What's so special about the suspension on the 2011 Infiniti QX56? A lot, actually. Some of it's weird, some of it's brilliant. On the weird side, it has two rear springs per side. Brilliance comes in the form of a hydraulic body motion control system that replaces the stabilizer bars, just like we saw in the McLaren MP4-12C, but in this application there's one additional advantage.
The 2011 Infiniti QX56 has a few more tricks up its sleeve because it's no longer an SUV that's been adapted from the Titan pickup platform. It now rides on the home-market Nissan Patrol, the flagship SUV in Nissan's international lineup. That alone frees up development cash for more interesting mechanical bits.
On with the show...
Up front, the 2011 QX rides on double-wishbone suspension. The lower a-arm (white) is beefy and made of welded steel. A lighter stamped steel upper arm (yellow) can be used because its high-mount location reduces the magnitude of the loads transmitted to the upper ball joint.
A coil-over front spring and shock (white) is used, and the hydraulic rack and pinion steering acts in front of the axle centerline. What's missing? We can't see any sign of a stabilizer bar or its drop link.
That's because this particular 2011 Infiniti QX56 is fitted with the Deluxe Touring Package ($5,800) which includes, among other things, Hydraulic Body Motion Control. In english that translates to "a series of interconnected hydraulic lines to generate roll stiffness instead of stabilizer bars".
It's almost exactly the same as the admittedly prettier stainless steel setup we saw a few weeks ago on the McLaren MP4-12C. Like the McLaren, a pair of hoses (white, yellow) sprouts from the top of the shock absorbers: one for rebound and one for compression. It's not quite clear which is which from outside, but my money says the white one is the rebound one.
It doesn't really matter though because, like the McLaren, the compression hose here will span across the car to the rebound side of the shock on the other side, and vice-versa. This "cross-wiring" allows the natural pressure increase on the lengthening rebound side of the inner shock to "prop up" the shortening outer shock's compression side to quell that very motion (and vice-versa).
But here's the trick that makes this system even better. The front and rear circuits are hydraulically compared to one another in a junction box (hidden, unfortunately). If the front and rear circuit pressures follow the same trend, the system knows the car is cornering with the axles and body rolling in-phase with one another, and it allows the rising pressure to quell body roll as described above.
But if the front and rear axle pressure trends are going in opposing directions, the system knows you are off-road in a frame-twist wheel articulation mode. In this case the pressure build-up is vented off to accumulators so there is instead zero hydraulic roll stiffness, a move that allows maximum "opposite phase" wheel articulation. This is a trick the MP4-12C has no use for because, well, it's no off-roader.
The ability to disconnect stabilizer bars, hydraulic or steel alike, has another benefit. The engineers don't have to deal with the roll stiffness trade-off that all off-road machines must face. A disconnect system allows the fitment of much stiffer stabilizer bars (or roll stiffness via hydraulics) for cornering than would be possible on a "normal" SUV that doesn't have such a disconnect system.
And so this QX56 corners much, much flatter than a 3-ton SUV has a right to. It's pretty damn nimble, in fact. It does not wallow. None of my passengers got the least bit carsick.
The arrows show where the two hoses make a turn and begin their journey to the other side of the car. One of them (yellow) is going into a T-junction, one leg of which runs to the back of the car.
The two hoses that cross the car are protected by this rock guard (yellow). Meanwhile, the T-junction and the pipe that runs to the back of the car (white) are easier to see here.
There's nothing odd about the brakes, though. Twin-piston (yellow) sliding calipers, albeit large ones, handle the stopping chores, and they do it well.
Here's another view of the brakes. But there's a piece missing from the axle nut, and I only just noticed it as I sat down to do this. There's supposed to be a serrated "castle" retainer and a cotter pin to catch things if the axle nut starts to loosen for some reason. This one is missing for some unknown reason. It's a backup system, and the axle nut shouldn't loosen if it's properly torqued, by the cotter pin assembly should be there nevertheless. Ooops.
Even though there's a lot to take in, the rear suspension is, in fact, a double wishbone arrangement. There's a lower wishbone (yellow), and upper wishbone (green) and ... wait ... two springs? And what's that other link (black) for, the one with the coil spring?
Yep, there are two springs. The coil spring is the primary one, but the rubber bellows that surrounds the shock tells us this is an air spring. Because it's not the only spring, it's there for load leveling, either on account of passengers and cargo or the considerable tongue weights that accompany an 8,500-lb tow rating. The use of a supplemental air spring means the main coil can be softer for decent unloaded ride comfort.
This view makes it easier to see the upper and lower (black) wishbones as wishbones. The upper one (white) is particularly difficult to see because it wraps around behind the supplemental air spring/shock assembly.
Here's yet another look at the upper wishbone (white), the lower one (yellow) and the air spring (green).
Our lower wishbone is a wishbone because it has just one lower ball joint.
With one upper and one lower ball joint, that means the massive "link" that carries the coil spring must be a toe-control link. Yep. Weird, huh? Weird or not, it seems to work.
Here's another look at it. Note how the outside pivot of the toe-control link (yellow) is close to the same elevation as the axle nut. Note also that this axle nut has the little castle-thingy and cotter pin that were missing from the front.
A rubber bump stop (white) keeps the suspension from stroking too far: X marks the spot where it makes contact with the upper wishbone (yellow).
Like the front, the rear shocks feature a pair of hydraulic hoses (white, yellow) that are cross-linked to the other side of the rear axle. Again, rebound on this side (white) goes to compression on the other side, and compression on this side (yellow) is linked to rebound on the other side.
Meanwhile, the smaller hose (green) brings pressurized air in from the compressor to the donut-shaped air spring chamber that encircles the lower half of the shock.
The compressor sits next to the spare tire and has two outlet hoses; one for each side.
Height sensors are attached to the rear toe-links to monitor the position of the rear suspension. If a computer feels than rear end is compressed too much, it adds air and increases the ride height. Air is bled out once the suspension position changes to indicate that people got out or the trailer was disconnected.
Rear braking chores are aptly handled by single-piston sliding calipers. The protruding "hat" section of the rotor is a sign of a drum parking brake within.
Infiniti is so convinced that QX56 owners in the USA will never take this beast off road that they paired these redonkulous P275/50R22 low-profile tires with that trick Hydraulic Body Motion Control system in the Deluxe Touring Package. Yes, such rubber optimizes handling and the low roll angles generated by the hydraulic stabilizer bars. But they're not something you'd ever want to risk off-road, where sidewall is king, so the off-road benefits of the hydraulic stabilizer bars in "disconnect mode" will be more or less invisible.
Off-roaders can of course rectify this by minus-sizing down to 19- or 20-inch rubber, because the brakes aren't filling all the space available within the dubby-two inch rims. It might even be possible for 18-inch off-road tires to fit over the calipers, but don't quote me on that.
None of this matters now, because Infiniti is probably right about the off-road thing for the near term. But in 5 or 10 years, when these beasts drop in value enough for real off-roaders to consider them, the minus-size strategy will be alive and well.
Oh, and these 22 rims and tires weigh in at 83 pounds apiece. That and their low profile doesn't do cracked-road ride comfort any favors. The QX56 doesn't ride harshly, but there is a slight edge to, well, edges. Too bad you can't get HBMC with the stock 20-inch rubber.
ant14 says:
09:29 PM, 10/11/10
That sounds good and all, but little does it help when it's wrapped up in a hideous package that no one will care to know much of anything about....
cruiserhead1 says:
10:01 PM, 10/11/10
The suspension tech is very interesting. It reminds me of Toyota's XREAS and KDSS systems.
The rear airbag secondary spring is a nice integration. For such a complex system, it looks surprisingly robust.
Being a truck guy, I am really disappointed that the legendary Nissan Patrol finally makes it to the USA (as this reskinned QX56) but the new design has lost both solid axles and any real 4x4 capability it once had.
OTOH, this package will probably do very well and is what most Americans want.
cz_75 says:
10:02 PM, 10/11/10
Being underneath this ugly tub is probably the best place, IMO, since you can't see the awful "styling." It's too bad Nissan doesn't offer the Patrol here - I'd rather have one of those.
questionlp says:
10:14 PM, 10/11/10
I think it'll look a bit better if it had fallen off of the jack stands. It makes me miss the still rather whalish previous generation (and it's cousin, the Armada).
93aero says:
10:26 PM, 10/11/10
kill the awful side vents, and paint it black. Over all, thats really all you can do to try n help its appearance. Such a shame such great technology is over shadowed by several tons of grotesque form.
vache1 says:
11:27 PM, 10/11/10
I'm really surprised about the missing castle caps and cotter pins. I wouldn't want the front wheel to fly off my ugly SUV at 70mph!
ocramidajzj says:
04:08 AM, 10/12/10
So I take it this is a new LT vehicle?
throwback says:
05:49 AM, 10/12/10
It does have some interesting things going on underneath, the interior is even nicely done. However, this is truly the ugliest SUV for sale in the USA, are they trying NOT to sell any?
stovebolter says:
05:54 AM, 10/12/10
Another great suspension walkaround!
I have to agree with the others - the underside is definitely the best side. I just can't see why they put those vents on the fenders - when Walmart sells them for anyone to stick on their '85 oldsmobile, it's time for the luxury marques to move in a new direction...
rsholland says:
05:59 AM, 10/12/10
@cruiserhead1:
"but the new design has lost both solid axles and any real 4x4 capability it once had."
Whatever 4x4 capability that was lost is due to the low-profile tires, not the IFS/IRS.
I just wish the new Nissan Patrol would also come here, but with higher-profile tires. I also prefer the new Patrol's styling over this vehicle's looks.
davisdvm says:
06:43 AM, 10/12/10
This thing makes a genital wart look good. (stole that from Top Gear!). How could this thing make it past the various marketing and development teams to actually be sold? thanks as always for a great analysis but I can't get past the hideousness of this vehicle. big doesn't have to be ugly, i think the Merc GL is a striking car from most angles.
carguy622 says:
07:01 AM, 10/12/10
Thanks for the suspension walkaround Dan!
I'm not even going to be politically correct... I hate this SUV. Ugly, oversized, wasteful, and 22" rims to top it all off!
ptcdawg says:
07:52 AM, 10/12/10
I can't imagine the cost of these components when they start to fail. Needless complication IMHO.
redgeminipa says:
07:54 AM, 10/12/10
They obviously never looked at the compressor under an aged Chrysler 5th Ave. Putting it underneath spells disaster in years to come, especially in the show belt. Road salt will eat that thing alive right after the warranty expires.
rsholland says:
07:55 AM, 10/12/10
It looks pretty darn good once you get inside. :)
audisport says:
08:03 AM, 10/12/10
Wow, what an absolute mess of a design! That thing is UGLY. Did those fender vents come on it or did you pick them at at Pep Boys for $6 bucks?
actualsize says:
08:07 AM, 10/12/10
@cruiserhead1: Toyota's KDSS system does use hydraulics to automatically disconnect the stabilizer bars in an out-of-phase situation, and its presence does allow the use of larger stabilizer bars for flatter cornering. But KDSS is based around stabilizer bars, weird, funky two-piece stabilizer bars, but stabilizer bars nonetheless. The hydraulics are far less grandiose and the shock absorbers have nothing to do with it. I hope to do a walkaround on that system soon. KDSS is available on the Land Cruiser, 4Runner and the Lexus GX460, maybe others.
As for the looks, I'm over being disgusted. Count me as a fan after spending a week inside the thing, where it drives like a champ (quiet, powerful, steady) and really does look good. From the driver seat, I can't see the questionable contours. And it's an SUV, for crying out loud. A box on wheels. Do any of them look stunning and exquisitely proportioned? No. Tolerable is about as good as it gets.
rsholland says:
08:13 AM, 10/12/10
^ Precisely. I'm always somewhat amused at people's comments about exterior styling (of any vehicle) when, as a driver, you spend 99.9% of the looking at the interior.
gtijake says:
08:32 AM, 10/12/10
Great stuff. I plan on coming back to this and getting my learn on when I have more time. Keep up the good work!
compressor says:
08:55 AM, 10/12/10
Dan, can you please do yourself and all impressionable readers a favor by not putting a car on jackstands that is halfway in the street. This is incredibly stupid, especially as it seems you have a driveway and this is not an emergency type repair. Though there are many things wrong with this, I'll state the major one.
- You are incredibly open to any dumb driver going down the street, or one that fails to look backing up. Jack stands won't help much when the car is pushed off of them.
cruiserhead1 says:
09:05 AM, 10/12/10
@actualsize
The KDSS system is a relatively simple system that is perfect for offroading while giving a firmer on-road ride.
Basically only two hydro pistons (giant ones) on either corner that "push down" the giant swaybars when the wheels come off the ground.
Toyota's very durable and clever solution; simple yet smart.
Toyota's XREAS is the system that uses cross-connected shock absorbers for dynamic handling. This was featured on some 4Runners.
Nissan's solution is not a copy but just reminds me of Toyota's. Obviously, Nissan has added more features and complexity. Toyota never combined KDSS and XREAS.
I like the two rear springs - doubling up allows softer spring rates as they share the load. Switching from comfort empty to towing or fully laden.
Conversely, the complexity of that rear suspension is a demerit and no one is offroading this car.
Besides the PepBoys side air vent, I think it has a premium look. Reminds me of Beluga whales and Narwhals...
actualsize says:
11:01 AM, 10/12/10
@compressor: Point taken, but please note a few things. My minivan is parked on the curb and is blocking the road on the upstream side -- oncoming cars can't get to the QX from there. This is a cul-de-sac with about 4 more pairs of houses on it -- traffic is extremely light to non-existent. The neighbors across the street are at work during the day, so they're not going to back in to anything. And, most of all, I take my pictures without actually going under the car in almost every case. I may reach under with the camera and snap off a few frames, but I rarely have to crawl under.
But yes, a car could conceivably come by a knock it off the stands. Driveways are a far better place to work on a car, especially if you're going to crawl underneath. And perhaps there's a case to be made for sliding the removed wheels and tires under the car as a backup system. After all, this is earthquake territory.
throwback says:
01:26 PM, 10/12/10
Dan I get what you mean about SUV's styling, but this monstrosity is just plain ugly.
zwiedower says:
03:47 PM, 10/12/10
The new QX56 is a masterpiece from an engineering standpoint, a huge step up from the previous QX. The Infiniti now easily out classes the Lexus LX570...
qristofer says:
07:14 PM, 10/12/10
Don't know what cool aide all these people are drinking from, but I think this car is gorgeous. I LOVE IT! My only concern as a used car buyer is how expensive all that hydraulic sh!t is going to be when it needs replacing.
cruiserhead1 says:
07:34 PM, 10/12/10
@zwiedower
I agree it is a big leap from the previous QX but I can't see how this outclasses the LX570.
I'll take the LX every day and twice on sunday over the QX. For a premium offroad capable SUV, the LX and Land Cruiser are the head of the class.
The QX will give the Escalade, Navigator and Denali a run for their money.
jdbosmaus says:
10:35 PM, 10/12/10
It's hard to see because of the splash shield, but... are those solid rear disks? On a $60k, 6,000 lb vehicle?
thegrocer says:
08:03 AM, 10/13/10
After looking at pics of the Nissan Patrol in wikipedia and Infiniti's website, I think the new QX looks way better than the old QX...maybe that's just me. Honestly, the hydraulic stabilizer system scares me less than the air suspension...Lincoln stuck air suspensions in every car in the '90s and look how that went...complete mess 10 years later.
rlyon says:
01:50 PM, 10/13/10
I saw on on the highway yesterday. It's fricking HUGE. And ugly. Not sure if it was the lady driver, or the blind spots, but she cut off like 3 people during the few miles I trailed her.
actualsize says:
05:26 PM, 10/13/10
@thegrocer: Remember, the air spring on the QX is supplemental - it isn't the primary spring so you'll never get the "Lincoln sag" even if the bags do "go out" or improperly delate. (And they're less likely to get to that point because of materials and developmental advances since then. Many semis and semi trailers use air springs.) In many of those early Ford applications (and my parents' GMC motorhome) the air bag was all she wrote, springwise. There was no primary coil spring like the QX has. Huge difference.
actualsize says:
05:30 PM, 10/13/10
@rlyon: Probably inattentiveness, poor judgment or cell-phone related. I found the visibility to be pretty decent compared to its size.
irvg37 says:
09:39 PM, 10/13/10
these technical entries are really, really awesome.
crashcanadian says:
03:12 PM, 10/14/10
Love these technical articles. Can we get a similar one on, say, a Panamera turbo??
actualsize says:
09:25 AM, 10/15/10
Maybe. All I need first is a set of keys to a Panamera Turbo. Got any? ;)
firstwagon says:
09:05 AM, 10/16/10
Seriously cool engineering but as someone who keep cars cars and truck long past the warrantee is up all I can see is a super complicated setup that will cost a fortune to repair and maintain.
lions208487 says:
10:09 PM, 10/18/10
Firstwagon has a point, however the suspension package that Nissan provides is intended to handle rough terrain and last for a very long time. So as long as you don't abuse this Infiniti, you should not have a problem, but then again if you could afford to buy this Lux SUV, then you shouldn't be complaining about repairs.
The exterior takes some getting use to, but the interior is the most luxurious cabin I have ever had the pleasure to sit in. It's even better then my co-workers E63 AMG, and the Mercedes is top notch in it's own right.
This will be a hit in southern CA, even with the current CAFE standards. If Infiniti adopts the hybrid in the M35H and makes use of it in this Q56, then it will be a win win for Infiniti.
norm_peterson says:
01:34 PM, 10/19/10
Very interesting (and this is coming from a person who is among those least likely to ever buy any SUV at all).
I would hope that the rear suspension chassis side bushings are relatively stiff - there does not appear to be a lot of vertical separation between LCA and UCA attachment points, meaning that forces will be relatively high and bushing deformations accordingly greater. Bottom line is greater rear wheel camber change in a turn on the wheels that you do not have direct steering control over.
Putting an air bag spring to work in parallel with the metal spring looks at least somewhat similar to what Kenworth does for the drive axles on its Class 8 tractors.
Norm
digitalzombie says:
12:41 AM, 10/23/10
Sweet! Nice work Dan! I think it's... kinda cute like a Baluga whale. But styling wise could have been better meh.
ne1butu2 says:
04:15 PM, 10/23/10
So not only is it ugly, there are axle pieces missing that could cause the wheel to come off. That's just a little concerning. Given that Nissan/Infiniti trucks have been some of the most defective laden vehicles on the road, this oversight is not a minor oversight on a brand new model. We can expect a full recall on this dinosaur very soon.
actualsize says:
07:56 AM, 10/25/10
@ ne1butu2 The castle nut retainer issue is not related to assembly line quality. This was a pilot-production engineering sample/press vehicle, which means that it very likely had final-spec parts installed after assembly my non ASE-certified mechanics. I would not read too much into this from a recall perspective.
cacressida says:
03:20 PM, 10/28/10
Wasn't the 2003 4Runner introduced in 2002 with the XREAS suspension technology? The left front strut is hydraulically linked to the rear right and right front to rear left to control body roll but Toyota never got rid of the sway bar. The XREAS system never hampered off roadability when axles articulated but helped control body motions on off camber ruts and stuff. Still interesting stuff.
I'm still hooked on the good ol technology if I want my rig to be burdened by above average 4x4 duty.
nasaser says:
07:20 AM, 11/ 9/10
I don't get the comments knocking the styling, i think it looks great on the outside and inside and outclasses in speed handling braking and interior and exterior style everything else out there.
For all you Mercedes lovers, go look at the new gas mileage ratings......even the Gl bluetec only gets 21 mpg on the highway, this thing which is 2.5 seconds faster to 60 gets 20 mpg.................