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Critical Damping Analysis of Ohlins, Tein, Ground Control, and more!
Critical Damping Analysis of Ohlins, Tein, Ground Control, and more!
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Old 11-03-07, 08:12 AM   #11
ace996
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Default Re: Critical Damping Analysis of Ohlins, Tein, Ground Control, and more!

Quote:
Originally Posted by stretch View Post
Hitting a raised manhole might be 20in/second, but a wrinkle in the pavement might be 8in/second. I doubt a track car often sees much above 5in/second.

I'd only consider a damper truly overdamped if it is above 65% critically damped through its entire range. Below that, you're right, I think I'd need more data to see how the slope affects things.
A performance application or race application is not going to consider a 20in/sec rate. The application will require a certain valving based for certain speeds - a rally car requires different valving than a tarmac car...and a car driven on the street requires different valving than a track or solo car. What is this thread shooting for?

And then there's the limited data from one set spec of springs. Those same cars mentioned...track/rally/street... will require different spring rates. So the overdamped strut on the street, at a certain valving, with 400s may very well be the dead-nuts-perfect damper for that same car with 600s.

And then there's the differences of track-to-track valving requirements. From my experience on track, with stock and RacecompEngineering Tarmac2 coilovers...with 500/400 and 600/500 rates..., each track will dictate different valving requirements. This is why racers keep datalogs and set-up sheets and laptimes.
To add even more uncertain footing on valving...temperature changes will effect damping. A shock may be perfect on the first lap, but be weak/underdamped on the 10th due to fluid heating. Many of the top damper manufacturers employ reservoirs to help with that fluctuation and bubbling.

I wonder if those graphs/plots were on cold dampers...that would be unfortunate.

So...for all the different variations of where one drives...what tires one uses...what swaybars one uses...what time of day/temperatures are experienced....to really have dampers that will be flexible enough to suit all theose needs is very difficult, close to impossible if they are not adjustable and marginally acceptable if only single adjustable.
To meet those needs...double adjustable with reservoirs, and a wide scope of adjustment, is nice to have. This seems to be why Konis and RCE T2s are so loved...they can handle a broad range of spring-rates and have the ability to be adjusted properly to those springs.

Finally....the driver needs to be comfortable with the set-up. One may have the best, in theory, set-up but if the driver prefers a softer or stiffer set-up due to driving style then it all goes out the window...


One can use all the theory/calculations/plots in the world, it still comes down to getting out on the tarmac and dialing it in.


Be good,
TomK
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Last edited by ace996; 11-03-07 at 08:23 AM.
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Old 11-03-07, 08:27 AM   #12
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Default Re: Critical Damping Analysis of Ohlins, Tein, Ground Control, and more!

Tom, I was agreeing with you. Different cars seen different shock motions. The 65% guideline is, as far as I know, always used in reference to driving on-road and not off.

While important, the comment of tuning for 65% critically damped refers to rebound only to control the reaction of the spring. It is an average, not a constant, and most shocks will show some amount of digression. You'll find advise elsewhere to stay within 1/3 of rebound forces for bump for any car; most dynos I've seen stay much closer than that. These are pretty vague requirements so it's not like anyone is saying there is one perfect strut that would work for everybody.

You're talking beyond the scope of this thread, though, with changing spring rates and valving for a specific track. The point of this thread is only that the strut has to match the spring, and that's what the graphs intend to show. Nowhere do these graphs suggest a spring rate.

Some guys may run tons of rebound or no bump to get a car into its desired response on a track, but that's usually more of a hacked fix for a different problem. So again, that's a different issue of compromising the damper settings to make gains elsewhere.

Again going back to Dennis Grant (sorry to reference him so often, but he's got the best online information on the subject), he has this to say on the topic:
Quote:
Note that I consider knobs on shocks as ways to get the forces to match on the dyno, or to rough in forces while testing; I never, ever, ever muck with the shocks during competition. I've run hundreds of shocks on my shock dyno and the repeatability of shock adjusters is downright horrible on anything except the highest end shocks (and even these have their quirks). When you have the damping right, it's right - unless you do something to change the natural frequency. Changing the shocks to try and change balance is an act of despiration - or of a Stock class car, which has little other options.

Last edited by stretch; 11-03-07 at 08:45 AM.
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Old 11-03-07, 09:05 AM   #13
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Default Re: Critical Damping Analysis of Ohlins, Tein, Ground Control, and more!

Quote:
Originally Posted by stretch View Post
While important, the comment of tuning for 65% critically damped refers to rebound only to control the reaction of the spring.

The point of this thread is only that the strut has to match the spring, and that's what the graphs intend to show. Nowhere do these graphs suggest a spring rate.
Stretch,
I believe each dyno has a listed spring-rate. How can one judge the under/overdamped-ness of a strut without taking into consideration the spring that will be used? You know, one is not independant of the other.
And most dynos show force x speed...those are CD x speed. CD can only be shown with a chosen spring rate.

I say those spring rates are too soft for track/solo. Perhaps nice street rates, though.

Be good,
TomK
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Old 11-03-07, 09:22 AM   #14
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Default Re: Critical Damping Analysis of Ohlins, Tein, Ground Control, and more!

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Originally Posted by DuncanG View Post
Promising project but only when backed-up by real testing.

When theory disagrees with reality then the theory is wrong. As an example the 'theory' as presented seems to indicate the Ohlins are horribly overdamped but I think you'll struggle to find anyone who says they are actually horrible. Lets not get too fixated on a 'golden' 65% number.
Testing is exactly what I'm asking people to respond with. For example, someone out there with say, Tein Flex's could read this thread and could try running his car at full stiff for a few days and tell us how that feels. The could run it at full soft for another few days. Then somewhere in the middle for a few days. Then the driver could come and share his specific thoughts on how each setting performed. In this case, there would be roughtly a 200% change in damping and alot of us probly don't know what that feels like. After getting a few different opnions, we might be able to draw some conlusions about what feels good and what performs good.
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Old 11-03-07, 09:23 AM   #15
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Default Re: Critical Damping Analysis of Ohlins, Tein, Ground Control, and more!

I'd love to see an Ohlins Fixed Perch with RCE Blacks.. Playing with Stretch's calculator and listening to those who have Ohlins, that combo seems like it'd be the ultmate DD/Track setup for those who don't want to go CO.
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Old 11-03-07, 09:23 AM   #16
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Default Re: Critical Damping Analysis of Ohlins, Tein, Ground Control, and more!

I have never seen a dyno plot of this particular damper. I would love to though, being as how everyone says how great it peforms.

Quote:
Originally Posted by chaos311clarity View Post
and how about some Ohlins FPS/RCE yellows, that seems to be a fairly popular street set up... and mine lol
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Old 11-03-07, 09:28 AM   #17
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Default Re: Critical Damping Analysis of Ohlins, Tein, Ground Control, and more!

I think what Stretch ment was that we should focus the discussion on the springs that come with the dampers. We could go off on a million tangents if we were trying to determine the best spring rate for a given damper. If it will help everyone focus their opnions, lets try to stick with street driving since I think that is the inteneded use of most aftermarket coilovers.

Quote:
Originally Posted by ace996 View Post
Stretch,
I believe each dyno has a listed spring-rate. How can one judge the under/overdamped-ness of a strut without taking into consideration the spring that will be used? You know, one is not independant of the other.
And most dynos show force x speed...those are CD x speed. CD can only be shown with a chosen spring rate.

I say those spring rates are too soft for track/solo. Perhaps nice street rates, though.

Be good,
TomK
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Old 11-03-07, 09:36 AM   #18
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Default Re: Critical Damping Analysis of Ohlins, Tein, Ground Control, and more!

Just wanted to say thanks to Myles for providing me with the actual spring rates for the RCE yellow springs.
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Old 11-03-07, 09:38 AM   #19
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Default Re: Critical Damping Analysis of Ohlins, Tein, Ground Control, and more!

OptimumG has some great reads pertaining to the same topic as this thread:
Untitled Document

They cite 65-70% critically damped as a good baseline for race cars just like everyone else. However, they're more specific than other sources by saying that should be the amount of low speed damping on rebound. They do say more may be required to account for sway bars during body roll.

Body roll happens at what, 3in/second? This split point will probably vary a bit from car to car, but beyond that split point, we should expect to never see beyond 70% critically damped (according to the articles).

OptimumG suggests tapering off to lower than 70% (much lower) in the high-speed region to minimize the reduction of grip from track bumps.


Quote:
Originally Posted by ace996 View Post
Stretch,
I believe each dyno has a listed spring-rate. How can one judge the under/overdamped-ness of a strut without taking into consideration the spring that will be used? You know, one is not independant of the other.
And most dynos show force x speed...those are CD x speed. CD can only be shown with a chosen spring rate.

I say those spring rates are too soft for track/solo. Perhaps nice street rates, though.

Be good,
TomK
The equations do take into account the listed spring rate. If one were to change from the default spring rate, the graph would change. Obviously the images aren't interactive, though. You can use my spreadsheet to plot the change to %cd due to a change in spring rate.
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Old 11-03-07, 11:16 AM   #20
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Default Re: Critical Damping Analysis of Ohlins, Tein, Ground Control, and more!

One thing that hasn't been taken into account here is the nature of progressive springs. We are just plugging in the spring's overall rate as if it were linear. However, especially on a street car, the rates of the progressive coils are important as well, and vastly complicates things. I'm with Tom on this one, real world testing is more important than analyzing graphs and numbers, although they both have their places. The one thing that I keep thinking is, if the engineers at these large companies (Ohlins comes to mind) didn't catch the fact that their coilovers are "overdamped" how is it that we can do it so easily? I think the testing done here is not nearly as thorough as it would need to be to even come close to giving a realistic view of a damper/spring's ability. There are other variables, like oil temperature and ambient temperature (as Tom mentioned). I just don't know if we have the resources to conduct testing on the same level as these manufacturers do, nor does this Dennis Grant guy. Just my opinion, take it or leave it. It's fun to analyze this stuff but it will take a long time and a LOT more testing to get a realistic view of the big picture.
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