Venture said:
Smart idea. I'm confused about one thing though. Everybody recommends the non-stretchy cord, wouldn't it be better to use the stretchy cord when doing this? If you're a single person trying to move the bike, wouldn't it be better to rig it up, build up tension in the rope, thereby effectively removing weight from the bike, then go back to the bike, move it forward (now possible due to reduced weight), go back to the rope, rebuild tension, so on and so forth? Or does the rope that is being used have enough stretch for this?
Dynamic vs Static
You want static rope. Dynamic (stretchy) cord, well, stretches. This means that for every one foot of pull through the system shown you would expect the object to move 6 inches (2:1) You will get a fair amount less than this with dynamic rope which means you will be pulling longer and more for a given distance.
Remember that with this 2:1 Z-rig system you are multiplying your force. If you exert 100 pounds of pull you are exerting 200 pounds of force to the object you are pulling. Twice the force, half the distance.
The pre fab systems are all slick but absolutely not necessary. The pulleys are nice as they reduce effective friction but not necessary. If you can tie a loop in a rope you can make this work. Figure eight on a bight, alpine loop, etc.
As for the rope, you could just go get yourself some basic flat tubular webbing from any climbing supply house (REI, etc.) Here's a link;
http://www.rei.com/product/783605/1-military-spec-tubular-webbing
You can carry a whole bunch of this in less space than rope and it has a 4000 pound strength rating to boot. When needed, cut enough to tie off an anchor to your immovable object and to your bike. Use the rest to rig your Z-rig. Pull, reset, pull, reset.
I would suspect most of us, I do, carry a tow strap. This is the same stuff usable for this. The uses for tubular webbing are endless! Just have a sharp knife and a lighter to melt the cut ends and you're off.
Hey, I'm a Fire Captain in the fire service. This 2:1 Z-rig is the bread and butter to all haul systems we use. Simple, effective, and works.