big-box hardware store, you can build your own splitter and improve your vehicle’s aerodynamics. As seen here at Auto Club Speedway in Fontana, Calif., the splitter is clearly doing some good at high speeds — we think.

As racers, we are always looking for that little edge against our competitors. Some of those advantages come at great cost and time, like an engine rebuild or new dual-adjustable struts. Conversely, there are other modifications that don’t cost much and can be purchased at your local home-improvement store. We are talking about building your own splitter, using basic tools and skills, and about $60 in materials from Home Depot.

To build your splitter, all you need is a piece of 15/32-inch plywood, a pencil and a plumb bob. The plumb bob helps you accurately outline the shape of the front of your car.

I don’t claim to be an aerodynamic specialist. I don’t have a wind tunnel. I certainly don’t model pieces in clay and run them through fluid dynamics tests to see if they lower the drag on my racecar. I simply walk around the paddock, see what the teams who win races are doing — then I shamelessly steal and copy their ideas. When it comes to a front splitter, the only knowledge I can provide you is this: Your racecar is a big fat brick trying to knock a massive hole in a hard wall of air. Air acts like a fluid and it has connective properties. The plan is to cut the air that is going under your car from the air that is going over and around your car, so that air loses its connectivity and stops fighting with itself at the front of your car, slowing you down. To be honest, that information may be completely inaccurate. Here is what I really know for sure: splitters just look cool.

To build one, all you need is some plywood — we used 15/32nds thickness — some plastic garden lawn edging pieces, a couple of pieces of flat steel, some rivets, and a few hours to kill. If you have some basic woodworking tools, you are all set. Just think, if your middle school shop teacher could see you now.

One of the first things to look at when designing your splitter is your rulebook. For Honda Challenge 4, the rules are specific that the splitter cannot protrude from the front of the vehicle. To ensure our splitter was legal, we used a plumb bob to outline the front shape of the car on a piece of plywood that was taped to the floor. We taped it so it would stop moving around while we worked. A simple jigsaw cut the rounded front shape and we had our basic splitter design. We decided to build a second splitter at the same time because we have learned while racing in NASA that splitters tend to die. Anything that is low to the ground and on the front of a racecar is going to have a short lifespan. For that reason we built two from the onset.

The plywood is going to try to slide all over the floor as you are working with it. The easy solution to ensure you are tracing the body outline onto the wood accurately is to mark the floor with some painter’s tape. This way if the wood shifts, you know exactly where to put it back.
We pulled the front wheels off of the car to make it easier to work under the vehicle. Now that you have your plywood on the ground and marked in place, use your plumb bob and pencil to trace the outline of the front of the car.

Regarding the sudden death of splitters, I’m reminded of the hardware materials we chose to use — and not to use. The simple way to connect your plastic vertical surfaces — the plastic garden edging used as fascia — is with self-tapping screws. The problem is that you are essentially building your own booby trap. Nothing goes through a race tire quicker than a self-tapping screw. So putting 40 of them in the lower leading edge of your car, directly in front of all four of your race tires is a bad idea. We used rivets to hold the vertical plastic pieces in place to avoid sabotaging ourselves.

It makes it easier and more accurate to have one person hold the plumb bob and pay attention to how it is moving while another person marks the plywood with the pencil. This takes a bit of patience to do correctly, but the time invested here is worth it, because this line determines how the wood is cut.
We made pencil marks on the plywood every inch and a half or so. We made marks closer to one another where there were more curves in the line. The closer the marks, the easier it will be to trace the overall line used as a guide for the jigsaw.
Once you have all your little marks in place from the plumb bob, simply connect the dots and draw your cut line. It should look like the outline of the front of the car.
Using skills you learned in junior high school woodshop, cut the line you created on your plywood with a jigsaw. When you are finished, you should have a splitter and, if you are doing it correctly, 10 fingers.

To mount the splitter to the car, we used flat steel, which we heated and bent to a 90-degree angle. On the lower portion of the steel, we welded on some nuts to easily mount the splitter board while under the car. The upper portion of the steel we slotted to mount to the side of the radiator support. We slotted the metal so we could adjust the height of the splitter for some tuning ability. To help adjust the height of our splitter, to ensure it was level side to side and front to back, we took two 4X4s and ran them through a table saw. The 4X4s then had two different set-up heights. We would set the two pieces of wood under the splitter — at whichever splitter height we wanted — and then tighten the bolts that hold the metal plates to the car. Super easy.

Let me tell you something about splitters: They get ripped off and destroyed at the racetrack. So, we made two. The second one was easy. As soon as we had one cut, we simply laid it on another piece of plywood, traced it and cut it.
Saw horses are great when you have the car on a lift and you want to position the splitter. This works a lot better than having friends stand around shakily holding the board and complaining that you are taking too long.
To mount the fascia of the splitter, and have a material that can bend along the radii that match the front bumper of the car, we purchased some gardening material called Pro-Flex. You can knock the tabs out between the plastic sections of the base of the material, which allows you to flex and bend the piece. We attached it to the plywood with screws.
We put the front wheels back on the car and set it on the ground to get the attitude of the vehicle. We took basic metal plate and put a 90 degree bend in it. One screw in the plate attached it to the side of the frame/radiator support, temporarily. We adjusted the angle until it was level using a simple bubble level. Once we had that correct, we marked on the vehicle where we wanted the plate to be mounted.
To mount the metal plates from the splitter to the car, we installed four rivnuts per side, which allowed an easy threaded location for the bolts to hold the plates in the correct location. The rivnuts do require a special tool to install, but they saved us from trying to weld something to thin metal.
Here you can see the Pro-Flex material curved to match the shape of the front of the car and screwed to the splitter. For additional height on the splitter, we used more gardening material, essentially edging material, and affixed it to the Pro-Flex plastic with rivets.
To mount the splitter to the metal plate, we drilled three holes per side. We drilled the matching holes in the metal first, the more difficult material, then used that as a guide to mark and drill the wood splitter.
Because our race car has adjustable ride height, we also wanted the splitter to be adjustable, so we slotted our metal mounting plates. This is a test fit, so the washers we used for final assembly are not shown.
Splitters hang low, and they aren’t trailer-ramp friendly, which means they have to be taken off the car frequently. To make things easier, we spot welded — poorly — three nuts on the metal plate so they were permanently attached. This is another place where we could have used rivnuts instead of welding.

Did the front splitter make the car 4 seconds a lap quicker? Nope. But it certainly didn’t make the car any slower, certainly at fast tracks like California Speedway in Fontana, Calif. We did find one quick disadvantage to our super cool looking splitter: The car no longer can make it up the trailer ramp. Yup, that means the splitter has to come off and on every time we want to get the car in the trailer. Racing sure is fun!

To read more from Rob Krider, or to contact him, go to www.robkrider.com.

Image courtesy of Rob Krider


  1. Hello, is the finisbed product the same as the Honda in the opening picture? It doesn’t look like it. Nice project write up, thanks!

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