Was the cable adjusted so the distance of the pad to the rims was the same in 'relaxed' position for both top and bottom slot trials?
I doubt it was a design, if it is indeed true it is likely a case of the arms flexing in the slot area.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk