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 Post subject: Shock Valving
PostPosted: February 21, 2017, 12:22 pm 
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Do any of you guys know where i can find a calculator to figure out the valving required for a digressive shock??

Thanks!

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 Post subject: Re: Shock Valving
PostPosted: February 21, 2017, 8:07 pm 
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Digressive? Did you mean to say progressive?

Cheers,

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 Post subject: Re: Shock Valving
PostPosted: February 21, 2017, 8:21 pm 
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No that was right.

This is the data I gave Bilstein.
Attachment:
valving 2.JPG
valving 2.JPG [ 105.39 KiB | Viewed 395 times ]

Attachment:
valving 1.JPG
valving 1.JPG [ 104.78 KiB | Viewed 395 times ]


And this is what they replied

Thanks for the info Mo,

 

"If your starting from zero in terms of damping based on a new suspension geometry then a calculator will get you somewhat in the ball park for general linear damping levels based on front and rear axle metrics. But in general our work is primarily motorsport and racing so our experience and decisions on damping curves are based purely on that database of developing many race cars.

As soon as you move away from that purpose and introduce an additional metric that isn’t totally performance driven, it gets much more difficult, as I’m sure you are aware.

My experience is that you will want to bias the damping forces and characteristics towards a road going spec, and then develop the track spec from that.

This ultimately allows you to give the driver a simple change in feel (low speed damping ) without destroying ride quality, pitch and heave modes that you will have spent a lot of time on getting right during your development.

Looking at your initial curves, I think you have the right philosophy with rebound bias and digressive compression. Not sure about the digressive rebound but that could work too for certain situations I guess.

Force levels are going to be totally dependent on your overall road spec configuration, so for development testing  I would suggest to start with digressive compression, linear rebound two way adjustable dampers so that you can get plenty of adjustment range of overall damping on the rebound side, with smaller incremental low speed compression adjustments. Then you can add a rebound digressive characteristic for a second build to test and see what that gets you.

I hope that helps, or gives some perspective at least"


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 Post subject: Re: Shock Valving
PostPosted: February 21, 2017, 11:35 pm 
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That is an exceptionally detailed and well thought out non-answer. It borders on the brilliant :cheers: In leaving you exactly nowhere. :BH:

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 Post subject: Re: Shock Valving
PostPosted: February 22, 2017, 11:00 am 
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Yep. But what I do get out of it is that (and i thought this too) is that the rebound needs to be more linear.

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 Post subject: Re: Shock Valving
PostPosted: February 23, 2017, 12:29 pm 
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mjalaly wrote:
Do any of you guys know where i can find a calculator to figure out the valving required for a digressive shock??
I'm confused. You appear to already have one...Speaking of which, is that a file/program you would be able to share? I'm always on the lookout for more options to compound my analysis paralysis.


Lonnie-S wrote:
Digressive? Did you mean to say progressive?
Lower damper velocities relate more to body motion (roll/dive/squat) control and rate of weight transfer, higher damper velocities relate more to ride control over surface imperfections. Progressive damping would result in weak body motion control and a prolonged weight transfer, while having a rougher ride over road imperfections.


mjalaly wrote:
...the rebound needs to be more linear.
Why?

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 Post subject: Re: Shock Valving
PostPosted: February 23, 2017, 1:05 pm 
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Driven5 wrote:
I'm confused. You appear to already have one...Speaking of which, is that a file/program you would be able to share? I'm always on the lookout for more options to compound my analysis paralysis.


That's from here
http://farnorthracing.com/autocross_secrets16.html

i too am looking for other calculators


mjalaly wrote:
...the rebound needs to be more linear.
Driven5 wrote:
Why?


You shouldn't see a lot of high speed rebound in the shock and I would want the low speed region to be linear to make turns more predictable. I guess it doesn't really matter too much if the rebound is liner or digressive but i would assume that the rebound knob would be easier to adjust if its linear all the way through. What are your thoughts?

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 Post subject: Re: Shock Valving
PostPosted: February 23, 2017, 1:24 pm 
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I think you're over-thinking it. If you come up with what you think is the valving you want, then what? Either you will:

A: Have custom-valved shocks made. In this case, I don't have anything to contribute because suspension's such a subjective thing. I like the story in one of Staniforth's later books, how a driver got a chance to drive Senna's winning F1 car and couldn't stand its suspension settings. The point being, what's fastest for one driver is completely wrong for another - you can't calculate such values.

B: Go with adjustable shocks and set the valving to where you find it does what you want. In that case there's little to discuss since you'll take a first pass at setting compression and rebound to something close, drive the car, make adjustments, and repeat.

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 Post subject: Re: Shock Valving
PostPosted: February 23, 2017, 1:38 pm 
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KB58 wrote:
I think you're over-thinking it. If you come up with what you think is the valving you want, then what? Either you will:

A: Have custom-valved shocks made. In this case, I don't have anything to contribute because suspension's such a subjective thing. I like the story in one of Staniforth's later books, how a driver got a chance to drive Senna's winning F1 car and couldn't stand its suspension settings. The point being, what's fastest for one driver is completely wrong for another - you can't calculate such values.

B: Go with adjustable shocks and set the valving to where you find it does what you want. In that case there's little to discuss since you'll take a first pass at setting compression and rebound to something close, drive the car, make adjustments, and repeat.


That's what I am getting at. I am going to get adjustable shocks from bilstein with a specified valving. You cant buy a digressive compression/liner rebound shock off the shelf... maybe its just really hard for me to find. Also, you only get so much adjustment so i want the initial valving to be close. Yes i can redo the shim stack later but that's just an additional cost i am trying to avoid if at all possible or until the shocks are ready for a rebuild.

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 Post subject: Re: Shock Valving
PostPosted: February 23, 2017, 5:35 pm 
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mjalaly wrote:
That's from here
http://farnorthracing.com/autocross_secrets16.html

i too am looking for other calculators

I'm kind of 'shocked' that I never noticed that there before. My damper spreadsheet was just built off the equations in the KAZ guides here: http://www.kaztechnologies.com/downloads/seminar-downloads/


mjalaly wrote:
What are your thoughts?
That the various rebound damping targets stated so far seem to be conflicting. Rebound biased. Not a lot of high speed rebound. More linear rebound. In my head, it's a 'pick 2' situation. Making the rebound more linear while keeping the rebound bias at lower speeds will result in more high speed rebound. Making the rebound more linear while keeping less high speed rebound will result in less rebound bias at low speeds. And making the rebound bias at low speeds while keeping less high speed rebound will result in a less linear plot.

Which returns me to my question of what advantage you and Bilstein both see in making your rebound more linear but not your compression? I'm not asking because I think it's wrong, or that I know any better, but more that I'm actually looking to better understand the logic behind such a recommendation. Because there are so many suspension tuning philosophies, it's interesting to learn more about the technical reasoning behind each of them whenever possible.

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 Post subject: Re: Shock Valving
PostPosted: February 23, 2017, 9:11 pm 
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I would always prefer degressive compression over linear because of track curbs and potholes that upset the suspension.

I think, and I may be wrong, that the linear rebound would be more predictable and stable on the track. You have more control over lower shaft speeds.

I actually may just pay fat cat motorsports to do it for me ; )

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 Post subject: Re: Shock Valving
PostPosted: February 24, 2017, 11:48 am 
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I asked Bilstein why they preferred the linear valving

Mostly for better range of adjustment during inititial testing. Digressive piston might limit overall damping adjustment across a wider velocity range as once you set the preload to definine your max damping force/ blow off force, you are limited to low/mid speed adjustments without re-valving the damper.
Its by no means the only or best solution, it depends on the number of set of shocks you have to test with. In an ideal world you would have one set of linear and one set of digressive so you can test both.
Dampers are multi functional so the less limitations you have if your starting from zero, the better.

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