While everyone else was busy covering the Paris Auto Show, I snuck a 2011 Chevrolet Corvette Z06 over to my place for a little photo session. I took the long way home, too.
But this is no ordinary Z06. This particular Z06 is equipped with the so-called Z07 option, otherwise known as the Z06 Ultimate Performance Package. Apparently, this setup makes the car a full Z0 better.
That's because the act of checking this box represents meaningful upgrades in the suspension, tire and brake departments. Carbon-ceramics and magnetorheological fluid are added to an already-impressive materials list that includes composites, a liberal use of aluminum and more than a little magnesium.
Massive 14-inch 15.5-inch brake rotors are blocking our view of just about everything. Try not to stare. Let's move in closer and take a peek behind. They'll get their chance later.
The Z06's front suspension is of the double-wishbone variety, but it's hard to see exactly what's going on because this hard foam air deflector (green) is partially blocking our view.
What we can see includes the expected forward-mounted steering (yellow) and a large front stabilizer bar (white). No surprises here.
Peeling the deflector back reveals an aluminum lower control arm (yellow) and the stabilizer bar's short attachment link (green).
We also get our first peek at the shock absorbers (white), which are different on this Z06 because of the Z07 option. Instead of the fixed-damping monotube shocks found on a "normal" Z06, these Z07 bits are GM's Magnetic Ride Control adjustable shocks.
Most adjustable shocks work by diverting a portion of the shock oil around and away from the byzantine network of tiny passages and shims that makes up a typical damper valve stack. Less diversion forces a higher percentage of the fluid through the valve stack, which creates more resistance and makes the shock firmer, more diversion gives more of the oil an easy way out, and that makes the shock softer. Sometimes the amount of bypass is "infinitely" variable in real-time with computer controls, other applications are manually set to a specific position by the driver using "clickers" or detents on an external adjustment knob.
But MRC shocks don't work like that. Instead of altering the flow path of the fluid, they leave the valve more or less alone and vary the fluid itself. The shock oil within MRC shocks is laden with particles that respond proportionally to the intensity of an externally-applied magnetic field. As field strength increases, more and more particles align themselves with one another, increasing the oil's apparent viscosity because the magnetic field is oriented at 90 degrees to the fluid flow direction in the shock valve. Computer-control of the field strength in real-time allows the shocks to be adjusted constantly to suit conditions.
Here's another view of the deceptively normal-looking Magnetic Ride Control shocks (white) and a better view of the upper (yellow) and lower (green) aluminum control arms.
The upper control arm bolts to the frame via tie-bars (yellow) and the whole thing is reclined, indicating a healthy dose of anti-dive geometry.
What's been missing so far? The spring. Corvettes use a transverse leaf spring (yellow) instead of coil springs or torsion bars. Transverse leaf springs date back to the earliest "horseless carriage" days of motoring, but that doesn't mean they don't have a place here.
This one is about as low to the ground as a spring can be, and it's made of a lightweight composite material. The "spring seat" is a mere pin that juts up from the lower control arm. There's no need for a nut at the top because, well, as you can see, this photo was taken at "full droop" and the spring is still preloaded and fully engaged with the arm.
Also, a single composite leaf spring (yellow) can span the entire width of the car and handle the left and right sides. The same pre-load that keeps it seated against the lower arms also holds it up against the magnesium front subframe (green), so a simple pair of light-gauge clamps are enough to keep it held in place.
That's right, I said magnesium front subframe. Magnesium is used here on the Z06 to save weight (it's 2/3rds the weight of aluminum) and improve front/rear weight distribution by saving that weight on the front end. It's also an engine cradle, because the forward pair of engine mounts bolt in from above.
Add the front knuckles to the list of suspension parts made of aluminum.
Suspension position sensors measure what the suspension is doing at any given time and help the computer decide how to tweak the MRC shock system at any given time.
The Z07 option also gives our car wider wheels and tires than a standard Z06, and these rub marks (yeah, that's a functional brake cooling duct) tell us there isn't enough room left for anything more.
So if you're thinking about an upgrade to you late-model Corvette, don't go any larger than P285/30ZR19 on 19x10-inch front wheels with a 40mm offset. Mounted and ready to go, the special Z07 forged aluminum ones weigh 58 pounds -- not bad at all for what would be big REAR tires on most other cars.
OK, enough torture. Let's look at these brakes. Once again, the Z07 package ups the ante, because these 6-piston front calipers are squeezing carbon-ceramic brake rotors.
And these are the most drivable carbon-ceramic brakes we've yet sampled. Usually CCBs are grabby when cold (and by "cold" I mean most low-speed driving away from a track). Oftentimes they squeak. It's enough to make them a pain in the butt for routine street use, and we usually recommend them only when track-days are in one's future plans. But these Z07 pieces are really nice. We don't see, feel or hear the usual CCB crankiness here, and of course they really work when pressed hard. If you have the money, go right ahead.
How much money, exactly? The Z07 package costs $9,495, and for that you get the brakes, the MRC shocks, big forged wheels and Michelin Pilot Sport PS2 summer tires and beefed-up cooling. We think it's a bargain. Porsche charges $8,150 for CCB alone.
Six-piston calipers have a massive pad window, so they need some sort of brace to keep the clamping forces from prying them apart. That's where this bridge bolt (yellow) comes in. It's easily removable when it comes time to change pads.
And you'll get ample warning when the time comes because the wire just above it (orange) goes to an electronic pad wear sensor. Trust me. You do NOT want to run these pads down far enough that the backing plates start tearing up your hyper-expensive rotors.
Those rotors attach to their central aluminum hub with 10 pins that allow them to float so left/right pad pressure (and pad wear) stays equalized within the fixed caliper.
Moving to the rear, another massive CCB rotor blocks our view of the double-wishbone suspension. This time it's a 4-piston caliper, but who's counting? Oh, that's right -- I am. You are. We all are. That's what we do here.
Here are your aluminum upper (green) and lower (yellow) a-arms, as promised. The single lower ball joint means there's also a toe-link (orange), and of course there's a rear stabilizer bar (white) and its short attaching link.
Like the front, the rear spring is composite transverse leaf.
Here's a better view of the spring seat (yellow) and how it interfaces with the lower control arm.
Also like the front, the rear transverse leaf spring (yellow) spans the car and springs the left and right sides. Unlike the front, the rear subframe to which it mounts (green) is made of aluminum, not magnesium. The use of magnesium here would save a bit more weight, but it would unnecessarily contradict the effort to improve front/rear weight distribution.
Here's my standard motion-ratio shot. Left-to-right, we've got the MRC shock (0.85:1, but less because of the lean angle), the spring (about 0.62:1, hiding in the shadows) and the stabilizer bar drop-link (more or less 0.5:1).
This is a perfect example of why some wishbones are called "a-arms". Yes, the knuckle it attaches to at the pointy end is made of aluminum, too.
Are those rear cooling vents "real"? Yep. The rear brakes thank you for asking.
These wheels measure 20x12 inches. The P335/25ZR20 Michelin Pilot Sport PS2 tires they wear are good for burnout stripes over 13 inches wide, if you're into that sort of thing. These massive mounted assemblies weigh in at 65.5 pounds, not bad at all considering the dimensions we're dealing with here.
So what's all this hardware worth on our track? How about two-way average of 1.02 g on the skidpad (1.03 g counter-clockwise, when the driver sits on the inside), 71.6 mph through the slalom and stops from 60 mph in 102 feet, all day long with no fade? Beyond the numbers, the Z06/Z07 chassis turns in crisply and stays neutrally balanced, produces heroic grip and exhibits brake performance that is, in the words of test pilot Chris Walton, "about as good as brakes can be."
They need to be, too, because the engine in this beast is good for 11.8 seconds and 122.7 mph in the quarter-mile. You'll want to be able to stop at the far end.
fuhteng says:
08:23 PM, 10/ 4/10
Wow Dan. Thanks. What a complicated, and amazing, machine.
So, how long until some brain-dead troll comes on here screaming about how a modern car uses leaf-springs? I give it until post #5 (assuming I'm post #1).
zoomzoom97 says:
08:59 PM, 10/ 4/10
Thanks for that, Dan
Couple of bone-headed questions:
Did the previous generations of Corvette use a transverse leaf spring front and rear? You guys have a Z06 - do any serious performance companies cater to that spring system (how would you corner-weight?) or do they switch to a coil-over setup like the ALMS teams?
Do the leaf springs block the incorporation of a more modern multi-link rear suspension and whatever camber-increase-under-load advantages that setup provides?
cz_75 says:
09:37 PM, 10/ 4/10
The Top Gear guys, or at least Clarkson, would have some bollocks to spout about the leaf springs.
I believe the transverse leaf spring dates to the 1963 Corvette, but I don't believe it was used up front. The 1984 Vette used these composite springs on both axles and so they have ever since.
dirtycarl says:
10:42 PM, 10/ 4/10
"Apparently, this setup makes the car a full Z0 better."
That comment deserves a medal. Love it.
kyolml says:
11:42 PM, 10/ 4/10
why is it that much anti-dive built-in in the front upper arm?
I always don't understand why use anti-dive control the body motion because it will cause unnatural suspension motion, which in turns causing understeering and locked-up wheel, bad steering feel when loaded, etc. They have MRC to control body motion already.
I guess it's less important when it's rear-wheel drive, but still.......
angry_mushroom says:
11:44 PM, 10/ 4/10
It appears that Corvette fanatics are in the same boat as Mustang maniacs. Both cars use "outdated" technology to unreal effect.
santiagofdz says:
11:48 PM, 10/ 4/10
http://www.corvetteracing.com/cars/c6r/chassis_specs.shtml
The race cars (at least GT1s) do use multiadjustable Coil-Overs. I'm guessing the need for fiddling with the set up is the reason for using coil-overs, but I have no experience racing, so don't listen to me too much.
--
So far C6 vettes still are my (affordable) dream supercars. A used z06/with the z07 specs would be mouthwatering for me.
campi3ell says:
12:04 AM, 10/ 5/10
You got some pretty good shots, given that you were working with about 6" of ground clearance...with the stands.
v8vader says:
02:55 AM, 10/ 5/10
love these articles. it's great to see the unique aspects of the Vette- i've always wondered what the transverse leaf springs looked like!
kevm14 says:
03:50 AM, 10/ 5/10
Very nice, Dan.
But one thing that is bothering me: no speculative comments about the splined wheel bearings on the front to accept a driven half shaft? AWD Corvette anyone? Or did they just reuse a part from somewhere else (like the rear)?
tankrust says:
04:37 AM, 10/ 5/10
zoomzoom97...
Corner balancing the Vette can be performed on the stock leaf spring suspension. There are adjustment bolts located at the end of the leaf spring where it attaches to the lower control arm. This will vary the ride height at that corner and therefore the weight distribution. Aftermarket manufacturers sell longer than factory bolts for people who like extremely low ride heights.
Tankrust
alexdi says:
05:29 AM, 10/ 5/10
The leaf spring is one of many solutions to the same problem. When it was first used is irrelevant; only current performance matters. I chafe at the Mustang comparison because the solid axle has significant compromises apparent even to unsophisticated drivers. It's an inherently inferior design that no amount of engineering can mask. The Corvette's leaf spring is, as implemented, comparable and even superior to coils.
throwback says:
05:55 AM, 10/ 5/10
Thanks again Dan, love these walkarounds. When you think about all the high quality materials that you get with a Vette, calling it a performance bargain compared to a 911 or 458 is an understatement. Ferrari use the same type of shocks, which they source from Delphi who developed them for GM.
octane77 says:
07:13 AM, 10/ 5/10
"kevm14 says:
03:50 AM, 10/ 5/10
Very nice, Dan.
But one thing that is bothering me: no speculative comments about the splined wheel bearings on the front to accept a driven half shaft? AWD Corvette anyone? Or did they just reuse a part from somewhere else (like the rear)?"
I noticed that too. What gives with the splined front hubs?
mptlptr says:
07:27 AM, 10/ 5/10
The front rotors are 15.5". Rears are 15". The standard Z06 brakes are 14" in front.
tatermctatums says:
07:39 AM, 10/ 5/10
To further comment on the brakes, the cost to replace them with factory parts is truly "hyper-expensive". The front pads will set you back about $900.00, while the rears are *only* $700.00. And the rotors will set you back $1800.00 each, front or rear. The price of the option seems to be just the price of the pads and rotors, which when you're already in this price range is sort of a deal... I guess.
audisport says:
07:46 AM, 10/ 5/10
Awesome hardware. Those Delphi shocks are awesome.
The only thing I see wrong with a Z07 is that most potential buyers who would break out the check book for one might just write the check for a ZR1.
cartester16 says:
09:39 AM, 10/ 5/10
Pertaining to the splined front hubs... Looks like they are same as the rear.
My biggest question is: are the lower a-arms too? Looks like they are the same, just inverted. Also, are they solid or hollow?
skidrive9 says:
09:41 AM, 10/ 5/10
Wow is all i have to say. It's just such an amazing piece of engineering. definitely one of the finest sports cars out there.
cartester16 says:
09:42 AM, 10/ 5/10
Another thing, I see that the big advantage of the leaf spring is packaging. It takes almost no room at all! Nice. I think a small fwd vehicle could benefit from this even more.
felonious says:
10:07 AM, 10/ 5/10
Drooooool. I would not hesitate to get that upgrade! You're right Dan, amazing bargain for what you get.
half_ton says:
11:31 AM, 10/ 5/10
These walk arounds are AMAZING! Please keep them comming but I have one question:
What would be the impact if the front subframe was aluminum instead of magnesium? Would more dive be the result?
sixwheeler says:
01:03 PM, 10/ 5/10
Are the front and rear hub assemblies shared? The splices say they are. Either that, or GM, still being GM, is trying to save money by using a hub assembly from some truck.
exnevadan says:
06:29 PM, 10/ 5/10
whats with all the green and yellow markings (not the arrows added for illustration purposes) on the front suspension pieces in the first few photos? the car certainly looks fresh of the factory line, little rust/grime, do they QC/QA their products w/ a sharpie?
another vote/thanks for the walk arounds.
how about a shot of the 427.
xollins says:
06:44 PM, 10/ 5/10
@fuhteng --> it was actually post #6. You were so close. And I was amused.
springs7 says:
07:53 PM, 10/ 5/10
zooomzoom97,
The leaf springs can be used with a multi-link suspension. The Corvette was one of the very first cars to use multi-link suspension starting with the IRS added in 1963. The C4 Corvette used a multi-link but GM switched to a double A-arm setup in 1997. Note that a double A-arm setup is actually a multilink design where several of the links just happen to form "A's". A-arm setups can have the same camber gain curves as multi-link setups. The primary reason to pick one vs the other is packaging.
For those asking about the front wheel splines, yes there is a good reason. To save money GM uses only two upright designs on the Corvette. The diagonal uprights are the same, ie the left front is the same as the right rear upright. Given that the car has A-arm suspension all around, there is nothing inherently special about using the same uprights front and rear. If you read All Corvettes are Red you can get a sense of the sort of cost saving ideas like this that were needed to make producing a low volume car such as the Corvette on it's own platform even possible.
zoomzoom97 says:
09:08 PM, 10/ 5/10
springs7,
Thanks for clearing that up!
slickersdrip says:
10:19 PM, 10/ 5/10
I love these posts. Thank you so much, Dan, for going out of your way to put them up and take pictures. I always feel more knowledgeable after reading them.
I wish I could hand you the keys to my RX-8 to do one of these on it and give me a better explanation of my own car.
wjtinatl says:
11:59 AM, 10/ 6/10
Unreal technology and results from what some would call outdated technology. I recall Audi once had a 5 valve v-6, that didn't make any more power or torque than competitors 4-valve motors. That said, imagine what gm and ford engineers could do with a 4 barrel Holley these days!
johnmval says:
02:42 PM, 10/ 6/10
I could read technical specs like these all days long! Well written and very nicely detailed...thanks for a wonderful afternoon read Dan. JohnV
cardesigner82 says:
03:27 PM, 10/ 6/10
Wow! That seems like such a fairly simple setup for what the suspension gives you in return on the ZO6/O7. $9k for the whole setup and Porsche charges $8k for the brakes alone?!? Yikes!
cello_one says:
04:54 PM, 10/ 6/10
That was a great suspension walk around. I love technology - and those springs rock! So cool.
actualsize says:
08:19 AM, 10/ 7/10
@mptlptr: thanks for the back-up on the sizes. I should gave grabbed a tape measure to confirm.
@manyothers: As for the splined front hub, there's nothing really wrong with sharing a part like this. You want the same bolt pattern, flange diameter and hub-wheel indexing diameter. The wheel bearing's inner diameter will be about the same, so why NOT share it? The maintenance of two part numbers, from logistical and production standpoints, is oftentimes more expensive than using just one, especially when the parts would be otherwise identical but for one simple machine operation -- that spline.
actualsize says:
08:43 AM, 10/ 7/10
@santiagofdz: Correct. Racers want to be able to quickly change spring rates, they want to have more ride-height control. They're always fiddling with the set-up, the fine tuning of the suspension. They like coil overs because they can quickly swap out the spring and shock as a unit by removing just two bolts. Coil-overs give them access to a wide range of off-the shelf racing springs (and sponsorships from the various companies that make them).
But the upper shock mount in those cases has to be strong enough to handle the combined force transmitted by the shock AND the spring. Here the upper shock mount is not carrying the weight of the car or the direct road impact loads -- it's only dealing with the damping loads created within the shock absorber itself. Yes, those loads are significant, but going to a coil over would add well over a thousand extra pounds to the load any of those upper brackets have to deal with. It's not just the static weight of a corner of the car, it's also the increased weight due to weight transfer under braking, cornering or acceleration plus the full impact force of any bumps, pot holes or apex curbing the car might simultaneously hit. Are these upper mounts robust enough for coil overs without reinforcement? I don't know, but we cannot assume that they are.
kyolml says:
08:16 PM, 10/ 7/10
Dan,
Can you explain why there are so much anti-dive on the front wheel? unnatural wheel control
nicholasrage says:
10:41 AM, 10/11/10
I didn't know the fronts used leaf spring too! I had always thought it was only the rear that used it.
The front knuckle looks like it has a splines in the center, for a drive axle. It'd be interesting to plug in the part number and see if this gets used in other GM cars.
tatermctatums says:
11:01 AM, 10/11/10
I looked up the part number for the splined front hub on this Corvette. As many others have already pointed out, the front hub and the rear hub are exactly the same part. Interestingly, this same hub can be found on other Corvettes, as long as it is a C6 (2005-up), and has the FE3/FE4/FE5 suspension package.
spencewilliams says:
09:56 PM, 10/11/10
These suspension walkarounds are one of the best things on the internet, porn included.
Thanks and keep'em coming!
sportyaccordy says:
06:30 AM, 10/13/10
Def keep the walkarounds up
I thought it was funny how the front wheel bearings had a pass through w/axle splines. Does the Vette share front knuckles w/some other car? AWD Vette?
csubowtie says:
12:01 PM, 10/13/10
Beautiful hardware. I believe another reason for the 10 pins holding the rotors to the hats is to allow for the thermal expansion of the rotors relative to the hats. Since they are different materials, and the hat doesn't see any friction from the pads, the rotor heats up faster and expands more than the hat does.
AudiSport: While many buyers might pony up for the ZR1, keep in mind that is a limited production car (2000 a year). The Z07 option can be ordered whenever somebody wants. Also, while $20-30k probably isn't much when talking about this cars competitors, a.k.a Ferraris and Porsches, it may be a deciding factor for someone in this price range.
norm_peterson says:
05:34 PM, 10/15/10
Belated thanks, Dan
Seems people see "leaf springs" and can't get past visions of 1930's Fords and 1950's/1960's US domestic sedan rear suspensions and the associated performance levels.
I'll bet that many don't realize that with the way the Corvette leaf springs are mounted, they add a little roll stiffness in addition to whatever wheel rate exists in two wheel ride mode. As far as wheel rate in ride is concerned, it's really a simple matter of once you establish that you need X amount of spring rate at 62% (or whatever) of the way out the control arm, what the spring looks like doesn't have to matter as long as you can iron out the details.
Did anybody notice that the shape of the rear lower control arm generally follows the shape of the moment curve for a simple beam loaded as the LCA is? That's detail with a purpose, not just there for its own sake.
Norm