SP-YA08-SSA002 
Spring rates 
spring rate differences 
spring rate differences
See also: http://www.motorlife.be/Artikels/Tuning/veren_progressieve.html
See also: http://www.motorlife.be/Artikels/Tuning/veren_progressieve.html
See also: http://www.motorlife.be/Artikels/Tuning/veren_progressieve.html