This is the question which comes up most often in regard to Cambio Corsa and Paris-Roubaix bikes. I see others have already explained the axle splines, but I've added a picture to my cambio Paris-Roubaix album to help illustrate:
http://www.wooljersey.com/
Aldo Ross
Middletown, Ohio
> When using the Cambio Corsa bike, when the rear quick release is
released
> and then re-tightened after a gear change, what insures the rear wheel
> will be straight in the drop outs? When I am doing this by standing
behind
> the bike on a regular rear drop out, it usually takes me a little
giggling
> to make sure the rear wheel is right down the center before I
retighten
> the quick release. If I don't do this carefully, the rear wheel will
often
> be a little cocked to one side or the other. Having the screw down
> adjusters in the back set evenly is a help but not a guarantee. On a
bike
> without even that assurance, I would imagine that it's possible to end
up
> with a dangerously off kilter wheel. The saw tooth drop outs on the
Cambio
> Corsa don't reassure me much either.
>
> Take Rae Dawn Chong's performance as a quick wheel changer in
"American
> Flyers". At the speed she did it, I would be very reluctant to trust
that
> bike for fear that either the wheel would be crooked or the tension in
the
> quick release would be too loose. Saving ten seconds for a wheel
change
> would be poor economy indeed, if you caused a crash down the road.
>
> Garth Libre in Miami Shores Heights Fl.
> http://www.bikelist.org/