StopTech Sport Rotors are also available with an optional cryogenic treatment. Although cryogenic treatment is invisible to the naked eye, many fleet customers are sold on its ability to extend the service life of the brake rotor. Deep cryogenic treatment is a one-time process that permanently improves the performance and wear characteristics of metal components, from brake rotors and engine parts to machine tools and gear sets. All new StopTech Sport Rotors may be ordered with cryogenic treatment for an additional fee. This extra process provides better rotor balance and creates a cleaner, more finished looking component. In addition, Rotors are inspected for balance and mill-corrected to a tolerance of less than 2oz This extra process provides better rotor balance and creates a cleaner; more finished looking component; In addition; Rotors are inspected for balance and mill-corrected to a tolerance of less than 2oz 2007 - 2008 BMW 335xi, 2007 - 2013 BMW 335i, 2009 - 2011 BMW 335d, 2009 - 2013 BMW 335i xDrive, 2011 - 2013 BMW 335is, 2011 - 2015 BMW X1