Hey everyone !

I think the LFS manual page got me wrong, but it says that increasing the rear compression setting will reduce oversteer at the exit transients while increasing the front compression setting will reduce oversteer at the entry transients.

Since the rebound damping work in the similar way (less damping at rear = more understeer in exits / less damping at front = more oversteer in entries), shouldn't the compression settings work in a similar way as well ? Or is there a specific reason (that I did not see yet) to explain that they operate in a completely opposite manner ?

From my experience, increasing the damping at the rear effectively reduce the oversteer, because the suspension will travel slower and behave like stiffer at the rear, which will transmit all the weight to the tires directly and not only to the chassis. So, about the front suspension, increasing the damping would mean more weight transfered to the tires directly (maybe load is a more appropriate term) instead of being transfered to the front end (I'm sorry, I'm tired and can't find the appropriate words ).

Or if there is a reason for this way of operation, please tell me, because I fail completely to see it

I'm not sure what exactly it is you're asking, but from what I understand dampers don't change the amount of load transferred, just the rate at which it is transferred.

Quote from titanLS :

I'm not sure what exactly it is you're asking, but from what I understand dampers don't change the amount of load transferred, just the rate at which it is transferred.

I must have explained myself in a weird way.

(See the attached picture).

Basically, what I have pain to understand is why a softer front compression setting result in more oversteer in the entry transient whereas a softer rear compression damping result in oversteer in the exit transient ?
Should it work like : a softer rear compression setting result in understeer at the exit OR a harder front compression setting result in oversteer at the entry (depending which initial statement is wrong, if so).

Because the rebound damping at both end of the car have the same result when changed (a softer rebound setting make the weight of a car transfer faster from one end of the vehicle to another). But the compression damping at the front and at the rear do not work in the same way... (as is a soft front compression damper fastened the load transfer, while a soft rear compression prevented it...).

So, I would like to know which of what is said on the picture is true there I think it is the explanation for the rear compresson damping setting and effect of this on the car, because when accelerating, making the rear spring compress slower is more likely to make the rear tires compress instead, this enhancing the understeer. However, for the front compression damping setting, it is the other way around...

So, my question is : Isn't something wrong explained on this picture, if so, what? And if everything is good as explained, if so, why setting the compression damping in a similar way (let's say softer or harder), will imply different effects on the car (or setting them in opposite way will result in similar effects on the car, in the appropriate transient of course).


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EDIT : Nah nevermind, I am getting all confused with the manual, because there must be something wrong about the rear rebound as well in entries, because increasing the rear rebound increases the understeer in entries, doesn't it ?

You sound very confused.

The image is correct, though the wording is not as clear as it might be.

Its basic message is this:

- To increase oversteer (both entry and exit) - soften front and stiffen rear

- To increase understeer (both entry and exit) - stiffen front and soften rear

Of course that's a simplistic view.

The aspect of your post that I will pull you up on is where you suggest,

"I think it is the explanation for the rear compresson damping setting and effect of this on the car, because when accelerating, making the rear spring compress slower is more likely to make the rear tires compress instead, this enhancing the understeer."

Making the rear spring compress slower will not make the rear tyres compress instead. What it will do is limit the load transfer to the rear tyres: less load = less grip = more oversteer.

So, if you stiffen the rear compression or the front rebound, you will tend to get more oversteer (especially on exit) because you are slowing down the transfer of weight to the rear wheels.

Your confusion about the rebound damping on entry is justified, but the solution of increasing understeer on entry by softening the rebound is based on the idea of making the car more compliant; that is, less likely for the rear wheels to skip across the surface.
Again, the issue is more complex and I don't really have time to go through it fully. But the basic message of that image is correct.

Increasing the rear rebound should increase oversteer during corner entry.

It seems everything listed on that chart for corner exit is opposite the way you'd think, not just rear compression.

For some reason I never really focus on the dampers that much for corner exit. I tune the dampers to help get the car turned in and rely on arb, tire pressure, and springs to help with stability on the way out.

Quote from VTRacing :

So, if you stiffen the rear compression or the front rebound, you will tend to get more oversteer (especially on exit)

Right, this is where the chart is off i think.

Quote from titanLS :

It seems everything listed on that chart for corner exit is opposite the way you'd think, not just rear compression.

Actually, I was wrong in my previous post. The image is incorrect to my mind, but only in terms of the compression settings on exit.

Rebound on exit is correct, but compression is back to front.

Sorry.

I was always under the impression that decreasing front rebound would increase oversteer, and increasing front rebound would increase understeer.

Quote from VTRacing :

Actually, I was wrong in my previous post. The image is incorrect to my mind, but only in terms of the compression settings on exit.

Rebound on exit is correct, but compression is back to front.

Sorry.

Yes but there is something weird with the rear rebound on entry then.
The higher the rear rebound damping will be set, then the harder it will be to transfer load to the front end, so the front will have less grip so the car will be more likely to understeer...
If the rear rebound is lower, then it will increase your turn in in entries, but it says the opposite stuff in the chart ?
And you agree with me if I follow your reasoning

Quote from titanLS :

I was always under the impression that decreasing front rebound would increase oversteer, and increasing front rebound would increase understeer.

Well, it depends what part of a corner you're in, really.

Front rebound doesn't have much effect during braking or turn-in. It has a bigger effect during the mid-corner but the largest effect is on the exit when it can help to control the lift (or not) of the nose, and therefore the amount of weight travelling to the rear of the car.

Softening (decreasing) front rebound can promote understeer because: it allows a fast transfer of weight to the rear under power, giving the rear more grip and at the same time it reduces the weight over the front, meaning less grip for the front wheels = more understeer.

At least, that's how it makes sense to me.

Quote from Zen321 :

Yes but there is something weird with the rear rebound on entry then.
The higher the rear rebound damping will be set, then the harder it will be to transfer load to the front end, so the front will have less grip so the car will be more likely to understeer...
If the rear rebound is lower, then it will increase your turn in in entries, but it says the opposite stuff in the chart ?
And you agree with me if I follow your reasoning

Yeah, I can see how it looks like that, but I've found it a little different.

The problem is that you haven't quoted the full image, the entry scenario you've selected is for a high-speed lift of the throttle rather than a braking situation.

I'm currently investigating the full image.

Quote from VTRacing :

Yeah, I can see how it looks like that, but I've found it a little different.

The problem is that you haven't quoted the full image, the entry scenario you've selected is for a high-speed lift of the throttle rather than a braking situation.

I'm currently investigating the full image.

Well speaking of actions that involve footwork, I admit that a higher front rebound would create more oversteer when trailbraking, in order to prevent the weight from going too much to the rear, but for the others there are a lot of things I dont understand ^^

Test, test, and test some more.

You'll find that some changes are more effective than others for your particular style.

Quote from Zen321 :

I admit that a higher front rebound would create more oversteer when trailbraking, in order to prevent the weight from going too much to the rear

I'm starting to confuse myself as well. To induce oversteer during trailbraking, wouldn't you want to focus on the front compression setting instead? Once the car is set and the forward load transfer is complete, don't the rebound settings only have to deal with minor oscillations in the track surface, at least until throttle is applied?

Or did I just make that all up? Where's a smart-ass engineer when you need one?

Edit: And by smart-ass, I don't necessarily mean smart, I mean Tristan.

Quote from titanLS :

I'm starting to confuse myself as well. To induce oversteer during trailbraking, wouldn't you want to focus on the front compression setting instead?

Trail braking is a process by where you reduce pressure on the brakes while increasing steering. So the theory is, you have simulataneous rolling and pitching, where the front inside spring is extending (i.e. rebound), and the rear outside spring is compressing (i.e. bump).

For years I developed sets with the assumption that:

A) rebound dampers are best set at around critical damping
B) compression dampers function much like springs but only for the transient portions of the corner. i.e.:
- more front compression damping = more understeer on entry (typically set around 60-80% of critical)
- more rear compression damping = more oversteer on exit (typically set around 50-75% of critical)

Anyone who has driven my sets knows they are not slow and handle quite well (see my FO8 @ FE4 set).

However, I sometimes wonder if this is too simplistic of an approach, perhaps with wild inaccuracies. It's worked for me thus far, though.

Quote from Bob Smith :

Trail braking is a process by where you reduce pressure on the brakes while increasing steering. So the theory is, you have simulataneous rolling and pitching, where the front inside spring is extending (i.e. rebound), and the rear outside spring is compressing (i.e. bump).

Ahh that makes sense. Thanks Bob.

People, I wanna avoid trying to explain everything because it's been done before. Everyone should just get VHPA (Bob's creation) because it already contains all the damping graphs (and cornering phases) that are explained here:

http://www.ozebiz.com.au/racetech/theory/shocktune1.html

So, read that, then open VHPA and adjust dampers there.

P.S. Phases are called slightly differently in VHPA than in the article, but they are the same.