j9chan

Hi guys,

I just feel like doing some learning today... I've been wondering what's the big deal with gas-filled or gas-pressurized shocks. How are they superior to stock shocks? What are stock shocks made of or filled with?

As for gas shocks, I understand that Integra shocks are gas-filled. What makes different gas-filled shocks different? (i.e., stock teg shocks vs. Koni, for example).

Thanks in advance for the lesson.

yO

Bump for something I wanna know too!

punkindrublic

i just got some tociko illumina's that a gas presureized and twin cylinder or something...

the advantage i can gather from being pressurized is that for one the shock could be "firmer" and for adjustablily you could just release some of that pressure into a secondary cylinder....

but i dont know for sure if thats how it goes

Cynikal.Mindset

there are gas filled shocks and oil filled shocks...gas are more expensive and when they blow there aint much to see opposed to oil filled (u'd see oilly sludge build up on the shock)...basically one uses gas to dampen and the other uses oil

thats about all I know

lordm

what i found out about the to is this
the oil filled shocks dampen the same as stock but with the up and down motion when u dive the oil builds up heat which inturn causes it to expand and break down.
the gas shocks do not generate much heat but will give u a stiffer ride and usally have adjustable dampening, ie koni yellows.
hope this adds to the other great respones'su got.

dingus8

gas is more stable than oil with heat..you woudl be suprised at how hot the fluid can get....aftermarket gas shocks have mroe dampening which basically means it is harder to move in and out...so it controls a very stiff spring better...but gas shocks are mroe expensive to make yada yada...oil is good for something liek a fork on a motorcycle cause there is a lot of stuff to lubricate in the fork system...dont' knwo if this helped at all but the point of an aftermarket shock is for more dampening to handle the "up and down" motion of a stiff spring so it wont' porpetually (sp) bounce forever in a sense

j9chan

That's some great responses guys! Keep them coming please!! So with aftermarket or gas shocks in general, they dampen better and could handle better springs? Do shocks have anything to do with ride comfort then? Or is that the job of the springs?

imported_loudsubz

http://www.tuninglinx.com/html/a_koni_vs.html

Isn't a gas shock better than an oil shock?
Yes and no. A popular misconception is that a gas shock works on gas where as an oil (normal) shock works on oil. All conventional automotive shocks work by forcing oil through a programmed set of holes, however a gas shock will use compressed gas to keep the oil under pressure.

This is done largely to minimise aeration or "foaming" of the oil which would reduce the effectiveness of the shock as air passes through the valves rather than fluid. To see what this is like, tip a conventional shock absorber upside down and pump the shaft a few times. You'll notice the movement become jerky and uneven as oil and air intermittently pass through the valves.

The gas also helps to dissipate heat which keeps the oil cooler and maintains the viscosity and therefore the shock "rate". Gas shocks are ideally suited to long travel applications like rallying and off road. In fact, this is where the technology was primarily developed in the first place as lots of spring travel over big bumps really tests a conventional hydraulic shock.

There are many types of gas shock, twin-tube, mono-tube and remote canister combinations for super heavy-duty use like rallying and off-road racing. Most of the economical gas shocks are of a twin tube construction (low-pressure) where as most performance or race gas shocks use a mono-tube (high-pressure) system. There is no such thing as an ideal system, it really depends on the application as mono-tubes may have advantages in some respect but the high-pressure gas can act as a spring complicating the suspension design process.

The main disadvantage of a gas-pressurised shock is cost; more of it compared with a conventional hydraulic. Which leads to a very simple rule of thumb to help avoid confusion. If faced with a choice of gas or oil for the same price, it's unlikely that the real working part of the gas shock is of the same standard and level of sophistication as the oil. You get what you pay for. And, choosing gas shocks generally mean you'll need to design the rest of the suspension system around that fact with spring and bar rates being affected.

imported_loudsubz

What about adjustables?
Adjustable shocks, why use them? A lot of people have recently asked us this question. Specifically why do we so often use adjustable dampers in our suspension kits.

In simple terms, the adjustment of a damper allows for 3 things;

Initial adjustment to allow closer matching of spring to damper rates.
Fine tuning in response to changes to components like tyres or swaybar rates.
Subsequent adjustment to maintain rate as the dampers inevitably wear.
With out going into too much detail as to the types and levels of adjustment, suffice to say that most adjustable dampers allow for changes to the "rebound" rate. This is the extension component of the dampers movement cycle and is the principal force that controls the spring's oscillations. That is, correct damper rebound rate is critical to the spring damper relationship.
Other types of adjustable dampers for the street use a gross bypass adjustment that simply controls the amount of bleed or bypass around the main valve mechanism. This is a very coarse adjustment that is not really suitable for performance tuning as it often forces you to change the bump or compression characteristics when you might only need some extra rebound and vice versa.

Now, being a hydro-mechanical device, the damper eventually wears out. The piston rubbing on the bore of the damper eventually wears the seals, the valve springs get softer allowing more oil to bypass the piston and valves, which control the oil flow and give the damper its "damping" characteristics. The more wear, the less "rate" you're left with.

With an adjustable shock we can compensate for this wear by increasing the rebound rate to bring us back to square one. Now before you start going off about your brand shock never wearing out, accept the fact that any hydro-mechanical device MUST wear out as its operation depends on friction, and friction is a natural wear component by definition. The only issue is how long it takes one damper to wear versus another.

The answer to this is almost directly proportional to the money spent. That is, the cheaper the shock, the quicker it will loose it's rate. This also means that an adjustable damper costing a little more than a non-adjustable will often be the superior choice for road use as it can be made to perform more consistently for longer.

imported_loudsubz

Piston diameter - when size IS important
Why is this so? Because it is often a direct measure of the rigidity of the unit and the oil volume. The biggest enemy of a shock is heat and that is inevitable when it starts to work hard. With increased heat you have decreased oil viscosity, which means a drop off in damping performance and you can understand why race cars use remote canister or reservoir designs to increase the volume of oil and gas. Even multiple shocks with extra reservoir’s are sometimes used in applications like off-road buggy’s and rallying.

Not only does viscosity reduce with heat, gassing and aeration increases further reducing performance. Not trying to be critical of specific brands but many popular twin tube adjustable shocks simply can't go past 2 to 3 laps of a typical supersprint with out the driver complaining of the shocks "going off". We use and fit a lot of this stuff all the time and recommend it but it’s simply not fair to expect say a 30-32mm piston twin tube to deal with spring rates in excess of 250lbs, big swaybars, high performance tyres and hard use.

A graphic example of why piston size is so important is to use Pr2 to highlight what this means in terms of surface area and resultant volume.

Lets first start with a conventional twin-tube stock front strut with a 30mm piston and 22mm shaft and do a rough calculation.

Using “ P” (pie) at 3.14 we get 30 x 0.5 = 15mm radius. Squared = 225 then x 3.14 (P) = surface area of 706 mm2. That’s the oil area below the piston (call it cylinder area), but we need to factor in the shaft above the piston.

That’s 22mm diameter which = 11mm radius, squared we get 121, x P we get 380 mm2. Take the cylinder area or 706 and subtract the shaft area of 380 and we’re left with 326. Hence using this and applying the same process to some alternative sizes we get:

Stock twin-tube strut 30 mm piston / 22 mm shaft = 706 mm2 below and 326 mm2 above. Average of 516 mm2

A nominal “40mm” inverted mono-tube strut design uses 36 mm piston / 12 mm shaft. (Some brands use sizing in their model descriptors which relate to body/shaft rather than piston size).

= 1017 mm2 below and 904 mm2 above. Average of 961 mm2

Group 4 non-inverted mono-tube strut design using 46 mm piston / 22 mm shaft

= 1661 mm2 below and 1281 mm2 above. Average of 1472 mm2

You can see that the nominal “40mm” product will have around 86% more oil volume than the stock strut given the same body size where as a Group 4 has 185% more than stock or 53% more than a nominal “40mm”.

Needless to say, a 46 mm piston in an inverted design will have even more fluid as you can get away with a 12 mm shaft thanks to the body acting as a virtual main shaft but at the expense of the drawbacks of an inverted design. (See separate FAQ topic.)

Obviously this stuff is only important if you plan to get serious and top performance is important but there is no doubt that “bigger IS better” when it comes to piston size.

Monotube shock absorbers - to invert or non-invert?
The following is an extract of a post to NASIOC in December 2003 that discusses the issues relating to inverted vs non-inverted mono tube shock designs. Specifically it addresses the various differences and how the relate to driver and vehicle.

The issue of mono-tube vs twin-tube designs is quite complicated and involved. We are far from worlds leading expert in this field but we've assembled a bit of knowledge over the last 10 years and in particular in the last 2 years while we've been working on our own damper solution.

To avoid restating information, I'd like to suggest that anyone not entirely familiar with the mono vs twin tube arguments also look at the next topic in this FAQ headed "Mono-tube vs Twin-tube - ride characteristics". This was formulated and published at the time that some of you started experiencing a "bouncy ride" with particular brands of coil-overs.

Since that time, we have learnt a bit more and will probably expand the FAQ to cover this better. However, in the meantime we can add a bit more to this debate hopefully making things a little clearer for those with problems.

Any conventional mono-tube (relatively high pressure design greater than 6 bar) has to deal with the problem of shaft displacement. As Archimedes found out, adding his body to the bath forced the water to displace somewhere, in his case on to the bathroom floor. So it goes that as a damper compresses, the shaft entering the damper tries to displace the oil. In a twin-tube this is taken care of by the secondary oil chamber (twin tube) surrounding the primary piston tube that can take the extra fluid via a foot valve in the bottom of the primary chamber. The relatively low pressure nitrogen blanket on top (less than 2 bar) and the use of the foot valve means that there is little force to oppose the shaft displacement except for the valving itself but what happens in a mono-tune running in excess of 6 bar?

The basic design of a mono-tube has the high-pressure gas chamber directly inline with the oil/shaft chamber separated by an additional floating piston. The gas keeps the floating piston hard up against the oil to minimise aeration and cavitation keeping the fluid cooler at the same time, hence why they are fundamentally more appropriate for serious and motorsport use. Unfortunately, you can now see the potential for competing interests with compression and shaft displacement.

The first issue is that at relatively low shaft speeds (comfort range) the entering shaft forces the floating separating piston to further compress the gas delivering a noticeable reactive force. (Note: it is a well known fact that replacing twin-tube with mono-tubes will often deliver a noticeable rise in ride height using the same spring. However we are yet to see any shock manufacturer officially acknowledge this.) The static pressure increases and that is why initial gassing pressure of a mono-tube is so important and part of the shocks “tunning” setup.

Within this same characteristic lies the issue of “cracking pressure”. (Our terminology but called different things by some manufacturers that DO acknowledge its existence/ Sachs Motorsport for one as they have started using revolutionary constant displacement designs in F1). We use this term to describe the shaft velocity and resultant pressure required to “crack” the valves open on the main piston. You can imagine what might happen when the shaft starts moving into the main chamber, a light enough force would simply move the floating separating piston further compressing the gas and acting like a momentary spring rate increase. A little more force however and we actually “crack” the main piston valves open allowing fluid to pass thru the piston, basically letting the shock do what it was designed for. We do not have sensitive enough instruments to measure this but it is our belief (backed by the experience of our backsides) that this contributes noticeable to what a mono-tube “feels” like to drive.

Needless to say we are very aware of this characteristics and therefore went to great lengths to find ways to try to “tune it out” of our Group 4 coil-overs. I believe we have gone 75% of the way to doing so but I guess it won’t be acknowledged until someone on the list actually fits a set and passes on some feedback.

The second issue is to do with inverted mono-tubes designs as mentioned already by many of you. There is no doubt that an inverted design HAS to have more friction than a non-inverted. One can argue till they’re blue in the face about how little extra friction their particular inverted design has but that can not overcome the physical fact that an inverted design has to have more due to the extra seals and guides necessary to make it work.

Imagine the entire body of the shock now operating as the shaft. The up side is that we can now use a 40 mm effective OD shaft (actual body) to give us greater rigidity and strength but we now need an extra oversize seal to interface between the shock and strut body. Secondly, we need extra guides inside the strut body to help the shock body move purely up and down with minimal side movement. Most contemporary struts operate inclined for caster and/or camber so poor guide or seal design and less than ideal material spec will lead to stiction as side loads are not directly transmitted to the vertical.

This is a particular problem for shocks originally designed for rally or gravel competition where the necessity for longer suspension travel means compromises in guide placement to allow long wheel “droop” and shock extension. I guess that’s one reason why our Group 4’s are specifically designed for tarmac or non-rally use to avoid this compromise on relatively short travel requirements.

You can sometimes see the results of stiction as a dulling or blueing of the shaft chrome on one side to the point that you can start seeing lines develop in the chrome. The quality and hardness of the chrome is critical but even the best finish will degrade rapidly if the seals are of a poor quality or the guides are inadequate allowing the shaft/body to deflect or grab through its travel. (or you allow too much dirt in around the shaft)

Now we can throw in some other interesting side issues like the need for air vents in the strut body to stop the shock body acting like an air ram as it moves into the strut. Once you let the air in and out that means you can potentially let water and dirt in as well. This leads to a dramatic rise in effective spring rate to the point that we have seen cars in our workshop that CAN NOT be bounced in the rear. It's as if the rear coils were removed and replaced with wooden blocks, hardwood at that. This is why some brands say that your inverted mono-tubes need an annual service and frankly why so few cars are fitted with inverted mono-tubes from the factory. The maintenance issues are a potential nightmare and are difficult to control within normal new vehicle warranty periods. A WRX Sti is one car that does have stock inverted mono-tubes and we have seen and know of cars that have required maintenance at less than 20,000 kms but this is not that common as many owners of these vehicles replace the factory shocks with something more upmarket and/or expect “motorsport” problems and issues.

Remember that the inverted mono-tube design has its roots in motorsport and rally where extreme use highlighted the benefits of a more rigid strut with long travel and they could afford to dissemble, clean and re-grease each shock after every race.

All of the above issues further contribute to the nature and characteristics of mono-tubes and inverted mono-tubes designs. It is an area that is quite complicated and in our view made more difficult by performance “fashion” trends pushed by certain manufactures as they try to find an edge over their competitors. This is all quite normal and we are in the same race I guess but we decided early in the design process that we did not want to enter the same competition and would do what we thought was best for the market we service and that is, serious road performance right up to weekend competition.

As for the issues of tyres, tyre pressure and strut tops and the effect these have on mono-tube ride quality, most of what has been said already is pretty true. Specifically, one must always think of the total effective spring rate of each corner of the vehicle and what parts of it are damped or undamped. The effective spring rate is everything between the tyres contact patch on the road and the theoretical centre point of the chassis/body the splits the car into quarters. That is, the tyre itself has a spring rate (undamped), the control arms, mounts and mounting bushes have a spring rate (undamped), the actual spring will have a spring rate (damped) and finally the body and chassis will flex with its own springs rate which is undamped.

Any undamped or uncontrolled rate is universally “bad” unless its factored into the handling equation like F1 (or any serious motorsport) tyres are. Hence why we say that there is no such thing as too much chassis rigidity and why race teams go to extraordinary lengths to remove as much undamped or uncontrolled rate as possible.

With this in mind, we can speculate on what would be better or worse in each case of tyre/spring/damper/mount combination but there is no easy or universal answer as it depends on the precise interplay of that particular combination and the shocks valving. If higher tyre pressure works then fine, if softer mounts help then that’s OK too. We on the other hand use some internal valve mods to dramatically dampen (bad pun I know) this issue at low speeds with out sacrificing control.

Even then, there is a chance that a customer’s particular chassis combination will result in some negative behaviour but I guess that’s why they’re rate adjustable.

Mono-tube vs Twin-tube - ride characteristics.
We've assembled some graphs showing the varying performance characteristics of mono-tube and twin-tube gas shocks. You may have seen arguments from time to time about how mono-tubes ride worse that twin-tubes or vice versa. There's also a perception that a mono-tube will tend to "bounce" more at low speed delivering a jiggly ride that some find uncomfortable. Whiteline argue that any high-pressure mono-tube design gas shock will deliver a certain "bounce" in the ride due to the inherent design of a mono-tube compared with a twin-tube. The accompanying information helps to explain why this is often the case.

The following graphs show a force/velocity trace line using a computerised shock dynamometer. Each pair of shocks within each graph was for the same application, using commonly available performance brands. They are "sport" valved for road use and are a good example of their "type". Please note the units of measure used and how they relate. Take particular note of the comment regarding the "Comfort Zone" which exists in the 0.0 to 0.15 m/s velocity range. It is also useful to note the relatively high amount of force in extension vs compression and that initial compression (bump) response is very important in analysing perceptions of ride comfort.

The actual vehicle application and shock brands used are irrelevant for this example and will not be published. The mention of any specific shock brand and design configuration within this article is purely for illustration purposes and may not accurately reflect the brands actual performance across all models. (Sorry, standard disclaimer required.). We also make some generalisations on pressures used and it must be understood that the same manufacturer will use different pressures for different models within the same general configuration.

The first graph (blue vs red) shows a "lower-pressure" mono-tube design vs a twin-tube design. A "low-pressure" mono-tube is a relative description as we are still comparing a gas chamber directly behind the hydraulic chamber with a pressure of between 35-50 psi with a twin-tube with between 10-20 psi as a light pressure blanket in the outer tube. Examples of lower pressure mono-tube shocks include KYB, Tokico, Sachs and Boge. The second graph (green vs red) shows a "high-pressure" mono-tube vs a twin-tube. Pressures here are considerably higher with ranges between 75-110 psi. Examples of higher pressure mono-tube shocks include Koni and Bilstein.





In either case, with any mono-tube you will see a relatively sharp and significant increase in the amount of force required to get the piston moving at slow speeds such as larger road surface irregularities at low vehicle speeds. The classic "anti-example" to this would be the sort of ride you'd feel in an old Cadillac or similar. However an increase in vehicle speed will increase the piston velocity over the same given road surface with a relative "softening" of the initial sharp bump trait felt at slower speeds. As you can see, this symptom is much more pronounced in a higher pressure mono-tube.

Its obvious that the green trace represents a shock with an overall higher base rate that would be felt by any driver however the initial step is the key in how the shock will "feel". In the case of the blue line, the ultimate bump rates of the 2 shocks meet but it is the nature of the beginning of the blue curve that give this shock its particular "ride" character.

These graphs can't deliver a conclusive answer for something that is largely perceptual like ride comfort but an understanding of the differences will hopefully help the driver appreciate what they are actually feeling on the road.

Why should I buy a Whiteline shock, arent they just #$@% brand with a Whiteline sticker?
If a customer was to buy a pair of coil springs from us that looked identical to another brand (from theirs point of view) would that mean that ours is simply a copy of another brand with a different colour? Lets assume not. Then if we acknowledge that we physically did not curl the spring wire into the coil shape with our own hands or equipment then are we somehow deceiving the customer? Is a Whiteline shock only a Whiteline shock if we physically made it in our factory?

Whiteline allocate a unique Whiteline part number to any product that we have added some value to the outcome. This may be as a result of a slight valving change, body modification or even no obvious physical change but the fact that it is listed as a part of a Whiteline kit means that it is designed to work as part of the kit.

In our experience, we regularly encounter situations where a supposed "high end" damper performs abysmally with a desired spring rate or design. This can also be true of cheaper dampers but just like buying shoes, as long as it is a reputable brand, the most comfortable one is arguably the best. KYB, Koni and Bilstein for example are amongst the best brands in the world for quality of manufacture and reliability. If their specifications for a particular damper is a good general fit with our package then we will use it as a base knowing that it will deliver a positive performance outcome and last. Equally, you will NEVER see us use certain brands of shock absorbers regardless of their valving appropriateness.

We do not publish exact composition details of our materials, designs or component interplay as that is the very essence of our value adding and is proprietary information. The testing, analysis and tuning process is what makes our product different and our kits so effective. Customers that choose to purchase our product believe in the value of this process and the positive outcomes it delivers. We do not expect everyone to believe us or feel the same way but we can not call a Whiteline part something else just because it might look like something familiar.

punkindrublic

matt i hope you didn't type all that out.... i read some of it...

good info

imported_loudsubz

you know how lazy I am

j9chan

You da man loudsubz...

bbarbulo

iTrader: (2)

Actually loudsubz is a girl

imported_gatherer

ok I just learnt a ton ...... wow thanks dude thats great chunk of information...

Biggy

good information, i read the first section the scrolled down a bit **** my pants at how much was there to read and went to clean up, havnt been back yet
good info tho, learned alot from that

scott newman

I have a little to add that would condense all of that good info and put it into terms that someone who doesn t know anything about it can understand. First of all, the shock shaft has a specific volume and on a conventional oil shock, there is enough gas, its not air because air will explode under pressure, in the shock body so when the shock shaft fully enters the shock body there is room for the oil to be displaced. Under high shock speeds, not vehicle speeds, that will air-rate the shock and cause the air to go through the vavle oraphis instead of oil, that is when your ride is sacrificed. So then someone decides, hmmm lets seperate the oil from the gas. So they did, there is a small chamber in the shock body that holds the gas usually nitrogen, why nitrogen, because it doesnt change when its warmed up, it wont explode or change pressure. Anyways, the gas is either seperated by a rubber bag that is full of gas or a piston. That is when you would classify the shock as an IFP internally floating piston. So as the shock shaft travels into the shock body, the piston moves toward the bottom of the shock body compressing the gas with the oil that is being displaced by the shock shaft. As for adjustable. the adjustment for on the shock is usually on the end of the shock shaft that is usually the reboud and when you turn the **** or screw or whatever system the shock may have, you are changing the diamiter of the by pass oraphis, that is a low speed adjustment. Thats low shock speed not veh speed. When your shock hits a larger bump and the shock speed increases to a point where the oil cant go through the small oraphis anymore that is when it will deflect the "valve stack" and once that happens there is no adjustment it is fixed. The only adjustment at that time, is to re and re the shock take it apart and tune the valve stack to your own liking. Remote resovior shocks are used to act as a radiator for the oil and sometimes to mount the shock in the intended area of the purpose of the shock. Any more info check on the Ohlins website, I have rebuilt and tuned countless amounts of shocks, not on cars, no one wants to spend the money on real suspension, I cant blame them I wouldnt. On my motorcycle the rear shock assy is around 2600$ before you spend money on valves and tuning. Hope that added a little insight

ryuujin

excellent post loudsubz

umm, there's so much information there, and it's taking awhile before my brain syncs the information.

Coles Notes: remove all undamped and uncontrolled rates and you'll be driving like an F1

spracingsports

that was an awesome read, i love learning this stuff

to loudsubz