NEW GT40 suspension tested and endorsed by JB


Roaring Forties is dedicated to the improvement and continual advancement of the RF GT40’s. Thanks to CAD modelling, the accurate manufacture of the chassis and it’s components and the implementation of OEM design and construction techniques like those employed by Holden, Ford and Toyota, Roaring Forties has not only improved their vehicles suspension – but has received a raving endorsement from Racing Legend John Bowe.

“Having been able to test the latest version of the roaring forties GT 40, I was staggered by how good it was. The car now tracks and steers as well, if not better, than the so-called exotics of the world." John Bowe

“It is quick, easy to drive and lots and lots of fun. The car flatters the driver, which is a huge achievement in a low volume car. The experience of the Roaring Forties engineers, formally of Holden, is very plain to see. This is a special car!”

(John Bowe, 2009)


The foundation for this improvement is Roaring Forties ability to produce a highly accurate chassis, and while this is allows for accurate computer modelling for torsion and beaming analysis, FEA testing and packaging studies, there is more.

Being able to laser cut all the structural members of the chassis (including the rivet holes) provides better quality control and ensures repeatability of manufacture. This is essential for the successful improvement of the vehicles suspension.

The ride and handling of a vehicle is extremely sensitive to the geometry of the suspension. The fundamental design of the suspension must be absolutely correct if the vehicle is to have any chance of behaving correctly on the road. Race teams, such as V8 super car & F1 teams, spend a great deal of time and money on suspension development because it is so critical to the performance and handling of the vehicle.

Roaring Forties felt that they could also improve on their vehicles’ suspension, and through the “RF Suspension Development Program”, have been able to engineer a car that John Bowe believes “tracks and steers as well, if not better, than the so-called exotics of the world.”

This Suspension Development Program was initiated not because there were problems with the vehicle, but rather that the early cast-iron front uprights were becoming difficult to source. As Paul Bottomley, chief engineer at Roaring Forties, had a great deal of experience with the design and manufacture of such components, he decided to make an RF GT40 specific aluminium upright from clean sheet design. This clean sheet approach gave Roaring Forties the freedom to ensure the best suspension geometry was imbedded in the design, and the best modern hardware was selected to be a part of the new suspension system.


CAD Drawing To improve on the original components, the existing suspension pickup points were first accurately measured with a FARO arm (a mobile, digital Co-ordinate Measuring Machine - CMM) and the data was recorded as a benchmark for comparison purposes. RF engineers then used computer analysis to determine the best location for suspension pickup points on the car, to ensure the suspension system would have the correct behaviour as it went through its motion in compression and rebound, while improving steering “feel” and effort. Iteration after iteration was trialled, until a solution was found that considered steering feel, weight, linearity, as well as foot-well space.

Roaring Forties An example of the computers accuracy in development was the predication that there would be 0.2mm of “toe” change throughout the suspensions travel from full droop to full bump. This is an outstanding achievement, even in finely tuned race cars. A “Track” configuration was also developed for those keen to get serious on the race track.

New hardware components for steering and suspension were chosen, to replace the ageing Cortina & Telstar parts, and to comply with the location dictated by the suspension development program. The new RF Suspension was to be manufactured specifically for this vehicle and as a result, it’s steering, handling and performance have been drastically improved.


To ensure that the suspension pick up points were positioned exactly and accurately, relative to the chassis and relative to each other, a new jig (fondly named “Superjig”) was designed on CAD and manufactured via precision laser cut parts. This would be located in the chassis during chassis fabrication, so that the pickups were exactly positioned, as per the computer based design. A similar jig was manufactured for the rear suspension. This virtually eliminates any possible error in geometry!


Roaring Forties Because all the components of the car are CAD modelled, and the FARO arm suspension pickup data is totally compatible with the CAD data, prototype uprights were produced for testing of the suspension geometry. This was to test that what the computer predicted could actually be achieved.

The prototype uprights were constructed using digitally controlled machinery before being TIG welded and the whole assembly crack tested prior to being fitted to the development car.


Roaring Forties Once the test parts were assembled, the wheel motion was physically measured using digital dial indicators. The result was an astounding 0.22mm of toe change at full bump. Correlation with the computer was proven, and the end result was outstanding.


Everything was indicating the new suspension would be outstanding, however the real test was how the vehicle would handle on the road and track. For this stage, professional Racing Driver John Bowe was commissioned to perform the vehicle ride and handling evaluation. These tests were conducted on a series of different roads and race tracks (Baskerville, Simmons Planes, Winton & Sandown), with 2 variations of geometry and several different tyre compounds and constructions. This was to cover the full spectrum of variables.

Roaring Forties

After final testing at Winton Raceway, John’s verdict was in:

“On the road or on the track, with road tyres or track tyres, the RF GT40 is now a sublime experience. Composed, well behaved and involving, it really put a smile on my face. This is a special car!”


Roaring Forties vehicles are now being built with this new suspension system as standard. The upgrade has been designed so that it can also be fitted into earlier model RF GT40s.

This level of research and development is unparalleled in the ICV world and is beyond what many car builders would consider necessary. However, Roaring Forties want to build the best GT40 replicas in the world, and this is just another example of the lengths that this team are prepared to go to in order to achieve that reputation.

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