The wings – not yet fabricated – will only be mounted for track events. I’m not impervious to what people think (partly because it can affect book sales) but also because I’d feel silly driving on public streets with them. While technically functional at all speeds, they’re realistically pointless at legal road speeds, so it’s sort of a lose/lose proposition. I mention this now because to a somewhat lessor extent, the same applies to the diffuser.
The diffuser will be a 24 x 48″ (610 x 1220mm) panel with the forward edge attaching to the rear-most cross tube. Due to the muffler, it’ll have a small angle toward the front, then a larger angle behind it.
This Racecar Engineering article and Willem Toet article were both very helpful (though the latter was obviously not proof-read!). Before reading the articles, I was going to leave out the strakes (the vertical vanes always seen on diffusers, but the figures graphically show why they’re a good idea. The articles were found while doing a Google search to answer whether a flat or curved diffuser works better. While neither article answers this directly, it appears that the sudden slope change at the front edge is necessary to initiate the spiral air currents drawn in from the sides. (On a related note, most forum discussions about diffusers are very inaccurate, go figure.)
Getting back to the question about street use, I’m sort of on the fence concerning the diffuser. Like the wings, even if it works, it’s of little to no practical benefit at legal speeds. Unlike the wings though, it’s not quite as “in-your-face”, being mounted down low. Also, there’s the practical issue of where to keep it when it’s not on the car. The wing assemblies will be tall and slender, and can be stored against a wall out of the way. Not so much with a large three-dimensional diffuser assembly. As of this writing I’m leaning toward leaving it on the car and putting up with the increased boy-racer look. That said, if I can drive down a leaf-covered street and kick them up high in the air behind me, that’s so totally worth it 🙂
Before anyone says “well what about the pretentious air intake on the roof?” Unlike the wings and diffuser, cooling the intake charge is of benefit whenever the engine’s in boost, which is often, so it stays.