All mountain slx hollowtech ii chainset is tough and aggressive yet also lightweight and excellent value the hollowtech ii chainset features hollow forged crank arms which are both lightweight and rigid whilst being incredibly strong and durable hollowtech ii integrated bottom bracket design uses a wide bearing placement with a large axle diameter for increased stiffness efficiency and added durability 70 degree spider arm for optimal rigidity for 11 speed dyna sys11 sm crm70 chainri