The first installment of our 991 GT3 RS upgrade journey sees us optimise the stock suspension ahead of major changes under the skin…
Porsche gave its 991 GT3 RS serious hardware from the get-go, but the standard suspension alignment is sub-optimal for track days. This situation affects practically all cars, performance and otherwise. It occurs because the manufacturer has to account for road use, different climates, varying tyre conditions, safety and tyre wear. It ultimately leads to a compromised setup that blunts handling when driving hard on circuit.
This makes the 991 GT3 RS an interesting car to work with though, as there is significant cornering performance just waiting to be unlocked with adjustments to the stock suspension and aerodynamics.
For a recent YouTube video (linked at the bottom of this article), we took our completely stock, 2016 (991.1) GT3 RS to Oulton Park and put professional racing driver and coach Chris Dymond behind the wheel. Rather than immediately fitting our upgrades, the aim of this test was to establish what could be achieved with setup changes alone.
As with our 718 GT4 and BMW G87 M2, we rigged up the GT3 RS with VBOX data logging equipment plus sensors measuring tyre temperature and ride height changes. This information provides even deeper insight into vehicle behaviour around a lap following setup changes.
The Standard GT3 RS Setup
The first few laps showed a familiar problem on a road-biased performance car: the front axle was running out of grip before the rear. Chris reported understeer, with the car particularly reluctant to turn and hold its line through longer corners. At Druids, a double-apex right-hander, the problem was obvious. The car was washing wide on corner exit, forcing the driver towards the outside of the circuit.
The tyre data backed up what Chris was feeling. The front left tyre was being worked extremely hard, but the problem was not simply a lack of temperature. With insufficient negative camber, the outside of the tyre was carrying too much of the load when the car was cornering. The tyre was being asked to do more work on its outer shoulder than it should have been.
This is one of the most important parts of setting up a track car. More grip does not necessarily come from adding more parts. Sometimes the tyre is already capable of producing the grip you need, but the suspension geometry is preventing you from using the whole contact patch effectively.
Changing the Geometry
The first changes were made without fitting any new suspension hardware. We reduced the ride height, introduced a modest amount of rake, and increased negative camber at both ends of the car. The GT3 RS was also given approximately 2mm of rear toe-in and some front toe-out.
The rake was deliberately kept conservative for this test, with the nose 5mm lower than the rear. This was to avoid unwanted changes to suspension geometry and bump-steer characteristics. There is more adjustment available once the appropriate upgrades are fitted, but the purpose here was to see what could be achieved while retaining the standard components.
We also changed the anti-roll bar balance, moving the rear bar from its middle position to full stiffness while leaving the front bar in its middle position. The rear wing was adjusted to generate more downforce, while the front bumper Venturi duct flaps were opened to increase the aerodynamic performance at the front.
None of these changes were particularly exotic. They were basic setup adjustments, but together they changed how the Michelin Pilot Sport Cup 2 tyres were being used and, more importantly, changed the balance of the car.
What Changed on Track?
The difference was immediately noticeable from the driver’s seat. The front axle had more authority and the car was no longer relying on the front tyres to scrub away speed as the steering angle increased.
At Druids, where the standard car had been running wide, Chris was able to carry more speed and keep the car on the intended line on exit. The steering required less correction and there was more information coming back through the front axle. Instead of waiting for the front tyres to give up, the driver could lean on them and feel where the limit was.
The rear tyre were also being asked to work harder because the front axle was no longer the limiting factor. That is exactly what you want when setting up a car like this. The aim is not simply to make one end of the car generate more grip – it is to create a better balance between the two axles so the available grip can be used properly.
The tyre temperature data showed another interesting change. The front tyres were not retaining as much heat as they had during the baseline run and were able to shed temperature more effectively on the straights. That points towards the front tyre being worked more efficiently rather than simply being overloaded.
There was a limitation to the temperature data, however. Due to the lack of space in the The sensors could not measure the full width of the tyre, particularly at the rear, so they should not be treated as a complete picture of the contact patch. They were nevertheless useful alongside the driver feedback and the other data collected from the car.
More Roll, but More Grip
The laser ride height sensors also produced an interesting result. After the setup changes the car showed more chassis roll.
That might sound like a negative result if you only look at suspension movement in isolation. The car was actually generating more lateral grip, which meant greater lateral acceleration and more load being transferred through the springs and chassis. The additional roll was a consequence of the car doing more work in the corner.
This is why looking at suspension movement on its own can be misleading. A car that rolls less is not automatically faster, just as a car that rolls more is not automatically slower. What matters is what the chassis is doing while it is moving and how effectively the tyres are being kept in their working range.
Around One Second Faster
The clearest result was the stopwatch. With the geometry and setup changes alone, the GT3 RS was approximately one second faster around Oulton Park’s 4.3km International Circuit.
Chris described the change as a major step forward. The steering felt better weighted, the balance was more centred around the front axle, and there was less front-end scrub. He could use less steering lock and carry more speed into corners, while having greater confidence in where the car was going to end up on the exit.
There was still a desire for more front grip at the hairpin, but that is hardly surprising when you have a racing driver pushing the GT3 RS around a circuit. As Chris put it, you can always be a little greedy when looking for more grip.
The braking difference was less dramatic, although there was some improvement in stability and reduced front-end dive. The car also felt less prone to tramlining. More importantly, the additional front-end feedback gave Chris more control over the car once it was loaded up in a corner.
Taking the 991 GT3 RS Further
This test is a good demonstration of how much is available from the factory suspension before changing the hardware. The 991 GT3 RS already has a useful amount of adjustment, and getting the alignment, ride height, rake, toe, anti-roll bar settings and aerodynamics working together produced a measurable improvement.
There is, however, a limit to the amount of negative camber that can be achieved with the standard components. That becomes increasingly important as you move towards high-grip track tyres and start asking more from the front and rear contact patches.
The next upgrades for this GT3 RS is therefore Suspension Secrets Camber Caster Plate Top Mounts at the front, combined with Suspension Secrets Rear Camber Shims.
The front top mounts provide a greater range of negative camber and add 2 degrees of positive caster, giving the 991 GT3 RS more scope to build front-end grip and steering feel. The additional caster also increases dynamic camber gain as the steering is applied.
At the rear, the camber shim kit provides additional negative camber where the standard 991 GT3 RS adjustment can run out for a serious track setup. The kit uses different shim thicknesses that can be stacked or staggered to achieve the required setting, allowing the rear geometry to be matched to the rest of the car.
Conclusion
This first test established what the 991.1 GT3 RS suspension is capable of when settings are fine-tuned for track work. However, as cornering speeds increased, limitations of the standard hardware came to the fore.
This is where the Suspension Secrets upgrade range for Porsche’s 991 GT3 RS enters the equation. To unlock more grip, traction stability and speed, greater ranges of camber and toe adjustment are required.
This is exactly what we will be exploring with our GT3 RS development car in our YouTube series. So make sure you’re subscribed to the Suspension Secrets channel to follow the progress.
