崎岖不平的

These rough roads soon wore the tread of motorcycle tires off.

这些崎岖不路很快就把摩托车轮胎磨了。

So the bumpiness, the rising high altitude, and the long duration of these two things made this short distance of the road the toughest.

崎岖不道路，逐步升高海拔，和很长持续时使这段路程为了最艰难一段。