Teardrop Wheels and z32 Calipers. Why Not?

[quad_ova]

Could someone tell me why a 15" teardrop rim from the 89-90 240sx's won't fit?

Is it because of the rims shape?
Or the calipers size?
Or is it because of the offset? If so, wouldn't spacers clear it?

Why am I asking? To learn something new of course. Besides I do not have a set on my car and the curiosity is strong within. Per usual, I have tried searching and all that comes up are the newer 7 spoke rims "will it fit" questions. Appreciate your calm responses!

[Tempast]

Because they BARELY fit under stock Z31 16" wheels on a Z31.
the calipers sit further out on the sides, and if you're using an adapter it moves the caliper out about an inch.

[gaz_moose]

because of the shape of the back of the rims and they were designed for tiny little breaks.

some 7 spoke wheels also massively foul the callipers where some have a different webbing on the rear and clear with a small spacer fitted

[quad_ova]

You guys rock. Thanks for the knowledge!