It’s very complicated designing a new body for the Locost 7 / Haynes Roadster. The CAD drawing below shows exactly what happens when a side window with only a small amount of curvature is wound down in a straight line. The glass would try to exit through the side bodywork.
To stop the window from crashing into the bodywork and jamming, the glass needs to be wound down along a curved path. This curved path must be the same as the curvature of the glass. If the path were different to the glass curvature, the window wound lean out-wards into the fast moving air. The effect would be similar to the fin of an aeroplane, with the wind trying to steer the glass out of it’s runners. It would also make a horrid buzzing noise.
Because of this, a side window needs to be chosen, that has the correct curve to wind down inside the cavity. This has a knock on effect on the shape of the hard-top hood; in particular the rear pillar.
The window’s path is also effected by door length. Because of the angled rear pillar, the window will want to travel down and diagonally forward. It can only travel so far forward before it hits the door hinge. With the complex side profile, the positioning of the hinge axis will always be an issue.
In other words, I have to find a suitable side window before the shape of the roof can be moulded and the length of the door can be calculated.