H&R RSS Coilover Springs for Ford Mustang 05-09 V6/V8 | 05-09 (29170CS3)H&R RSS Coilover Springs for your 2005 2009 Ford Mustang Convertible V6 V8 are optional replacement springs for H&R RSS Coilover kits RSS29170 RSS29170 2. These springs offer different spring rates. H&R RSS Coilover Springs are produced from special spring steel, with a strength rated at 290,000 psi resulting in unrivaled tensile strength and resiliency. Every spring produced by H&R comes from H&R's engineering and manufacturing facility in Germany.