I still dont quite understand how to read these shock dyno graphs. I learned quite a bit after reading what resolute and akomsr1 had to say.

In for further reading..

 

Ok ok! I think im starting to understand alittle more how to read this.

First, to make sure i understand the velocity side:

Velocity side stands for the number of in. per sec. the shock's compression travels, correct? Does this side stand for both compression and extension in velocity? Does the -/+ on the force side govern where the shock is being compressed/extended?

Next, please explain to me force side of the graph alittle bit?

 

Here, this link should help clarify

http://www.circletrack.com/techartic...yno/index.html

Few basics (We will only concentrate on rebound for simplicity) Keep in mind the charts shown on that sight and what's posted here:
A car's pitch and roll during corner phases occur at a shock velocity of around 2in/sec or less. Therefore, a vehicle's balance will be determined by the shock forces produced at a velocity of 2in/sec or less (This is called low speed rebound).
-With a digressive curve, higher shock setting will result in a higher rebound force at a velocity of 2in/sec or less. This valving has the most effect on low speed rebound (Greater increase per higher shock setting) thus provides the greatest change in vehicle balance with different settings.
-A progressive curve will not have any effect on rebound force at a velocity of 2in/sec or less. This means you will not be able to tune a car's balance adequately using a progressive shock curve.
-A linear curve does effect shock forces at a velocity of 2in/sec or less but not as much as a digressive curve.

Anything higher than a velocity of 2in/sec or less is a result of a car hitting road imperfections.
-A digressive curve will taper off the slope of force/velocity so the shock will not produce too much rebound at high shock velocities so the wheels can stay in contact with the road.
-A progressive valving will exponentially increase shock rebound with velocity. So, higher shock settings on a progressive valve will 1)not effect low speed rebound needed for corner phase handling 2)produce too much rebound at high speed causing the wheels to bounce over bumps.
-A linear valving will be in between both.

*Note: Sometimes a linear valving is preferred over progressive valving depending on vehicle setup.

Also, please look at this link. A lot of articles pertaining to how to setup a vehicle and what shocks do. The most important articles are the ones under "Chassis Newsletter" written by Mark Ortiz located near the bottom of the page
http://www.auto-ware.com/techref/lib_index.htm

And this might be of interest to some:
http://www.theoryinpracticeengineeri...ter/2001_7.pdf

 

So then a system with a digressive curve would be the best for a race setup, because you can adjust corner balancing (under velocity of 2 in/sec) ?

Linear would be the happy medium between a race/street setup

And progressive would be purely street and worst for race?

 

The Koni's and buddy clubs seem to be the direct opposite of the Arks. They are digressive on the negative force side whereas Arks are digressive on the positive force side.

 

Message too short....

 

IMO, you never want a progressive valve for any reason. Not good on the track. Rebound forces ramp up exponentially at higher settings so they will be overdamped on the street (theoretically).

Remember though, in the real world as proven by the actual shock dynos, a shock can move from being progressive to linear to digressive as settings change. Also, most progressive shocks become linear at higher speeds so they don't exponentially ramp up shock rebound to infinity (shock locks up). Is a progressive shock fine for the street? Sure, if comfort is you main goal it doesn't really matter.

Note: A shock dyno cannot determine how your car will handle, how well it will dampen spring forces, how comfortable the ride is, etc. These graphs don't tell us anything about the real world. You'd need to put a bunch of sensors on your car to do that =)

 

Awesome articles bro, just read them, and i understand a ton more now.

-going back to look at Ark's results...

 

To me the Ark shock looks like (no offense to Ark) nothing special at all, but simply an almost perfectly linear shock. Rebound seems to stay linear with an increase in velocity, and the compression changes with settings, but not as much as the changes in rebound per each setting.

To me the shock is obviously much better than a progressive, but it should be anyway if digressive is the newest technology. It is very average in terms of control of damping at a velocity at or less than 2 in/sec. Like stated above, there is a lack of "knee" or digressive curve at and before 2 in/sec.

And this shock doesnt seem to have any adjustment from Progressive to linear to digressive or vice versa.

Is this a fair assesment, or am i still reading wrong?

 

You don't want the shock to be going from progressive to linear to digressive (although it does beat just having the shock be progressive at all settings). I just showed that as an example because it does happen and it happens a lot, unfortunately. If the shock's force curves are changing with each setting, then you are not getting consistent force changes in the low speed with each new setting. This can cause problems when tuning the vehicle.

Idealy you want a digressive curve (or sometimes linear, but very rarely) at all settings and an equal amount of increase in force per shock setting. This helps with the consistency needed for fine tuning. In the real world you probably won't find a set of shocks that do this for less than $2000 so don't expect a set of $1000 coilovers to be without flaws =)

 

Without any comment on anything anyone has said, this is what I see.

Mild low speed control that digressively tails off to mild high speed contol on the compression side. Rebound is faintly progressive at full soft, but at about a 20lbs variance it's not worth mentioning, might as well call it linear. Full stiff on the rebound side front and rear is linear. IMO, Ride quality should be decent and high speed events like sharp bumps and tar strips shouldn't be too bad. What we don't see are the quicker ramp ups in low speed control to really call these preformance dampers, but that absense is also why we can say ride quality should be pretty good, but we cannot forget the spring rates are on the high side, kind of wild card and why just sitting here looking at all the numbers isn't a 100% guaranteed thing.

Where I see them giving some ground to some of their peer's, would be in the level of low speed compression at full soft* in the rear and how at full stiff front and rear, 0ips to 3ips, low speed compression is exactly the same front to rear. To me these differances would effect at the limit behavior. Seeing the valving and knowing the high spring rates I'm struck with the thought that it's a odd pairing, the rates suggest a higher performance calling that the valving doesn't suggest that, just seam's odd to me.

One thing that does concern me, the force vs absolute volocity plots suggest the presense of internal pressure imbalances or hysteresis. If I could have the raw PVP or CVP files emailed to me, I can confirm or deny that.

The dyno's shown were on the dark side, I brightened them and cropped them to fit, hope no one minds.

 

Hey guys, DG from Far North Racing here.

Firstly, good on you guys for insisting on dyno plots.

Secondly, good on the manufacturer for stepping up and providing them. That's a good first step.

I can see there's some confusion on what the plots actually MEAN (and I'm going to add a page on the site to discuss that shortly) but here's the nutshell summary.

1. These plots were done at high speed, which means a peak speed on the order of 10 in/sec. That's fine; high speed plots tell you how the shock is likely to react on bumps. To get the whole story though, there needs to be a run at low speed (peak speeds of ~ 3in/sec) which is where all the "handling" stuff happens.

Can't you just look at the low-speed portion of the high-speed maps? No. Inertial effects and time delays (it takes a finite amount of time for shimstacks, check valves etc to open/close) plus a raft of other factors mean that the low speed plots and the high speed plots are usually substantively different. Usually, running the shocks at high speed will "smooth over" low speed effects - an easy way to make a marginal shock look better is to run it at high speed. Not that this is what happened here - no rocks being thrown. But many manufacturers have been bitten by only running shocks at high speed and missing oddball low speed behaviour.

2. It looks like we got two runs here: one at full hard and one at full soft - at least, that's what I hope I am seeing. If those are two separate shocks with the same valving, then we have a problem, because while the curves are similar, the forces are way different.

Let's assume that these are two runs on the same shock with different settings - because that is far more reasonable than the alternative.

OK, so we have a single-adjustable that changes both compression and rebound at the same time. That's a basic adjuster. Normally I like to see independent adjustments (ie rebound only or compression only) but it can be very difficult to completely isolate adjustments and a little bit of crosstalk is normal. There's too much change here for this to be just crosstalk, but the range on the compression side is also fairly narrow so it's not too too bad. I have see eg Teins that exactly mirrored compression and rebound and those are simply unworkable.

As far as the shape of the curves go, the shocks are fairly linear. Compression is digressive-ish (there's no hard knee) but really, that's neither here nor there. The fade towards digression will help somewhat with higher speed bumps, but these are smooth-road shocks, not WRC shocks.

Forces I can't analyze because I don't have enough information - I'd need to know natural frequencies, motion ratios, spring rates, corner weights, unsprung weights etc.

My initial take is that these are a reasonable budget shock, but there's a lot of information missing.

First, I'd want to see a full sweep of each shock at 3 in/sec, where a full sweep is a run for every click of the adjuster (or for a Koni, a quarter-turn) The 3 in/sec peak speed gives you the low-speed behavior of the shock, and the full sweep (one run per click) tells you how the adjuster behaves. Perfect is a linear step between each click. Reasonable is the force increasing by some degree with each click stiffer, with some clicks (usually on the soft end of the range) doing nothing. Fail is the shock getting softer with each click stiffer.

Then what I'd want to see is 2 or more shocks with the same part number overlaid, at both 3 in/sec and 10 in/sec. Full sweeps are usually too busy to read, but a hard/soft run for each is fine. What I'd want to see is the forces the same for each shock to within at least 3%. More than that is a fail.

When I was selling shocks, EVERY SINGLE SHOCK I sold came with a full sweep at 3 in/sec, and a hard/soft at 10 in/sec in the shock box. If you bought a pair, you got a hard/soft 3in/sec overlay with it's mate, and if you gave me a spec for where you wanted to start, I'd tweak the adjuster to meet your spec and match them left and right as closely as possible - and you got a plot showing the two shocks overlaid where they were out of the box.

I consider that the standard for a performance shock. This means that a shock vendor had better own his own dyno....

DG

Read my book: http://farnorthracing.com
Read someone elses: http://farnorthracing.com/stu/books.html

 

Cool, thanks for the info.
Welcome to the forum.

 

Hi Dennis we've talked a couple of times on Sccaforums. Curous, if these plots show a smooth road shock, what and where would you reshape the curves for less then smooth roads? I based my comments that the ride quality "should" be decent on haing done R&D for FatcatMotorsports on a Bilstein revalve, looking at the trial and error plots from that and from the Ohlins PCV setup I'm on now and the plots from that setup. I don't see the spring rates this kit comes with allowing the 0ips to 3ips range to be lowered all that much, though I still don't care for how much control the rear has at full soft vs the front.

To answer some of the unknow's

The Ark coilover shown comes with the following spring rates
675/616

Front Motion rate .688 = wheel rate based on above 318lbs
Rear Motion rate .649 = wheel rate based on above 259lbs

Typical corner weight from a base 2006 350Z

Total: 3,217 lbs.
Front: 1,792 lbs. - 55.7%
Rear: 1,425 lbs. - 44.3%
Left: 1,583 lbs. - 49.2%
Right: 1,634 lbs.- 50.8%
Cross (RF/LR): 1,598 lbs. - 49.7%

LF: 889 lbs. RF: 903 lbs.
LR: 694 lbs. RR: 730 lbs.

With Driver

Total: 3,432 lbs.
Front: 1,890 lbs. - 55.1%
Rear: 1,542 lbs. - 44.9%
Left: 1,741 lbs. - 50.7%
Right: 1,691 lbs.- 49.3%
Cross (RF/LR): 1,697 lbs. - 49.5%

LF: 966 lbs. RF: 924 lbs.
LR: 775 lbs. RR: 767 lbs.

 

Props to ARK for stepping up and publicly releasing info that could very well have buried their product!
Judging by how nobody laughed at and/or started ripping the charts apart, the product must be AT LEAST decent.
Although I tried to keep up with what everyone was saying... is there someone who could compare them to other real-world examples? DG-FNR hinted that there is no solid way to predict how these will run... but can these be compared to other coilovers based on the dampener alone? For example, do you believe these are similar to say.... Stance or Bilstein or BC? Mostly just to figure out just how good of a value these are in comparison to other brands.

 

No their isn't a solid way to know how they would run. But, I have been on several different setups that I have dyno plots on, so I know how the platform react's to different damping forces. Spring rates don't operate in a vaccum, so that is a factor as well.

Their are some basic conclusiion's we could draw, if someone were to provide dyno's for Stance and BcRacing. They'd have to come from a end user, don't see either of those manufactuers using the same standards and was seen from ARK.

I have plots for Bilstein Pss9, Kw Varaint 2, Ohlins PCV, Truechoice Phase 4, TcKline and OTS Koni Yellows. Unfortunately, I am bound by a promise I made to FatcatMotorsports that I will not post the plots, sorry.

 

Of Course here at ARK Performance, we want the best for our customers. We will continue to provide more detailed information to the community while setting a higher standard for Suspension Coilover performance. Like I have mentioned before we will also be working with Performance Shock to gain more information.

Alex

 

There isn't enough information provided in the plots to make a determination yet. The shape of the footballs is reasonable enough (no major lags or asymmetries) but really, that's neither here nor there.

One of the major challenges that comes with being a racing engineer is you cannot react on gut feelings or brand loyalties. You need to restrict yourself to hard data and try and keep personal feelings out of the mix. Ark would not be the first supplier to be really nice guys with crappy product.

Oh no you don't. I'm not providing consulting for free - I have to eat too you know.

You can, however, run these numbers through my suspension calculator and see how they look: http://farnorthracing.com/autocross_secrets16.html

With a purely linear shock, forces increase with increased suspension speed. Eventually, you reach a point where the shock forces are so large in relation to everything else that the suspension is effectively locked solid.

This problem can be addressed with digressive valving. Effectively, once the suspension is moving fast enough that it can only get there is response to a bump, you back the damping force off so the force gain with speed isn't as steep.

It doesn't appear that the amount of force in the digressive part of the curve is really critical. Bumps happen very quickly, so I think it is more about getting the shock "out of the way" than it is an active control issue. I've seen ranges from 0 slope (shock is capped at a certain force value) to 35% slope and everything seems to work here - at least from a racing perspective. I'm not a ride quality guy (although I do note that when race shocks work really well, the ride quality is usually very good even with insane spring rates)

Where the knee needs to happen is simple - outside of the range of chassis responses to cornering inputs. That normally means north of the 3 in/sec range, but the only way to be sure is to record suspension movements and see the chassis responses yourself.

As a general rule of thumb, you want 65% of critical damping from 0-3in/sec, and then flatten the curve off after that.

DG

 

Gotcha, makes total sense. I appreciate you guys helping me understand these results alittle more!

I wonder how these would compare to the Tein Basics, minus the damping adjustability in the Arks, just for purposes of ride quality at different heights. Id love to know, seeing as how both are in the same price range, only the Ark offers added benefit of the adjustable damping.

Also, curious as to why this dyno was done in only full hard/full soft? Why not throughout the settings like the Buddy Club/Koni dynos? Wouldnt this the prudent test?

 

Now as we keep on getting more information with these dynos. I challenge the community to get dyno plots from other companies. Such as stance, D2, BC, Tein, JIC, Tanabe and etc. We did what we did as a manufacture to provide a 3rd party dyno shock. We want to compare other street coilovers in the market now.

Members should start a general post so the community knows exactly that they are paying for.

Alex