Bicycle Mechanics - Cable instead of a downtube?

like here:
http://matt.pintglass.org/wp-content/sling.jpg

this is more out of curiousity than anything - I have no resources or motivation to achieve such a thing. I guess I'm mostly wondering if it really is a feasible design and what kind of pros and cons it creates.

I wonder if the cable actually provides structural support, or if it's just routed that way to look cool.

Either way, doesn't look like the strongest ride.

The design has been around for quite a while. It seemed fine when I rode one - perhaps you should try riding one too. There is more than one way to skin a cat...

The DT is not purely in tension, there is torsion s well so I dont think cables are ideal.
A much better use of cables can be seen in the Pederson (http://www.dursley-pedersen.net/).
In 1893, he produced a very practical, fast, comfortable bike weighing in at 19lbs.

On the bike that the OP pictured, the seat tube has to be very stiff and bear all of the bottom bracket torsional load, and the top tube must also be torsionally very stiff.
the cable, as noted by MichaelW, is purely in tension and keeps the frame from collapsing by "splaying" at the seattube/headtube joint.

They've been around for awhile. I've never ridden one, but I've seen some pretty favorable reviews of them from time to time. My thinking is that if it's such a great idea, you'd see more bikes using the design, or something similar. Here's a link to a 1990 Slingshot mountain bike: http://www.firstflightbikes.com/1990_Slingshot.htm

I rode one of these years ago. The downtube cable was actually terminated with a spring, and the top tube incorperated a stiffened hinge at the seat tube so that the frame could kind of inchworm over bumps. Sort of a badly designed suspension system. Surprisingly, the bike was quite ridable, if a little flexy. Hard front braking would cause the TT to arch the other way, and the HT would steepen, giving a not so secure sensation.

Those Slingshots have a cult-like following, as they offer a suprisingly good ride, but I suspect the odd looks kept sales low.

Are Slingshots still being made? I remember a long time ago when people were talking about them as the next big improvement to MTBs after threadless headsets and V-brakes, an improvement that "everybody" will be copying.

http://www.slingshotbikes.com/

I'm surprised to see they are still in business. Haven't seen one in years.

I've ridden one, felt like riding on a blow-up mattress. Any which direction you pushed the thing would give. Extremely flexible laterally as well. I swear the rear-wheel skipped sideways a foot when I started sprinting. Might be good for a downhill bike, but I wouldn't feel safe coming down a mountain road with switchbacks @ 40-60mph when the front-end likes to aim in a different direction than the rear end under braking & cornering.

I've ridden one, felt like riding on a blow-up mattress. Any which direction you pushed the thing would give. Extremely flexible laterally as well. I swear the rear-wheel skipped sideways a foot when I started sprinting. Might be good for a downhill bike, but I wouldn't feel safe coming down a mountain road with switchbacks @ 40-60mph when the front-end likes to aim in a different direction than the rear end under braking & cornering.
I'm not sure I would feel safe coming down a mountain road with switchbacks @ 40-60mph on any kind of bike :D

Thanks for the responses everyone, pretty much what I figured.