Discussion Starter · #1 ·
I am a bit dissapointed in the brakes. For such a large car the front brakes look small. It was very interesting to see how the PAWs system works though.
2014 Acura RLX Suspension Walkaround
More Than a Dressed-Up Accord
A quick glance at the 2014 Acura RLX may cause one to believe they've just seen a dressed-up Accord with an Acura badge, but there's got to be more to it than that, right?
For one, its basic dimensions are all larger. Remember, Honda doesn't have a larger sedan in its U.S. lineup beyond the Accord, unlike Toyota, which has the Avalon. Honda seems to have decided to put an Acura badge on its larger sedan.
Compared to the Accord, the 2014 Acura RLX is 4.7 inches longer overall, has 2.9 inches more wheelbase and stands 1.6 inches wider. And its front and rear track widths (64.3 and 64.2 inches, respectively) are 1.5 inches wider than an Accord.
This last point is of interest to us because of our suspension-centric worldview. With curiosity piqued and a Rotary two-post lift standing at the ready, there's only one thing to do.
Let's lift it.
It is readily apparent that the 2014 Acura RLX differs from the 2013 Honda Accord in the very first photograph. Here we see a high-mount upper control arm that is commonly used on modern double-wishbone front suspensions. If this were an Accord we'd be staring at a MacPherson strut.
The high-mount upper control arm surrounds a coil-over spring and shock assembly. Acura says the front and rear shocks are "Amplitude Reactive Dampers," which sounds like something electronic but isn't.
I don't know the exact internal details of the valve design here, but there are many ways to mechanically alter the damping based on the actual (or expected) displacement of the shock in response to a given road input. It comes as no surprise that there's nothing external to point out here.
The double-wishbone characterization starts to fall apart when we look down below because here we find two distinct links, one of aluminum and one of steel, instead of a single L-, T- or A-shaped lower control arm.
Each of the two lower links attaches to the knuckle through its own ball joint. The steel one is the forward-pointing tension link and the aluminum one is the lateral link.
There isn't really a good agreed-upon name for this layout. Acura nominally calls it a double wishbone because conceptually it is structured like one and mechanically it behaves like one until you crank on the steering wheel.
Others call this "double wishbone with a split lower arm." This is a mutually exclusive combination of words that I nevertheless understand completely despite knowing full well that a wishbone is a one-piece structure until after Thanksgiving dinner is finished. I found one paragraph in Acura's press kit that calls it a "double wishbone, double pivot" suspension, which makes a kind of sense if you're looking at a photograph like this one.
Whatever you call it, dual ball joints such as these improve the steering geometry by moving the lower steering pivot point outboard of where it could never hope to be if only one ball joint was present. The idea is to move the steering axis closer to the center of the tire contact patch in order to reduce the so-called "scrub radius."
Many steering-related benefits spring from this. Chief among them on front-drive machines such as this is the near elimination of torque steer, which is a good thing if your 3.5-liter direct-injected V6 makes north of 300 horsepower.
But dual ball joints and dual links cost money. The 2014 Acura RLX starts at $48,500 and tops out north of $60K, so the justification to spend in this area was there.
In case you've been wondering why the steel front tension link (yellow) has that massive curve to it, here's your answer: It provides clearance for the front tire at full lock. Meanwhile, check out that nifty aluminum front subframe (black.) Looks like the oil filter might dribble on it a bit, though.
As in all other front-drive machines with sidewinder engines, the RLX's steering (yellow) does its work from behind the front axle centerline, and the stabilizer bar (green) runs right alongside.
Nearby, the lower end of the coil-over spring/shock assembly connects to the lateral link via a two-tined fork (black) that surrounds the front drive axle.
The RLX employs a hefty 33mm front stabilizer bar, but it has to be large because the motion ratio that results from its connection point midway along the lateral link is no better than 0.5-to-1, maybe less. Further out, the coil-over's motion ratio is closer to 0.8-to-1 or thereabouts.
The stabilizer bar's connecting link is curled like a pig's tail to get where it needs to go in tight quarters.
A look at the tension link's forward mounting point. The aluminum front subframe is of the perimeter variety that completely encircles the lower reaches of the engine compartment and carries the weight of the engine and transmission in addition to its steering and suspension locating duties.
The 2014 Acura RLX uses single-piston sliding brake calipers up front. The bolt-on logo plate seems to serve no other purpose than to make it look like a racier monoblock caliper to the casual observer. Acura isn't the only one involved in this sort of fakery: I saw a Mercedes-Benz C250 on the road this very morning with the exact same sort of factory-installed single-piston sliding caliper "jewelry."
Like or lame?
The 12.3-inch front rotors have the usual radial vents beneath the clamping surface, and there are additional vent (and lightening) holes down by the hub and wheel bearing.
Acura describes the rear suspension with the rather non-specific term "multilink," but we can see from here that the upper end, at least, is located by an A-shaped wishbone. We expect to see three more links down below.
The coil-over spring/shock assembly is pretty fat up top, which isn't the best approach in terms of trunk space encroachment. Depending on the audio system option you choose, the RLX offers 15.1 or 15.3 cubic feet of trunk volume. Not bad, but not fantastic either.
The coil-over shock (yellow) attaches to the upper wishbone, which makes room for the drive axles of the SH-AWD hybrid version that's coming later. But in this view the lower links are still not visib.... What the heck is that?
"That" (green) is an active toe link. Our 2014 Acura RLX is equipped with PAWS, another in a long line of odd Acura acronyms that stands in this case for Precision All-Wheel Steering. Apart from heavy equipment and forklifts, rear steering systems only move the wheels in or out a tiny amount, which means the usual sort of steering rack isn't a strict necessity. PAWS moves plus or minus 2 degrees per side (about the same as others) but it turns out, a pair of active toe links such as this can easily manage that slight amount of movement with precision.
Meanwhile, the RLX's two lower links (yellow) locate the lower end of the suspension knuckle in the usual way.
The small displacement of the PAWS actuator is reflected in the small size of its bellows (yellow.) Of course, when alignment time comes along you still adjust the static toe-in the same as usual, with an eccentric adjusting cam (green) on the inboard end.
The unit contains a fast-acting electric motor and gearset, and each actuator weighs about 7 pounds, half of which is counted as unsprung weight. If they ever build a version without PAWS they could easily substitute a pair of garden-variety fixed-length toe links here instead.
I drove the system in Japan on an Accord test mule a few months ago, and it was very effective at curbing understeer and adding stability under braking. Unlike other rack-based rear-steer systems, this design can toe both wheels in at the same time if the need arises, such as hard braking. On a small handling course at Honda's proving ground, the Accord PAWS mule was indeed very stable under heavy braking.
And that was the case even while braking into a turn. Because left and right aren't forced to move in lock step, one can imagine other sorts of subtle variations to the left and right steer angles in all kinds of situations. The understeer solution can be layered atop the braking solution, for example. This independent rear steer approach really does open up a lot of possibilities.
Here's another potential advantage that goes with the actuator-based rear-steer approach: Acura was able to leave the toe link in the forward position it seems to prefer.
In a recent suspension walkaround of the Lexus GS 350, we saw how Lexus had to locate that car's toe links behind the rear axle centerline to clear a path for its optional rack-based rear-steer system. It's hard to know for sure, but if Lexus hadn't decided to offer four-wheel steering, it may not have moved the toe link to the aft position after all.
The 2014 Acura RLX model lineup will soon include a SH-AWD hybrid model. The spring and shock may be high up out of the way, but the rear stabilizer bar on this front-drive RLX cuts right through the middle of things and will most certainly be routed differently on the SH-AWD hybrid to make way for the drive axle.
Rear braking chores are handled by single-piston sliding calipers and 12.2-inch solid rotors.
Entry-level RLXs come with 18-inch wheels and tires, but this loaded example is fitted with Michelin Primacy MXM4 245/45R19 extra-load all-season tires on 19-by-8-inch aluminum alloy rims. Together they weigh 58.6 pounds, which isn't terribly overweight for a 19-inch factory setup of this size.