Suspension is a push / pull area between what the driver wants in slower speed corners vs the designers demands for downforce in the high speeds ones. A driver likes a softly sprung car as it helps him feel the car much more making the grip tangible whilst the designer requires a much more stiff platform for his aerodynamic principles to work across a wide spectrum. An F1 car goes through a rollercoaster of attitude adjustments through the course of a lap and of course that then becomes a fight between Aerodynamic efficiency and Mechanical grip, both of which can be very subjective to driver feel during the switching points.
Aerodynamicists will argue that given a stiff car / rigid aero platform they can create enough downforce that the suspension becomes irrelevant, with the forces acting on it regulating the drivers ability to corner as the car is effectively sucked to the ground. The most recent account of this would be Off Throttle Exhaust Blown Diffusers with the rest of the car being setup taking account for the fact that by virtue of creating a 'Sealing' effect with the exhaust plume at all times, rear downforce is generated on a consistent level. This gave the driver a buffer or zone to work within as he knew the car, unless a failure occurred would have sufficient downforce to make corner entry at speed as downforce was continuously fed to the car even when they were in the braking phase.
If we look back through F1 and moreover a topic that I have covered most recently in my section on the Williams FW14B for Grand Prix Merchandise teams have been looking to bridge the gap between a rigid aerodynamic platform and Downforce for some time. 'Active Suspension' created this bridge back in the 80's, early 90's with the driver given a more consistent window of downforce as the computers fought the car's wantant needs to pitch or roll. The interlinked suspensions of today are doing a similar thing but passively through the use of Hydraulics.
Lets start out with a few scenarios without interlinked suspension so that we can understand what the teams are trying to achieve:
Scenario A: The driver is entering the braking phase from a speed of 180mph into a slow left hand corner, as he decelerates the balance of the car shifts forwards destabilizing the rear of the car. This is what we refer to as 'Pitch'
NB: In this example the height of the diffuser increases as the car pitches forward, coupled with the loss of the exhaust plume's sealing effect (as the driver is off throttle), means the Diffuser is subjected to 'Tyre Squirt' and results in a less compliant rear end)
Scenario B: As the driver completes the braking phase in Scenario A he turns into the left corner the car rolls to the right. This will result in the car leaning on the right tyres as the car's weight transfers (This is why you sometimes see drivers fighting opposite lock / oversteering out of a corner as the transmission of speed is too much for the force applied on the given tyre)
Scenario C: As the driver straightens the car from Scenario B he applies the throttle and the balance of the car pitches rearwards (Squatting)
Interlinked suspension helps to manage these effects retaining a more stable aerodynamic platform, in all three scenarios an interlinked suspension can counter the car's natural tendency to shift forward, sideways or rearwards. This allows the aerodynamics to be much more aggressive and tailored to a much smaller operating window. Mercedes (and Lotus to a smaller extent) are the only team I'm aware of using Left to Right and Front to Rear interlinked suspension thus they control the whole platform of the car as it pitches or rolls. Some of the other major teams including Red Bull, Ferrari & McLaren are all believed to have left to right interlinked systems that help the car adjust it's attitude in Roll.
It's not a fool proof system by any means though with Mercedes utilising their system for around 3 years now, also Caterham share rear end technology with Red Bull purchasing their gearbox and rear suspension from the Championship winners. So why do some have more success than others using the system? If we were back in the days of unlimited testing I'm quite sure the teams would have it nailed by now but with limited track time and the effects difficult to model on conventional suspension design systems the teams have had to invest time and money in the tools required to model it.
It's not a fool proof system by any means though with Mercedes utilising their system for around 3 years now, also Caterham share rear end technology with Red Bull purchasing their gearbox and rear suspension from the Championship winners. So why do some have more success than others using the system? If we were back in the days of unlimited testing I'm quite sure the teams would have it nailed by now but with limited track time and the effects difficult to model on conventional suspension design systems the teams have had to invest time and money in the tools required to model it.
So now you know what the teams are doing I'm guessing you want to know how, well it's an area that is difficult to explain in it's entirety with images due to the teams hiding it and most of the system being enclosed under bodywork. But in a rare shot of the rear end of the Mercedes W02 we can see how the team are hydraulically linking both sides of the suspension.
In the image above found by @F1Talks – www.f1talks.pl and courtesy of www.suttonimages.com from the Korean GP in 2011, we can see a damper connected to the bottom of the Pull Rod which takes care of 'Roll' and/or 'Heave' (Heave is the up or down motion of the car) we can also see 2 Hydraulic pipes are connected to the damper and lead to a central valve block. A hydraulic pipe is connected to either the high or low pressure chamber of the damper which leads to the central valve block where it's counterpart or opposite from the other side of the suspension meets with the valve block too. This connection allows a displacement of hydraulic fluid on one side of the suspension to have a counter displacement on the opposite side of the car helping to level it.
Above: A very basic drawing breaking down what we can see in Sutton image above
In the case of Mercedes they went one step further than some of their counterparts (appears Lotus may have a similar system too) by connecting the Front & Rear to the interlinked system too (FRIC – Front/Rear InterConnected).
Above: Giorgio Piola illustrates the method employed by Mercedes to alter the level of hydraulic fluid present in the FRIC system
This means the team control the pitch angle, allowing the team to have a good handle on one of the biggest aerodynamic pitch sensitive issues fought by the teams: Rake
These interlinked suspensions therefore help to keep a more constant aerodynamic platform allowing the team to set the rake angle such that they need not fear it bottoming out, maximising the downforce that can be generated by the Diffuser / Exhaust Sealing.
With Pitch angle being able to be controlled we don't have the same issues we saw back in Scenario A as the car doesn't pitch forward under braking the way it normally would resulting in the Diffuser being able to retain the downforce generated for a more sustained period of time.
A trend seems to be emerging with teams both softening the rear suspension and lowering tyre pressures to further aid in the braking and turning in phase. This not only aids in reducing the Diffuser height as the suspension counteracts the car pitching in the braking phase but modulates the tyre, generating heat and grip.
In Malaysia we saw Red Bull and Mercedes soften their suspensions and run with less tyre pressures than in Australia having perhaps witnessed Lotus adopting this style. Meanwhile Lotus and moreover Raikkonen went a little backwards suffering perhaps with the aerodynamic changes made to his car whilst still running an aggressively soft car. (Raikkonen suffered with snap oversteer throughout the race)
In Malaysia we saw Red Bull and Mercedes soften their suspensions and run with less tyre pressures than in Australia having perhaps witnessed Lotus adopting this style. Meanwhile Lotus and moreover Raikkonen went a little backwards suffering perhaps with the aerodynamic changes made to his car whilst still running an aggressively soft car. (Raikkonen suffered with snap oversteer throughout the race)
It will be interesting to see how this plays out throughout the rest of the season especially as I see no reason why Pirelli should heed the calls of Red Bull to switch back to 2012's tyre construction. Furthermore Mercedes have spent 2 painful years already trying to perfect their more complex FRIC system which creates a link between the front and rear of the car and caters for Pitch and Roll. Therefor I don't see teams being in a rush to copy Mercedes this season especially as the gains aren't substantial in terms of overall pace when as much can be made up by key aero upgrades.
Below are a few images caught of the Mercedes W04 caught during build up
Below are a few images caught of the Mercedes W04 caught during build up
In this video from Australia below we see Nico Rosberg retire from the GP it could be the angle/perception change as the camera pans out but I believe as the car comes to rest the FRIC system corrects the pitch angle of the car rearwards. I leave it for you to judge:
Merc FRIC in action? Pitch control by dm_5167cd137b13d