I had IS- 17, large, great fit initially, but loosened up too much quite quickly. Also internal visor spring return went weak leaving it halfway up.Seemed a big shell and lots of padding with a bit of a round shape, medium was too tight on forehead. Bought RPHA 11, medium, very snug fit, more oval, and still doesn't move at speed, brilliant helmet, light but no drop visor. Now bought RPHA 70 (piotrek pic) which is same fit as 11 but with visor, just a tad heavier. So...I'd give thumbs up to rpha 70, pic below, but that's just for my head shape. Therein lies the problem of recommendations, were all different. Btw. Some complain of internal visor misting. I use mine slightly down, like a car sun visor.