This race inspired design is known for its great fit and great value with similar features to the s works prevailmdashlike the tri fix webbing system and 4th dimension coolingmdashthe propero ii handles even the most intense efforts on the pavement hairport sl fit system is ponytail compatible and features four height positions and micro adjustable dial for easy on the fly adjustment specialized propane ii womens bike helmet features 4th dimension cooling system with mega mouthport