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.
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.
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.
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...
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).
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.
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.
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.
The Audi S5 uses single piston (yellow) sliding calipers with a unique two-piece design.
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.
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.
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.
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).
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.
There's barely enough room among all of these convolutions for the rear shock absorber's damping force adjuster.
Like the front, the rear suspension has a position sensor (white) that feeds into the damping-control computer.
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.
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
ktinsd says:
09:50 PM, 07/10/09
What an immaculate lift! It's great to get the direct from below angles.
ssaxsma says:
10:43 PM, 07/10/09
The rear parking brake is actually not activated by solenoid, but rather by a small electric motor acting through an innovative planetary gear reducer with an approximately 150:1 ratio which then pushes the piston against the disc. I know, because I was part of the team at TRW that designed it.
shaddai says:
12:48 AM, 07/11/09
Awesome. Now I have to take off a wheel or two to see how it compares to my B7 S4.
cruiserhead1 says:
07:59 AM, 07/11/09
shaddai,
looks similar up front but the rear suspension is revised quite a bit compared to the B7.
Dan,
Really enjoy the suspension walkarounds. They are interesting and allow one to view how the money is spent where consumers typically do not look.
ddoouugg says:
09:43 AM, 07/11/09
Why are stabilizer bars always so curly and spagetti-like?
zcalvert says:
10:00 AM, 07/11/09
Love these posts...makes me really want to take the wheels off my GTI
One request: since you're using a lift, any chance of wider-focus pics of the underside of the car as a whole? I like seeing the bigger picture and the "cleanliness" of the drivetrain/exhaust/suspension layout.
hondacura4 says:
01:09 PM, 07/11/09
"Really enjoy the suspension walkarounds. They are interesting and allow one to view how the money is spent where consumers typically do not look."
Cruiserhead, unfortunately, a lot of people simply just say "that car is overpriced" without looking at the details that make it pricey. The overpriced word is used a lot in regards to the German manufacturers, however, (depending on model) the same can be said for all manufacturers.
In terms of suspension layout, sure... 2 cars may have double wishbone suspensions but it doesn't mean both are executed the same way or that both used lightweight and/or exotic materials. Of course using the latter would drive up the price substantially and of course be passed on to the consumer.
I'll use the NSX as an example as numerous people have said the car was overpriced yet failed to understand WHY it was so expensive.
Gordon Murray stated:
"Both the body and suspension are aluminum, and it probably couldn’t be helped that journalists’ attention has been focused on praising the aluminum body. However, the suspension is the much more impressive use of aluminum."
It’s lightweight, tough, yet compliant. Also contributing to the refined NSX’s handling and ride quality are 17 inch wheels and tires that are not overly large. The NSX’s suspension is truly an ingenious system, and back then I imagined the development costs must have been ENORMOUS. To achieve that unparalleled accuracy and superior ride quality, longitudinal wheel movement is allowed via the use of a compliance pivot.
Compliance refers to when you travel over a bump, the tire experiences a longitudinal force, which the tire and suspension must move with and absorb the shock. The pivot couples the upper and lower arms. It is connected to the arms via ball joints so that they move as a unit. When encountering input, the pivot rotates, keeping alignment changes to near zero while retaining compliance (see diagram). The inspiration obtained from this NSX suspension system would later influence the development of the McLaren F1’s suspension."
The details didn't stop there as the parts that made up the suspension system were beautifully crafted and unexpectedly pleasing to the eye. Yes, the NSX was expensive but details and execution of this level aren't cheap.
To add to that, the seat frames were aluminum and the suspension was forged aluminum not cast.
NSX rear suspension cutaway:
http://www.nsxprime.com/FAQ/General/modelinfo/jp02-22.jpg
NSX front suspension cutaway:
http://www.nsxprime.com/FAQ/General/modelinfo/jp02-21.jpg
actualsize says:
09:56 PM, 07/11/09
@ssaxsma - thanks for setting me straight. I should have caught that. That's what I get for posting a blog late at night.
@ddoouugg - stabilizer bars have to take what space is left over after the suspension arms, springs, shocks and drive axles are laid out. Stabilzer bars aren't bothered by such bends, so they can slip in from almost anywhere.
kingkhalas says:
09:48 PM, 07/12/09
Note total lack of rust compared to challenger
tryan says:
04:20 AM, 07/13/09
Dan;
Another great walkaround, and what a beautiful shop Sevan has!
Not surprisingly similar material choices as compared to the M3, yet it seems much more elegantly executed (the rear suspension mostly)
I agree with most of the comments about 'where the money goes' for relatively expensive cars like the S5, but most people wouldn't care about or notice the practical advantages of such exotic manufacturing, at least beyond bragging rights. This is especially true in the case of the A5/S5, whose main selling point is its style - which is wholly unaffected by what material the suspension is manufactured from.
tonkatoytruck says:
07:34 AM, 07/13/09
Thanks for a GREAT article. One of the best I have read in a long time. I think we should see more technical articles like this, more often. I realize it takes a gifted and knowledgable writer, something one does not see too often, IMO. But, there are readers like us that appreciate and can fathom the details and technical aspects and appreciate them.
Keep up the good work and I hope you encourage your staff at Edmunds to write more articles like this. Suspensions, engine valvetrain control, and electronic computer control is where it is at in today's cars!!!!
stingray454 says:
09:07 AM, 07/13/09
For some reason, the S5 really looks bad (not in a good way) sitting on the lift with no wheels on. Looks like a large Camry Solara from the side. Perhaps much of the S5's good looks are actually from the wheels?
hurls65 says:
09:45 AM, 07/13/09
Dan...
Love these walkarounds, by far my favorite feature on the blog. (I'll repeat myself that I hope you throw the A4 Avant up on the lift as well, as I'm curious about how much of that expensive aluminium made it downmarket to the A4 platform).
The lift made it even better, and the bigger pics are a bonus too. This is car porn at its best!
areitu says:
12:49 PM, 04/16/10
I thought I was looking at a Honda Accord for a second, with the wheels off. As elaborate a setup as this is (and expensive to repair when the balljoints need to be replaced) what is the purpose (with regards to handling, roadholding etc) of having the virtual upper and lower axis?
praeceps says:
07:54 PM, 05/11/10
Damn, no wonder the S5's ride is so so responsive yet comfy. More expensive, but you're paying for something better. I like it.