Originally Posted by
HillRider
Yes, front shifting is definitely more effected by chain tension and, given enough tension it it may be nearly impossible to shift between chainrings.
That's only because the front derailer is designed wrong. It relies on the spring to knock the chain off during high torque situations while using the cable to drag the chain off the chainwheels during low torque situations. The rear, on the other hand, works in the opposite, and proper, way.
Shimano's RapidRise is (mostly) a failure because they concentrated on the wrong derailer in an effort to have the shifters work the same way. Long ago Suntour made a front derailer that use the cable to drag the chain off on to low gears in high torque situations and it worked wonderfully. None of that "CLATTER! CLATTER! CLATTER!, drop the chain" foolishness especially in off-road riding. Shimano would have had a real winner if they had done RapidRise on the front derailer.