Author Topic: Shock absorber tech and Dyno Graphs  (Read 4014 times)

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Jeff Goji

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Shock absorber tech and Dyno Graphs
« on: November 13, 2010, 12:35:05 PM »
Alright ladies and gentlemen, I decided to share the shock absorber knowledge wealth and post up some shock dyno graphs for everyone's shock absorber education.
I've also taken the liberty to write this somewhat brief explanation of how shock absorbers work, what the two different types of damping are, and a small explanation on what damping speeds are.
The point of this thread is to help educate anyone looking for shock information or looking to find a dyno graph data which I'll supply as it becomes available to me.

Shock absorber function:
Shock absorbers, or more appropriately, Dampers, have the primary function of helping to control the energy stored up by the springs.
A spring is a remarkable depository of energy.
When the spring is compressed by a bump or a change in load on the spring, it stores the energy of the initial motion and feeds much of it back in the opposite direction.
Without control, the spring would go through a number of cycles of compression and extending in response to it's first deflection, losing little energy with each cycle.
If the springs were allowed to go uncontrolled (undamped) every time they encountered a bump or change in inertial loading, the car would be bouncing all over the place and be, for the most part, uncontrollable.


Bump and Rebound damping:
The shock absorber or "damper" has resistance to motion in two directions.
It resist compression (making it shorter) and it resist extension (making it longer).
When some force acts on the suspension system to compress the spring, it also compresses the shock.
When the shock compresses, it's called "going on the bump."
If the load is removed from the suspension, the spring gets longer and the shock extends  - a state known as "going into rebound."


Low-speed damping:
Controls the springs through slower shock movements such as body roll movement or the speed of weight transfer.
Too much low-speed damping will hurt overall grip, too little will make the car feel like a "boat at sea" and will be slower to react to driver inputs.


High speed damping:
Controls the spring under high speed movements such as when you hit a pothole or other sharp and abrupt bump.
Too much high speed damping and the spring can't absorb the bump properly and you get a very rough ride and the tire can lose adhesion over multiple bumps such as on a rough road.
Too little, and the spring energy isn't dissipated fast enough and the tire can lose adhesion over rough section of road or over an abrupt bump.


Putting it all together:
Low speed damping is the 0 - 2.5 IPS (inches per second) range and is where shock absorbers spend most of their life, unless you drive on bad (Houston) roads often.

This is one of the reasons that Mazda commonly piles on loads of low-speed damping with their "sport package" options (99-Sport and Mazdaspeed Miatas).
It gives the car a much "sportier" handling feel and makes the car feel like it's sporting stiffer springs than what it really has on it.

Anything above 2.5 IPS is considered to be high speed damping, it's a sudden "spike" in shock speed when you run over a bump or hit a pothole.


Everyone has an opinion on how much compression damping a vehicle needs...
Some people believe that you let the springs do the actual work on the "bump" side and dial in just enough compression to adequately control your un-sprung weight.
After all, if you have an actual spring, why do you need more compression than necessary to further dampen the un-sprung weight into almost a "death grip"?

Well, this brings us to the second camp... This camp is like Mazda, they believe in using more compression damping then needed to control the un-sprung weight to give the vehicle a more sporting handling behavior and not have to fit stiffer springs.
In theory this seems like a good idea, and in practice on dry, smooth as glass roads or on a smooth race track or autocross course, it can be applied with much success.

The third camp, believes that rebound and compression are symmetrical and you need to increase one with the other to maintain a balance in all-out grip and handling, and maintain ride compliance.
FatCat Motorsports tunes it's shocks along these lines, and it works in proper moderation.
However, when you start applying so much compression damping that it's acting as a replacement for spring rate, you run into problems as mentioned above.


The one thing every camp can agree on however, is damping on the rebound side.
None of us want to over-damp a spring in rebound damping, as this leads to "jacking down" onto the bumpstops and will cause an overly harsh ride and even worse handling.

Well actually... I say everyone, but in truth the Autocross community is one of the worst for running shock absorbers with entirely too much rebound damping (and often compression damping as well).
You mostly see this in stock classes, where the rules prevent you from changing springs.
Basically they crank up the shock absorbers as high as possible, giving up all-out grip in favor of transitional response and feel.

The one time the average stock class autocross guru will go against this conventional wisdom of the herd is in the wet, where the higher grip of the more relaxed damper settings will payoff much better than the "death grip ultra responsive" over-damped settings.

An example of this comes to mind back in 2007...
Paul's MSM was on road race tires and stock MSM Bilstein shocks.
The MSM Bilstein shocks have amazing amounts of low-speed damping, especially in the compression range, and are at home on a dry track.
In the wet however, it was the slightly under-damped 2007 NC on less grippy street tires that I was better able to balance in the wet at the limit, and set times just as quick as the more powerful and higher damped MSM.
Very surprising to me at the time given how absolutely horrible the NC felt to me in the dry.


My personal opinion on shock absorber damping:
I think it depends ENTIRELY on your use of the car and the condition of the roads, race track, or autocross course you are going to drive on.

There just isn't one damper setting that will work for EVERY condition out there; this is the reason we are seeing more and more "magnetic ride selection" options being made available for various sports cars from various manufacturers all over the world.
It's the reason the GT-R, Corvette ZR1, and Porsche 911 Turbo just to name 3 examples have multiple shock absorber damping profiles to fit varying conditions.

The super soft under-damped shock absorbers found on the 06-08 NC sport models will not be optimal for autocross or track driving, and may not even be suitable for someone seeking a truly sporty handling vehicle.
And the inverse is also true in that a autocross or track driving setup will not be optimal for the 06-08 NC owner seeking a comfortable cruising car.
What's best for absolute grip in the dry on 225/50/15 R-comp tires on a smooth as glass autocross course will never work properly on the same car sporting 195/50/15 street tires on a bumpy road in the rain.

Shock absorber damping is like anything in life, it's a compromise.
The trick is figuring out the priorities, and spending your money accordingly knowing full well the pay-offs and compromises involved in your decision.
« Last Edit: November 13, 2010, 10:04:07 PM by Jeff Goji »

Jeff Goji

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Re: Shock absorber tech and Dyno Graphs
« Reply #1 on: November 13, 2010, 12:52:04 PM »
NB Rear dampers: NB Showa (OE), 99 Hard S, MSM:


NB Rear dampers: NB Showa (OE), NB Bilstein Sport, NA Bilstein HD.



NB Front dampers: NB Showa (OE), NB Bilstein Sport



Jeff Goji

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Re: Shock absorber tech and Dyno Graphs
« Reply #2 on: November 13, 2010, 12:57:09 PM »
NA Bilstein HD front, NB Bilstein Sport front:


NA R-package Bilstein Shocks, NA Bilstien HD shocks


OE: NB Showa, NA KYB AGX, Koni Yellow.

Offline Mikeymx5

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Re: Shock absorber tech and Dyno Graphs
« Reply #3 on: November 13, 2010, 04:52:50 PM »
to much for me to understand,  what is an Ideal curve?
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Re: Shock absorber tech and Dyno Graphs
« Reply #4 on: November 13, 2010, 09:32:31 PM »
to much for me to understand,  what is an Ideal curve?

You're not alone, Louis!  ???   That's why we aren't SCCA champions...the attention to detail...!  If my butt-o-meter get's out of calibration, I'm in big trouble.  :o   
 
Spring weights and shocks may not have saved you at Kerrville.  I think tires would have given you a better outcome.  :-\
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Jeff Goji

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Re: Shock absorber tech and Dyno Graphs
« Reply #5 on: November 13, 2010, 11:06:35 PM »
to much for me to understand,  what is an Ideal curve?


Completely depends on your selected spring rate and usage.
Here's the general formula:

Here is the equation to determine critical damping, taken from Milliken and Milliken:
 
  cd = 2 * sqrt [(CW)*(SR)/(MR)^2]
 
  where:
 
  cd = critical damping {lb/(in/sec) or lb/ips},
  CW = corner weight (lb)
  SR = spring rate (lb/in)
  MR = motion ratio (0.66/0.735 f/r for NA and NB)
« Last Edit: November 14, 2010, 12:01:15 AM by Jeff Goji »

Offline Byrdmen

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Re: Shock absorber tech and Dyno Graphs
« Reply #6 on: November 14, 2010, 06:00:31 AM »
I recall reading this guy's write ups and agree, there is one all around shock that works, no real need for adjustables.  His recomendation was also what led me to Bilsteins and why I will eventually get them revalved.  I just need to complete my graduate ME degree to understand the terms he uses.

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Re: Shock absorber tech and Dyno Graphs
« Reply #7 on: November 14, 2010, 11:14:04 AM »
OK so if I have factory NB sport springs... what is the best shock to give me a factory feel but better performance? I dont like how the AGX tend to bottom out easily and can make the car hop on dips in the road.

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Re: Shock absorber tech and Dyno Graphs
« Reply #8 on: November 14, 2010, 12:35:17 PM »
Strickly speaking from a laymans point of view (and again the TLR Manual), I think you would be satisfied with the Bilsteins.  Revalved or not I would not even dare to venture into this realm as my Posterial Degree has not advanced to the point I'm ready to present my theisis.   :P 
 
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Re: Shock absorber tech and Dyno Graphs
« Reply #9 on: November 14, 2010, 05:32:44 PM »
Louis, your shock is not the problem.  You are not running enough spring rate.  Your car too easily bottoms the shock.  Of course, once you get enough spring rate, you might easily overpower your current shock.
 
One of the reasons Fat Cat runs symmetrical compression/rebound curves is to avoid jacking down.  Even a stiff spring and shock will suffer jacking down if you don't have any compression damping.
 
There is no ideal curve for all situations.  As Jeff intimated with the Corvette/Porsche mentions, the ideal curve depends on spring rate, roll bar stiffness, road condition and vehicle speed and weight.  Chevy and Porsche adjust the shocks for road condition and vehicle speed, maybe weight, too.
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Offline Jeff Goji

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Re: Shock absorber tech and Dyno Graphs
« Reply #10 on: November 20, 2012, 01:16:42 PM »
I need to clear up a few things on this thread that have been bothering me for a while now...

The part about compression damping is still spot-on for the respective camps.
In my driving experience since writing this all three setups can ride well, but increasing your bump/rebound damping in a more symmetrical manner like what Fat Cat does is the best way to go for ride and grip purposes.
Rally cars even use more compression than rebound damping and the pay-off is pretty amazing.


The one thing every camp can agree on however, is damping on the rebound side.
None of us want to over-damp a spring in rebound damping, as this leads to "jacking down" onto the bumpstops and will cause an overly harsh ride and even worse handling.

Well actually... I say everyone, but in truth the Autocross community is one of the worst for running shock absorbers with entirely too much rebound damping (and often compression damping as well).
You mostly see this in stock classes, where the rules prevent you from changing springs.
Basically they crank up the shock absorbers as high as possible, giving up all-out grip in favor of transitional response and feel.

The one time the average stock class autocross guru will go against this conventional wisdom of the herd is in the wet, where the higher grip of the more relaxed damper settings will payoff much better than the "death grip ultra responsive" over-damped settings.

First and foremost, the one thing everyone is NOT in agreement on is how much rebound damping a car needs.
The general rule of thumb is you need to be 65% of critically damped in the 1-3 IPS range.
Some people think you need to run even more than that and they end up sacrificing grip for "feel."
the MSM shocks for example are upwards of 200% critically damped in the 1-3 IPS range on the stock 215/lb/in spring and would be better suited to a much stiffer spring.

My street car actually runs a little less than 65% of critical in the rear, and the grip and ride quality are second to none that follow the 65% critically damped rule of thumb.


My personal opinion on shock absorber damping:
I think it depends ENTIRELY on your use of the car and the condition of the roads, race track, or autocross course you are going to drive on.

There just isn't one damper setting that will work for EVERY condition out there; this is the reason we are seeing more and more "magnetic ride selection" options being made available for various sports cars from various manufacturers all over the world.
It's the reason the GT-R, Corvette ZR1, and Porsche 911 Turbo just to name 3 examples have multiple shock absorber damping profiles to fit varying conditions.

The super soft under-damped shock absorbers found on the 06-08 NC sport models will not be optimal for autocross or track driving, and may not even be suitable for someone seeking a truly sporty handling vehicle.
And the inverse is also true in that a autocross or track driving setup will not be optimal for the 06-08 NC owner seeking a comfortable cruising car.
What's best for absolute grip in the dry on 225/50/15 R-comp tires on a smooth as glass autocross course will never work properly on the same car sporting 195/50/15 street tires on a bumpy road in the rain.

Shock absorber damping is like anything in life, it's a compromise.
The trick is figuring out the priorities, and spending your money accordingly knowing full well the pay-offs and compromises involved in your decision.

First off, I'm so dang wrong on this that it isn't even funny.
The damping curves on the Nissan GT-R for example, are completely screwed up and the car benefits greatly from getting the shocks re-valved.
Even on it's softest setting it's still un-godly over-damped, and that only gets worse when you hit the "sport mode" button.
So yeah, even the factories are doing it wrong. Favoring damping profiles that use huge amounts of rebound damping for "feel" and acting as a crutch for the soft springs that come on the car.

Another thing I was completely wrong about is the adjustment of the damping.
Once the shocks are properly damped, that's it, you're done! There is NO reason to go out there and start playing with the damping.
If you're having to tune the shock to "balance" the handling of your car, you're doing it wrong and need to look into the source of why the handling balance isn't right to begin with. And this means a spring and/or sway-bar swap at the very least.

And the last item of contention on my last post: You CAN have a car that rides great, handles great, and has enormous amounts of grip.
Hard to believe I know, but with the right combination of spring rate and bounce frequencies and proper bump/rebound damping ratios, it can be done.

A big item to consider in the suspension puzzle that I didn't touch on in the first post in this thread, is the "bounce frequency ratio." This is the ratio showing how close the front and rear bounce frequencies are to each other and is effected by the spring rate.
For a "flat ride" over bumps and over surface elevation changes, a Miata that has a BFR of 1:01 to 1:03 with spring rates closer together (lets say 500/375 lbs/in front/rear) will ride flatter than a Miata with spring rates further apart (lets say 800/500 lb/in springs) and BFR of 0.96 or below.

In some cases like Autocross and some track cars, you will want to sacrifice the closer BFR in favor of handling balance.

So yeah. Those are my minor updates.  :)
And to finish it off, here are a couple of brand new shock dyno graphs.

The first graph is a force-velocity plot showing the cavitation of a set of FM AFCO shocks:


And here are some regular shock dyno graphs on the infamous Xida CS!
Xida Front:


Xida CS Rear damping curves:



Looking at the Xida curves, it becomes pretty apparent why it's perhaps the best riding and handling "off the shelf" coil-over option out there.
My only complaint on the damping with Xida is the lack of high-speed compression damping. It could benefit from a little bit more for street driving.
I also hate the bumpstops that Xida comes equipped with. Too hard on engagement, too jarring.
« Last Edit: May 06, 2013, 04:05:14 PM by Jeff Goji »
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Re: Shock absorber tech and Dyno Graphs
« Reply #11 on: November 21, 2012, 09:37:08 PM »
You would not believe how glad I am that you have the numbers worked out! 
 
I'm such a lazy mechanic.  It's a good thing that all my repairs and overhaul on aircraft are bench jobs.  Working aircraft on the line is at such a furious pace with passengers watching you work...and those looks.
 
All I got to do is call my good buddy Jeff and he knows what parts I need to use.
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Re: Shock absorber tech and Dyno Graphs
« Reply #12 on: November 22, 2012, 01:17:34 PM »

And the last item of contention on my last post: You CAN have a car that rides great, handles great, and has enormous amounts of grip.
Hard to believe I know, but with the right combination of spring rate and bounce frequencies and proper bump/rebound damping ratios, it can be done.



My car is "living" proof.  Took an early morning drive on 150 from Willis to Coldspring yesterday early morning, I have driven down this asphalt logging road many times and the undulations are usually fairly unnerving.  Even in my truck with stock springs and Bilstein 5100s it is fairly uncomfortable.  I have driven it at the posted 70 MPH in lots of comfortable cars over the years and it is lousy.


In the MSM at 80 it was VERY comfortable and controlled.  Lots of grip in the corners and a ride that makes you want to go even faster.
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Re: Shock absorber tech and Dyno Graphs
« Reply #13 on: November 24, 2012, 05:45:01 PM »
If you like to autocross somewhat seriously or track your car get Jeff's setup...if you're more casual then Scott's car is the way to go.

BTW Scott what are your spring rates? I recommended your setup for Karter's miata when he finally does build it right
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Shock absorber tech and Dyno Graphs
« Reply #14 on: November 24, 2012, 10:40:21 PM »
550/440, I think.  I'll double check and edit if that's not it.

Let me know if anyone wants a ride.
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