About dampers in bump vs rebound

iirc "by far worst setup guide on the planet". You forgot the by far and the on the planet

 

Adding to my text..

Some examples of what usually confuses people:
(Taken from the real world helping people with their suspension)


Soft is that the same as slow? No or Yes, need to know more of what you mean...
Hard is that the same as fast? ----//---------

I want to reduce movement should I reduce dampening? No, the opposite. Increase damping to reduce movement.

Slow/fast is that the speed i'm riding(driving the car). No it is the speed of the movement of the suspension.

I bottom out the suspension should i increase LCD to make it harder. No, get the correct spring rate and fine tune with HCD or bump stop (or reduce size of expansion chamber).

 

In most cases, the default value is balanced, except for road car which the suspension is tuned for street tire or road use I suppose. I'm simply claiming that changing the aero setting require change in the bump & rebound value to keep the thing balanced.

 

I doubt the influence is that high. With changed aero, we're not talking about 2× more downforce in most cases, but rather in the range of 10%.
I think the only big influence on dampers would be the suspension setup (including ARB).

Edit: Ok maybe in a car like the 917/30 for which the total weight would change significantly if you run with a full tank, but even then the primary influence would be on the suspension and then secondary on the dampers.

 

Let me tray to put this in other words, not saying you are wrong or right.

Adding aero makes the car effectively heavier (all dependent on speed and the car and so on).
A heavier car need stiffer springs to not bottom out and/or keep its natural position in the travel range.

I don't know how fast aero loads can change on a car and how big the changes are but lets make a hypothetical example.

Car weight = 500 kg
Aero load = 500 kg
Total force on the wheels ~10 000 N

The springs need to be stiff enough to handle the total force so that the car won't bottom out.
A spring stores energy when compressed. The stiffer the spring the more energy.

Lets say that all areo load dissiperas in 0,001 sek. Than 5000 N of force is released from the springs in that time and punschig the car up in its travel (unsettling the car). This is where rebound damping comes into play. How fast should the suspension be allowed to extend to its natural position when only 500 kg och load is applied.

What's important is how fast the the force on the suspension is changing, how much energy is put in to the spring/stored into the spring and how to handle that energy.

To be honest I don't know if aero is relevant here depending on how fast/solw it is applied/changes.

However!
Lets say you drive on a bumpy track, you have springs that can handle 1000 kg load.

You drive into a pothole with one wheel and all the energy that is stored in the spring (car load + aero load) pushes the wheel down. Do you want a slow or fast rebound?
If you had less areo there would be less energy stored in the spring and the opposite.

A fast rebound lets the wheel go into the hole and find traction in the bottom of it, but then the wheel needs to climb back up again.
If you have slow rebound the wheel my just stay in the air and float over the hole not unsettling the car (climbing back up) but also not getting traction from the bottom of the hole.

The example above is not only relevant when adding aero load since aero load is just another type of load. Kids fighting or your daughter having fun in the backseat with her boyfriend are other examples where weight/load/force transfers from wheel to wheel in different speeds.

On mountain bikes there's a lot of personal preferences when it comes to how much you want the suspension to move. All depending on A LOT of things.
How it is in car racing I really don't know. Is there a holy grail or is their personal preferences. I think that on mountain bikes (motorbikes as well) the riders weight, riding style and body language is affecting the ride more then a driver driving in a car which would imply that the with of the holy grail in car racing is narrower. This is where experience comes into play and as I said I don't have that from cars...

Then we have all the differences with on road and off road...

/An

 

There certainly is no holy grail. Like just about everything setup-related, it's a question of which compromise you choose.
And which one is the best might depend on your driving style.

I have seen one approach for damper optimization which was a bit more analytic, involving MoTeC (for GTR2).
In this case you're basically using a scattering/correlation plot for the damper/spring travel speed and then optimize for a specific range.

But I don't know how many people really follow such a route in sim racing.
I guess most don't touch the damper settings at all, even on GT cars or open wheelers.

Edit: I also don't recall seeing values for that in RaceStudio.
(Don't want to use MoTeC for AC, because it's illegal.)

 

Haven't heard about MoTeC before but data acquisition system are quite common now days among the pro DH-racers. They even connect it to the brake hoses to get the brake pressure so that they can see how much the brakes are affecting the suspension.


https://www.pinkbike.com/photo/14813629/

 

There's also the change in center of gravity that actually impact a lot how rebound value need to be set differently while you can keep the bump value about the same. When you brake & accelerate, the amount of force will be different when the center of gravity is changed along with a different brake balance. The car kind of wobble, make the tire heat more than it should or get tire damage if it's not set correctly.

Indeed there's some compromise; how you take corner, the track layout, track condition & compound choice.

 

I won't say how they call that place.
Don't be the guy standing there.

 

Well, it seem I am again correct.

@PhilS13 I use this link as a reference-> https://www.psychologytoday.com/blog/living-the-questions/201401/six-keys-understanding-women

 

Ok, here is some graph taken from telemetry.
It's the SF15-T @ Barcelona, this is an extract from turn1 entry up to the braking before the Repsol corner and it's relative to the rear left.
I'm suffering heavy oversteer when applying throttle through the Renault corner.

The suspension travel is pretty steady but the the wheel load suffer heavy oscillations.
This is the graph of the suspension velocity of the rear left:

What should I try?
Increase the fast dampers to reduce the oscillations?

 

See it like this: bumpers will stop the wheels to go up and the tyres to lose contact with the road and rebounds will bring the wheels back down after going up.
You'll want the bumpers with enough resistance (higher values in the setup) that the tyres are always in contact with the road and the rebounds with enough strength (again higher values in setup) to bring the wheels down as fast as possible back to road if the tyres ever lose contact. This way you'll have always enough grip and traction to control the car according to your own inputs.
Keep in mind, however, that you don't want the bumper so stiff that the suspension doesn't absorb enough the tyre impact, which will make the car lose grip and compliance and make it harder to control and you also don't want the rebounds so strong that the wheels will bounce thus over complicating driving again by cutting traction.
The use of stiffer or softer bumpers or rebounds is mainly track surface dependent but also how willing you are to use kerbs, particularly if they are significantly high, which may unsettle the car to much when riding them, and even can be used to help braking as the car plummets into the road (front wheels going up, once the front suspension is compressed - bumpers - and rear wheels going down, as the rear suspension is extended - rebounds).

 

I don't know what absolute numbers make sense here so I'll stay relative: if the load changes a lot while the suspension travel doesn't, I'd try and turn that around. So I would start and soften the fast dampers and see if the tyre load graph gets smoother while the suspension travel graph gets more spiky.

The graph on the suspension velocity I'd put aside for a second and focus on the absolute travel first. Harmful oscillations should be visible in that one. What's the x axis unit on the suspension velocity graph btw?

 

That's an interesting suggestion, but does it apply to all kind of front understeer?

 

No. In the original context of my post it applies but there might be other reasons for understeer where it doesn't apply. Too little negative front camber, too stiff front ARB e.g.

 

@LeDude83 I have that feeling it's a bad idea to do that on a FWD car

 

My posts were made with an RWD car in mind. But I don't know what single "bad idea" you talk about. Please don't try and turn my thoughts into black and white rules. Understand what a damper does and then reconsider what makes sense in a FWD car.

My take on acceleration understeer in a FWD car: the fronts need to apply acceleration and lat force at the same time while it's being unloaded (load shifts to back). So with your front rebound dampers, find the sweet spot where there's enough force pushing the tyre down during the transition phase. Soft damper takes the load off, slowly. Stiff dampers takes it off, quickly. I lean towards soft dampers - just like with the RWD.

At the same time I'd stiffen rear bump to make the tail step out a bit. AFAIK FWD race cars run very stiff rear dampers for exactly that reason.

Guess this is what I recommended for RWD cars, too.

But the FWD will just rape the fronts no matter what. Only thing that properly helps is a front diff.

 

^^^
You mean transaxle

I like how the bump rebound function as to control the speed of the spring as explained by @agrip 2. It make a lot of sense & much easier to understand how the spring work. Technically the spring doesn't push the tire down, but more the force of the car that do it with arbitary bump value. Which is what the sim gamer have control.

From what I understand with a FWD car it simply pull the weight. Technically depending how fast the car accelerate to follow the wave oscillation from longitudinal transition from point A to B (or circling whatever...), from the braking to acceleration... in my opinion, in may need a faster rebound for maximum efficiency.

If you look at RWD car with a front mounted engine. The car is pushed from the back forcing the front to lift more easily thus again, why in this situation should the car has weaker rebound value as the back end may lift the front? Kind of obvious... it's due because of the bump value is weaker on the back end. It compress so the car stay flat during the transition of acceleration & braking. Ideally you setup the car to follow that wave oscillation on the longitudinal transition.

It's a puzzling translation for sure. Post #30 sure is useful in all sort of situation.

 

Edit:
I think I got you now . Had to read it 2 extra times.
Yes you are right!

Eample:

If you lift a pillow of the ground it will leave the ground "bit by bit", taking the load off the ground slowly.
A soft/fast damper allows for more weight transfers aka taking the load off slowly. That's how you got slow and soft together .

If you lift a steal cube of the ground it will leave the ground instantaneously, taking the load off the ground fast.
A hard-stiff/slow damper allows for less weight transfers aka taking the load off fast. That's how you got hard-stiff and fast together .


Original message :
---------------------------
Could you please clarify this for me?
Soft, hard confusion again.

Do you mean that soft is the same as more damping, aka slows down the movement of the spring?
From my experience people usually say that soft is the same as less damping since more movement in the suspension makes the ride "feel softer".

I quote myself.
"
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.
"

 

A Aha moment!