An expert's warning the wide spread under-grading of how difficult or dangerous mountain bike tracks are remains a potentially deadly problem and a single nationwide standard needs to be introduced urgently. Simon Noble from Envisage New Zealand audited Marlborough's Wither Hills mountain trails and found nearly all had been under-graded in terms of their degree of difficulty. Only two of the parks 37 tracks were actually consistent with the gradings, meaning they were actually harder than indicated. The report was presented to Marlborough District Council last week. Recreation consultant and trail auditor Simon Noble spoke to Lisa Owen.