Another use for a front derailleur Tech analysis by John Stevenson Missing: 91g of insurance Photo: © Monique du Bois Dave Millar's failure to win the prologue of the 2003 Tour de France will probably go into the history books as one of the greatest avoidable losses ever. While Millar himself has blamed Cofidis management for the lack of a special chainring on his time trial bike, one has to ask: why wasn't he just using a front derailleur? Of course, on the flat route of the Tour prologue there was no need for a front derailleur to perform its usual function of shoving the chain between chainrings. Riders only needed one chainring and most selected something in the 55-tooth range. Speed was the order of the day. But when you're using just one chainring, a front derailleur can still have a useful function: keeping the chain in place. With wide modern sprocket clusters and short chainstays, the chain can end up at quite a sharp angle across the bike, which means there's a substantial force trying to pull it sideways off the chainring. Throw in modern chainrings with shaped teeth that are designed to allow the chain to move off the ring, and you have all the ingredients for a disaster, Millar-style. McGee in prologue-winner yellow Photo: © Sirotti Of course, bad luck is also a factor. Even with the odds stacked against it like this, the chain might not spontaneously dive off the chainring unless something else goes wrong, like a combination of hitting a bump and freewheeling or back-pedaling... just as you might do to set up for a corner on a prologue course with lots of cobbles. Brad McGee also had an attack of the gremlins, with a puncture softening his rear tyre in the last 500 metres. But a rear puncture will just slow you down a little, not stop you pedaling entirely, and the image of Millar desperately trying to remount his chain by hand is one that will make mechanics wince for years to come. It doesn't seem productive to point fingers, and you can bet that whoever prepped Millar's bike has been kicking himself since Saturday afternoon. Call it a learning experience, then (albeit a costly one for Millar): even when it's not moving the chain around, a front derailleur is 91g of insurance against the chain going walkabout.