@kpsxtyone I'm assuming you have the real car parked in the garage and making a scale model of it?
Otherwise creating the flare is going to be difficult to measure and draw without existing dimensions.
You can use 3D sketches and surfaces to approximate and then thicken, but would be easiest if you have the car.
If you do have the car you can get measurements by making a simplified point cloud.
This may sound a bit ridiculous, but have used this method many times with accurate results.

- Draw a line parallel to the car with chalk or tape 3" from the outermost point of the car. (Blue)
- Draw hash marks every 1". (White)
- If you have a large cardboard box this would work best. (Brown)
- Cut vertical line in box, draw hash marks every 1". (White)
- Insert wood dowel, tape measure, or ruler into cut line. Have distance hash lines on dowel. (Orange)
- Move front edge of box to parallel line, keep level and move dowel outwards to touch car fender. (Red)
- Create a point matrix on graph paper, as you move along the x-axis mark the dowel depth.
- Go along entire x-axis, return to front, move up 1" in y-axis, repeat.
- Within inventor your can create a 3D Sketch, set the as points and draw a spline through them.
This may look tedious and sound strange, but works well for prototyping complex surfaces and doesn't take that long.
Or you could just 3D map it and bring into ReCap Photo.
A bit more outside the box than you were thinking, but hope that helps!
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