Every day, not too far out in the Foothills, the dramatic rivalry between car and bike is replayed between bike and runner. Only this time, it's the bike hurtling recklessly down Central Ridge Trail instead of a car down Hill Road, and the trail runner leaping into the sagebrush to save his or her shorts-clad heinie. Word to the helmeted: This ain't the Greenbelt. Forget the bell: shout and do it early.