Race suspension

Most of it is concealed from view, but F1’s super-stiff springing is crucial to keeping the power on, By Gordon Cruickshank

Today’s suspension solutions look radically different from only 20 years ago, but the aims have not changed, even though the forces involved have soared due to downforce and sticky rubber. You still must prevent the wheel moving fore and aft or sideways, while allowing controlled movement up and down. And despite a thousand variations among road cars, most racing cars rely on the simple and pure double wishbone, some form of twisting metal for springing, and a hydraulic damper to calm everything down. Setting aside active suspension, now banned in Formula 1, it’s only in the last area that we have seen a major new idea lately — mass damping.

But first, back to the major principles. The suspension’s function is to maintain as consistent a load as possible on the contact patch, the tyre’s toe-hold on Mother Earth, while the car above moves around. On a road car those motions are substantial, and the paths of all the swivelling parts are plotted to interact so as to keep the contact patch flat — or rather at an ideal negative camber, or inward lean — even when the body leans like a yacht in a Force 5.

The priorities on a racing car are different: the track is extremely smooth, the forces far higher, and driver comfort isn’t on the menu. And above all, the immense downforce on an Fl car means that the suspension must be unyielding to maintain minimum ground clearance even at high speed with full tanks. From the on-board camera you will barely see the suspension move.

Normally, car designers keep the upper and lower arms far apart for best location of the upright — not possible with an Fl car’s raised nose, where the floor is level with the hub. Single, twin keels and vee keels with an open central space have all been used to locate the arms, but new front wing restrictions make airflow to the splitter critical. So keels have vanished, the lower arms now hingeing on the monocoque edges. The aero gain outweighs the higher centre of gravity and theoretically inferior geometry.

It’s a long time since the springs were out in the airstream; pushor pull-rod systems are universal, making for compact packaging with the rod acting through rockers on small inboard torsion bar springs. Due to the rocker, the bars can lie in any orientation that suits — fore and aft, vertical or anywhere in between. It also allows the designer to convert the tiny wheel movement to a larger damper movement for better control. This is also where there is sometimes a third spring and/or damper. Because it connects the rockers it has little effect when one wheel rises, merely pushing the other wheel down. But when both wheels rise as the car dives it’s compressed between the rockers, giving extra resistance to pitch and thus better height control, crucial to downforce with only 20-30mm ground clearance and 170kg weight change between full tanks and empty. This separation of roll control from ‘heave’ — up and down car movement — can be even more extreme outside F1. Some hillclimb cars rely purely on sprung washers for roll resistance, with a single coil spring for heave.

Another Formula 1 detail is the disappearance of spherical joints. Because of the minimal movement — ride height on an F1 car alters only 3mm from empty tanks to full — the ball-joint is replaced by a flexing metal blade bolted to the chassis. This obviates free play, cuts friction and weight, and avoids ‘stiction’. The ride height is varied by fitting shims of different thickness at the top of the pushrod, or more radically by rotating the torsion bars by one spline.

Pushrods have become almost universal in F1 because they give clear air around the front splitter and rear diffuser tunnels. However, after diffusers were restricted for 2009 (and before Ross Brawn thought of a double version), Adrian Newey used a rear pull-rod set-up on the past two Red Bulls. Mounting the springs and dampers low and forward left a cleaner air path to the rear wing, boosting its effect, and keeping the mass low. With double diffusers banned for next year, rear pull-rods may be back in fashion.

Perhaps you have seen how some skyscrapers protect against earthquakes with a huge concrete block suspended inside. Carefully tuned, the block lags behind the building sway, reducing the extent of movement. This is mass damping.

Renault’s Bob Bell exploited this principle by mounting a sprung 9kg mass within the nose of the R25 in 2005, giving him a win in the eternal trade off between soft springs (good for grip) and hard (good for consistent downforce). By reducing vertical movement this let him run softer springs without stiffer dampers, so the car was particularly good over kerbs, as the wheels stayed on the ground for longer. It was brilliant — but the FIA banned it in ’06 on the grounds that by controlling pitch it was a moveable aero aid. However, inertial damping has continued invisibly, usually within the third damper.

McLaren was here first with its so-called ‘J-damper’ in 2005, and it was a long time before the secret came out. Now called an inerter, this encloses a geared-up flywheel which spins up as the suspension moves. Remember push-and-go toy cars? The principle is similar: small movements producing a lot of rotation. And if you run one back and forth rapidly you feel all the inertia of a heavy object but without the weight — the flywheel adds ‘virtual’ mass. The inerter contains a spiral shaft on which a flywheel spins as the shaft slides, like one of those plunger egg-whisks, but unlike a KERS flywheel this one is not free to spin; as the wheel droops again the flywheel has to reverse. Whereas a hydraulic damper dissipates energy, the inerter stores it and feeds it back out of phase. This restricts wheel accelerations, smoothing out load variations on the tyre contact patch. Brilliant lateral thinking, but like everything else, it only works as part of a delicate package.

Every track puts different demands on the suspension, and teams have a huge array of springs, dampers, wishbones and even spacers to alter wheelbase. For super-tight Monaco teams install special extra-lock steering with stronger wishbones notched for extra wheel clearance, plus an even faster rack, or shorter steering arms which give more angle for the same input. Tuning for each race has been made harder by the rule forbidding alterations between qualifying and the race, so alight, agile qualifying set-up may get you a good grid position but will handicap you early in the race while you run with heavy fuel. Deciding where to pitch your optimum suspension set-up is one of the black arts, and no matter how many simulations you run, real life rarely conforms.