I engine brake all the time in all gears except first. My brake pads do last a very long time, back tire, not so long.
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Definitely NOT something I want to see happen on a regular basis! The loss of traction can be catastrophic, and I try hard to avoid that. The quick reversal of force on the drivetrain can't be healthy, since it's suddenly directing immense force in the opposite direction from usual.
Once you get the hang of engine breaking the benefits will become obvious.
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