Originally Posted by
carleton
Track racers use different gear ratios regularly. On a road bike, the rear derailleur takes up the slack in the chain, so the wheel can actually be in a fixed position and as close as you can get it.
On a track bike if a racer went from a 51x14 (where the wheel is slammed up in there) to a 47x14 (which moves the wheel back about 2 inches) that would create lots of slack in the chain.
This is why track racing bikes have long dropouts, to allow for the adjustment of the wheel to take up the slack and tighten the chain.
"Why not use a shorter chain for the 47x14 combination?" you ask...
Because that would be a pain in the butt and very time consuming. Track racers change gears several times during a training or race session. Uninstalling and installing a chain for different gear combinations is simply impractical, and more importantly, unnecessary.
So, yeah, it is actually supposed to happen.
Now, when you have street fixy guys that run the same gear ratio 100% of the time, sure, they can remove chain links (and add half-links) to get that rear wheel right in there for the photo shoot. But, it's simply not practical.
Ah, ok. That all makes sense. However, if they're going to carry a few chainrings and cogs/rear wheels to swap ratios, why not carry two or three extra chains of extra length so that it can always be slammed? Does having it tucked not matter or create a bad wind situation as Hairnet has suggested? I get that swapping chains is impractical, but when you're already changing the rest of the drivetrain, why not do that too, just to keep the aerodynamics the same?