Damping

[Spiny Anteater]

To be honest, all through FM2 I pretty much left the rebound as was, and set the bump to half that with a possible slight reduction to rear rebound if I needed traction to get out of the corner in a RWD. There was just something about it that I couldn't get my head around - for some reason damping made me feel like I'd received a brain transplant from Jessica Simpson

Then a couple of weeks ago I joined Feuerdog in a room, and he mentioned that he used the damping settings heavily in his tuning, so I figured I ought to make a renewed effort to work damping out. I used it a bit in the Saleen S7, but it was yesterday while building out the Miura Concept when I found the key to my understanding.

TRANSITIONS

Once it clicked that I should adjust the damping to manage my transitions, I felt I was finally getting somewhere again. So today I tried with a B Class RX-8. Initially it oversteered going into and accelerating out of corners but understeered right the way through the middle. Previously I would have tried to tune out the understeer with the ARBs and then messed around with the springs, brake bias and in extreme cases the aero as well to try and sort it. This time, I stiffened the rear ARBs to get the nose to go where I want through the corners. And then reduced the rear damping values (both rebound and bump) to stop the back end coming round when I didn't want it to. The car now feels much more balanced - I think it's faster but it's certainly easier to drive.

So really this is just a big thank you to FD for setting me on the path to damping enlightenment

[feuerdog]

Glad to have helped. It's a really exciting time in tuning when you come to the realization that the numbers don't matter anymore, it's all about the relationships.

As far as damping is concerned, and all other tuning for that matter, remember the method of only changing one thing at a time and only a little at a time.
I only say that because you adjusted both bump and rebound in the rear when you probably only had to adjust rebound.

I said it someplace else, but,.....you adjust bump for how the track moves the car around, and you adjust rebound for how the car moves around on the track,...or something like that.

By softening the rear rebound(and/or stiffening the front rebound) you allow the rear to be more transient(less stable), which promotes weight transfer oversteer.
By stiffening the rear ARB you are adding steady state(mid-corner) compliance(grip) to the front, again promoting oversteer.

These are the two different tuning effects you tuned for....
-The rebound is tuned for transitional response -check
-The ARB is tuned for steady state cornering balance - check

Bump should have nothing to do with it,... not directly anyway.
By softening the rear bump you are actually making it initially slower to respond to throttle inputs.
Easier to drive, yes, but less likely to quickly accumulate grip in acceleration.

Bump should be tuned to allow the springs to absorb impacts(curbs/jumps) without unduly unsettling the chassis(high subjective). These are typically high velocity movements, not the relatively slow ones of chassis movement.

I'd return your rear bump to its initial value, and if throttle applied over/understeer is a problem then i'd revisit the rebound first, the differential or gearing second, and lastly and more drastically the springs. And then there is always the issue of driver input to consider.

So, not to discourage you,....but the train hasn't stopped yet.

[Spiny Anteater]

By softening the rear rebound(and/or stiffening the front rebound) you allow the rear to be more transient(less stable), which promotes weight transfer oversteer.
By stiffening the rear ARB you are adding steady state(mid-corner) compliance(grip) to the front, again promoting oversteer.

These are the two different tuning effects you tuned for....
-The rebound is tuned for transitional response -check
-The ARB is tuned for steady state cornering balance - check

Thanks Feuerdog, and I can see the reasoning for the bolded bit. Only thing is, that doesn't appear to be what I'm seeing in game. It feels that reducing the rear rebound is making the car less prone to turn-in oversteer - I thought I saw that with the Dark Dog S7, and tuned both the Miura and the RX-8 according to that principle which seemed to work (Dirt and Bimmer both saw that car in action last night). I (briefly) tried just reducing the rebound on the FXX as well with similar results.

As for the bump, if there had been no other noticeable changes, I would now be taking your advice about putting it back to its original value. However, I've been using Catalunya National as my test track and it now rides those curbs on the left-right piece at the back of the track much better than it used to. From you response above, that is probably due to me reducing the bump settings and for that reason I intend to leave it as it.

Thanks again. The train may have a long way to go yet, but at least it's cleared the station now.

[Ske]

I recently read something similar (it might have been in one of Feuerdog's posts ) on .net
The essence of it was something like this:

• rebound - driver input and grip
• bump - road surface and traction

It seems to make sense when tuning, and since I'm a sucker for rough and simple explanations this works as a guide for me

But re:Spiny, I've also found that lowering rear rebound tightens the car up during deceleration and lift... which could mean that the default tunes tend to be overdamped. Based on what happens with minimal rebound I don't think the sliders are reversed. Instead there seems to be "sweet spots" in damper tuning in F3 much more than in F2, where higher rebound was (almost) always better.

[Blooze]

Mine, and other's, reasearch into initial setups have found the bump settings to be quite a bit stiffer on the outset than they used to be, and than they are for the "Race" car types.  In the Race cars, the Bump is set to 50% of the Rebound initially, the same as it was last year for all car types.  This year, Production and Pre-tuned types have the Bump set to 70% of the Rebound.  My thoughts are that the Bump values should be reduced immediately, maybe not to 50%, but somewhere in that area (I am starting with 54% and that is working well).  I lay much of the wild behaviour of the short coupled FF cars at the feet of the high Bump settings.  Things like swapping ends in the middle of high stress corners and flipping over from hitting the rumble strips, stuff like that.  The very high ARB values have significant baring on this behaviour as well.

$

[Spiny Anteater]

Thought I'd try this out a bit in the current car (Ferrari FXX) with some extreme settings to try and sort this out better in my head. I ran with 3 tunes: 1) My current tune, 2) Tune with soft rebound, 3) Tune with stiff rebound

Methodology

Run 5 laps of Catalunya National in the FXX. All settings are equal for each run with the exception of the rear rebound setting. Note fastest time from laps 3-5 (laps 1 & 2 are to get up to temperature) and spread of times. Note effect of taking final corner on full throttle on lap 6 (if not used in timed run, lap 6 to be taken at racing speed to keep the temps up). Note any other noticeable effects.

Results

1) Current tune setting (rear rebound = 9.4). Fastest lap was 1.08.9xx with a 0.3 second spread. Car felt stable under braking with good turn in. Full throttle was used on the final corner in the timed laps and the car gripped with just a hint that the back end would break away if I tried to tighten the line any more.

2) Soft setting (rear rebound = rear bump = 4.7). Fastest lap was 1.09.8xx with a 0.4 second spread. Car was very stable under braking and acceleration but seemed to take a long time to settle into a steady cornering state. Full throttle on the final corner induced mild understeer which caused the car to run wide and end up approx. one car width off the track.

3) Hard setting (rear rebound = maximum = 12.0). Fastest lap was 1.08.8xx with a 1.2 second spread. Car was slightly unstable under braking but had excellent turn in. Full throttle on the final corner induced a lurid drift.

Overall, I wasn't surprised to see the version with mild understeer being the slowest - understeer is known for being a racing driver's worst enemy after all. I was surprised that the extremely hard setting was fastest though, but it was also the hardest to drive as can be seen from the time spread. The consistency of the intermediate setup does seem to support Ske's "sweet spot" theory though, at least for this car in a race environment. I'm a little concerned though that my results don't seem to be tying in with FD's advice, so do get a feeling that I've made some elementary error here.

Anyone else got any thoughts on these results? I suspect I may be missing something here but am not sure what.

[feuerdog]

The cars you're mentioning Spiny are mid-engined.

With the relative levels of spring strength and weight transfer effects the results of just rear reound will be tangible but not strong. The generally weaker front springs in combination with the rearward weight bias will make the front end the agile end of the car. The rear being the anchor around which the rest of the car rotates.

By only adjusting the rear rebound you are weakening the overall rebound damping effect, which will in turn change roll transients(cornering) and pitch transients(brake and accel.). If your best time was acheived with a maxed out(12) rear rebound then i'd suspect that your accumulated rebound value(front +rear) might be better a little higher than what you had it.

This time though, when you adjust the rear rebound, also adjust the front proportionally. In this way you retain your overall roll damping(within the limitations of chassis flex) but still adjust the pitch response you are looking for.

Now, on cars with strong front or rear weight biases, the need for more drastic damping adjustments may be needed. A 37/63 RR or a  60/40 FR the spring bias tuning will play a part in how effective the damping rates perform. In these cars you may have to use a little more fine tuning on the heavier end, and forgo some of the proportional damping.

As for this...

Thanks Feuerdog, and I can see the reasoning for the bolded bit. Only thing is, that doesn't appear to be what I'm seeing in game. It feels that reducing the rear rebound is making the car less prone to turn-in oversteer - I thought I saw that with the Dark Dog S7, and tuned both the Miura and the RX-8 according to that principle which seemed to work (Dirt and Bimmer both saw that car in action last night). I (briefly) tried just reducing the rebound on the FXX as well with similar results.

As I mentioned before, by ONLY adjusting the rear softer(faster), you made the front firmer(slower), because the overall ratios only changed in proportion to the rear, the rear will have the more tangible effect. To get back the turn-in response you lost you need compensate according to the spring bias but also at both ends proportionally, like I mentioned earlier. Its complicated.
It's not about soft or stiff, its about force application over time.

Try this:
Raise the front rebound by half of what you stiffened the rear.
Counteract any turn-in understeer you get with a rearward anti-roll bias.
Counteract throttle oversteer with a forward spring bias, and retune accordingly.

In my opinion the "sweet spot" is a combination of settings relationships, not something that is specifically preprogrammed.
 

[feuerdog]

I reminded myself of this a little while ago,...."control the end of the car where the weight is".
By control, you can easily replace stiff springs and firm damping.
I learned this lesson from looking at data for RR and FF cars from real world settings.

Porsche 911's have very firm tails, very well damped and sprung. It's the front end, the light end, that has all the movement and rapid responses.
This is the reason the Porsche is needs "maintenance throttle" to keep the rear in check,....if you let off the throttle the nose will pitch in, bite, and WHIP,...snap oversteer. To plant the rear end on throttle, you needn't do anything but keep the front out in front. The weight transfer and minimal front rebound allows the rear to squat, take a set quickly, and the firm springs allow for instant grip response.

In simpler terms, the light end of the car is where you'll make/see the significant rebound adjustment differences.

For your FXX, and the other mid-engine cars, the adjustment you want to make is stiffer front rebound. If understeer is still an issue, then there is probably an ARB or spring imbalance that will work better.

I'm curious though,....would you mind sharing build data?
If you post yours i'll post what I can get with my custom calcs.

[Spiny Anteater]

Thanks for all your help FD - I will post the FXX build data, but not until tonight when I have the box fired up and the laptop down in the same room. Incidentally, I ran it in the Positano stages as suggested by Career Dude - 37th place on C Reverse and fastest FXX so your advice certainly helped there

Last night I revisited the RX-8 as it seemed from your comments that that was a better test mule. I'll put the build up for that one, but I went back over it using your comments about tying together all the different parts. I think my head is just about cooling down now but I'll put that one up for reference as well.

[Spiny Anteater]

As promised, here's the build data for both cars. The FXX was pretty good out of the box, the RX-8 has undergone more work being taken to B Class via a D Class tune.

R3 800PI FXX:
Engine & Power - Race Flywheel only
Drivetrain - All parts upgraded to Race
Rims: Stock size WedsSport TC105N

Power: 789bhp
Torque: 506lb-ft
Weight: 2529lbs
Weight Bias: 41% front

Tyres: 27/27
FD: 4.34
1-6: 2.89, 1.99, 1.51, 1.20, 1.00, 0.88
Camber: -1.0/-0.8
Toe: 0/0
Caster: 5.0
ARBs: 10.51/8.60
Springs: 512.9/738.1
Ride height: 4.4/4.4
Rebound: 6.8/9.4
Bump: 3.4/4.7
Aero: 331/182 (max)
Brake balance: 47% front
Pressure: 100
Diff: 40% accel/25% decel

B500 RX-8:
Engine & Power - Sport Air Filter, Oil & Cooling, Race exhaust and Flywheel
Drivetrain, platform & handling - All parts upgraded to Race (incl roll cage & weight reduction)
Tyres: Race compound, stock width
Rims: Stock rims
Aero: Front & Rear bumper

Power: 319bhp
Torque: 210lb-ft
Weight: 2566lbs
Weight Bias: 52% front

Tyres: 27.0/27.5
FD: 5.30
1-6: 2.89, 2.04, 1.55, 1.27, 1.07, 0.89
Camber: -1.1/-0.9
Toe: 0/0
Caster: 5.0
ARBs: 24.40/24.20
Springs: 664.8/597.5
Ride height: 6.1/6.1
Rebound: 8.6/7.6
Bump: 4.3/3.7
Aero: 100/200 (max again - don't worry, not all my cars are like this!)
Brake balance: 47% front
Pressure: 100
Diff: 40% accel/25% decel

I know it can be expensive building cars up, so let me know you want a loan of either of these

[barumba]

Spiny, et al, here is a link to a list of useful commentary, especially relevent to this thread are the links towards the end of the list, wheel alignment and shock settings.
Much to learn, but I found these helpful in sheading light on this discussion.
http://www.forzacentral.com/forum/showthread.php?t=33371

[feuerdog]

I'm at work right now so I can only analyze the numbers, but I think I can see the issue you're having.

1. Your high speed cornering is fairly balanced, yes? Maybe even a touch oversteery if you're not careful?
2. Throttle stabs don't do much, it isn't until you can commit to the throttle that the front end will bite,.....but at the same time, you understeer on slow speed corners.
3. Initial turn-in and corner exits feel sloppy, like the car is loose.
4. Everywhere else the car handles well, absorbent to bumps, curbs, and rough tracks like Positano.

Initial observations:
1. Very soft ARBs,....especially compared to the RX-8, which has very stiff. I would double your ARB values on the FXX to start. The ratio is the same so the understeer/oversteer balance should hold staedy, but the transition response should get better overall.
2. Damping,....hmmm. I'd restart testing at 4 bump, 8 rebound, for both front and rear.
3. Aero - The FXX has a strange front aero imbalance, making tuning tricky. I run lower downforce values overall too keep these effects manageable. The FXX is a missile in R3 to begin with, not a grip machine.
The aero is also affecting your high/low speed barking balances. Low speed braking balance, with high speed braking oversteer?
The aero is also messing with tire temps which is why you're running such low pressures. Another issue is maybe the tire sidewall height, I think i'm running 20's on my FXX to keep camber variations in check.


I don't need credits or cars, but I should be able to get the cars driven tonight or tomorrow.

[Spiny Anteater]

There's no rush FD, it's always good to get someone else's input but I don't want it to feel like a job. As for the issues you suspect:

1) Sounds about right.
2) The front end is pretty good on the FXX, even in slow corners - there isn't too much in the way of understeer.
3) Turn in feels good, but the car can be loose on the exit from slow corners if provokes.
4) The car was actually built up for the the Amalfi stages and the high front d/f seems to be a benefit here where (I feel) turn in is very important.

And for your observations:

1) Soft ARBs - to be honest I tried the default tune and ran from there changing the balance according to under/oversteer.
2) Damping - I'll give your settings a go and see what happens, if I'm honest I think I got a bit messed up with this car on that (see below)
3) Aero I've dealt with above (I think if I'd built the car for a 'normal' track I would have run less), but a note on tyre pressures. I've found the FM3 tyres seem to work best around 30-31psi and that is my target for warm tyres. Even with high d/f cars the tyres aren't exceeding 210F (and most are <200F) so they are still well in the green zone on the tyre heat chart.

Looking at your comments and some of Barumba's links (before my brain began to hurt ), I think I may have been using the wrong tool for the job. The Mazda especially had a few (not too major) oversteer issues when the power is applied and I was trying to deal with that by adjusting the rear rebound settings. Both you and the links suggest that I should have been adjusting the front rebound which makes sense now I think about it: by adjusting the rear rebound I was trying to control the extension movement of the rear springs which is obviously not much use when those springs are compressing. If I understand this right, I should be adjusting the front rebound since I am trying to damp down the extension which these springs experience under acceleration.

So, 2 projects for my spare Forza time: 1) Try your recommendations to the FXX and try to get a feel for the changes that has induced. 2) Try changing the front rebound on the Mazda to see if I can control the on-throttle balance that way.

[feuerdog]

Hmm,...i'm not as smart as I might think.

Nice tune Spiny, but I think i'm right about the damping.
I went ahead and ran a hotlap of Positano(my favorite track) and posted myself a decent baseline time for R3. I'm ranked #113 now with your tune and a time of 5:59.639. I went ahead and saved the replay to my storefront for you too.

I can see how it gets loose now, the rear end doesnt seem to always plant well, but it drifts decently enough if you stay on the throttle. Tio me thats a sure sign of too much rear rebound. The front aero definitely keeps the nose tied down, and it s definately sticks the nose into the corners well,.....but it does push a little through mid-corner.
Compared to my tunes it feels well setup, but slightly overdamped. Bump is OK, its the rebound ratios that are throwing it off I think.
I was surprised the ARBs were effective as they were in relation to tire temps. I thought I would eat the tires up,...but it didn't. The springs may be stiff enough to compensate here, and they might play into the over/understeer issue too.
I plan on building my own variant of your build, softening the springs for more pitch, stiffening the ARBs for similar roll resistance, and reworking the damping and aero a bit. We'll see what happens.

I only had to change a few things on my R3 FXX to get it like yours.
I was running lightweight pistons, 20" rear wheels, a sport trans, race oil+cooling, 1.5 diff, and Compmotive ML wheels.

[feuerdog]

OK, interesting results.

The problem with these results is that despite the numbers I do not think they are an improvement on your tune. Your tune is VERY capable. It's easy to drive, control, and push beyond its limits, and even then its easy to keep a hold of.

My retweak of you tune cannot improve your cars turn-in abilities. I didn't even try, to be honest. Your car is set up to turn-in well, but it sacrifices rear end traction to do so. If you tuned out that lack of traction I strongly believe the cars turn-in would suffer. If you could get both of the ends to comply then you'd probably lose some of the cars control-ability.

I threw your build at my new calcs, did some laps, and had a hard time dealing with understeer. I managed a 5:50 lap time , but it was dirty and far too aggressive to be considered easy. Especially compared to the run I did in your tune.

I retweaked my spring bias by 1%, softened the rebound damping overall, and played with all the settings I mentioned I would. After a few more laps, some calc retweaks, and another set of laps of testing, I reset and ran this final lap. Note: the damping values are unadjusted, they are part of my new tuning methodology. They won't make sense, but they work because of other relationships in the values. They do hold value in relation to you settings though, because the concepts of damping are the same.

This tune is not just for Positano, I consider it an ANY track tune,....as such you should experience more understeer than your build, but at the same time it should stay competitive and balanced on any track. I managed a cold start lap on Positano of 5:47.276, which puts me at #45 on the boards. Again, it's not that its a better tune than yours, it's just an alternative for you to consider.

R3 800PI FXX:
Engine & Power - Race Flywheel only
Drivetrain - All parts upgraded to Race
Rims: Stock size WedsSport TC105N

Power: 789bhp
Torque: 506lb-ft
Weight: 2529lbs
Weight Bias: 41% front

Tyres: 27/27
FD: 4.34
1-6: 2.89, 1.99, 1.51, 1.20, 1.00, 0.88
Camber: -0.9/-0.9
Toe: 0/0
Caster: 4.9
ARBs: 22/18
Springs: 505/700
Ride height: 4.7/4.7
Rebound: 6.8/6.9
Bump: 5.1/5.1
Aero: 270/180 (3:2 ratio)
Brake balance: 47% front
Pressure: 100
Diff: 40% accel/30% decel