A Running the chain from the inner ring to the outer three or four rear sprockets forces it to run on to the chain ring at a severe angle, which creates a natural tendency for the chain to ride off the chainring to the outside. Unless the front mech shifts the chain far enough inboard to drop on to the inner chainring teeth, it will tend to ride on the tips of the teeth as described. This can be dangerous as, with no drive, any attempt to pedal may result in loss of balance and a fall.
It should be possible to adjust the front mech to nudge the chain further inboard on the downshift without falling off the inside. First check the mech cage outer plate is parallel with the outer chainring and, if so, that the inner plate does not rub on the chain when it is on the largest sprocket. If this is the case, try angling the tail of the cage slightly inwards and repeat the previous check. If these don’t work, a professional mechanic will be able to find a solution.
In any case, 50/23 is much the same gear as 34/16 so it’s easy to avoid having to run the chain on the stated gearing combinations. To find a higher gear than 34/16, simply use the big chainring.
Cycle’s Technical Editor