2012 Lexus LFA: Suspension Walkaround

2011 Acura TSX Sport Wagon: Suspension Walkaround

This time it's the 2011 Acura TSX Sport Wagon's turn for the suspension walkaround treatment, the first one shot in my new driveway.

As we go along, take a moment to refer back to the 2010 Honda Accord Crosstour walkaround. Apart from the TSX's obvious lack of AWD, there are many similarities in the overall suspension layout and the basic look of the various bits and pieces. Some of the parts may in fact be shared, but it's quite likely that many are not.

That's because the TSX Sport Wagon is smaller and more svelte than a Crosstour. Our TSX Wagon is 2.3 inches narrower, 7.8 inches shorter (less tall) and 7.4 inches shorter (less long). Its front and rear track widths are 2.7 inches narrower and it rides on a wheelbase that's 3.6 inches shorter. Our Sport Wagon weighs some 282 pounds less, too.

Let's take a look.

Just like the Crosstour, the TSX benefits from double wishbone front suspension. The upper wishbone (white) is a high-mount A-arm, while a forward-facing L-shaped arm (green) does the business down below. A coil-over spring and shock assembly (orange) keeps it all suspended at the proper height.

Sometimes this type of coil-over is mis-identified as a strut, but that's utterly incorrect. A strut is a specific type of beefy shock absorber that also locates and secures the upper working end of the suspension, doing away entirely with the need for an upper arm. Here, with an A-arm doing the location management, this shock absorber is just a shock absorber, a non-locating suspension member that literally puts a damper on things lest they get out of hand. The fact that it carries the spring, too, is not the defining characteristic that would make it a strut.

The TSX uses a forward facing L-shaped lower wishbone/control arm. Lateral loads are taken up by a fairly rigid rear pivot bushing at the crook of the "L".

A softer forward bushing absorbs the fore-aft component of things like pothole strikes, which come into the control arm at the ball joint (black). That force amounts to a torque that pivots around the harder rear bushing, sending the energy to the forward bushing as a momentary lateral deflection.

The upper arm can be made of thinner material on account of the leverage afforded by its high-mount position. As is customary, its pivot axis inclines up in the direction of the front of the car to enhance anti-dive characteristics under braking.

Like nearly all front-drive cars with transverse-mounted engines, our TSX settles for steering that comes in behind the axle centerline. The engine and transaxle occupy the space ahead, resulting in a strip of available space between the engine and the firewall.

We're peering down into that space from the engine compartment, and what we see is a rack-and-pinion unit with electric power assist working directly on the rack itself. This is preferred from a driver's perspective, as the shafts and u-joints of the steering column itself retain a bit of unmasked mechanical feel.

This is also a better way to go for durability because the assist is downstream of the rack and pinion mesh point. Column-mounted EPS acts upstream, resulting in high loads on the gear teeth as the full brunt of the power assist feeds through the pinion teeth.

Lightweight cars can get away with column EPS because the assist loads aren't terribly high; something like a Ford F-150 has far higher steering loads and must use rack-mounted EPS.

The coil-over shock absorber employs a fork (yellow) that splits the load path in two and diverts it around either side of the drive axle, terminating at a bolted joint at the lower control arm. The connection itself sits inward from the lower ball joint, which results in a motion ratio for the spring and shock that's something less than 1-to-1 from the tire's perspective. Looks to me like it's 0.7-to-1 or thereabouts.

The TSX's stabilizer bar link connects to the lower arm (yellow) at a point even further inboard than the spring and shock. An apparent motion ratio of 0.45-to-1 results, which means the stabilizer bar itself (green) is thicker and heavier than it would otherwise need to be for the same roll stiffness if it had a motion ratio closer to 1-to-1.

Engineers know this stuff very well, but packaging considerations oftentimes run the show.

Press on the TSX's brake pedal and you'll be squeezing one-piece ventilated cast-iron brake rotors with single-piston sliding brake calipers.

In case you're new to the walkaround, here's the skinny on sliding (aka floating) brake calipers. Basically, the hydraulic piston rides inside a caliper body that slides on two pins. Little bellows keep the sliding surface clean and retain the grease within.

When you press on the brakes the piston is hydraulically pushed out (yellow) against the inner brake pad, which promptly contacts the inner face of the rotor. At this point it can go no farther, so the floating nature of the caliper and the principle of "every action has an equal and opposite reaction" conspires to send the caliper body itself in the opposite direction (black) instead.

But the caliper body has fingers that wrap behind the outer brake pad, and before long these pull the outer pad up against the outer face of the rotor. In case you lost count this is the point at which both pads are gripping the rotor, the point at which braking begins

All of this happens very quickly because the clearances involved are tiny; the two-step nature of the process is not readily apparent in most cases. The lion's share of the sliding happens gradually over time as the pads wear down and the at-rest position of the caliper shifts inward.

The TSX's rear end rides on a multilink setup. An upper A-arm locates the top while two lower links (black and green) locate the bottom. A short toe link (white) keeps the wheel pointed in the right direction.

This view from below shows how the two lower links (yellow and green) approximate a lower control arm. Also, the shortness of the toe link (white) relative to the rear lower link (green) is there to create a stabilizing dose of roll understeer. When compressed together the toe link's tighter arc pulls the front of the wheel inwards, a trait that is especially useful when the outer tire's suspension loads in a corner.

The rear stabilizer bar (green) comes in from behind to meet up with its short drop link.

Another view of the same stuff, but here the aluminum knuckle is more visible.

We haven't been able to clearly see the attachment points for the coil-over shock (yellow) and the stabilizer link (green) and this view is only slightly better. The important thing to note is that both connect directly to the aluminum knuckle, which means they move in lock-step with the tire at a 1-to-1 motion ratio.

Also, the toe link (black) sports an eccentric cam on its inner end for easy toe-in adjustments.

The coil over mounts high in the fender, which means it needs a pretty big shock tower to live in. This isn't a bad plan for a sedan, but it takes a bite out of cargo space in a wagon. It's no wonder the Acura TSX and Honda Crosstour suffer a bit in the cargo department.

Solid cast-iron rotors and a single-piston sliding caliper handle the stopping chores at the back end.

The rear brakes are of course hydraulic, but the parking brake function is energized by a cable and lever (yellow) that actuates the piston mechanically.

Hey, look -- I found my scale. The TSX wagon rides on 225/50R17 Michelin tires that come mounted on 17-by-7.5-inch aluminum alloy wheels. Together they weigh 46 pounds -- about average for OE hardware in this size.

The term "Sport" in the name raises expectations in the minds of some enthusiasts. The 2011 Acura TSX Sport Wagon is not something you'd want to autocross, but its suspension works from a design and concept standpoint. As is, it's a comfortable and well-mannered wagon that is fun and entertaining to drive in the civilian sense. A set of stickier tires and perhaps some mild aftermarket tuning bits would likely make it come alive.

Dan Edmunds, Director of Vehicle Testing

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