Can we talk about dampers?

I'd like to know more about dampers and how they work.

I found a couple of youtube videos on the subject, however some of what I have read seems contradictory.

On the AC Setup screen page for example it states at the front, if you lower the rebound, you should get better front end grip. However from other sources, its the bump setting which does this, not the rebound.

As I understand it, the fast bump / fast rebound settings are for kerbs and severe bumps and the normal slow bump / rebound are for car movements / pitch changes etc.

What would be really helpful would be some animated diagrams showing these things in context. I always find its easier to absorb into the mind when you have such things. Does anyone know of such images?

Any damper help would be appreciated.

 

Suspension tuning is probably the most complex thing to grasp in motorsports. I've spent 4-5 years trying to understand it on my real cars, but honestly until you have enough seat time, it's hard to really know how to make adjustments to improve the car (aside from very generic rules like softening the rear to reduce oversteer, etc). I find it even more foreign in sims. I rarely touch suspension settings in AC because honestly they don't seem to make a quantifiable difference for me. Alignment on the other hand, make a huge different.

 

Sorry for my ignorance, what do you mean by "alignment", alignment of what?

 

Camber and Toe adjustments. The factory adjustments on most of the street cars cause a lot of understeer. I gain 1-3 seconds over a lap pretty consistently just by adjusting those 2 settings.

 

It would be nice to have an app that would load the telemetry and give some advice on the diferent elements of setup.
Ex:

• light understeer - reduce x
• Suspension travel too low the car is bottoming up too much
• 3r gear not optimized - you should increase the ...
• Car too loose at hi speed (rear) - you have two options a or b...
• Rebound too high car losing contact with the ground too often - try a and b...

Maybe it's just a dream but I wonder if the top teams don't have this for further help, the same way they have a software to help them in realtime in race strategy.

Edit: The app could be called "racing engineer" as it would analyze the telemetry the same way a racing engineer would do.
Edit: Probably not a good idea as setups would tend to be the same for everyone.

 

I know a few pro drivers personally and they all do it by feel. They have an incredible sense of what the car is doing through their butt and know just how to take that info and make proper adjustments. They say you just start to get it with tons and tons of seat time and experimentation. I wish I was a Nikki Lauda.

 

One does not simply talk about dampers (at least without swearing profusely).

 

For tuning the slow damping I usually use this chart
http://www.ozebiz.com.au/racetech/theory/shocktune1.html

The whole thing is quite complex but in the end the basic rules are simple.

Where is the car weight going ?
Do I want that weight transfer to happen faster or slower at the rear or at the front?

The most useful are definitely front rebound and rear bump. They affect balance at the release of the brakes and at the application of power. (Phase 2 and 4 in the chart)

A simple example is power application coming out of a turn. Weight is going from the outside to the rear. Outside front moves in rebound, inside rear moves in bump. The other two are considered stationnary. If I increase rear bump, I speed up the rear weight transfer, giving momentarily more rear grip at that instant.

Careful, some dampers in AC have VERY LOW speed threshold so they operate quite often in fast damping even with only body movements. Don't be afraid to play with FAST values they can have an impact on car balance as well.

 

I think a lot of the contradictions come from the street tuning scene where you mostly buy overdamped coilovers that only have one rotary dial that no one really knows exactly what it does. What happens when you adjust those can be way different than adjusting slow-fast bump-rebound independently.

 

So is a lower number (in AC) a slower bump setting or a faster bump setting?

 

No it does not. It states that it reduces front understeer under acceleration. Thats different and IMHO its important to re-read the sentences there over and over and try to grasp their full meaning.

What reducing front rebound does is that when we push the accelerator and weight transfers from front to the rear, the front suspension will act as if it had softer springs for a brief moment, changing the grip balance to the front. This effect is over as soon as the car settles in the new position, but the balance change can settle it with more aggressive yaw angle, making it feel that it works through most of the exit.

While FST_BUMP mentions kerbs mostly, it does have an effect on normal track grip, especially if the car is fast, and track is rough. Silverstone comes to mind - it does not feel "bumpy" but the surface is rough enough to produce high speed vibration for which, in some cases, increasing fst_bump helps with raw grip.

Same goes for slow bump, it does affect grip, less slow bump that you can get away with without wheel bouncing and stability issues, the better grip. But remember that what is important is the strength of the damper in relation to the springs used. If you for example install stiffer springs, or the car starts riding on packers (or even bumpstops) it will need stiffer dampers as well.


Food for thought: try to differentiate "grip" from balance change, and raw "grip" from tyre-track interaction. Some publications will not make clear distinction between them and it starts to be confusing/contradictory as they are independent of each other.

 

This stuff makes my head spin. All that I really know about damping is what can be applied to shocks on mountain bikes. Had a couple of bikes with nice Fox Shocks that allowed adjustment of normal, fast, and rebound damping, plus spring-load (air pressure). One even had travel adjustment, which was fun. If you run too much rebound damping, your shock will still be compressed when you hit the next bump. Not enough and you will bounce and lose traction that way. Easy enough to adjust as needed on the trail for experimenting. But a car? with four wheels plus cambers etc.? Forget it.

(Now I just ride a Surly Krampus with 3" tires. Big tires and my knees+elbows are all the suspension I need anymore.)

 

Dampers... The final frontier of car setup. Just when all other setup options are conquered, then come the dampers.

What I'd like to know is what the front bump damper gives me. In AC it pretty much just says more precise handling and tyre temps (from memory). There must be more to it than this?

 

I think it's faster. If you look at the car engineer app, it shows you how much you have damped your springs. Values less than 1 mean the spring will continue to oscillate after the compression. A value of 1 means the spring is perfectly damped (in a physics sense, not in a car tuning sense), and the spring will do 1 oscillation after being compressed i.e. it will return to its original position and not bounce. Values greater than 1 mean the spring is overdamped.

The point being, that reducing the damper values in the setup screen reduces the damping ratio in the car engineer app, so I take that to mean that the spring is able to move faster.

Optimal damping ratios is a whole other story. The car engineer app should show the fast damper ratios too (like it used to do in netKar Pro), but it doesn't. It only shows the slow damper ratios.

 

Check out that link from ozebiz a few posts up. That can be a damper Bible for setup changes.

This is also a pretty comprehensive guide, talking about booth spring frequencies and damper ratios. http://www.kaztechnologies.com/wp-c...rs-Chapter-from-FSAE-Book-by-Jim-Kasprzak.pdf

One thing I always wonder is just because that theory works in real life, is it necessarily going to work in AC? The answer is possibly no.

 

Dampers are like differentials. So tricky to adjust and discuss because adjustments may have very different effect depending of the situation.

I think this bolded part means that when you're driving over surface variations which are not big enough to go into the 'fast'-territory, by increasing front rebound you're adding a counter force which will fight against the springs that tries to push your front tyres against the track surface and therefore causing understeer.

Bump-related understeer is because when you increase the front slow bump, you decrease the amount of mass moving into the front axle during deceleration or when rolling over surface variations. Actually the force is still there but it doesn't go towards the tyres but it's going straigth forward instead.

That's how I see it. Can be total BS too.

Basing my thoughts for the years of damper setupping experience in RBR and talking with real life rally drivers and mechanics.

 

Nice to see some discussion about dampers, it´s pretty much the one part of setups that I´ve neglected so far. Or as Guybrush put it, the final frontier, well said. Well, vertical and lateral vehicle dynamics wasn´t my best class either, even though we didn´t touch stuff like this there, more like damper and spring charts (dynamic force/deflection), vehicle oscillating frequencies and stuff like that.

I have adjusted dampers more with an eye to bumps and kerbs, weight shift is a very good point, got to fiddle with that.

 

You also need to factor in driving style.

If you stamp on the throttle like an elephant you're going to provoke much more rapid weight transfer to the rear of the car than if you accelerate smoothly. Likewise, if you stamp on the brakes fully instantly you'll get more dive than if you ease them on more gradually, or if you brake lighter for longer.

I'm a fairly smooth driver so I generally need to have somewhat lower slow damper settings than most people, particularly front slow rebound or I get too much understeer. But it's the same for me in every car in every sim so I always end up making the same damper setting changes, with a bit of experimentation you'll find out what works for you. Or it might result in you leaving the dampers alone and just using the brake and the throttle pedals a bit differently, whatever makes you go faster

 

Neither. Lower numbers in the setup screen in AC (and lower numbers IRL) mean less damping (stiffness), not different speeds (although that in turn will allow the suspension to compress/decompress faster or slower depending on if you're lowering or raising the damping stiffness).

This is a good demonstration:

In the video, the smaller the gap gets, the more damping there is. This is what you're adjusting in the setup menu.

 

The easiest way to manage (slow) dampers is to understand their effect on the tyre.
In a very simplified way, looking at every suspension like an oscillating damped spring-mass system, basically the reaction forces transmitted between tyre and chassis via suspension may come from:
- springs: more squat --> more force
- dampers: more velocity in compression/extension --> more force
So, basically the dampers are the primary source of force transmission when the car start to roll or pitch, in general when there is a weight transfer on a suspension, indeed in those instants the force that comes from spring is low because the spring displacement is low.
When the car is running straight or is cornering at constant speed, the slow dampers are quite ineffective.
Higher dampers means higher coefficient of damping then higher forces at the same suspension velocity (F = c*v).
Then "stiffening" a damper is like having a stiffer "virtual" spring that works only in those instants when the suspension undergoes travel variations (velocity) and the higher this velocity, the stronger the force.