Garage Hack Aero PT3 1


This chunk of wood got a lot of compliments, until people found out that it was wood. Truthfully, I felt just fine about it, until I had to tell people what it was: birch plywood. A mature individual recently approached me about buying the WRX. His words to me were something like, “I like what you’ve done with the car a lot, but that plywood under tray… what were you thinking?”

I corrected him immediately. “Birch plywood.”

“Fine, birch plywood,” he said, “it’s still just wood, I would have used arena board or something else, just not wood.”

And then I was so offended that the agreement we had come to had to be terminated. Ha. Not really… but I do still have my car.

The truth is that birch plywood is hands down the best budget material you can make a splitter out of. UHMW plastic (“arena board” in this case), is strong as hell and easy to work with, but in order to get the stiffness required you need a whole lot of thickness, and that turns into a whole lot of weight.

ABS plastic, gets used for underbody aero in a lot of exotic places (check that Ferrari in your neighbours garage), but it’s not a great material for a splitter itself. It is a lot stiffer than UHMW, but doesn’t offer any of UHMW’s impact resistance. It is quite cheap, but again, to get real stiffness you’re going to want a 1/2″ sheet or more… and that gets quite heavy.

Aluminum might be the next best thing. But the most commonly available 1/8″ plate doesn’t provide adequate stiffness for a real splitter, and 1/4″ or 3/8″ plate is pricey enough that you might as well stop hacking and make yourself something proper.


Hence the wood. I’ve been using 1/2″ thickness until now, and properly fastened to the car, it is stiff enough that I can put around 100lbs on the leading edge with minimal deflection. It is also relatively light. Searching around will reveal that a lot of guys have produced ABS or aluminum splitters that weigh 15-20lbs. Mine, which goes from 3″ past the lip all the way to the front axle on a long nose car, is only 14lbs. It is however, not all well and good as you can see.

On the AE86 I ran a splitter of similar construction, and it survived a couple hard years of auto-x, backroad attacking and driveway ramp smashing. This is the third splitter I’ve had on the WRX in less than a year. Snowbanks killed the first two, as I expect that they should, but this one was actually smashed by a pylon. Something new and improved is in order.

I’m going to make a new one out of balsa wood.

If cost was no object I’d make one, or have one made, out of carbon kevlar with a nomex honeycomb core. That would cost me in the neighbourhood of $1500. It also wouldn’t be garage hack, and would clash with my welded diff. Balsa, is natures honeycomb, and fibreglass is the retired grandfather of carbon kevlar. With limited experience using composites, I decided not to waste my money on something cooler than fibreglass (it’s almost 1/10th the cost of carbon kevlar). If all goes well, maybe I reinforce with an outer layer of the expensive stuff… if the added protection against cones that kevlar or carbon kevlar gives isn’t worth it, then at least I can tell people that it’s made out of something that Car & Driver thinks is sexy.

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