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-   -   Shock Tech, 101 (https://www.miataturbo.net/suspension-brakes-drivetrain-49/shock-tech-101-a-53073/)

Bernie S. 10-29-2010 09:40 AM

Shock Tech, 101
 
I want to start a new thread on Shock Tech. It seems there are a lot of questions pertaining to both the technical side and the performance side of shocks.

Shocks aren’t based on black magic, and there’s no reason for anyone to remain in the dark. The better you understand how your shocks work the better you will be at setting up your car for your driving style, and the happier you’ll be with them and your own performance.

In this thread I want to go into detail about the parts that make up a shock, along with their function. What changes in a shock to make a graph look a certain way, and why. We’re going to drill way down into the workings, even down to what I torque the piston nut to.

To get the ball rolling, does anyone have a shock question they can't get an answer to? Maybe something you have been wanting ask, but felt like everyone else already knew. Trust me, you’re not alone and certainly not dumb or inexperienced for not knowing.




MODERATOR NOTE: off topic discussion will be eliminated. questions and shock discussion only please. ie don't post that you subscribed.

webby459 10-29-2010 09:48 AM

Subscribed, with many thanks to Bernie for starting this.

I guess the question I have is how much can increasing low-speed compression damping help the transitional behavior of my car? I'm in a CSP Miata, light-prep (for now), and 550/350 springs. It's too light a spring for the grip of the A6 (it rests on the bump stops in front on course), and my complaint is that it isn't as sharp as it should be in transitions, like slalom. It takes a little long for the body to take a set, sometimes still going one way while I need it to go the other.

Thanks for the feedback.

miatauser884 10-29-2010 09:56 AM

I'm subscribed as well. I am a complete novice when it comes to shocks and would appreciate all the info you can provide.



I think we should keep the brands out of this thread. The info should pertain to any shock (correct me if I'm wrong). I just don't want to see a "brand war" and diverge away from the useful data.

miatauser884 10-29-2010 10:03 AM

When going around a track, what determines if a spring is sufficient, too stiff, etc? Is faster rebound always better because the car is usually transitioning very quickly, or can this lead to loosing traction? how does someone start to gauge the optimal setup for there car based on feel alone. i don't have a large budget for shock trial and error? As springs get stiffer, does lateral grip diminish because the weight transfer over the tires around a corner becomes less?

Sorry about all of the questions, but i'm curious.

webby459 10-29-2010 10:13 AM

Quote:

Originally Posted by djp0623 (Post 649767)
I think we should keep the brands out of this thread. The info should pertain to any shock (correct me if I'm wrong). I just don't want to see a "brand war" and diverge away from the useful data.

Good idea-brand edited out. It pretty much doesn't matter, as long as the valving is suited to the spring rate, which mine definitely is.

sixshooter 10-29-2010 11:18 AM

I am on a never ending quest to save my girlfriend gain understanding.
http://images2.wikia.nocookie.net/__.../91/Xandir.jpg

sv650_ck 10-29-2010 12:46 PM

Starting with the basics of how a shock works and the components that make up the shock would be helpful to the less knowledgeable like me.

chpmnsws6 10-29-2010 03:42 PM

Symptoms of too much/little valving for your spring rate: Hops, skips, shutters etc.

Thucydides 10-29-2010 04:08 PM

I have a question. One of the primary reasons I chose your shocks was that you don't install a Schrader valve unless the customer asks for one. I had heard of valves breaking off, and of valves leaking gas, two things I wanted to avoid.

But given there's a couple hundred pounds of nitrogen pressure in it's own chamber within the shock body, would you please explain how I can be sure the nitrogen hasn't leaked past the floating piston into the oil side of the shock?

Bernie S. 10-30-2010 01:05 AM

Perfect question. This is exactly where I would like this thread to go. The debate on handling can be found many times over on multiple sites. Let's get technical, the stuff nobody else talks about.

A sealed monotube shock, like Bilstein, would have to push out all of the oil before the nitrogen would mix with the oil or leak out of the shock. The reason it would have to push out most of the oil is that the separator piston has equal pressure on both sides, the reason it floats. The o-ring in this application is mainly to prevent cross contamination, not for sealing purposes. Only when the separator pushes out the oil and is pushing on the end of the shaft will there be a pressure differential, and then the nitrogen could leak. For the nitrogen to come out, 2 seals would have to fail first.

Quote:

Originally Posted by Thucydides (Post 649959)
I have a question. One of the primary reasons I chose your shocks was that you don't install a Schrader valve unless the customer asks for one. I had heard of valves breaking off, and of valves leaking gas, two things I wanted to avoid.

But given there's a couple hundred pounds of nitrogen pressure in it's own chamber within the shock body, would you please explain how I can be sure the nitrogen hasn't leaked past the floating piston into the oil side of the shock?


jacob300zx 10-30-2010 05:22 AM

By dynoing a shock can you tell what spring range it can handle if you have the motion ratio of the vehicle/weight? How do you read a shock dyno? Can you open up a PSS9 and actually make the settings do something worth while for a track guy?

Thucydides 10-30-2010 02:37 PM

Quote:

Originally Posted by jacob300zx (Post 650286)
By dynoing a shock can you tell what spring range it can handle if you have the motion ratio of the vehicle/weight? How do you read a shock dyno? Can you open up a PSS9 and actually make the settings do something worth while for a track guy?

Here's a great source of info on how a shock dyno graph is generated and what it's measuring:

http://www.roehrigengineering.com/Do...s/dynograf.pdf

I hope Bernie doesn't mind me jumping in, but since he gave me this info I feel I'm on reasonably safe ground.

As for the other two questions, I'll stay out of them.

Thucydides 10-30-2010 02:45 PM

Quote:

Originally Posted by Bernie S. (Post 650210)
A sealed monotube shock, like Bilstein, would have to push out all of the oil before the nitrogen would mix with the oil or leak out of the shock. The reason it would have to push out most of the oil is that the separator piston has equal pressure on both sides, the reason it floats.

So, the gas charge is pushing on one side of the floating piston with a certain pressure, and the shock oil is pushing on the other side with essentially exactly the same pressure. Without any reason (pressure differential) for one to go to the other side of the piston they pretty much stay were they are unless you loose the oil, which you would see as it would be all over your shock. Pretty simple.

Follow up questions:

How much Nitrogen gas pressure is in a shock and what are the ranges of pressures and why?

Given that the gas is there to prevent cavitation of the shock oil as it passes through the damping piston, do you use different pressures depending on the viscosity of the shock oil?

y8s 10-30-2010 08:34 PM

my question: where on a shock dyno is "high speed" and "low speed" and what are some examples of driving conditions during which you experience both?

ie. high shaft speed is over freeway reflectors, low shaft speed is over a speedbump or hard left turn

JasonC SBB 10-31-2010 12:45 AM

Low speed is that which can come from the springs as they return to center after being comrpessed or extended. High speed is outside that. Large sharp bumps generate hi speed shaft motion.

hustler 10-31-2010 11:46 AM

I've never understood how you can have differing damping rates for high and low-speed with one valve in the shock.

JasonC SBB 10-31-2010 12:59 PM

Different slopes through the force-velocity curve. Shocks can have blowoff valves.

Gotpsi? 10-31-2010 02:28 PM

I thought I should ad this interesting note, Koni sells there shocks with a nitrogen charge, but when they rebuild them they do not recharge them, when I asked them why they said that they only sell them initially with nitrogen because it is the industry standard, but they do not recharge them when they rebuild them because they say that they see no advantage in there testing.

Thucydides 10-31-2010 02:45 PM

Quote:

Originally Posted by hustler (Post 650658)
I've never understood how you can have differing damping rates for high and low-speed with one valve in the shock.

At low speeds the shock oil passes through the damper piston through a low speed circuit. At higher speeds the disk springs (shim stacks) are deflected open by the increased oil pressure which opens additional passageways, thereby allowing for a different rate of damping.

Have a look at page 15, here:

http://www.penskeshocks.co.uk/downlo...TechManual.pdf

Thucydides 10-31-2010 02:58 PM

Quote:

Originally Posted by Gotpsi? (Post 650707)
I thought I should ad this interesting note, Koni sells there shocks with a nitrogen charge, but when they rebuild them they do not recharge them, when I asked them why they said that they only sell them initially with nitrogen because it is the industry standard, but they do not recharge them when they rebuild them because they say that they see no advantage in there testing.

You've been fed an extra large portion of bullshit from the rebuilder.

The nitrogen pressure is to prevent cavitation within the shock oil as the piston moves through its stroke. Without positive internal pressure the oil turns to an air/oil emulsion with very poor damping characteristics in comparison to the pressurized oil. Go to the 3 minute mark of this video and you'll see the problem:

http://www.youtube.com/watch?v=W4ZZYqRVzLc

What the re-builder meant to say is that they don't have the equipment necessary to recharge the shocks, have compensated with a different viscosity oil or valving, and most customers don't notice. They've taken a high pressure shock system and converted it to function as a low pressure system. High pressure is the industry standard because it's so superior.


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