The Tri-Five Chevy is arguably the first GM muscle car. This popular platform is also extremely versatile and continues to enjoy immense popularity even today. As handling has increasingly become a “must have” for many builders and owners, products have been developed to meet those demands.

This August, at the Street Rod Nationals in Louisville, KY, Heidts introduced the latest version of their PRO-G IRS rear suspension system designed for the popular Tri-Five platform.

The PRO-G system is a radical departure from most traditional four link and leaf spring style systems. The system replaces not only all of the rear suspension components but also the differential, brakes and drive axles themselves. Upgrading the leaf spring system which is a design that’s now over 100 years old, to a modern fully independent rear setup.

Heidt’s designed this version of the PRO-G IRS as a true bolt in for the Tri-Five. There is no fabrication involved, meaning that whether the build is in progress, or the owner simply wants to update their rear suspension system, the job can be done without having to spend hours fabricating a solution. Simply remove the stock rear differential and axle assembly as well as the leaf springs and install the new PRO-G system. Heidts says most customers should be able to complete the installation in a weekend.

The PRO-G IRS system is also designed with strength in mind as a response to customer demands for a suspension system that could handle high horsepower. Standard features include:

  • a fully-welded and boxed, upper cross member
  • heavy-duty upper and lower control arms
  • fully welded uprights
  • heavy duty constant-velocity joints and axle shafts
  • Heidts’ own cast center section with nine inch ring and pinion
  • 10.5-inch inboard mounted disc brakes with four-piston Wilwood calipers

Based on the build and application Heidts will also help the customer select the proper spring and shock package based on their offerings. Track widths are available in 56 or 58 inches, also dependent upon the build requirements.

The cross brace which runs across the center of the system has been designed with an arch to it. The arch allows for improved exhaust clearance allowing installers to route the system under the differential.

Ride is one of the biggest benefits to installing an IRS system in any vehicle. As such the PRO-G system when chosen with the proper spring package will offer owners a very comfortable ride. The system is much better suited to soaking up bumps and uneven pavement than the car’s original leaf spring configuration.

When we set out to develop this product, our engineering team had one goal: make this the best bolt-in IRS solution on the market, period. -Jim Shaw

Plush ride aside though, the PRO-G system should also give owners exceptionally improved handling. The Tri-Five may have been state of the art in passenger car transportation when it was new, but it’s handling, especially by today’s standards leaves something to be desired. The PRO-G system already has a reputation of making other cars great handling machines, it should do the same for most Tri-Five’s out there as well. “When we set out to develop this product, our engineering team had one goal: make this the best bolt-in IRS solution on the market, period,” says Jim Shaw, one of the engineering team members at Heidts that developed the PRO-G IRS for the Tri-Five.

The system does lower the rear suspension several inches. Heidts, however, is quick to point out that if used in conjunction with their front suspension components ride height can be achieved as desired. This includes setting the ride height in a manner similar to the original factory rake, which is often popular with today’s builders.

Left: The system is a true bolt on solution replacing the stock leaf springs and axle assembly with no fabricating of custom brackets, or mounts required. Right: The arched center supports allow for improved exhaust clearance.

The PRO-G system comes standard in raw finish, however polished and chrome options are available. Other options for the system include:

  • 56- or 58-inch Wheel Track Widths
  • Choice of Gear Ratios
  • Choice of Rear Spring Rates
  • Choice of component finish: raw or “Show Package” of polished and chromed steel components & polished center section
  • Parking Brake Kit and Cable Kit

Heidts recently sent us this video of the PRO-G IRS system in action on their in house test 55 Chevy. You can see from the in car video that the car’s ride is drastically improved over stock. What is perhaps most impressive is towards the end. The car is taken on a track. It completes a sharp corner and then several slalom style maneuvers, something that would have likely sent the car careening out of control were it still equipped with factory style suspension.

MSRP for the PRO-G IRS for Tri-Five Chevy’s starts at $7,995. Options will increase that cost. Heidts has complete units in stock ready to ship to their dealers or customers nationwide.