2009 Nissan GT-R: Suspension Walkaround
June 05, 2009
At last we come to the suspension walkaround for the 2009 Nissan GT-R. I've been holding off waiting for answers from Japan to a couple of clarifying technical questions. But I can't wait any longer. I'll point them out as we go along.
As you'd expect, the GT-R has a lot of interesting things going on, but much of it is obscured. To get at some it we'll have to take the GT-R to a real lift at a later date and remove multiple covers and undertrays that are not found on mainstream cars.
I know you didn't hear any of that because you were hypnotized by the humungous 6-pistom Brembo brake calipers and two-piece rotors. They're two piece because the rotor is pinned to a lightweight aluminum hub (black). But you need brakes like this if you're going to orbit the nurburgring in the mid 7-minute range and stop in less than 100 feet from 60 mph.
They brakes are so huge that they almost totally obscure the double control-arm suspension. But from here we can see an aluminum high-mount upper arm and the curved upper portion of the aluminum hub carrier.
We can just see the lower end of the Bilstein monotube shock aborbers (yellow) and the split fork that makes room for the drive axle on the way to the attachment point on the lower control arm (LCA).
I'll go into the difference between monotube and twin-tube dampers another time, but for now know that the single-wall construction of a monotube shock expels heat readily and provides a larger inner diameter that allows for a larger piston and valve assembly and higher gas pressures, which in turn allows them to generate higher damping forces, be more sensitive and be more resistant to cavitation (foaming).
The rear bushing of that aluminum L-shaped lower control arm is hidden behind a plastic panel, but before it disappears, it dips down to make rom for the steering rack and tie-rod ends (red). The GT-R's steering is mounted behind the front axle centerline because of the presence of front drive components and a generally crowded underhood environment. If that's the price I have to pay for twin turbos, I'll take it.
Here's a close-up of the close quarters that house the steering rack, which barely fits beneath the drive components that supply torque to the front differential. We'll have to wait for another day to strip off all the covers and undertrays on a real shop lift to show you the driveline.
Oh joy! More plastic covers. The Nissan GT-R has a lot of tight-fitting airflow management panels under the car and within the wheel wells. Here the large front stabilizer bar (white) emerges from one of them. And we get our first glimpse of the progressive rate coil-over spring (yellow) that surrounds the Bilstein shock.
This head-on view of the lower control arm shows the arm ratios for the coil over (about 0.65) and the stabilizer bar (about 0.5). The actual motion ratio of the coil-over will be lower-still because of the angle at which it leans inward.
So far, all of this is conceptually identical to the Infiniti FX-50 suspension. But the detail dimensions that represent the geometry (otherwise known as the hard points) are different, the tuning is different and I'd wager that none of the parts are interchangeable.
By now you're used to seeing the sloped upper arm that comes with anti-dive suspension geometry, so it's no surprise seeing that the GT-R has plenty of it. Look up and down the coil sping (black) to see that the coil spacing varies and that plastic shields appear on a couple of coils. Both are signs that this is a progressive-rate spring.
The weird part is the mysterious molded construction of the structural panel that the upper suspension bolts to (green). It shows mold lines and sprues as if it were cast or molded from a composite material. I'm still waiting for a definitive answer on this.
Here's a close-up of one of the attachment points for the upper arm.
Here you can see where the mystery panel bolts to the steel unibody (yellow). The top of the Bilstein shock admits the wire for the adjustable damping feature. Inside there's a needle valve that slides in and out of an orifice to vary the amount of shock oil that bypasses the valve. More bypass reduces the amount of fluid going through the valve, and that results in softer damping for a smoother ride (relatively speaking, of course). Less bypass forces more fluid through the valve and produces higher damping forces for more control.
There isn't any room for a stress bar between the two shock towers (yellow) so Nissan ran steel stiffening panels from the firewall to the frame horns, a move that accomplishes the same thing while it gives that bolt-on shock towers someplace to attach to.
It should be no surprise that the GT-R has a multilink suspension. This one has a Y-shaped upper contol arm made of aluminum (yellow) and three steel links (white, black and green). Yes, steel.
And of course if has massive 4-piston fixed Brembo calipers over two-piece rear vented rotors that block the view of most of it.
Bilstein monotube shocks with coil-over springs are used in the rear, too. The springs have equal coil spacing, which implies a straightforward linear rate.
The approximation of a lower arm is made by a trailing link that angles forward (green) and a short lateral link (white). The lateral link has a curious dent about midway along it's lower surface. At first I thought this might be rock or debris damage, but a quick check showed that the other side has the exact same indentation, which makes me think it's intentional.
Why? My theory is that it provides for controlled collapse in the event of a high-g lateral impact, like a curb strike. Not sure why the GT-R would need that, particularly, when almost no other cars have this. I suppose it might prevent subframe and unibody damage, but then I'd think everyone would do it. It might be of particular advantage in the event the damage occured at a track: a link replacement is an easier trackside fix than a subframe swap.
But I'm still waiting for Japan to tell me if my theory is correct.
The last link is the rear toe link (green) which basically makes sure the wheels point in the right direction. Like other such links we've seen, it's longer than the lower link, and that means the outside rear tire will toe in slightly as the suspension compresses, creating a touch of understeer at the rear as the body rolls in a corner (called roll understeer). After all, you don't really want the outside rear tire toeing OUT as you turn into a high speed sweeper. That's forklift behaviour, and it can lead to a sudden loss of control in a high-speed corner or an emergency lane change.
The circle indicates another view of the mystery indentation, and the yellow arrow points to a rear stabilizer bar that's skinnier than expected.
Of course it's all surrounded by aerodynamic panels.
Here's another view of that stabilizer bar (white). It mounts directly to the knuckle, via a bolt-on bracket. The resulting 1:1 motion ratio is a partial explanation for its tiny size. The shock absorber also bolts directly to the knuckle (yellow), so the dampers and springs are about as efficient as they can be, too.
The white circles show that the inner attachment points of the lower lateral link and the toe link are adjustable with eccentric cams. The former takes care of camber adjustment, and the latter allows static toe adjustment.
There's more than this. I have more shots of the brakes, tires and other assorted details, but I'll save that for part 2. Stay tuned.
Dan Edmunds, Director of Vehicle Testing @ some forgotten number of miles.