Use a stud finder to find the studs in the wall and screw a horizontal 2 X 4 about six feet up. Basically, hold up your largest bike against the wall with the rear tire about an inch or so off the floor, and mark a spot a couple of inches above where the top tire is touching the wall. Next hold two bikes next to each other with the handle bars touching, and measure how far apart the frames are. Now add about 8 inches to that distance, then divide by 2. This spreads the hooks so that you can hang each bike alternating up and down. One bike goes front wheel up, the next bike goes back wheel up, and so on. Basically, you can fit three bikes in the space of two plus about 8 inches as long as you alternate them up and down. It was pretty simple.

BTW: Sorry the picture was so small but I couldn't figure out how to make it bigger, using the picture upload tool. If your eyes are good, you can see that each bike is alternates pointing up and down. You can get the hooks in Lowes or Home Depot.