Unbeatable performance for TT or triathlon. Front to back, every curve & shape of the new Rivet TT is fine-tuned through Computational Fluid Dynamics for optimal aerodynamics. & on the road, it de Livers unrivaled fit & comfort to real-world athletes like triathlete Tim Berkel, who helped refine its design. Protected for 12 months by Giants Helmet Crash Replacement Service. Western: S (51-55cm);M (55-59cm);L (59-63cm Asian: S (52-56cm);M (56-60cm);L (60-64cm Weight: 300g (size M, CPSC/CE Certifications: CPSC/CE;AS/NZS