Depends on the specific parts mixed. There's no question that it can be fine...e.g. see http://www.velonews.com/2013/09/bikes-and-tech/drivetrain-compatibility

Depends on the specific parts mixed. There's no question that it can be fine...e.g. see http://www.velonews.com/2013/09/bikes-and-tech/drivetrain-compatibility-hidden-in-plain-sight_303199 http://www.velonews.com/2013/09/bikes-and-tech/drivetrain-co...