2009 Audi S5: Suspension Walkaround

2009 Audi S5: Suspension Walkaround

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A lift! This week I was able to borrow time on a real shop lift, thanks to the generosity of Sevan Garabedian of Integrity Motorcar, an independent shop in my hometown of Yorba Linda, California.

Good thing too, because the fully-exposed wheelwells of out 2009 Audi S5 reveal a few unique surprises.

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At first glance, you might take the S5's front suspension for another double wishbone suspension setup with a high-mount upper arm, just like our 2009 Nissan GT-R or 2009 Nissan 370Z.

But that would be a mistake, because that upper "arm" looks a little funny from here.

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In fact, the upper "arm" isn't a wishbone at all. Instead, the arm has been split into two links, each with its own personal ball joint. We've seen this before, at the bottom end, in place of a lower wishbone. But Audi uses this setup topside, and for the same reason: it moves the steering pivot axis outboard to the point where the axis of these two links would intersect if projected out.

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You wouldn't use the dual-pivot setup at the upper-end unless you used it at the bottom, too. And so it is with our Audi S5. The bend in the rearmost arm is there to clear the wheel and tire at full lock.

All together, the A5/S5 front suspension employs four links instead of two wishbones, and all of them are made of aluminum. Audi has variously referred to this as "4-link suspension" or "5-link suspension" depending on whether or not they include the steering arm in the total. But I don't like either term, especially "5-link", because that name has been applied for years to coil-spring solid axle rear suspensions found on truck-based SUVs.

This is certainly not that.

Even though it doesn't exactly roll off the tongue, the way to think of this is "high-mount double wishbone suspension, but with split, dual-pivot upper and lower arm-substitutes that amount to pairs of links."

Or, you can simply say "5-link" and move on...

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That steering arm (orange) is mounted ahead of the axle centerline, an arrangement that improves steering precision. The stabilzer bar (white) loops over the top before joining-up with the stabilizer link (yellow), which in turn connects directly to the coil-over spring & shock assembly (green).

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But the stabilzer bar cannot be said to be direct acting, because its forces feed into the lower link just inboard of the ball joint, for a motion ratio of about 0.7:1 or so.

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Here we see the bottom end of the front shock and its damping force adjustment mechanism. These shocks employ Sach's CDC (computer-controlled damping) system. Unlike the 750i we looked at a couple of weeks ago, these have only one damping adjustment mechanism.

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Like the BMW, the S5 has suspension height sensors attached to the lower links. Their output feeds into the CDC system and the auto-levelling mechanism for the HID headlights.

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The Audi S5 uses single piston (yellow) sliding calipers with a unique two-piece design.

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Here you can see the unique two-piece caliper body, in which the hydraulic side that has the piston (white) bolts to the rigid half (orange) that wraps around the the rotor to grab the pad on the other side. The yellow arrow indicates the pin on which this assembly slides back and forth as the brakes are applied and released.

Further to the left we can see that the front subframe (black) is aluminum like the BMW M3 in order to reduce front axle weight and improve weight distribution.

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The Audi's independent rear suspension doesn't look that unusual from here. They call it "trapezoidal-link" suspension, but from here we only see the link part of that equation. There's a single upper link (black) and a toe link (white). The trapezoidal lower arm (yellow) can barely be seen.

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The upper arm (white) is not only aluminum, it's hollow. Same goes for the large trapezoidal lower arm (black). But we're still not seeing where trapezoidal comes from.

Meanwhile, a stabilzer bar (yellow) snakes its way to a stubby link (orange) that connects midway along the lower arm.

By far the weirdest piece in this picture is the large aluminum knuckle (green) that provides separate direct-acting mounting points for the coil spring and shock absorber.

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Now we're getting somewhere. The reason for the trapezoidal moniker becomes clear when we look at the non-parallel pivot axes (yellow) of this distorted h-shaped lower control arm.

And check-out the complexity of the hub-carrier/knuckle assembly (green).

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Here we car see that the h-arm attaches to the elaborate hub carrier (green) through large bushings (black and white). I don't have access to all the engineering data, but it looks to me that the rear bush (black) is quite rigid, while the the forward one (white) is somewhat softer. That allows a little give as the toe link (yellow) swings through its arc, allowing it to alter toe-in as the suspension moves up and down.

On a totally unrelated note, the rear single-piston sliding brake caliper employs an electric motor solenoid (orange) to activate the parking brake.

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There's barely enough room among all of these convolutions for the rear shock absorber's damping force adjuster.

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Like the front, the rear suspension has a position sensor (white) that feeds into the damping-control computer.

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Here's the rear suspension's urethane bump stop, atop the shock. And without a coil over spring, the slender rear shock absorber doesn't take up much trunk space. The felt fender liner material helps reduce "stone pecking" noise in the wheelwells.

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Thanks again to Sevan at Integrity Motorcar, an outfit that specializes in European car repair in my hometown of Yorba Linda, California. Hopefully we can do this again.

Dan Edmunds, Director of Vehicle Testing @ 5,289 miles

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