2009 Infiniti FX50S: Suspension Walkaround
April 24, 2009
I don't want to overload you people on this stuff, but the 2009 Infiniti FX50 is the Car of the Week, so I have no choice.
Since Infiniti is a branch of Nissan (gasp!), you'll see quite a bit of similarity between this and the Nissan 370Z I reviewed recently. Some parts even look interchangeable.
The FX series vehicles are rear-drive based, but ours has all-wheel drive. LIke the Z, it uses a double control arm suspension, with a high-mount upper arm. The upper ball joint (green) and the lower ball joint (yellow) define the steering axis (yellow line).
A coil-over spring/shock assy (coral) attaches to the aluminum lower control arm (red). But, because front drive is involved, it attaches via a fork that splits and straddles the front drive axle, instead of being directly mounted, like the RWD Z-car.
The large front stabilizer bar (white), attaches about midway along the lower control arm via short link (sky blue).
The stab bar and the front bush of the lower control arm (LCA) attach to an aluminum subframe that is direct-mounted to the chassis (purple) with no intervening rubber bushings. This makes steering and handling more precise, but it doesn't bode well for ride and NVH plushness. Infiniti apparently assumes that FX customers don't have those things as their top priority, so they've taken the direct-mount approach.
And you can see that the FX50 has 4-pot fixed brake calipers that have easily-removed pads, a la STI.
Here you can see the entire L-shaped lower control arm (black) and the other solid mount for the aluminum subframe (yellow).
The rear-mounted steering rack's tie rod end (red) attaches to an aluminum steering arm that is part of the front knuckle/hub carrier (green). The thickness of the carrier at the green arrow and a front brake rotor with a shallow hat depth (purple) indicate to me that the wheel bearing concealed inside is deep set. And this makes is likely that the steering axis hits the ground quite close to the center of the contact patch, producing a small (though probably still positive) scrub radius.
The rear pivot bushing for the LCA employs a unique floating design that bolts directly to the body (orange) and is steadied by a steel crossmember that spans underneath the car.
Here is a view over the top of the tire to the upper ball joint. You can also see the amount of anti-dive built in by the angle it sits at.
There isn't much space between the tire and the knuckle, so oversize replacement tires are tricky business and any aftermarket wheels need to have the correct offset. I wouldn't advise this route anyway, because the standard 265/45R21 Dunlop tires and 21 x 9.5" enkei alloys wheels weigh enough as it is. Care to guess how much?
73.5 pounds on my bathroom scale. Each.
Dubs are silly. That's a lot of unsprung mass for a suspension to deal with. Aluminum suspension bits aren't necessarily a performance enhancer in this case--they're just about required to offset those porky dubby-ones. And the low-profile rubber doesn't help much either--there isn't a lot of sidewall to take the edge off of, well, edges. Make sure you go on a decent test drive that includes railroads tracks or tortured asphalt before you sign the sales contract.
Onto the rear suspension, a multilink affair with a y-shaped upper control arm (green) and 3 links (yellow, black, and another that is not visible here.) A steel subframe carries the suspension, and it is mounted to the body via rubber bushings (light blue).
The final link is made of steel (yellow) and the hub carrier (green) is made of aluminum.
But things start to get weird over here on the left (white) where the bloated link that carries the spring pivots.
This FX50S has rear steering in a kinda-sorta way. An actuator (yellow) shifts the two inner link pivots (green) together in the same direction to generate a few degrees of rear steer effect.
On the G37, it's portrayed as a performance option. But I stongly hated it when driving a G37 with this option on the track. I like to use a well-timed lift to boot the tail out slightly to prevent understeer on corner entry, but the computer sees this as an impending loss of control and intervenes with this actuator to negate my efforts. And I could not turn this feature off on the track.
We got along fine as long as I thought of it as an enhancement to stability control in non-track situations. No one's "tracking" an FX50 (or at least I hope not) so this shouldn't be a point of contention.
It may or may not do some tricks in low speed parking situations, but I didn't notice any super-human parking abilities. What I noticed instead was an occasional "klunk" during low speed change-in-mind changes of direction. Perhaps I confused the system, or perhaps the noise was something else entirely.
The rear stabilizer (green) looks pretty stout. The link (yellow) only attaches miday along the upper y-arm, but the stab bar's arm (green) is short, so a little suspesion arm movement still generates a decent amount of anti-roll torque in the bar.
Finally, we come to the shock absorbers. The yellow circle shows that these are Sachs CDC units (computer-controlled damping); the actuator is shown by the green arrow. All four are similarly adjustable, but the rear was the easiest one to photograph. I'll go into how this works another day: it deserves its own post.
And for those of you who don't want to believe that an Infiniti is a gussied-up Nissan, I give you this Nissan label, circled in red (or is it scarlet?)
Dan Edmunds, Director of Vehicle Testing @ 12,022 miles