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I'd imagine you'd get a weird pulsing effect, which would do very odd things to your pedal stroke... you'd probably have a moment that felt like spinning out every time the magnet passed by. I reckon that would be more tiring than any gain you'd get from pushing the magnet. And you'd need a far bigger magnet on there than normal to get any real gain anyway, which would unbalance your wheel, and and and
^This. I thought it would be impossible to detect and might be pretty good at high speeds. it could be even set up to recharge with induction when not pushing.
If an induction charger could be felt when pedalling, the opposite should work with you, especially on both wheels