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What makes 2004 Z06 shocks so good?

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Old 08-30-2013, 02:29 PM   #1
joenationwide
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Default What makes 2004 Z06 shocks so good?

Cliff notes:

2004 Z06 shocks/dampers are some of the best performance dampers available for the C5,
because of extensive testing on the Nurburgring, they were valved for maximum grip.

The real benefit to the rear 04Z shocks is the rears.
There is more compression damping with the 04Z shocks which means more rear grip, and less wheel hop.
Also, the 04Z shocks have slightly more low speed rebound, and much less high speed rebound.
This allows the damper to limit body roll (slow shaft speed) and take away minimal grip (high speed).


2004 Z06 shocks vs. Bilstein shocks

Bilsteins are excellent shocks for their price, they have good performance damping characteristics, and they last forever.

However, the 2004 Z06 shocks really are probably the best OEM performance shocks ever created.
This is because they ran laps on Nurburgring (a 12+ mile road course) and tried different valving until they found which resulted in faster laps.
I'm not sure if they did shake rig testing, or just tried different valving based on lap times and driver feedback, but whatever it was it worked.

I'll give my best explanation of why the 2004 Z06 shocks are so good by comparing them to another good performance shock baseline: the Bilstein Sports
Dyno graph is from Dennis Grant's Autocross to Win website.


Understanding the Graphs
The horizontal axis (x axis) is the speed of the shock shaft movement.
The vertical axis (y axis) is the force.
Everything above "0" is compression force.
Everything below "0" is rebound force.

Front Comparison
Comparing the front dampers, the 04Z and Bilstein Sports are almost identical.
The 04Z dampers have a bit less high speed damping (both compression/rebound).
04Z front shocks have marginally less harshness over bumps, and marginally better grip, but would be hard to tell the difference.

Rear Comparison
The real benefit to the rear 04Z shocks is the rears. There is more compression damping with the 04Z shocks which means more rear grip, and less wheel hop.
Also, the 04Z shocks have slightly more low speed rebound, and much less high speed rebound.
This allows the damper to limit body roll (slow shaft speed) and take away minimal grip (high speed).

Summary
Just by running 04Z shocks, a C5 Z06 will be much more planted in the rear, be able to put power down sooner coming out of a corner or on
rough roads, and will be much more stable and give more confidence to drive faster.


But be careful making absolute statements about shocks.
Do 04Z shocks make the car corner flatter than Bilsteins? No.
Do 04Z shocks provide better grip? Yes.
Shocks that make the car feel more tied down, and have sharper response may be giving up grip in order to make the car feel more like a go kart.


I think some background is important, since very few people understand damping.
IMHO damping is one of the most difficult to understand aspect of a performance car. Only in the last two decades have engineers/race teams really been able to understand how to properly tune dampers.


How do shocks control the car?

Shocks (dampers) control the speed at which the body rolls and at which the tires move up and down against the road surface.
Springs control the total amount of roll or movement.
Shocks control "transitions" like going from gas to brake, turning in, and exiting a corner.
If you were going around a skid pad (circle) at a constant speed, your shocks don't come into play.

Compression and Rebound
Shocks do two things, resist compression forces (shock compresses) and resist rebound forces (shock extends).
Sounds simple, but shocks really do give the car its character, even its soul.
To me, nothing transforms a car more than its shocks.

High Speed vs. Low Speed Damping
The term "speed" here means speed of the shock shaft going up or down.
Interestingly enough, when the shock shaft is traveling slowly (0-3 inches per second), the car is likely going through a turn or performing some handling manoeuver.
When the shock shaft movement is fast (6-20+in/sec) the car is likely hitting a bump or a rough road.

So generally shock tuners will want strong low speed damping to control cornering performance, and then want to bleed off force at the high
speeds so they don't knock your teeth out hitting bumps (too much HS compression) or pull the wheel off the ground (too much HS rebound).

Compression
Simply put, compression controls the unsprung mass (the wheel and tire) and forces it down onto the road.
To little compression and the tire will not have the grip it needs.
Too much compression and the tire will chatter over the surface and feel very harsh.

Rebound
Rebound controls the rate of body roll.
When people install aftermarket shocks and they say the car feels so much flatter in turns, or it handles more sharply, with instant response....that is because of more rebound damping.
Too little rebound damping the car feels mushy, and slow to react.
Too much rebound damping the car loses grip, even though it feels more like a go-kart.


I'm sure most everyone is thinking TL;DR (too long didn't read).
But I thought it might be worth it to attempt to explain this. Any opinions or criticisms welcome.

Last edited by joenationwide; 09-01-2013 at 09:09 AM.
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Old 08-30-2013, 03:37 PM   #2
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Please state your source(s) for the Bilstein comparison data.
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Old 08-30-2013, 11:01 PM   #3
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A lot of good info here. My question is why are 04 ZO6 shocks so expensive and 2012 ZO6 shocks can be had for $250 for all four. The C6 shocks fit the C5 and if GM dumped all the money into R and D why change them. Logic would dictate they did the same R and D for the new ZO6. I guess I'll find out, my C6 ZO6 shocks are due in on Tuesday. They will be bolted up to my 97 coupe , should be a good match for the C6 Z51 sway bars I put on last week.
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Old 08-31-2013, 12:01 AM   #4
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I've seen the Bilstein comparo charts before in here. What I'd like to see is comparisons of various Coil-Overs vs the '04 Shocks. Yes, I know most are fully adjustable, but not all are. You also get the benefit (how much I'd like to know) of getting rid of the transitional response given by the Leaf Springs.
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Old 08-31-2013, 01:13 AM   #5
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Quote:
Originally Posted by JETninja View Post
I've seen the Bilstein comparo charts before in here. What I'd like to see is comparisons of various Coil-Overs vs the '04 Shocks. Yes, I know most are fully adjustable, but not all are. You also get the benefit (how much I'd like to know) of getting rid of the transitional response given by the Leaf Springs.
apples and oranges.

shocks designed for coilovers and leaf springs aren't really something you compare straight up

the bilstein sports are from what i remember almost identical to the 2002 z06 shocks

my wild *** guess on the price difference between the 06+ z06 shocks and the 04+ shocks is that the 04s are made by sachs. the 06s? who knows.

suspension is one of those things you either "get" or you don't. there really isn't a best anything with suspension as some of it is driver preference.

Last edited by racebum; 08-31-2013 at 01:16 AM.
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Old 08-31-2013, 07:57 AM   #6
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Quote:
Originally Posted by skyavonee View Post
Please state your source(s) for the Bilstein comparison data.
Those curves were developed by Dennis Grant (Far North Racing) who has extensive experience in developing shocks for racing and autocross applications. He knows his stuff.
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Old 08-31-2013, 08:33 AM   #7
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Joe has provided a good explanation as to why the 04 Z shocks are very good, but remember that any shock setup is a compromise between harshness and handling, and front and rear shocks are matched to provide balance in the overall setup of the car.

The 04 Z shocks were developed for performance. A group of GM ride and handling engineers were at a test session at Grissom in 2002 where we were also testing and they ran a number of different shocks on the car fine tuning the handling on an autocross course. The purpose was to teach a young ride and handing engineer about shock tuning, and also to get the car dialed in for autocross performance.

All that said, if you are on the track and autocross course, running stickier tires, there may be more to be had if you are willing sacrifice some ride comfort for performance. You will note that all of the serious competitors at the SCCA Solo II nationals in the Super Stock class run expensive double and triple adjustable and often custom valved shocks and the stock shocks go on the shelf until the car is sold. Shock valving that can be adjusted for the particular course and grip available has always been an advantage and the stock shocks, while very good, are fixed valving and that doesn't get you the last bit of performance that can win you a national championship.

I've tested with both the stock shocks and double adjustable Koni's and the car is slightly faster with the Koni's that are set up right. The stock shocks do provide a lot of forward grip coming off of corners, but they are a bit soft for ultimate handing on DOT slicks compared to a more sophisticated shock that is a bit harsh on the street.

Also it would take a really well calibrated backside to tell the difference between a set of Bilstien Sports and the 04 Z shocks. A ride and handling engineer would notice it, but unless you are a serious racer or a suspension engineer and running the car on a track you really won't. The Z shocks will feel a bit more plush on sharp small bumps, but other than that you won't feel any difference if you aren't tracking the car and trying to use that forward bite.

The bottom line is that while the Z04 shocks are indeed very very good, if you aren't taking the car to the track or autocrossing the car you aren't going to notice any real difference between them a and the Bilsteins. The 04 Z shocks, like all GM OE shocks won't last nearly as long as the Bilsteins, and are more expensive to start with, so there is the economic factor in favor of the Bilstein's also.

JMHO and experience
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Old 08-31-2013, 12:52 PM   #8
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Old 08-31-2013, 02:46 PM   #9
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I'd love to know how the chart was generated. You'd need some specific equipment to be able to record data of that type accurately.
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Old 08-31-2013, 03:29 PM   #10
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Quote:
Originally Posted by onspeed View Post
I'd love to know how the chart was generated. You'd need some specific equipment to be able to record data of that type accurately.
The charts are generated by the computer output of a shock dynamometer. The shocks are run through their travel at various speeds and the forces measured as they are running. The computer records the force/deflection data and that is used to generate the charts. Basically the shock is attached to a crankshaft that is driven by a motor and has a force transducer that reads the force and position of the shock.
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Old 08-31-2013, 09:36 PM   #11
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Quote:
Originally Posted by SPEED750 View Post
A lot of good info here. My question is why are 04 ZO6 shocks so expensive and 2012 ZO6 shocks can be had for $250 for all four. The C6 shocks fit the C5 and if GM dumped all the money into R and D why change them. Logic would dictate they did the same R and D for the new ZO6. I guess I'll find out, my C6 ZO6 shocks are due in on Tuesday. They will be bolted up to my 97 coupe , should be a good match for the C6 Z51 sway bars I put on last week.
Supply and demand, they are selling a lot more of the current shock, and still in production.
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Old 08-31-2013, 09:39 PM   #12
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I will be putting on the DRM Bilsteins in a few months.
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Old 08-31-2013, 09:41 PM   #13
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Now that would be a great add to the chart above, modern Z06 shocks....
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Old 09-01-2013, 05:50 AM   #14
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Quote:
Originally Posted by JETninja View Post
Now that would be a great add to the chart above, modern Z06 shocks....


I would like to see the Pfadt/Johnny O'Connell shocks added as well. I can already feel that there is room for improvement on my 2003 Z06, so the information would be most useful.
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Old 09-01-2013, 07:14 AM   #15
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Quote:
Originally Posted by 95wht6spd View Post
I will be putting on the DRM Bilsteins in a few months.
You will be pleased with these. Have them on my C5Z and my C6Z.
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Old 09-01-2013, 10:45 AM   #16
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Quote:
Originally Posted by Solofast View Post
The bottom line is that while the Z04 shocks are indeed very very good, if you aren't taking the car to the track or autocrossing the car you aren't going to notice any real difference between them a and the Bilsteins. The 04 Z shocks, like all GM OE shocks won't last nearly as long as the Bilsteins, and are more expensive to start with, so there is the economic factor in favor of the Bilstein's also.

JMHO and experience
Let's not forget about the 2001 Z06 shocks. They were completely different so the 2004's are going to be a major upgrade for me!
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Old 11-18-2013, 07:35 PM   #17
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So why does my stock 2004 Z, wheel hop so bad? The shift from 1st to 2nd is terrible. I can even do a, 2nd gear roll and stab it. And it will wheel hop. Just not as bad as the 1-2 gear shift. What do I need to do to fix this?
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Old 11-18-2013, 08:45 PM   #18
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I've had 04 shocks on my 02 for about 6 yrs now. Back then they were compared to the bilstien sports, nothing has changed, the 04's are still better. Even though I roadrace I have no interest in after market coilovers because of the price, but I will be replacing my 04's soon, with 04's if I can still get them.
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Old 11-18-2013, 09:37 PM   #19
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Quote:
Originally Posted by GeorgeZNJ View Post
I've had 04 shocks on my 02 for about 6 yrs now. Back then they were compared to the bilstien sports, nothing has changed, the 04's are still better. Even though I roadrace I have no interest in after market coilovers because of the price, but I will be replacing my 04's soon, with 04's if I can still get them.
they are still available. i bought a set a few months ago from my local dealer for $450 {they give me shop cost since i use to be a tech in the area and got use to dealing with them}
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Old 11-18-2013, 09:44 PM   #20
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Quote:
Originally Posted by bada View Post
So why does my stock 2004 Z, wheel hop so bad? The shift from 1st to 2nd is terrible. I can even do a, 2nd gear roll and stab it. And it will wheel hop. Just not as bad as the 1-2 gear shift. What do I need to do to fix this?
If the problem is with the shocks its because they are blown. The 04 rears were designed to significantly reduce wheel hop.
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