Polystrand GT-Lite CRX: Part 3 – Simulating the Suspension
At the end of Part 2 of the Polystrand GT-Lite Project, we had finalized the preliminary design for the independent rear suspension (IRS), generated the CAD model, and sent our CRX off to the bodyshop sans rear suspension. Thanks to Rassini, we had our virtual computer model of the chassis courtesy of Chris Galea’s work with the FARO unit, and Tony Berlingieri prepared the car by removing the old rear suspension and a lot of the now unnecessary supporting structure. Additionally, before the car left on the flatbed, Tony added some framework to which we’ll install the new IRS unit when the car comes back.
The big empty hole. This is what we were left with after the rear suspension was surgically excised. We still have a few things left to do before she leaves for the body shop.Before we set the final design in stone, however, we needed to do everything we could to insure that our design not only fit into the vehicle, but that the components would do what we want them to do under load. Of particular concern was the location of the trailing links that attach to the chassis (the links that go from the rear spindle mounts forward to the chassis). We were hoping that we could get away with only one lateral link on each side (the links that go from the center of the subframe out to the rear of the spindle mounts). The ability to do this depends upon the angle of the trailing link from the centerline of the vehicle. If we can get enough angle on those arms, we’ll have enough lateral rigidity so that we don’t need the additional linkage, saving us some unsprung weight.
A view from the bottom. Tony’s busy cleaning things up and preparing to add some structure to mount the new IRS.
This car’s been around the block a few times. Tony patched a few holes and prepared some clean surfaces to weld in some bracing.Think of the lateral link/trailing link assembly as a large A-arm or wishbone, and you’ll get the idea. The problem we have is that the fuel cell in the car is right in the middle of where we would like to place the trailing link mounts. We’d like the links to be long enough so that we don’t have too much toe change when the suspension goes through its travel, but we definitely don’t want to move the fuel cell, because it’s in a great location – low and in the center of the car – which means that as the fuel load decreases during a race, it will not have a big effect on the handling balance.
Since we won’t be using coilovers anymore for the rear suspension, we removed the heavy coil towers and cross-brace from the car. We’re adding some of that weight back with the extra framing, but it will be lower in the chassis, bringing the center of gravity down.
