Strut spring design?

[texases]

That’s because adjustable spring perches are much easier to design if they’re smaller diameter. But @Mustangman ‘s answer goes into more detail about the other reasons.

[Mustangman]

Did you miss this?

@Mustangman

The size of the spring is to get the spring stiffness, or spring rate, low enough to provide a good ride while producing enough load to hold the car up.

And this:

@Mustangman

The diameter does one other important function; it offsets the sideload caused by the position of the strut relative to the tire.

And this;

@Mustangman

The spring and spring seats are designed to add bending force in the opposite direction to reduce that friction. To do that the spring is offset toward the tire which is why the spring seat overhangs the top of the tire and why the diameter is so large.

Hope that clears it up