What function does a SLOPING top-tube serve over the tradition flat top-tube?

Question

What function does a SLOPING top-tube serve over the tradition flat top-tube?

Answer 1

it effectively shortens the seat tube, which saves weight and increases stiffness for a given sized frame.  it also in effect raises the head tube on some models so that the stem is a little higher for comfort.

Answer 2

Mainly it's a gimmick so manufacturers can make fewer frame sizes (to save costs) and just use longer seat posts to fit.

Answer 3

I think Glenn has it right.  While the frame is theoretically lighter, this is offset by the longer, heavier seatpost.  They can be a bit stiffer, but this too is offset by the long seatpost flex.

Manufacturers and retailers figured out during the mountain bike boom that they could stock far fewer sizes if they changed to the compact, sloping tube (S,M,L) scheme for road bikes as well.

So why do so many pros now ride them?  Because they are paid to ride them, and the marketers figured out that people wanted to ride what they saw the top riders on in the Tour de France.  The few teams that don't have a bicycle sponsor invariably choose the older style frame geometry.