Although airlines, bus companies, and railways are generally accustomed to transporting bicycles, there is always a risk of damage. Proper boxing can minimize the risk of damage or loss.
You must anticipate the possibility that your bike will be dropped, stacked in cargo bins, or otherwise handled roughly once it leaves your sight. Don't travel with your bicycle unless it is boxed!
Some airlines have boxes available. Some airlines require several days' advance notice that you'll be traveling with a bicycle. Give this notice directly to the counter where you will be departing.
You can often get used boxes from bicycle shops, especially if you call a few days ahead. While you're at the bicycle shop, get two boxes (for each bike you want to ship), preferably one slightly larger than the other. A single box can be modified to protect your bicycle fairly well, but one slipped inside another to form a double-walled container, braced internally, will give your bike better protection and give you greater peace of mind.
It takes time to box a bicycle, especially if it's your first try, so don't wait until a half-hour before your flight is scheduled to depart to begin working on it. What you'll need:
pocket or utility knife
some extra strips of cardboard
some scrap wood
filament or duct tape
some light rope, twine, or stout cord
Shift the gears so that the cables are slack.
Deflate the tires halfway for more shock-absorbing capability.
Remove seat and post as a unit.
Remove the front wheel. Cut a small block of wood to fit between the front-fork dropouts, and tape it in place. This will help prevent the fork blades from being bent.
Loosen brake cables enough to rotate handlebars. If your bicycle has a very long wheelbase, it may help to completely remove the front brake so the fork can be rotated 180 degrees.
Remove the handlebars and stem as a unit by loosening the stem bolt two full turns. Then, protecting the bolt with scrap wood, hammer to loosen the internal wedge, and pull the stem out of the steering tube. Retighten the stem bolt to avoid losing the wedge.
Remove the pedals. Remember that the left pedal is a left-hand thread; the right pedal is a standard right-hand thread.
Tie or tape the front wheel to the right side of the frame, padding between the wheel and the frame with cardboard. Turn the crank arms parallel with the box bottom and tape in place.
Make two 6-inch square "washers" of several layers of cardboard with a center hole. Make them thick enough to prevent the front-wheel axle or quick-release end from puncturing the box. Tape these in place over the exposed front axle end and the end of the rear axle opposite the derailleur.
Unbolt the rear derailleur (but don't disconnect the cable) and tape it to the rear wheel spokes below its normal position so it doesn't stick out past the frame. Pad the derailleur with a roll of cardboard also taped in place.
Cradle the handlebars and stem over the top tube or around the fork and head tube if space permits.
Preparing the Box
Cut five pieces of cardboard, each about one foot in length, and wide enough to fit snugly across the inside width of your box. Form tightly rolled tubes and fit them inside the box. These tubes will absorb forces from the sides and prevent the box walls from collapsing into the bicycle.
Place one tube inside the box near the lower end of the front fork. Place two tubes, slightly flattened to fit, through the rear wheel and tape them in place. Place other tubes where the top and down tubes meet, through the front-wheel spokes, and below the top tube, toward the front of the bike. Tape each tube in place.
Lower the bicycle into the box, and add cardboard pads wherever any remaining sharp or fragile parts might contact the box. Anchor the cross-bracing cardboard tubes further by punching holes in the box sides to match the tube centers, and securing the tubes with tape, rope, or both. The rope can also be padded and used as convenient carrying handles.
Wrap the saddle, pedals, and other parts in newspaper or cloth and secure them inside the box. You might also want to place the tools you'll need to reassemble the bike in an easily retrievable bag inside the box.
Seal the box with tape, and clearly label it with your name, destination, flight number, and home return address.
In the illustration above, holes have been punched corresponding with the cardboard tubes which will protect the bike against side loads. The tubes have then been held in place with tape. Finally, rope acts as both support and temporary carrying handles.
Remember, on most airlines you will have to sign a waiver which will remove the airline from any responsibility for damage to your bicycle. It is to your benefit to spend some time carefully packing your bike. It's no fun to get to the trailhead of your long-awaited tour only to find your bicycle has been damaged.