Pinched this from another site but its quality....I remember this being in BMX Plus and it amused me back then so I was surprised when I found today...enjoy!
HOW TO BUILD AN INVISIBLE HALF-PIPE
Good God man! If you're poor like myself and can't build your very own half-pipe or don't even live in an area where such an endeavor is feasible then listen up brother. Here's a nifty little idea that first debuted in an old copy of BMX Plus! many moons past. Ain't half-pipe riding fun? Yeah! Doesn't the crashing suck? Yeah! Would you like to have all the fun of a half-pipe without actually building one? Well here's how! You really can build something that will operate somewhat as if you're riding a half-pipe. This is great for beginners. You can learn without getting hurt. This is great for me. I haven't rode a ramp in so long I would likely kill myself. If I can find a suitable spot I'm gonna' build me one of these here doo hickies again. Yessir. You see, back in the day I had an invisible half-pipe in my back yard. I was the hit of the neighborhood. The neighbors themselves thought I was insane. OK you're saying out loud at this point, "Crikey! Get on with it retard! What is an invisible half-pipe!?" Well, guess what? It's a tire swing. Yep, a tire swing. And it's fun. Here's what you need:
1. Either 2 or 3 used bike tires. You can use new ones if you want but wasting new tires on a tire swing is a little freakin' stupid. You're the boss. Do whatever you want. We used 3 old Tiogas.
2. A very strong rope. Don't use some crappy rope. This is your butt on the line here. Literally.
3. A tree. A big tree. A big, strong tree. No joke. It had better be strong or your 150lb body will bring that thing down when you start grabbin' serious air. The tree needs to have a seriously thick branch high up off the ground and unobstructed by anything else including other branches. How high up off the ground is up to you. Don't put it too low and don't put it too high. BMX Plus! recommended at least 20 feet high.
4. Some type of padding. We used foam rubber. Foam rubber sucks. Our arm pits were perpetually red and purple and hurt. We rubbed lots of lotion in our armpits for relief. Rubbing lotion in your armpits does not bring relief. Use foam rubber if you want. We were crazy. Are you?
5. A piece of plywood. Lay this on the ground under the tire swing. If you don't do this you will wear ruts into the dirt and eventually kill yourselves when you ride into them. It's your life tiger, ride the ruts if you want.
6. Duct tape. You gotta' tape the tires together silly! And absolutely DO NOT use scotch tape. This just doesn't seem to work.
7. Don't laugh. This works and it's fun. I mean it.
First duct tape the tires together. Do a good job you lazy punk. Then find a boy scout to climb the tree and tie a good strong knot with the rope. We had two boy scouts present. The first one scurried up and tied a freakin' granny knot. He did not tell us this. This did not hold. I sent the other boy scout up the tree and he used something I think he called a half clove hitch knot. Whatever the heck it was it held up forever. The moral? Do not use boy scouts that have no merit badges. That jackass.
Lay the plywood down under the swing. Lay your choice of padding inside the swing. Place your head and arms through the swing and test it out by swinging around without your bike. If it holds then get on your bike and pedal you animal! It should be said however, that you must make sure that the tire swing is snug under your armpits while you're standing up. If it isn't you're gonna' get a nasty surprise when you pedal off and the tire swing begins taking up the slack by raking you up the front of your chest. This happened to us a lot at first. We eventually tied the swing low enough for little Joe and the rest of us adjusted the swing for ourselves by spinning the tire swing until the rope twisted up to the correct height. And you can do the same! How about that! Wait. You don't even know Joe. Good for you. He once stripped naked and threw all his clothes out of a moving car. Anyway....
When you get into the air turn around and come back for more. Simple as that. This is very fun and very painful if your padding sucks. I was the first guy in the neighborhood to pull a 540. It was on accident. I borrowed a friend's Redline to try it out on the invisible half-pipe. I was used to my Torker. I fired off and turned way too much. One of my feet slipped off a pedal. I spun like crazy and did a 540 without even trying. Everyone's jaws dropped. None of us had accomplished this trick yet. And even worse, it was an accident so I figured I wasn't going to be able to do it again. I nailed it down though and was doing them nonstop. The fella' with the Redline became the other big rider in the hood. We both were the best on our glorious little tree swing. Nobody else could compare. The great thing about this "half-pipe" is that you cannot get hurt unless you are a serious reject. Try any trick in the world. If you mess up then drop your bike and swing to a stop. If you're a beginner this a great way to learn things. If you've been riding ramps then this is a way to practice crazy stuff you don't have the cajones to try for real.
Invisible half-pipe picture 1 invisible half-pipe picture 2
