Actually it was hard packed snow covered by a layer of ice. Studded tyres do love having some ice beneath them. Worse if there's a small spot of frozen snow with no ice on the top. The e-bike gets a jerk when a wheel (especially the rear one) hits that spot. I rode rather slowly and respectfully... While an e-MTB on tyres such as Schwalbe Ice Spiker Pro could ride the same terrain at the full speed and no worries at all! (Winter Plus are good but not that good. These are ideal on black ice or on smooth ice).