For over 25 years, Heidts Hot Rod & Muscle Car Parts has been building suspension upgrades for just about everything from street rods to street machines. A couple of years ago, the company created one of the coolest suspension systems you could strap under your car, and called it the Pro-G IRS. First introduced for the Camaro platform (tested in Super Chevy in the January 2011 issue), followed by the Nova, the bolt in suspension system is now available for the iconic '55-57 Chevys.
There are a few key benefits to converting to an independent rear set up, but most notably is the left and right sides act (as the name would imply) independently of each other. When a solid axle car goes into a corner, the outside squats, which in turn lifts the inside. Now the outside can squat without affecting the other side. The design of the arms allows for -0.5-degrees of camber curve, which greatly improves the handling capabilities of the car over a solid axle. Another good thing is when one rear tire hits a bump it will not adversely affect the other side of the car, providing a smoother ride on rough roads and uneven pavement. Also, since the center section is solid mounted, there will be no pinion angle change under acceleration.
The Pro-G IRS system starts with a 9-inch based aluminum center section that uses heavy-duty constant velocity (CV) joints to transfer the power out to the wheels. Hooked to the center section is a set of control arms that are made from DOM tubing, which run out to heavy-duty spindles. The upper arm has Heim joints for smooth articulation and adjustability. Holding the weight and providing control of the bounce is a set of billet single adjustable coilover shocks with chrome springs.
Braking comes via a set of polished, inboard mounted Wilwood Dynalite four-piston calipers and 10.5-inch rotors. Heidts also offers drilled and slotted rotors and an e-brake set up for an additional charge. Because the brakes are mounted inboard, another benefit is the car sees a reduction in unsprung weight, further improving handling. The IRS is available with a different number of gear ratio and spring combinations. The set up is a true bolt in installation, with only a few holes needing to be drilled. It comes complete, but disassembled. It retails for $8,295.