About dampers in bump vs rebound

At this point I'm starting to understand Damper settings, I may not have a perfect understanding, but can pretty much get the cars I want to behave the way I need (more or less).

What still confuses me is: How do I set them up for bump vs rebound? I mean, the 650 GT3 has very low bump and very high rebound on all corners , while I believe the LMS Ultra is the other way around. So when do I know I have to ajust just the bump, and when do I adjust only the rebound?

 

Frequency/oscillation considerations should give baseline values but I have no clue about that and always work my way from the Kunos defaults by feel.

You should always exactly know what bothers you about the current setup and never go to the setup screen with a mixed bag of feelings trying to fix it all at once.

Some examples:

If your car understeers under braking, the force is likely transferred to the fronts too abruptly. The front suspension needs to compress (bump) more softly so the tyres can build up lat force. So, lower the bump value.
You can also try the opposite thing in the rear to treat this symptom: stiffen the rear rebound.

If the car understeers under acceleration, the front bump doesn't matter but the front rebound - soften it.

If the rear slides out under acceleration, try softening the rear bump.

Understand the mechanisms and you won't need rules of thumb - you can then systematically approach any issue.

If your car understeers basically everywhere, for example, I'd rather go for anti roll bars, spring rate and ride height (rake angle) first before touching the dampers.

 

Like OP, I have the basic idea how to adjust balance of the car by dampers but is there any good material to study dampers from engineering perspective?

 

In order to understand dampers I use this idea:
Damper is a device that will tell how fast the force will transmit to the attached wheel.
By reducing the dampers function , I will reduce the speed of force.

Example : if I have understeer in corner exit that means that the force due to weight transfer is moving away too fast from front wheels. As such i need to slow down the process and keep front wheels more time under load. So I will soften front rebound or/and rear bump .

Thinking dampers as that I have my thinking more clear.

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I will probably never understand dampers, especially when it comes to more complex settings like fast bump, fast rebound..... But I think I'm getting an idea too..

By reducing dampers rebound stiffness you will make the spring extend faster (force is transmitted to the wheel faster), by reducing bump stiffness you will make the spring compress faster (force comes down slower).

What you said in your example is wrong IMO (somebody will correct me if I'm wrong, I hope - because dampers lol). If you understeer in the exit softening the front rebound will probably help, because front wheels will be pressed harder towards the surface while the weight will be pitching to the back of the car, but with softening rear bump you will speed up the weight transfer as front spring will extend faster and rear spring will compress faster, so even if softer rebound at the front will help to place more load to the wheel faster, part of available weight will also be moving to the back of the car at faster speed. But load on the rear wheels will arrive slower because it will take more time as the spring will be compressing more, lol its pretty messed up with dampers haha

NOTE: I could possibly be wrong anywhere, but I hope not.

There is also lateral weight transfer, and then lateral weight transfer combined with longitudinal... it really gets messed up.... Also dampers affects weight transfer and works together, my brain shuts down here.

Also tire itself is a spring too, now it gets really messed up. Also tires rubber can only take so much... If you understeer in corner exit for example, it is possible that there is TOO MUCH load on them too, because they only can take so much of it (I think in this situation is more due to lateral body roll and weight transfer so ARB setting might work, depends on many things such as elevations, cambers, and curves types....)... I guess it is expected from road tires, maybe vintage tires too IDK...

ALSO there are anti roll bars which are also a bit like dampers for lateral weight transfer, if they are stiff then they are quick. Quick is good for quick short curves, but quick is bad for long fast bends as it gives it all too soon and then tires can't take it, while slow short turns needs available grip soon and quick and for short time. Also AFAIK ARBs also affects weight transfer a lot and works together, it is really too hard to understand for me.

NOTE: I could possibly be wrong anywhere, but I hope not.





I just realized that I don't fully understand how the springs work, are they compressing/extending in steady rates or is there any progression, for example logically spring will compress faster at the beginning, than towards its maximum compression, and the opposite way when extending - will stop extending towards its maximum self extension point. But I guess dampers works together with that....

 

Rebound should usually be stronger than Bump. That is to prevent oscillations.
However, the settings in AC do not represent actual values (with proper units) but are in arbitrary units.
So I'm not sure if you could say that setting e.g. 4 for both Bump and Rebound would mean the same damping characteristics for the two damper operations.
If that were the case, then Rebound should be approx. 1-2 clicks higher.

Don't know if Aris wants to continue his driving school series, but if so, then I guess dampers will be one of the topics for sure.

 

Please somebody, these explanations seem very contradicting, and which way is stiff and which way is loose, higher or lower numbers? and is higher number on compression the same stiff/loose the same or opposite as higher number on extension ? Many thanks for a simplified explanation?


T300rs , t3pa with Bodin load cell brake conversion, t8ha, pc, htc vive, gt omega rig, etc.

 

Lower value = less damping or "softer" in any direction.

Problem is to stick with the correct terminology and I'm sure I fail a lot of times.

Another try: the damper adds resistance to the spring and therefore defines how fast (!) the srping may compress and extend.

Now what does that mean regarding the force on the tyre?!? It means the stiff damper will be reluctant to the force applied to it and forward the force to the tyre, relatively quick without the spring changing length much (remember the stiff damper prevents the length change so the force is applied to the tyre).

Now the soft damper will allow the spring to change length more quickly than the stiff one. During this phase the tyre sees less force pushing down and can use some more grip to take a lateral force (turning). Energy is needed to change the spring length and that energy is what the tyre doesn't need to handle during the force transfer stage.

In both configurations, the pseudo-static force to the tyres should be identical. So under steady cornering when the forces have all been transferred, the dampers' job is done. Up to this point (!), a soft damper will reduce the amount of force pushing the tyre down and a stiff one will increase that force.

I strongly suggest for people struggling with dampers to make some drawings for different situations.

@mantasisg 2 you're right that Jim's example was flawed regarding the rear damper tweak.

 

It's important to work out WHY you're not getting maximum grip from the tyres.... are you overloading them making them slide? Or are you not using the weight transfer of the car to load them up enough? Or is the car over damped and not allowing the springs to do their job? You can find out by adjusting your driving style and seeing what happens.

Depending on which situation is happening will decide whether you soften or stiffen the slow damp settings, there's no simple "just do this to fix understeer" or "do dat to fix oversteer"

People have different driving styles and that often manifests itself in how they approach braking and corner turn-in, and also how they get on the gas to exit a corner..... these are the areas where slow dampers do most of their work and where one driver will prefer one kind of setup whereas another driver will want something different. Which is why if you ask 5 racing drivers you'll get 10 different opinions

The good news is that once you've figured out what works for you, it'll probably work on most cars you drive (the non aero ones anyway )

 

I'm interested too on the matter, in particular about the fast dampers.
Is there any way to tweak from the data gathered from telemetry (suspension velocity and histograms)?
What should be the target shape of the histogram?
Which time interval should be considered for the histogram (a lap, a sector, a corner, etc.)?
Currently I'm tweaking it with a try & drive approach, but the differences in a fine tuning are so subtle that is impossible to achieve it only from driving feedback.

 

Of course every driver is different. But when your driving style makes the car - for example - understeer under acceleration then you can start talking numbers. "What damper tweaks should I apply when my car understeers under acceleration?" should not result in 10 different answers from 10 different people unless at least 8 of them don't know what they talk about.

 

So a simplified line of thought would be:
On braking (and entry) you're taking weight off the back and putting weight on the front. So it will influence front bump and rear rebound.
During acceleration (exit) you're taking weight off the front and putting it on the rear. So adjust front rebound and rear bump.

Does that make any sense?

 

I don't know what charts etc. we can generate from AC but they should show the tyre load when the car drives over undolations such as curbs or bumpy road segments.

Ideally, the fast dampers will work in a way that the load on the tyres remains the same over the undolations.
The slow dampers will be bypassed, AFAIK by some valve trickery.

When there's a bump in the road the fast bump damper needs to be soft enough to not make the car jump. It also needs to be stiff enough so the tyre isn't bounced all the way up by the road bump thus loosing ground contact.

When the tyre has passed the road bump and the suspension expands again, the fast rebound needs to be soft enough to let the tyre down quickly so it doesn't loose ground contact. It also needs to be stiff enough so the tyre doesn't bounce back up after touching the ground.

So, if telemetry shows the same force to ground of the tyre as you go across the bump your fast dampers are well set.

 

Almost correct. It's not weight but force. You got the idea though.

 

I'm not sure if a constant force is possible while going over a bump. I think more likely what you want are smoth transitions of force, as opposed to uncontrolled oscilations caused by tyres jumping up and down.

 

Constant force is your goal during these tweaks that you likely won't reach. Get as close to it, as you can.

 

Higher numbers is stiffer. Stiffer bump is happening faster. Stiffer rebound is happening slower. You want your wheels to have optimal load at all times. You don't want to have your wheels to be loaded or unloaded too fast or too slowly.

But I'm never 100% sure about anything life lol

 

I explain about it in my setup guide & @PhilS13 openly claimed it's the worst setup guide on reddit:
http://steamcommunity.com/sharedfiles/filedetails/?id=912315488

In my opinion:

The rebound value is dependent to the downforce or total weight(mass + G's), as the spring is already compressed from the weight of the car already. The more total weight you have, the more it will likely have a higher rebound value. In big, as soon as you change the aero, knowing how to setup somehow is kind of essential.

The less total weight it has, the less reason it need bump resistance, thus also need less rebound value.

A higher bump value resist more, but allow less for the suspension to absorb energy for the suspension motion, while the rebound value act more like a speed value to handle the energy that have been absorbed by the suspension. Obviously with the car rolling in motion, it also act around that energy.

If the tire slide, the bump value resist less & the rebound work less as nothing is holding. Tire compound absorb energy by holding the car in place. Some of the energy isn't used by the tires which goes to the spring which result compression.

 

I have been tinkering with mountain bike suspension for almost 20 years. I know how springs/dampers (high speed low speed, mids troke ans so on) work and how to set them up properly on bikes. On cars (in sims) however I think it is much harder so I can't really help you with that more than in theory and what has already been said. What I can help you with is both the theory and practical side of how suspension in general works. I'll try to be as clear as possible.

Spring = What determines the stiffness of the suspension.
Hard spring - Stiffer car.
Soft spring - Softer car.
Preload = The amount of force that is put on the spring in it's extended position.
The formula for a normal spring i Y = K * X When adding Preload you get the formula Y = K *X +M
Preload is usually used to raise ride height with out altering the linkage or changing to a stiffer spring.


Damping = What determines the SPEED of the movement of the spring. It does not make the shock harder or softer although it may feel so.
Compression = How fast the spring is allowed to compress.
Rebound = How fast the spring is allowed to extend.

Low speed compression damping (LCD) = Is used to control the speed of the compression when the piston is mowing SLOW through the oil. (weight transfers when braking/accelerating/turning, slow G-outs and so on.)
Let me know if you want a more in depth explanation of different types of valves and how they work.

Blow of valve = When you hit a curb the shock and spring want to compress fast. The piston is forced fast through the oil. Since the LCD-valve blocks the oil traveling fast through the piston there has to be a mechanism to get around this and let the shock compress as fast as needed. When enough (spike) force is applied to the LDC-valve it opens complacently (aka Blow of valve) and lets the oil continue to the High speed compression valve.

High speed compression damping = Is used to control the speed of the compression when the piston is mowing FAST through the oil.
HCD can therefor be the force that is needed to open the BoV or it can be a secondary valv that the oil hits after it has gone through the BoV (or both). All depending on what the manufacturer wants to call it, usually from a marketing point.

Rebound Damping = exactly the same as compression but controlling the speed of the extension of the spring.

Different shocks have different types of combinations av LCD, BoV and HCD valves and they all work in different arrangements.

Adding LCD makes the shock compress slower.
Reducing LCD allowes the shock compress faster.
In my opinion you should never use harder or softer when talking about damping it just confuses people.

Then we have allt the fun stuff with air springs, negative air chambers, bump stops, floating pistons, travel limiters, double barrels (Öhlins), open oil bath, piggy backs, torsion bars....

Let me know if this only confuses you or you want to know more.

disclaimer, when writing something like this I usually mix something up that "was sorted" in my head.

/Anders

 

I doubt that such comparisons make sense since the damper settings seem to be arbitrary values.