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The Mercedes AMG GTR is unofficially known as the ‘The Beast of the Green Hell’ in honour of both its most eye-catching paint option called ‘Green Hell Magno’, and for the intensive Nürburgring-based dynamic development programme that AMG undertook when creating the car.
The result of AMG’s hard work was a car that was faster, lighter, sharper and even more capable than the standard AMG GT sports car.
When our customer brought his AMG GTR back from the Nürburgring for additional upgrades, we began to wonder: what if we unleashed the beast and made the chassis as track-focused as possible in the pursuit of ultimate on-track performance.
In this blog piece, we’ll explore the journey that took a fairly standard AMG GTR to the next level of cornering performance.
Understanding the AMG GTR
The standard AMG GTR platform is an excellent starting point for a performance car. The GTR has a long wheelbase; a wide front and rear track; a front mid-engined layout; double-wishbone suspension front and rear mated to electronically-controllable and ride-height adjustable coilover style springs and dampers.
In the interest of improving chassis rigidity and cornering grip, the AMG GTR does feature solid monoballs in the lower rear control arms, but every other bush in the suspension is rubber, which leaves plenty of scope for increasing the chassis stiffness for even greater performance.
Chassis Upgrades
The first dynamic point of focus for this project was to increase the negative camber available at the front and rear axles. Negative camber is essential for improving cornering grip whilst also eliminating unwanted understeer.
The camber angles on the AMG GTR are not adjustable as standard, but camber can be increased by installing camber shims. Camber shims fit between the suspension wishbones and the chassis – this adds much needed negative camber. We laser cut a range of camber shims of varying thicknesses, (thicker shims add more negative camber) and for this project we fitted our thickest front shims and a set of medium shims at the rear axle to create a good front-to-rear camber balance.
With the camber angles improved versus the stock values, we then looked to improve the chassis stiffness, which would enable the improved camber to be used most effectively.
This led us to the idea of replacing all of the rubber bushes in the suspension wishbones with billet aluminium housings that contained high-precision bearings. These monoballs increase stiffness and cornering grip as they cause more g-force load to be exerted into the chassis. The increased g-force loads are also transmitted through the chassis which results in faster direction changes, and an increased sense of connection to the car for the driver.
The other benefit of going to solid joints is that they do not flex during heavy cornering. The original rubber bushes flex during cornering, which causes the position of the wishbones to shift very slightly. This flex causes the suspension geometry (particularly the camber angle) to shift dynamically which reduces overall cornering grip, and causes unwanted chassis instability during high-speed cornering.
As previously mentioned, the AMG GTR already has monoballed rear lower wishbones, so we turned our attention to the front lower wishbones, as well as the front and rear upper wishbones. We removed these wishbones from the chassis and pressed out the OEM rubber bushes. We then used CAD to design monoballs for the remaining wishbones.
Our in-house CNC machines allowed us to turn parts around quickly and soon the AMG GTR’s arms were fully monoballed and refitted to the car.
At this point, the chassis was finished in terms of hardware changes to the suspension arms and geometry. This left the springs and dampers as the only thing left to upgrade.
The OEM dampers on the AMG GTR are electronically controlled units. These dampers offer decent performance and the ability to switch modes from comfort to more track-oriented modes is useful, the outright performance of the dampers is limited.
In light of this, our customer elected to replace OEM coilover units with a 3-way adjustable coilover kit from American brand Motion Control Suspension (MCS).
MCS did not offer a kit for the AMG GTR at the time, so we removed the OEM shocks from the AMG GTR and took comprehensive dimension measurements that we then relayed to MCS engineers in both Europe and the USA.
Once the kit was finalised, MCS put it into production.
About MCS
Motion Control Suspension (MCS) is a premium motorsport damper manufacturer based out of Georgia in the USA. With over 28 years of top-flight motorsport experience, MCS coilover kits are ultra-high quality and are fully customisable in terms of additional parts such as remote reservoirs, spring rates and lengths.
What makes MCS coilovers unique is their gas-pressure adjustability. Every MCS coilover kit features Shrader valves on the ends of the damper reservoirs. This enables the customer to either increase or decrease the air pressure in the damper. What this effectively does is retain the damper profile but moves the entire damper curve either upwards or downwards in regards to the force/velocity needed for the damper to operate.
This gives you unparalleled setup control, as if you are driving in the rain, you can release air from the damper, making the car more supple, without compromising on the actual performance of the damper. A traditional adjustable coilover could also be adjusted in this situation, but you’d be compromising how the car felt in this attempt to unlock more grip in the wet.
Again, if you went on a track day on a very smooth, open circuit, you could increase the air pressure in the dampers in order to stiffen the car as much as possible in an attempt to unlock as much grip as possible.
The kit we opted to choose for this application was a 3-way adjustable kit, which features 18 clicks of high-speed compression adjustment; 10 clicks of low-speed compression adjustment and 18 clicks of rebound adjustment. This adjustability, in combination with the ability to control the dampers’ air pressure levels gave us complete control over the handling characteristics of the car.
Sometimes we’re asked if 3-way coilovers are too much, or ‘overkill’, and whether or not an amateur driver would be able to feel the benefits from a 3-way adjustable coilover. The contrary is actually true – a non-professional driver needs a chassis that is stable and consistent across all conditions, whereas a pro driver can ‘drive around’ or compensate for a car’s dynamic downsides.
This is why 3-way coilovers are so important and influential. The ability to have a car that is very stiff in the corners for maximum grip whilst being supple over kerbs and bumps (thanks to the independent high-speed bump controls being set to very soft). This gives an amateur driver a car that they can drive consistently to their own limit without having to compensate for any awkward handling characteristics.
After a quick turnaround, the MCS kit landed at our base and we installed the kit, and then corner weighted the AMG GTR before aligning it ahead of its shakedown session at Oulton Park.
Taking to the Track
At this point, all we had to do was give the car a thorough shakedown and to see the difference of this massively-transformed chassis.
We began the shakedown with Andy, the owner of the AMG GTR, going out for a few extended sessions so he could refamiliarise himself with the much more capable chassis and suspension. The car performed well, and Andy quickly settled into a consistently fast groove.
Despite the car being on Michelin Pilot Sport 4S tyres (temperatures on the day never exceeded 11 degrees Celsius), the amount of grip the chassis and suspension were able to extract from the chassis was remarkable.
After the initial few sessions, Andy pulled the car back into the pits for some feedback. Following this feedback we reduced the pressure of the air in the rear shocks down to 10 bar from 12 bar in order to unlock more traction at the rear. We kept the front pressure at 12 bar as the front of the car was handling nicely.
Once the pressure balance front-to-rear was altered, we then used the damper adjusters to then fine-tune the car’s cornering performance to suit, and Andy went out again.
After a whole day at Oulton Park, Andy was delighted with the performance of his new and improved AMG GTR.
The beast has truly been unleashed.
