I don't want to overload <Rush> you people </Rush> 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.
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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
estreka says:
05:16 PM, 04/24/09
I'm confused more by the color selection than the complex geometry.
subytrojan says:
05:17 PM, 04/24/09
Give Dan a raise!!!
trjnflip says:
05:18 PM, 04/24/09
Your suspension articles have been really great. How about including some underbody and engine bay pictures and explanations?
actualsize says:
05:41 PM, 04/24/09
I hear you estreka. Just know that the colors only apply to the photo directly above. I have to change them around because the available contrast changes in subsequent shots. I'm still tweaking this.
carlisimo says:
05:43 PM, 04/24/09
Thanks, I love these.
If I were you I would draw letters next to the arrows, in the same color as the arrows. Then you could just refer to 'A' instead of 'burnt mauve' or whatever.
greenpony says:
08:03 PM, 04/24/09
Coral? Are you sure it's not salmon? Or peach?
Other than that, great article. I like learning things, and all these detailed posts on suspensions and brakes are very informative. Can you post anything about a live axle (Jeep, truck, Mustang), or FWD suspension, or the Smart?
CycloneRcr says:
08:39 PM, 04/24/09
These are great, informative articles. I really enjoyed reading that recent post of yours. Fantastic job, keep them coming!!
BTW, I don't see any problem with color arrowing, it's just very clear!
billt9 says:
09:29 PM, 04/24/09
color arrow is definitely better than A B C D.
If only you could put the colors in the description text too.
This suspension setup is freakin complicated. Good thing suspensions last the life of the car.
nasag03 says:
09:41 AM, 04/25/09
i'm loving these suspension walk-arounds and technical overviews.
can you go a little more into detail and talk about virtual swing arm length, scrub radius, kingpin inclination, castor, camber, and toe and talk about how these all affect handling.
it's been about 6 years since my vehicle dynamics class at A&M, so a refresher would be nice!
jwfisher says:
01:00 PM, 04/25/09
This is a great series and thanks for a very thorough job.
However, one thing missing is adjustability. Enthusiasts need toe and camber adjustment capability for performance events and apparently the "new" FM platform still doesn't have camber up front. This was a major problem in the old Z and is apparently still the case in the 370Z.
Can you add discussion of adjustability or lack therein in your articles? Thanks!
-jeff
DrivingEnthusiast.net
cx7lover says:
07:33 PM, 04/25/09
I want to see the SX4 or some other basic car's suspension wrkins.
trjnflip says:
09:26 PM, 04/25/09
How about posting the suspensions of the GTR and R8?
kevinlch says:
11:26 PM, 04/25/09
wow, i'm impressed!
Impressed by both the design of the suspension and your article. You should have your own column just to talk about technical stuff of cars.
cruiserhead1 says:
03:09 AM, 04/26/09
Looks like Nissan has reverse-engineered a lot of Audi's. If you have to copy, copy the best
wobbly_ears says:
08:30 AM, 04/26/09
Love these posts Dan!
I wish you guys would do this with every LT car you have. Infact, I really want to see the suspension details of the GT-R, M3, 7er & Genesis.
Better yet, can you do a side-by-side comparo?
wobbly_ears says:
08:35 AM, 04/26/09
I agree with Subytrojan, Dan needs a big raise! His posts bring this blog to a whole new level of sophistication.
Great job dude!
athens says:
04:15 PM, 04/26/09
"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?)"
Any more than Corvette is a "gussied-up" GM-Chevy or Audi is a "gussied-up" VW (with VAG insignia)?
bbechtel16 says:
09:00 PM, 04/26/09
"wow, i'm impressed!
Impressed by both the design of the suspension and your article. You should have your own column just to talk about technical stuff of cars."
I agree! It would be a chance for you guys to make up to us for taking away from Karl's postings.
Below is a repost of the comment I just made on the 370Z article, for fear of it being missed since it's old:
>"After reading a previous write-up about front
>caliper placement, I've been wondering why the
>Nissan FM platform cars, such as the Z and the
>Infiniti G35/G37, have the calipers on the
>leading edge, indicating the steering rack is
>behind the front wheels.
>Since the FM is rear-wheel drive, I wondered why
>Nissan didn't choose the front attachment point,
>which should allow for better steering dynamics.
>I suspect it's because the FM is also the basis
>for the Infiniti FX, which is all wheel drive.
>Or is there a different reason?"
>I have the same question. Glad I just happened
>to stumble on this! I was actually looking for
>the long term page for the Smart. Anyone have
>linkage?
bbechtel16 says:
09:07 PM, 04/26/09
I think I also need to mention that my 215/45-17 wheel/tire package weighs about 35 pounds per corner :-) My suspension design however...not exotic by any means :-(
tryan says:
03:41 AM, 04/27/09
As I said previously, I think these technical articles definitely distinguish Edmunds from the mounds of other online publications. I would even venture to suggest they deserve their own blog...
Good job Dan! Engineers and non-Engineers alike thank you!
dougtheeng says:
06:07 AM, 04/27/09
Great article. I'll second the commenter above who asked for this kind of walk around of other parts of the car - engine, underbody, etc. I think they would be well received.
vvk says:
06:38 AM, 04/27/09
Even underneath these things are ugly.
73.5 lbs per wheel?! Wow, that's just idiotic.
What is the point of being able to change the pads without removing the brake caliper? You need to remove it to change the brake rotor anyway... Some people will try to save money by changing just the pads but that is extremely ill-advised on high performance cars.
Dan, thank you very much for your review. I really enjoyed it!
rick8365 says:
06:40 AM, 04/27/09
Great stuff .... thanks!
trackwrex says:
07:21 AM, 04/27/09
great article and breakdowns, dan. i enjoyed this.
actualsize says:
08:06 AM, 04/27/09
Thanks. I appreciate the feedback...and the enthusiasm. It's hard to judge how much tech people can take before they lose track and lose interest.
We've talked internally about underhood versions of this, and we're working towards it. But we need regular accesss to a real 2-post vehicle lift to get the cars up where we can see and photograph stuff. We can't get at everything we want to talk about from the top.
Suspensions, on the other hand, are fairly easy. I just pull a wheel off and it's all right there--in my own driveway, with my own jack and tools.
wobbly_ears says:
08:21 AM, 04/27/09
Dan, I think you guys know that many regulars on these forums are more knowledgeable than your average auto buyers. As an engineer, I can say that nothing interests me more than understanding how something works rather than it looks. And if someone is willing to dirty hands rather than me, I'll be happy ;)
A few posts like this interspersed between 'Waah, the navi gave me wrong directions!! CTS sux!' crybaby posts can strike a nice balance. After all, we all need flamewars once in a while.
Now, stop wasting time & get to work & show us that suspension on the car of the week CTS.
crowb says:
08:40 AM, 04/27/09
Yeah, Dan, these posts are great!
I saw that someone else asked you guys to post other walk throughs of the rest of what's going on under the body and in the engine bay.
I'd like to second the engine bay walk through especially? Just a general description of what we're looking at on an engine/transmission and the accessory systems. What's doing what, what's controlling what. That sort of thing.
I think that would be very informative as well.
joefrompa says:
08:40 AM, 04/27/09
I was really curious to see this post, as I wanted to see if I could "see" the suspension being beefed up to handle some modest off-roading (i.e. not rock climbing).
It appears to be like the front suspension components and links appear "thicker" than usual. Could just be a visual effect.
The rear looks alot like the other Nissan product recently examined...
I realize this is supposed to be a on-road SUV. I'm just curious to see what items are "beefed up" on a vehicle that expects to see some more off-roading than a car.
That tire/wheel weight is absolutely obscene. 55 pounds would be more reasonable, IMHO.
wobbly_ears says:
08:48 AM, 04/27/09
I wish this suspension walkthrough was done when they had that Jeep Wrangler! Talk about time travel!
roadburner says:
05:53 PM, 04/27/09
I hated to see BMW move away from fixed calipers(although they are back on the 135i). I could change the pads at all four corners in less than 30 minutes.
chriso59 says:
10:11 AM, 04/28/09
Dan, I'm really enjoying these walk throughs! Keep up the good work!
mashal says:
04:22 PM, 12/ 8/09
Great Article. As a mechanical Engineer it helped me a lot. I have an FX50s, and i wanted to ask you about that "klunk" you mentioned. I just noticed it while parking my car into a type spot with the windows down. Everytime i turned the steering, at a specific point i heard a "klunk". I thought somethin is wrong with the car.
Can you explain the sound more...
Once again, Great job with the article.