The real issue is that any "mountain bike" with Tourney gear really isn't made for hard off-road duty, it's a beach cruiser with gears.
The Tourney rear derailleur is a huge step down from even an Altus, has much more flex due to looser manufacturing tolerances and more of a tendency to swing into the spokes when used hard. Moving up the ladder, Altus and Acera are both listed as "MTB-like" groups by Shimano. Alivio is their bottom rung "recreational mountain bike" group.
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Originally Posted by
ahsposo
Ski, bike and wish I was gay.