Assetto Corsa Competizione Version 1.8.11 Released to Steam

Kyuubeey said:

But I just told you that it's a fully treaded tire. As in the image filename says it. So I'm not sure what you're refuting because I never mentioned racing tires. Nor have I seen data to indicate otherwise for racing tires. Do you have some conflicting data about race tires?

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I'm refuting that the trends you are showing are for a completely different tire construction and completely different and overloaded conditions that no car even on the road will see. Therefore the trends are 110% meaningless for what we are talking about and could be completely the opposite of what is shown there (and very likely indeed are).

MadDriver11 said:

I'm refuting that the trends you are showing are for a completely different tire construction and completely different and overloaded conditions that no car even on the road will see. Therefore the trends are 110% meaningless for what we are talking about and could be completely the opposite of what is shown there (and very likely indeed are).

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Okay, although it's not overloaded at all.

Why do you think they're opposite? All experimental testing in real-life suggests at least road and track tires follow this general trend. People claims slicks too, but I don't know.

Kyuubeey said:

Okay, although it's not overloaded at all.

Why do you think they're opposite? All experimental testing in real-life suggests at least road and track tires follow this general trend. People claims slicks too, but I don't know.

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Did you even look at the pictures @wolftree mentioned? Even if you did not do you know about engineering?
Increasing or decreasing tires pressures does not always yield the same trend. It depends on which side of the optima pressure you are for that given application (i.e. vertical loading including downforce and tire construction).
As I tried to convey before, race tires are very different in the way they rely on pressure than standard tires. Even racing tires among themselves are very different: high wall F1 tires up to 2021 are relying on pressures in a different way from extremely low profile GTE or prototype cars.
Without knowing what is the construction of a tire and therefore which is the optimal pressure to counter self weight and at least the ballpark levels of downforce saying that decreasing pressure will always make the tires stiffer to lateral load is just not correct.
If you go to underinflation compared to optimal in a given vertical loading condition, by decreasing pressure your tires will decrease their lateral stiffness. This is what those graphs should be telling together with common sense: have you ever seen a slowly puncturing tire being stiffer than an inflated one?

MadDriver11 said:

Did you even look at the pictures @wolftree mentioned? Even if you did not do you know about engineering?
Increasing or decreasing tires pressures does not always yield the same trend. It depends on which side of the optima pressure you are for that given application (i.e. vertical loading including downforce and tire construction).
As I tried to convey before, race tires are very different in the way they rely on pressure than standard tires. Even racing tires among themselves are very different: high wall F1 tires up to 2021 are relying on pressures in a different way from extremely low profile GTE or prototype cars.
Without knowing what is the construction of a tire and therefore which is the optimal pressure to counter self weight and at least the ballpark levels of downforce saying that decreasing pressure will always make the tires stiffer to lateral load is just not correct.
If you go to underinflation compared to optimal in a given vertical loading condition, by decreasing pressure your tires will decrease their lateral stiffness. This is what those graphs should be telling together with common sense: have you ever seen a slowly puncturing tire being stiffer than an inflated one?

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Cornering stiffness ie: tread behavior ie: contact patch behavior does not necessarily correspond to just the direct sidewall lateral stiffness.

Anyway, you can be right; but do you have any data to back it up? I am yet to look at wolftree's source.

EDIT: I looked at the source now. Well, take into account FSAE tires have nothing at all to do with any kind of racing car or passenger car tires, so indeed some weird things like super low optimal pressures and "inconsistent" trends can be seen. The data looks okay and I trust it.

Like I said, it will not be linear. At some loads, maybe you can have a small Ca increase going up from optimal pressure; but then quickly there is often a Ca decrease. As can be seen in the paper's data. At 150lbs, 9psi optimal pressure, going higher from optimal strictly resulted in less Ca always; but also going lower from optimal pressure.

I think the kind of condition I am familiar with is when the Ca curve is "offset" behind the lateral force curve, so in a TYPICAL condition, you will gain Ca by lowering pressure, and lose Ca by raising pressure above optimal. Up to a point, before the tire is too under-inflated and probably it begins to lose Ca as you say when pressure is lowered.

With "over-pressure" I generally mean quite large over-pressure, like overheated road tires. I said I don't really know about slicks and maybe you are right. Surely as you said the Fz matters and I will add that the camber angle is likely the biggest component, although that is my assumption.

EDIT 2: Something like this perhaps. Not to scale or correct shapes at all, but to illustrate. Load perhaps....4000N?

MadDriver11 said:

2.25 to 3.10 bars pressures aren't nowhere close to racing tires conditions. They are probably on the right path to 18 wheelers territory LOL

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Not really, the Hoosier "semi" slicks I run IRL have an optimal range in the mid 30s, and you'd probably be surprised to find out what prototype cars run. Treaded tires will generally be a bit higher, so that range is representative.

As for the FSAE data, 350 lbs at those pressures is very near the debeading load of the tire, so isn't a particularly representative case (a few of the tires tested in the TTC can't even handle that load). I have some modern FSAE data, but can't confirm the trend shown by Milliken due to the lack of testing at that load (at least in lateral). 150, 200, and 250 lbs all show a similar trend trend to the 150lbs plot shown by Milliken et al. Some more 150 lbs data below.

That trend appears to hold true for each of the 5 tires that were tested. I would also quite heavily disagree with Arch's statement that these tires "have nothing at all to do with any kind of racing car or passenger car tires." It's just baseless.

Anyway, all of the data I have for racing tires (ranging from bias ply slicks to LMP tires) shows a trend towards lower cornering stiffness with increased pressure at operating loads. Of course it will depend on the construction of the tire, etc, but it seems to be a fairly consistent trend.

edit: typo + correction + another typo, really on a roll

Kyuubeey said:

Well, take into account FSAE tires have nothing at all to do with any kind of racing car or passenger car tires, so indeed some weird things like super low optimal pressures and "inconsistent" trends can be seen. The data looks okay and I trust it.

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That seems both a rather broad category use and a very bold assertion. Does the category "any kind of racing car or passenger car" permit any other car category, beyond single-seater 'bubblecar'? What kind of tyres might such cars utilise?

My advice? Write fewer words, post less frequently. When you do post, think carefully about what you write. When unsure of your ground, incline toward posting caution.

Sim modding experience alone does not equate to or imply vehicle dynamics knowledge in depth. Nor does it make an expert in the simulation itself - unless one has access to the sim source code and the coding and dynamics knowledge base needed to fully understand it. Even then, all simulations without exception, have their limitations and therefore curious edge cases where the simulation breaks down and is exploitable by those who can find them.

Thanks for your recent posts Jackson; very interesting and thought-provoking material.

However, all of this has nothing to do with the subject of this thread, a new version of ACC, so as @Bram Hengeveld has recently requested, it might be best for someone interested in these matters to start a thread or submit an article relating to simulation fidelity in general. Then we can all post away without annoying those who want to discuss the subjects of threads like these.

BT7 Driver said:

That seems both a rather broad category use and a very bold assertion. Does the category "any kind of racing car or passenger car" permit any other car category, beyond single-seater 'bubblecar'? What kind of tyres might such cars utilise?

My advice? Write fewer words, post less frequently. When you do post, think carefully about what you write. When unsure of your ground, incline toward posting caution.

Sim modding experience alone does not equate to or imply vehicle dynamics knowledge in depth. Nor does it make an expert in the simulation itself - unless one has access to the sim source code and the coding and dynamics knowledge base needed to fully understand it. Even then, all simulations without exception, have their limitations and therefore curious edge cases where the simulation breaks down and is exploitable by those who can find them.

Thanks for your recent posts Jackson; very interesting and thought-provoking material.

However, all of this has nothing to do with the subject of this thread, a new version of ACC, so as @Bram Hengeveld has recently requested, it might be best for someone interested in these matters to start a thread or submit an article relating to simulation fidelity in general. Then we can all post away without annoying those who want to discuss the subjects of threads like these.

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Yeah, you are likely right. I thought about it more and I don't really have enough *good* data about FSAE tires to make a judgment like that. Probably with a more comprehensive and reliable data set, you'll end up finding similar trends on most car tires if you look correctly.

My advice is to not make assumptions about what experiences and knowledge other people have if you're not sure.

So should one get excited?

I'm really starting to get concerned all we're going to get for the GTWC America dlc is 4 one make category cars and COTA, which will be disappointing in my eyes. New cars are fine but I was really looking forward to the full slate of GTWC America tracks. Given the lack of any teaser for other tracks, is concerning.

Releasing COTA and nothing else would be a waste, imo. I hope I'm wrong