After a couple of years of putting it off, I finally decided to build my very own bike trail in my yard. I found a few web sites on trail building, and got started. This instructible shows guidelines and techniques that helped me a lot when building my trail.
Remember-- Never build any sort of trail unless you have permission from the land owner. Even on public land, it is illegal to build. Many great areas have banned mountain bikers from riding on trails because of illegal trail building. Mountain bikers are being watched under a microscope because of this, so don't ruin it for everyone-- get permission first.
With that said, lets get started.
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Step 1: Find a Location
This is one of the hardest parts, especially if you live in a city. I live in the mountains, and have two acres, so I didn't have to go anywhere. You also need to decide what you want in your trail, and who will be using the trail. I wanted to build a main loop that was fairly easy for the kids in my neighborhood to use. I then added a couple of other branches off the loop that are very technical and challenge me. When scouting, ask yourself questions such as: Technical rocks or smooth dirt? Steep hills or mellow ones? Once you find a good general location, bring paper and a pen and walk around. Take notes of sections that would be nice to have in your trail (drop-offs, meadows, etc) as well as sections that would not be so good (big cliffs, dense forests, swamps etc.) Also take note of any obstacles that need to be removed. I had to cut out a few bushes and some small trees for my trail to work. The trail itself will only be about a foot wide, but i would recommend four to six feet of clearing for your handlebars to fit through. The faster the trail, the wider the clearing needs to be.
Step 2: Outline the Trail
After you scout out the area, sketch a basic map of your trail. Then, you might want to walk through and mark the trail with tape. Since I know the area where my trail is so well, I skipped the tape, and just sketched on paper. With longer trails, the tape can be really helpful. Now, walk through the outlined trail and look carefully at the terrain. Can you make it up that hill? Is that turn too sharp for a bike? Is that too big of a drop-off for me? Think about how you would do the trail on a bike, and re-route as necessary. Remember: Hills and corners are much harder on a bike than on foot.
Step 3: Build the Trail
Pull out whatever tools you need. I used a shovel, handsaw, clippers, a sithe to clear out brush. The weed-eater was very helpful for grass. Then, get some friends to help you. Tell them that if they work hard enough, you might let them use your trail. We started out with the hard stuff and cleared the bushes and trees. I'm not going to go into detail on how to clear things, because everyone is going to have different things to clear, and a simple Google search will tell you all you need to know if you can't just use a saw or some clippers. After all of the brush and trees were out of the way, we fired up the weed-eater and cut the trail out. Don't worry if you don't get to dirt-- when ridden, any grass will be packed down. Just be sure that you can see where the trail is.
Step 4: Make It Perfect
After you have cut the trail down to dirt or thin grass, it's time to work on certain areas that will erode if left alone. Places that will need this are where the trail is at an angle greater than a few degrees. Ideally, the trail should always be slightly slanted to shed water, but when it is at a big angle, it needs to be cut out. If the trail is left as is, then when people ride it, they will slide down the trail, slowly eroding it. The best way to dig out the trail is to start at the highest part, and make it level with the lowest part by removing dirt. If you don't want to do this much work, there is an easier way. Start digging as normal, but instead of removing the dirt, put it on the lower part. Now, you are cutting out the part that is too high, and building up on the part that is too low. Cut out the trail where ever it is needed, and you won't have to do as much work later, after it is ridden of if it rains. Also, on corners, it is helpful to dig small trenches and put logs in them. The logs keep the dirt from sliding, and help riders see where the trail is going.
Tip: If you plan on making berms, jumps, or rollers, (next step) then put any extra dirt into a wheelbarrow so you don't have to dig as much later.
Step 5: Add Fun Stuff
Now, It's time to add some jumps, berms, rollers, bridges, of whatever else you can think of to your trail. I didn't build any jumps or rollers, but I built two berms, and two bridges.
Berms: The easiest way to add berms is to cut them out of a hill. I made a small one like this. Simply cut out the berm, pack it down, and go. The dirt you cut out could be used to make the berm longer, or for something else. The harder way to build a berm is to pile dirt above ground. I stacked logs, filling dirt in between them, until I got the berm to the height I wanted. Then, use dirt to shape it, then pack it down. If you are building lots of berms or jumps, you should probably get a pickup truck load of dirt to work with, unless you want to dig. I only built two berms, so I had enough dirt from digging the trail to build them.
Bridges: I added two wood bridges to the trail for fun. The bridges were some type of crate made with 1x4's that I had in the basement. I put them in places to that they aren't really hard to ride, so kids can go on them without worry of falling. The first one went right on top of the ground. I screwed four 1x4's to one side to make a ramp up to it. The second one is narrower, and I propped it up on concrete blocks. It was not very stable, and I didn't want to dig, so I screwed some log supports on.
Step 6: Ride!
Get your friends to ride the trail for a few hours, and everything will smooth out. Don't ride too fast, though, because you don't want to have people loosing control and wrecking the trail. Once the whole trail is down to dirt, let them go as fast as they want. Don't be disappointed if your trail is bumpy. I freaked out and spent about an hour re-finishing a berm only to have it turn out just as bumpy as before. Just ride the trail and everything will smooth out.
Step 7: Maintenance
It is very important to maintain your trail if you want to keep it safe and fun. Any problem that happens will only get worse if left alone, so it is best to fix any damage as soon as possible. Go out to your trail after a rainstorm and see if they are any big puddles or parts of the trail that have washed away. Fix these spots by digging the trail again so water runs off. (See step 4) Once the trail has no drainage issues, you don't have to check as often. When I see a problem, I generally try to fix it that week. It is also important to check any wood bridge you have on your trail. Make sure it is sturdy, and that it isn't going to fall apart when someone rides across it. If there is a problem with a bridge, be sure to block it or do something to tell the riders that they shouldn't ride it. Your trail will last forever as long as you are able to maintain it. If for some reason you don't want or need your trail anymore, just let it sit and the grass will grow back.