2012 Fisker Karma: Suspension Walkaround
We may not have had enough time for a full test of the 2012 Fisker Karma in the short time we had it, but a suspension walkaround takes almost no time at all, especially now that we have our Rotary 2-post lift.
The Fisker is so new that Rotary doesn't yet have a lift point cheat sheet on it. The Karma's owner's manual was AWOL, too, so we went ahead and used subtle marks left behind by what we presume was Fisker's own shop equipment. Going slow in cases like this is key.
As a series plug-in hybrid, this unique machine is sometimes powered by electricity stored in a large lithium-ion battery running down the center of the car, between its four seats. Other times it's powered by a 2.0-liter direct-injected turbocharged four-cylinder engine and generator set that's mounted longways between the front wheels. In Sport mode both of these happen at once for extra ooomph.
In all cases the Karma is driven electrically by a pair of motor-generators that sit between the rear tires. There is no driveshaft; it's all done with wires.
The front end rides on a double wishbone suspension of Fisker's own devising.
Aluminum abounds, mostly in cast form. The upper wishbone (green) has the classic A-arm shape, while the lower one is more L-shaped. A coil-over monotube shock handles the springing and the damping.
The steering tie-rod end (yellow) mounts quite low on the front knuckle, but that's because the front-mounted steering rack (green) is positioned quite low on the front subframe. There's lots of steering rigidity here; the steering rack itself is hard-mounted to the front subframe, which in turn is hard-mounted to the chassis.
An EPS unit supplies the power assist, though the column-mounted unit is not visible here. The Fisker's steering response is quite direct, but the EPS steering effort tuning is probably heavier than it needs to be.
The bottom end of the Sachs-made front monotube coil-over mounts to the lower arm with a simple tie-bar...
...with long bolts that go all the way through.
Front camber and caster are easily adjustable via a pair of eccentric cams built into the inner attachment points.
The pivot axis of the aluminum upper control arm is tilted back to provide a dose of anti-dive geometry.
Karma's front stabilizer bar is mounted ahead of the steering.
Another look without arrows this time.
A car-spanning cast aluminum front subframe cradles the 2.0-liter turbo-4 engine. There's nothing in the central tunnel but batteries, so the entire exhaust system lives in front of the firewall.
After exiting the turbo and catalyst, the exhaust dumps into a central muffler before splitting in two, with each half flowing through another silencer to exhaust pipe. The dual exhausts exit from a cutout low in the front fender, ahead of the front door and behind the front tires. Each front fender sports a small grille opening directly above the exhaust pipe to help expel exhaust system heat.
Here's a closer look at one half of the exhaust system.
Little noise comes from those exhaust pipes, which are dormant half the time anyway when the Karma runs on battery power. At those times this speaker is one of two that emits an artificial noise to alert pedestrians at speeds up to 25 mph.
The front brakes are impressive-looking Brembo 6-piston fixed calipers with a removable bridge bolt for easy pad swaps. They squeeze two-piece floating calipers with an aluminum center hub.
But they don't do anything below 0.25g of deceleration in order to let the rear-mounted motor generators recover all the braking energy they can. An initial 100% rear brake bias sounds weird at first, but 0.25g stops are mild enough that it doesn't feel all that odd.
The calipers are nevertheless prefilled to move the pads up against the rotors during such stops just in case you press harder or if the stability control needs to kick in for any reason. They also work in normal fashion when the battery is full and has no room for any recovered energy.
A computer sorts it all out, but you'd never know it. These brakes feel powerful and sure-footed. At some future date we'll drive the car harder on the test track, but we don't expect to be disappointed except maybe on one front: the Karma weighs between 5,200 and 5,300 pounds. It's unlikely to set any stopping distance records.
Another double-wishbone setup with lots of aluminum bits supports the Karma's rear end.
Here we can see the upper arm (yellow), the lower arm (green) and the toe link (orange.)
The Fisker's toe-link sports a turnbuckle (yellow) midway along its length for easy adjustment. And check out the general massiveness of the double-shear outer attachment at the hub end (green). Probably has to do with the grip potential of the massive 22-inch wheels and Eagle F1 Supercar tires back here.
Camber adjustments are made with an eccentric mounted at the outer end of the upper arm.
The Karma's rear stabilizer bar (yellow) sweeps in from behind to meet a drop-link that connects to the lower arm. But the interesting thing to note here is the large-diameter rear shock. This is something Sachs calls a Nivomat, an automatic self contained load-leveling monotube damper.
A Nivomat auto levels entirely via hydraulics within. Why put one here? This is not a minivan or SUV. I asked someone at Fisker and they told me they wanted the Karma to sit low, and it fact it does. But it also seats four. Getting away with both requires impossibly stiff springs or some sort of load leveling scheme.
I've personally worked with Nivomats before. It's a good solution to that sort of problem, especially when you don't want the complexity and cost of an air suspension system.
The point where the Nivomat coil-over mounts to the lower control arm (yellow) is mighty beefy, with a wraparound arm to put the joint in double shear. The more lightly loaded stabilizer bar link (green) just above can make do with a single shear joint.
The all-aluminum rear subframe (yellow) is welded up from several pieces. In addition to carrying the suspension, it cradles the electric motors and rear differential.
The differential and electric motors reside in a common housing. Imagine a regular ring and pinion diff, with power coming in through the pinion shaft. Now imagine that shaft being long enough to punch through the back of the differential housing and out the other side. Place one electric motor on the front and the other one on the back and you have the Fisker power unit.
Both motors act as one, turning the pinion shaft together. Any differential action required is meted out with gears in the usual way. Yes, it is a limited-slip diff.
Also, these are motor-generators, meaning they generate electricity to plow back into the battery under deceleration.
Pretty neat stuff.
The Fisker's pedestrian warning system makes noise at the back of the car, but these rear bumper inserts are fake speakers.
The real speaker is hidden dead center under the rear bumper, close to the rearmost of the two electric motors.
Four-piston Brembo calipers do the braking chores in back, but, like the front, they don't do much until the regenerative braking system tops out at 0.25g of deceleration.
All of this interesting hardware rides around on meaty Goodyear Eagle F1 Supercar rubber. Up front you'll find 255/35R22 W-rated tires on 22-by-8.5-inch rims. The rears are 285/35R22 on 22-by-9.5-inch wheels. I still don't have a scale at the shop, so I can't tell you what they weigh. I know, I know.
I didn't know what to expect before I put the Karma up on our Rotary lift, but after doing so I think they really have something here. I really have to hand it to them. None of what we've seen is parts-bin stuff. They really have designed an entire car.
Yes, it's heavy. But it is a couple inches shy of 200 inches long and is over 78 inches wide, which makes it slightly shorter and somewhat wider than a Maserati Quattroporte. And as a plug-in hybrid it carries around two kinds of propulsion in the form of a turbocharged 2.0-liter four up front (with intercoolers, the works), a big battery in the middle and two large electric motor-generators in back. And don't forget the weight of the third generator connected to that front-mounted engine and all of the power electronics and battery cooling subsystems.
We have a pretty good idea how well it goes on gasoline and electricity, but we have yet to test how all of this hardware works when pushed to the limit. Stay tuned.