Dan, an REI Outdoor School instructor, shows how to fit your road bike properly in this video. To check that your bike is the right size for your legs, straddle the bike: You want about an inch clearance above the frame. To check the seat height: get on while a friend holds the frame steady—you want your leg about 90% extended (still slightly bent). The seat can also move forward or back; when your pedal is all the way up, you want that bent leg vertical so that your knee is over the ball of your foot. The bike fits your torso when your back is at a 45-degree angle and your arms are somewhat bent; you may need to change the handlebar stem out for a longer or shorter one to get the right torso length.