Reference Beta

Universal Front Splitter

A front splitter generated from a handful of numbers you can measure off your own car. It spans the whole range from a bolt-on lip that follows the bumper to a full front undertray the bumper sits on top of, with the nose arc as its leading edge, squared outer corners, and a notch cut out of the trailing edge to clear the crash beam or subframe. It can cut openings for the Splitter Extractor Cowl straight into the floor, drilled with that part's own bolt pattern, so the two bolt together. Because no printer has a 1.4 m bed the board is cut into tiles both across the car AND fore-and-aft; each tile carries dovetails on the joints it owns and the matching sockets on the others, so joined tiles cannot pull apart sideways.

aero
splitter
undertray
downforce
front
universal
tiled

This part is in beta. It renders and exports, but the geometry is still moving: dimensions may change between versions, and it has not been through a printed fitment check. Worth knowing before nine hours and a kilogram of filament.

Printing it

Material: PETG / ASA
Minimum wall: 6 mm
Bed splitting: Cut into tiles across and along the part, so a board wider than any printer bed still prints. Joints carry dovetails, so tiles cannot pull apart sideways.

Print each tile flat with the UNDERSIDE on the bed. Nothing overhangs in that orientation: the countersinks open downward and taper inward at 45 degrees, and the top edge treatment leans the same way, so no supports are needed anywhere. SIZING THE TILES: cut the board BOTH ways. A tile is the total width divided by the column count plus a 15 mm dovetail, by the depth divided by the row count plus another 15 mm. The default 1400 x 620 mm board in 7 columns x 3 rows gives tiles of about 215 x 222 mm, which fits a 220 mm bed diagonally and a 256 mm bed easily. Some grid positions come back as empty -- the board does not reach the rear corners -- and will tell you so. BE HONEST WITH YOURSELF ABOUT MATERIAL: the default board is over 7 litres of plastic, and it will flex and eventually fold at road speed however well the tiles are joined. Print it full size to mark out and cut a real one from 10 mm ABS, aluminium composite or plywood. Solid infill through the fastener rows, the vent rings and the dovetails, whatever you do elsewhere.

Parameters

Every number this part is generated from. The geometry is built from these rather than scaled from a fixed model, so a value you can measure off your own car is a value you can type in.

Outline

Parameter	Range	Default	What it does
Total width	800–1900 mm	1400 mm	Tip to tip across the car. Measure the width of your bumper's lower edge, not the track.
Board depth, centre	20–900 mm	620 mm	How deep the board is on the centreline, from its leading edge to its trailing edge. This one number decides what kind of splitter you get: at 60-100 mm it is a lip that follows the bumper, and at 500-800 mm it is a full front undertray that the bumper sits on top of. Measure from where you want the nose to be back to wherever the board can be clamped.
Board depth, ends	10–900 mm	430 mm	The same measurement at the outer ends. Shallower than the centre means the trailing edge is cut forward as it goes outboard, which is how a real undertray clears the front wheels. The taper between the two is quadratic.
Tip sweep-back	0–450 mm	190 mm	How far aft the tips sit relative to the centreline: the single number that makes the outline follow YOUR bumper. Hold a straight edge across the front of the car touching the centre of the bumper and measure back to the corner.
Nose shape	1.2–3	2	How that sweep is distributed. 1.2 is a blunt nose that starts curving away immediately; 3.0 stays flat across the middle and turns hard at the corners. 2.0 suits most road cars.
Corner radius	5–250 mm	70 mm	Rounds the two outer corners, front and rear, leaving a straight side edge between them. It has to leave that side edge: at half the end depth the two corners meet and the end becomes a semicircle, which is right for a narrow lip and absurd for a deep board.
Notch width	0–1200 mm	520 mm	Width of the bite taken out of the middle of the trailing edge to clear the crash beam, subframe or sump. Set either notch dimension to 0 for a board with no notch at all.
Notch depth	0–600 mm	240 mm	How far forward the notch reaches. Its shoulders are blended rather than radiused, which leaves no sharp inside corner for a crack to start from -- the two places a real board fails first.

Board

Parameter	Range	Default	What it does
Board thickness	6–25 mm	12 mm	Real splitters are 10-12 mm. Thinner prints faster and flexes more; thicker mostly buys you weight.
Top edge	Square · Chamfered · Rounded	Chamfered	Applied to the whole top perimeter, not just the leading edge -- relieving only the front would leave the outer tips as a shin-height blade. The underside stays perfectly flat either way, which is the face that matters aerodynamically.
Edge size	0.5–10 mm	5 mm	Chamfer leg, or radius. Still range-checked when the edge style is Square, where it has no effect. The limit against the tip extension is real: the perimeter is offset inward to make this edge, and offsetting further than the radius of the rounded tip would turn the top face inside out.

Extractor vents

Parameter	Range	Default	What it does
Extractor openings	None · One, on the centreline · A pair	A pair	Cuts an opening through the floor with the exact fastener ring a Splitter Extractor Cowl drills into its own flange, so one bolts straight on and vents the high-pressure air trapped under the board. Heads countersink into the underside, shank up through the floor and the cowl flange, nut on top. Set to None for a solid floor you would rather cut yourself.
Vent spacing	200–1600 mm	900 mm	Distance between the two openings' centres. Ignored for a single vent.
Vent setback	30–800 mm	300 mm	Aft of the leading edge to the cowl's front edge, measured along the board's own nose line so a vent stays square to the flow wherever you put it. Behind the radiator exit is the usual place.
Cowl flange width	120–400 mm	230 mm	COPY THIS from the Splitter Extractor Cowl you are pairing with. The bolt pattern and the size of the opening are both derived from it by the same code that part uses, so the two cannot drift apart.
Cowl flange length	120–340 mm	200 mm	And this one. Vent fasteners use the size set below for the bumper row, so set that to match the cowl's too.

Tiling

Parameter	Range	Default	What it does
Fit to my printer	On or off	Off	Work the tile grid out from the bed size below instead of setting the two counts by hand.
Printer bed	100–600 mm	220 mm	The largest square that fits on your bed. 220 for an Ender 3 or a Bambu A1 mini, 256 for an X1 or P1, 350 for an X1E or a large Prusa. Tiles come out this size less the 15 mm a dovetail reaches into its neighbour.
Tiles across the car	1–12	1	Tiles across the car. Each is the total width divided by this, plus a 15 mm dovetail reaching into its neighbour. Leave at 1 while you dial the shape in: you want to see the whole board, not one tile of it.
Which tile	1–12	1	1 is the leftmost. Render and download each in turn with everything else left alone; the tiles are cut from one board so they always line up.
Tiles fore-and-aft	1–8	1	Cutting only across the car is not enough for a deep board: it would give you tiles narrower than they are deep. This cuts it the other way as well, so a 1400 x 620 mm undertray in 7 x 3 comes out as tiles about 215 x 222 mm.
Which row	1–8	1	1 is the frontmost. Some combinations are empty -- the board does not reach the back corners of the grid -- and say so rather than handing you an empty file.
Joint clearance	0.1–0.6 mm	0.25 mm	Gap between a dovetail and its socket, per side. 0.25 mm is a firm slide fit on a well-tuned printer; go up if your first pair will not go together, since a dovetail cannot be forced.

Bumper fasteners

Parameter	Range	Default	What it does
Fastener size	M4 · M5 · M6 · M8	M6	For the row that clamps the board to the bumper or crash bar. Holes are ISO 273 normal-fit clearance.
Countersink heads	On or off	On	Sinks every head flush into the underside, so the aerodynamic face stays flat. Turn it off for plain clearance holes if you are using flanged or button-head hardware from above.
Mounting row span	200–1800 mm	1000 mm	Lateral distance from the first hole to the last. Keep it inside whatever the bumper's lower edge can actually be bolted through.
Nominal pitch	40–300 mm	120 mm	Spacing along that row. The real pitch is nudged to divide the span exactly, so the row stays symmetric about the centreline. A hole that would land on a tile joint or on a rod anchor is dropped rather than made useless.
Bumper row setback	15–800 mm	110 mm	Measured AFT of the leading edge: how far back along the board your bumper's lower edge lands. The row follows the nose arc at that distance. A hole that would fall past the trailing edge or into the notch is dropped rather than left hanging.
Trailing-edge row	On or off	On	A second fastener row 30 mm forward of the trailing edge, following it round the notch, using the same size, pitch and span. A deep undertray needs to be held at the back as well as under the bumper; a lip does not.

Support rods

Parameter	Range	Default	What it does
Rod anchors	None · One pair · Two pairs	One pair	Anchor holes for the tie rods that run up to the crash bar and stop the board folding under load. Two pairs puts the inner pair at half the outer spacing.
Rod spacing	200–1600 mm	900 mm	Lateral spacing of the outer rod pair. Wider braces more of the board but needs somewhere on the crash bar to anchor to.
Rod inset	15–200 mm	55 mm	Aft of the LEADING edge, unlike the mounting row. The further forward these sit the more they resist, but they have to stay on the board where it is deep enough.
Rod fastener	M5 · M6 · M8	M8	Rod ends carry far more load than the bumper row, so they usually want to be a size or two larger.

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