I've found some old 18mm Conti Supersonic clincher tyres that I had forgotten about. They are in good condition, no nicks, sidewalls don't seem to be perished. But what do I ride with them? 25mm is supposed to be proven to be faster than 23mm, so what was the idea behind such skinny tyres, is it climbing and straight line speed? They don't look like something I'd want to descend fast on or throw round corners.