DIFFERENT SPOKES for different folks: "Quicksilver," a sort of downbeat "D.C. Cab" on two wheels, is about the fleet street life of bicycle messengers, the real "urban cowboys."

Kevin Bacon plays Jack Casey, a hotshot young options trader who one day risks -- and loses -- everything, including all his parents' savings. So cocky Casey shifts gears and trades the chaotic crush of the stock market for a freewheeling stint as a bicycle messenger.

Casey uses his quick-money know-how to help a few of his new friends, most of whom are trying to escape the gypsy job he finds so liberating. On the serious side, the movie takes a brief but refreshing look at the eclectic makeup of street-level entrepreneurs, and also reminds us of how close we all are to falling from the most secure positions.

In fact, "Quicksilver" could be seen as one of the first anti-Yuppie movies. Spurning the "you can have it all" lifestyle, Casey comes to learn you can leave it all and still be happy.

As Casey, Kevin Bacon relies on his mumbling, sulking charisma. Jami Gertz is appealing as Terri, a vague, evasive girl with a mysterious past, who gets trapped into delivering for the no-good drug dealer Gypsy. Paul Rodriguez is earnest and sweet as Hector, a Mexican messenger who dreams of owning a chain of hot dog stands.

Tom Donnelly directed from his own swift- moving screenplay, which seems to have lost some essential elements in the editing room. There are annoying holes in the logic and continuity, particularly when characters are introduced only to be forgotten.

If it's difficult to pinpoint the urban locale, that's because "Quicksilver" was filmed in San Francisco, Los Angeles and Manhattan. The camerawork by Thomas Del Ruth is exciting, zipping perilously in and out of city traffic with a bike's-eye view, getting particularly hair- raising in a "Ben Hur" bike race down -- and up -- the steep San Francisco hills.

Despite its flaws, "Quicksilver" coasts by entertainingly, with some ingenious twists on the standard car chase, and even creates a new dance variation. There's a bicycle/ballet pas de deux between Casey and his dancer girlfriend, followed by a series of handlebar stands, fancy dismounts and other fairly astonishing stunts by Olympic cyclist Nelson Vails and the other make-it-look-easy riders. Maybe it's a trend -- call it"bikedancing?"