Is there a legitimate place for overdamping in real life racing and thus in a simulator?

I see it used in a remarkably high number of WR sets and as a consequence in a lot of sets that float around the community. I have the feeling it alters the handling in unrealistic ways and allows for other weirdnesses, e.g. brake balance can be moved more rearwards than it is possible in other sets, which in turn allows for shorter stopping distances.

I've been thinking about this for some time, and I also believe overdamping might be one of the reasons why some people think some other sims (most notably iRacing) are more lively and realistic, and overall have better force feedback (of course iR also has improved surface but that's not the point)

Your thoughts?

PS: for those who have fiddled with sets in iR, can you confirm or deny the assumption it does not allow overcritical damping? thanks

I too have noticed a lot of sets in LFS making extensive use of overdamping. I never really understood it and never used it in my sets. I think my sets tended to be much easier on the tires as a result, perhaps more driveable too, and equally as fast as far as I could tell, if not faster.

I haven't really taken a good crack at making setups in iRacing yet. I also realized just how much I relied upon the "Drop" button in the garage in LFS, Bob Smith's VHPA, and f1perfview.

when i share my sets with people they often complain that they are "too bouncy", yet when i drive their sets i think to myself, "feels about as responsive as a dead hooker".

i don't know if there is any real world use for an over-damped setup. maybe, just maybe, it might be useful for off road truck racing. those things get massive air, but stick like glue when they land, but even so, i don't know if you have to go over critical to get that behavior.

I've read about over-critical damping being used on real race cars to make up for a direct lack of damping in one of the four modes of damping (those being bounce, roll, pitch and warp). Unfortunately finding the text where I read it is likely an impossible task, and I wish I knew where I read it now, it would make for interesting reading*. I can't even remember if it was online or in a book.

One thing that springs to mind is that anti-roll bars make your suspension stiffer during roll, so would that not change the critical damping coefficient for the majority of the time spent on track?

Edit: Note at the bottom of this page says ARBs are undamped, which is true for the mechanical device, yet you can't twist the ARB without compressing at least one damper: http://www.ukcar.com/features/tech/suspension/antiroll.htm

I'll code this up quick and see what it comes out like.

Edit again: check out the quote of Carroll Smith in this thread: http://fsae.com/eve/forums/a/tpc/f/125607348/m/49910379711

*Edit once more: I think the document I was reading was to do with a new suspension and damping system being test at Le Mans, all done with fluids and controlled through a central box of some sort. Editing the edit: aha, found the article, although it's not the one that mentions over critical damping, it's still interesting all the same.

In my experience an overdamped front rebound (which is what I'm seeing the most) takes longer to understeer in a long turn - I can only assume it has something to do with a lower roll centre/centre of gravity by not letting the car get up to its normal ride height... It's probably the primary reason why partial throttle application doesn't seem to exist in LfS... The only downside is the lack of reaction on quick direction changes - you have to force the car turning in the other direction...

I'm surprised you haven't noticed all those squatting cars though... The rake on pretty much every slick-shod car would never been used in RL... That's for braking (more load on the front tyres under braking -> shorter stopping distance)...

As for iRacing: you couldn't tell... The only thing you're setting are clicks under or above standard damping, there are no absolute values given so who knows what you're setting there...

Quote from bbman :

I'm surprised you haven't noticed all those squatting cars though... The rake on pretty much every slick-shod car would never been used in RL... That's for braking (more load on the front tyres under braking -> shorter stopping distance)...

Don't you mean rear tyres?

Not unless I've got something wrong... This setup seems to make the car nosediving under braking and the bias is usually pretty much forwards... I remember (faintly) that once I corrected the rake of such a setup with less ride height and stiffer front springs while leaving everything else untouched, it were the fronts that locked very soon...

Well of course, with more weight at the rear, the brake balance will need shifted rearwards a bit.

So I couldn't have meant the rear tyres then... Either a softly sprung high ride height produces more load on the fronts under braking like I said or a stiffly sprung low ride height keeps the weight more rearwards, can't have both...

Quote from bbman :

can't have both...

Forgive me if tiredness is making me thick, but aren't they opposites? So one being true makes the other true?

A high, soft front is obviously to shift more weight to the front under braking, I don't know why you think I mean the rear... More weight at the rear is true on throttle, but that doesn't seem to be the main point of such a set...

Quote from bbman :

A high, soft front is obviously to shift more weight to the front under braking, I don't know why you think I mean the rear...

Oh I agree a higher CoG will shift more weight under acceleration. I thought you might have meant the rear seeing as more weight at the front is worse for braking, not better:

Quote from bbman :

That's for braking (more load on the rear tyres under braking -> shorter stopping distance)...

Generally speaking at least.

Anyway, more on topic, although I couldn't find the reference to over critical damping being used, from reading up last night I understand why it could want to be used (the lack of having dedicated roll or pitch dampers), and I can now calculate critical damping for roll and pitch modes. Although it won't be coming to VHPA as part of the next release, I'll add it in to the one after, and I'll whip up a little spreadsheet now and post it here when it's ready.

Not made it pretty to look at, I'm not even sure if some of the calculations are correct to be honest, if you want to pick apart bits you don't understand or you think or wrong, I'm happy to discuss!

Regarding overdamping in iRacing, it should be possible to check if it is allowed even without resorting to analytic calculations. There are certain track conditions that can be used to highlight the uberslow weight shifting that happens with overdamping. E.g. I remember if you use enough of it, the XRG does weird things on the last chicane on BL1. So it should be just a matter of finding the right combo and stretch of track to make a test.

@ Bob, I've looked at the spreadsheet, very interesting stuff, I'm certainly going to play with the sheet a bit to check my own sets I've tried to follow the logic behind the formulas and it seems consistent to me. BTW can you suggest an online resource explaining where they come from?

Back to topic, basically what people are doing is giving up on proper wheel control to manage the weight shifts instead and obtain the handling they want.

This only works because of shortcomings in LFS' simulation models i.e. tyres and suspensions. The car should be jumping around and losing grip on even the most insignificant flaw of the road, and even if the track was perfectly flat the temps would be insanely high, that is if everything I've read on the subject so far is correct and I understood it well.

Concerning squatting and diving, I take they should be controlled through suspensions geometries instead. So is it correct to assume a better susp sim model would render overdamping much less useful than it is now?

And back to iRacing again, assuming it has working anti-squat/anti-dive geometries, there would be no need to use overdamping in the first place

Has anybody an idea if it really has that?

Quote from NightShift :

Concerning squatting and diving, I take they should be controlled through suspensions geometries instead. So is it correct to assume a better susp sim model would render overdamping much less useful than it is now?

Are you saying LFS doesn't have anti-squat/dive geometry on the suspensions? I did not know this.

If so, that explains alot about why the XRG was pitching so hard when I put in the rates from the real springs and dampers on a Starion.

All I've read so far about LFS indicates that is the case. However when it comes to using data from real sets, my readings suggest the lack of spring preload is to blame for excessive chassis movement - if certain assumptions are not proved false, within a few months we should be able to make meaningful comparisons with reality (or so I hope)

The roll and pitch damping equations came from the spring & damper tech tips series from optimumg.com

As far as I'm aware either, there is no anti-pitch geometry in LFS. I'm not certain how it would affect critical pitch damping, if at all.

Quote from Bob Smith :

The roll and pitch damping equations came from the spring & damper tech tips series from optimumg.com

As far as I'm aware either, there is no anti-pitch geometry in LFS. I'm not certain how it would affect critical pitch damping, if at all.

It would have a very big effect on alot of the setups I see. As it is now alot of people are setting values that are too stiff (and low) for proper traction in a realistic instance because the squating has to be dealt with through crazy suspension rates and ride hight settings.

One more thing I see all to often is people lowering the car too much, even a fue of the setups that come with LFS have oddly low ride hights, sometimes at one end of the car and not the other.

The ideal setting would be to have the lower wishbone paralel to the road as this gives optimal mechanical grip, but some of them have crazy low settings that have the wishbone inclined in the direction of the wheel. This causes odd handeling characteristics in just about every lowered car I've driven, even ones with spring kits to increase the rates to compensate.

Oh I'm sure it would certainly have an effect on setups. It's the specific nature of pitch damping that I was referring to, as although anti-roll bars affect the roll stiffness, I'm not sure that anti-pitch geometry affects the pitch stiffness of the vehicle.

My reason for this doubt is that, while an anti-roll bar reacts to roll, I don't think anti-squat geometry does reacts to squat - rather it reacts to weight transfer. Hence why it's possible to get over 100% anti-squat, such as used on top fuel dragsters. If they reacted directly to squat, even 100% would be unachievable, as there would be no squat for them to react to.

It depends what is causing the car to bottom out. If all four wheels are bottoming out, then it could just be an issue of not enough suspension travel.

Even road normals give more grip than your typical road tyre, thus giving excess pitching under braking. Scawen is aware of this, and it might get adjusted so that the Scirocco does not unduly suffer from this issue (as the aim is for the fixed setup to be as close to real life as possible).

Quote from Bob Smith :

The roll and pitch damping equations came from the spring & damper tech tips series from optimumg.com

Thanks Bob, in one of their pdf about suspensions and dampers they actually say something along the lines of

'some teams use damping values over 100% to control pitch'

BTW I have been reading a book about setups recently and the only mention I found about this was something like 'if the driver reports the car lacks feel and is slow to respond, it is usually overdamping so tone down the damper settings'

So it would seem the answer to my question is, overdamping has a legitimate place in racing, but its usage would probably be much more limited than what we see in LFS.

I have not the chance to check now but the above quotations should be correct in the spirit if not in the actual words.

PS: TBH I was expecting your reply to be a bit longer and more in-depth, but thanks anyway.

PPS:

Quote from Bob Smith :

It depends what is causing the car to bottom out.

Care to comment about my point on spring preload?

Spring preload will stop the chassis from moving initially until the preload is overcome, but then it behaves like it wasn't preloaded - i.e. preloading does not make the spring stiffer.

I doubt cars like that XFG have any anti-dive geometry in real life - mainly because it feels horrid and isn't required at the ride heights of road cars anyway.

Quote from tristancliffe :

Spring preload will stop the chassis from moving initially until the preload is overcome, but then it behaves like it wasn't preloaded - i.e. preloading does not make the spring stiffer.

Of course not, otherwise there would be no point in fitting soft springs to a road car. In my posts, I was talking about the excessive suspension travel that we see in LFS whenever we use realistic values (i.e. taken from real car specs) rather than the bottoming out.

E.g. if you take the FXO and set it up with values (e.g. <30 N/mm), you'll see the front extend to dramatic results as soon as it goes uphill a bit.

My source stated preload limits excessive suspension travel and then went on to say 'on race cars preload isn't used anyway' so it did not explain in detail how this is supposed to work, if you can suggest any good links I'd be grateful

Quote from tristancliffe :

I doubt cars like that XFG have any anti-dive geometry in real life - mainly because it feels horrid and isn't required at the ride heights of road cars anyway.

99.9% of all hatchbacks use trailing arms which do have a pronounced anti dive effect

I'm pretty sure every production car has some level of anti-dive and/or anti-lift encorporated into the suspension.

Frontwheel drives tend to have anti-lift in the suspension to keep the wheels planted properly while accelerating, otherwhise the weight transfer of the car would lower traction.