Developing a Proper Suspension Model

[Racecomp Engineering]

Originally Posted by cdrazic93

This just popped into my head (either its a super simple answer or complicated) if you match the perfect spring rate to the dampening force, you achive the critical damping ratio (~0.65). When you add adjustability, wouldnt that change the critical ratio? Or is the ratio more of a range thats acceptable given on road circumstances, i.e. higher ratio would be for track and a lower ratio would be on a street car.

The critically damped ratio is 1.0. The 0.65 recommendation is to get minimal overshoot and settle the car quickly.

The Kaz link posted was pretty good (also the part about not getting hung up on ride frequencies, but that's for another time).

"In reality, the damping curve of an actual damper is composed of at least four damping ratios or damping rates. These are typically low speed compression, low speed rebound, high speed compression and high speed rebound"

You may not want the same damping ratio throughout all piston velocities (read: you can do better than that). It bothers me a little when you see a blanket recommendation of "You want to be 65% critically damped" with no further explanation.

As the article said, the "correct" damping ratio is the one that makes your car go fast. It is true that 0.65 is a good place to start your testing. Same idea with the common recommendations on spring frequencies.

There is much more to talk about and I hope to write something later.

- Andrew

[cdrazic93]

i had a feeling that each adjustment needed its own ratio, but i only knew of the 0.65 (.707), didnt know that was for low speed...

[RBbugBITme]

When you have the ability to manipulate all areas of the damper curve you can easily end up with greater than 1 damping ratios in some areas and zero damping in others depending on the application. Understanding this, the knock on affects to springs/ARBs, and the ability to apply it is more critical to going fast than most people are aware. Engines are so much easier to deal with.

[Racecomp Engineering]

Right on.

- Andy

[fika84]

Dampers are confusing to think about because you have to think of something adjusting depending on speed instead of displacement... How do you tune for every different slope change on the ground??

@cdrazic93 It's even more confusing when you start to think that Formula 1 adds acceleration to the mix! https://www.google.com/search?q=j-da...sm=93&ie=UTF-8

[cdrazic93]

Originally Posted by fika84

@cdrazic93 It's even more confusing when you start to think that Formula 1 adds acceleration to the mix! https://www.google.com/search?q=j-da...sm=93&ie=UTF-8

[cdrazic93]

Originally Posted by RBbugBITme

When you have the ability to manipulate all areas of the damper curve you can easily end up with greater than 1 damping ratios in some areas and zero damping in others depending on the application

What would that translate to on the graph? When you say all areas im assuming you mean a quadruple adjustable shock.

[Shankenstein]

Originally Posted by cdrazic93

*cue the angelic chorus*

[fika84]

Originally Posted by cdrazic93

What would that translate to on the graph? When you say all areas im assuming you mean a quadruple adjustable shock.

It modifies the slope of the line. The slope is the damping rate (N-s/mm) when the graph is Force (N) vs Velocity (mm/s).

[cdrazic93]

Originally Posted by fika84

It modifies the slope of the line. The slope is the damping rate (N-s/mm) when the graph is Force (N) vs Velocity (mm/s).

Theres no real time graphing you can do to tune a shock with its adjustments...are there? Besides a shock dyno, like leaving it on the car? Do any of the suspension models get computational enough to take all this into effect?

[fika84]

Originally Posted by cdrazic93

Theres no real time graphing you can do to tune a shock with its adjustments...are there? Besides a shock dyno, like leaving it on the car? Do any of the suspension models get computational enough to take all this into effect?

There are probably some clever ways to do it. You can input real data into the shock dyno for a given track. You can run the shock dyno at multiple different programmed speeds and use the data in data acquisition to get as close to real time damping ratio as possible with linear potentiometers on the shocks to measure displacement and velocity.

The hardest part about trying to do it purely computational is coming up with the right equation for the road surface... it's not a sine wave . Best way to do it computationally would be to drive the surface, take the data from the linear potentiometer and use that as the input for your differential equation.

[Racecomp Engineering]

Originally Posted by cdrazic93

Theres no real time graphing you can do to tune a shock with its adjustments...are there? Besides a shock dyno, like leaving it on the car? Do any of the suspension models get computational enough to take all this into effect?

Do you mean like shock position sensors? Those are incredibly useful for dialing in shocks...generally not used for adjusting on the fly though.

EDIT: i'm slower than fika84 today.

- Andy

[fika84]

Originally Posted by Racecomp Engineering

Do you mean like shock position sensors? Those are incredibly useful for dialing in shocks...generally not used for adjusting on the fly though.

EDIT: i'm slower than fika84 today.

- Andy

And I don't even OWN a racecar...

[cdrazic93]

Originally Posted by fika84

And I don't even OWN a racecar...

oh dear. Shots fired.