Independent Rear Suspension (IRS) refers to a rear suspension design where each rear wheel moves vertically independent of the other, connected to the chassis via separate control arms and a fixed differential. IRS provides superior ride quality, better single-wheel bump absorption, and reduced unsprung weight compared to a solid rear axle. The trade-offs are higher cost, complexity, and harder launch behavior in straight-line acceleration. The 2003-2004 Cobra and 2015+ Mustangs use IRS from the factory. Griggs Racing manufactures IRS-specific suspension components.