Physics right or wrong?

[Frederic Schornstein]

Disclaimer:
First of all please don't make that a fanboy discussion. I always try to be objective and leave my personal preferences out of the way. I am always willing to accept, if something I don't like on emotional basis, is better than what I like on emotional basis.

Ok I hope I covered that part and this won't get into a "You are a fanboy of this and that thread".

Prequal:
Like most people I eagerly awaited the release of Assetto Corsa. I read about all the licensed content, loved the screenshots and everything. I didn't drive the tech preview, because I didn't want to get a false impression, because it was all still WIP. The day AC was released on Steam I bought it.
I started really testing it after the first update were the FFB was fixed.

I do really like the game and wanted it to be good and so far my only issue are the physics. Most people praise them and they get a lot of love and I do confess, that in external videos they look great.
The car dives in on the braking, you see all the weight transfer and everything. No other sim offers that!

Example:
But as soon as I drive it, it feels just so wrong to me. Just one example: I tested the BMW Z4 GT3 at Monza. I know the track very well and usually drive GT cars, so a perfect combination for me.
Despite all the massive understeer you get everywhere in AC even with setup tweaks, I wanted to point out something you can judge on a much more objective level. So I will talk about the braking distance.

Every racer knows how hard the first braking zone in Monza is. You have a low downforce car and arrive at 260+ kph and have to break down to 60-80kph. So if you look at a lot of GT3 onboards on youtube even with cars, that do have ABS and are a bit restricted due to BOP. They all break before the 200meter board.
That said, I can brake at the 300meter (270kph) board and have the car at a total stand still at 150meters. If I brake for the corner I can brake at or after the 150 meter board.
So we already have a 25% shorter braking zone compared to a real life car with equal or less power and ABS, which I didn't use.

Test conditions:
So now people would start arguing, that I maybe run more downforce and stuff and that is the weirdest thing. I tried to figure out the "worst" braking performance. I used hard tyres and removed all the downforce from the car for this test.

I don't want to get to much into the details of the cornering behaviour and the understeer and that you can just pull on tons of lock and don't get any turn-in oversteer.

Is my opinion qualified?!:
A lot of simracers don't have a lot of reallife experience and I didn't race a GT3 car in my life, but just a quick background:

I drove Race07, rFactor1 and now rFactor2 and I am a pretty good driver in rF2 especially in rear wheel drive touring or GT cars. Even in the new Civic I was racing for wins after 30mins on an unkonw track, so I can quickly adapt to new cars and tracks etc.

In my free time I did some kart races with friends and even on an unkown track with for me unkonw more powerful karts than the average rental karts on a bit cold track I got within 1,9 seconds of the track record within 15min and reduced it to 1,5 seconds in a further 15min.
Keeping in mind that real professional Kart drivers practice their and I had maybe 2 or 3 hours track time in karts ever, I would say I am not a bad driver.

So when I jump out of rF2 into a kart it just feels like home. I apply nearly the same technique and everything. When I jump into AC it all feels wrong. It is so hard to get wheelspin. You can turn the wheel so much, that you would end up in a wall in real life.

I also spoke to some guys with actual racing experience and they got the same feeling.

The end:
I really wanted AC to be a very good sim and I do love everything about it, but these physics keep me from driving it.
In a sim I don't want it to be easy, I want it to be as realistic as possible, but in AC you can apply some really bad driving technique to get quicker laptimes.

 

[Simon Roberts]

Patience....That will be implemented by V1.0.....along with brake fade, flat spotting of tires, etc..

Will they be in 1.0 Michael?

 

[Michael Hornbuckle]

EDIT: Nothing offensive now

 

[Michael Hornbuckle]

EDIT: Nothing offensive now

 

[Andrew Ford]

 

[Bram Hengeveld]

@Andrew Ford if you keep abusing the rating system we will have to temporary disable your account for a couple of days. I suggest you refrain from using it from now on.

@Michael Hornbuckle You need to watch your language in this thread. Do me a favor and edit those offensive parts.

 

[Andrew Ford]

@Andrew Ford if you keep abusing the rating system we will have to temporary disable your account for a couple of days. I suggest you refrain from using it from now on.

@Michael Hornbuckle You need to watch your language in this thread. Do me a favor and edit those offensive parts.

Thanks for the warning Bram. I would be interested to see the stats of individuals who have disliked my posts as well in this thread. if i am to recieve 10+ dislikes from 1 person to affect my "rating" then what is the point in the rating? Only a suggestion for the future which you can cast aside as it's your site...but might be useful if everyone was obligated to give a reason for a rating. my point is that its very easy for people to jump on the bandwagon and post dislikes just because someone else did. and i fail to understand why people are giving dislikes just because someone chose to raise a concern over issues in a game. You can see from your side that my posts were in response to others abusing the system. i am a stubborn sonso...but only ever in response to people abusing things.
I hope that others are not allowed to "dislike" my posts now or that will clearly be to provoke.

 

[Michael Hornbuckle]

EDIT: Nothing offensive now

 

[Bram Hengeveld]

Your smart abbreviations to bypass our swearing filter aren't appreciated and I am not going to have extra work with it either.

@Andrew Ford you obviously have no understanding what "rating points" on this forum means as it has nothing to do with likes or dislikes which are to appreciate a thread/post.

Now lets continue the discussion on-topic.

 

[Matt Sentell]

Matt, your argument appears to based on the conjecture that the AC tire model is a simple one layer model. This appears to be incorrect based on the very fact that you can change the sim to be driven by surface temperatures in the ini files. You do appear to be correct that the model is driven by the temperature of a single layer rather than multiple layers. However, that doesn't mean the temperatures in the surface layer are ignored by the model.

I don't want to ignore your post since it's reasonably stated, nor do I want to seem dismissive. I've actually read through your functions a few times trying to make sense of what you're suggesting, but at the end of the day I'd rather just address the bit about "conjecture."

I'm very careful about making assumptions and drawing conclusions, and I've often been heard to say that I'm not 100% certain about damn near anything. And that's why in my original post I repeatedly said I don't know for certain that the thermal model isn't more complex than I suggest. However, I also explained that I wasn't basing it just on my own perceptions.

I swear I had originally included a link to Aris' post on their forum, but maybe that isn't allowed and was deleted. Here it is again, in case it's okay to link to:
http://www.assettocorsa.net/forum/i...-temperatures-and-wear.2723/page-2#post-26274

The most relevant bit is this comment:

Good news though, the way AC simulates tyre temperature, it's up to you to simulate either surface or core temperatures.

That's a fairly specific statement and it's an either/or statement. If I wanted to go and open a dialog with them I could ask for more clarification, but unless it's a misstatement or oversimplification then it's already clear enough to me what it means. Since the behavior I observe in the sim is consistent with that, I see no need to bother them with the question. If anyone discovers information to the contrary I'd be happy to learn of it.

 

[Goes To 11]

The most relevant bit is this comment:

Good news though, the way AC simulates tyre temperature, it's up to you to simulate either surface or core temperatures.

That's a fairly specific statement and it's an either/or statement. If I wanted to go and open a dialog with them I could ask for more clarification, but unless it's a misstatement or oversimplification then it's already clear enough to me what it means. Since the behavior I observe in the sim is consistent with that, I see no need to bother them with the question. If anyone discovers information to the contrary I'd be happy to learn of it.

I take that comment to mean something different from you. If you had a single layer tire, it wouldn't matter whether you called one the core and the other surface because they would be the same and would behave the same. The only way to do this is if they are different. So the core model HAS to take into consideration that it is under a surface layer. There is no other way to do it. Similarly, the surface model has to take into consideration that it is on the surface. There is just no way around that otherwise both would give the same results.

As I understand it. The temperatures that the sim are reporting are consistent with temperatures taken deeper in the tire and insulated from high fluctuations in the surface temp.

 

[eobet]

If anyone discovers information to the contrary I'd be happy to learn of it.

I tried to tweet both @KunosStefano and @Aristotelis about your posts, but so far no response. If either of them could comment it would be so cool!

This very technical discussion the last few pages has been a pure joy to read, especially considering who is posting.

EDIT: Maybe we already have an answer from over a year ago... http://www.racedepartment.com/forum...ne-of-assetto-corsa.53467/page-2#post-1201969

 

[Matt Sentell]

I take that comment to mean something different from you. If you had a single layer tire, it wouldn't matter whether you called one the core and the other surface because they would be the same and would behave the same. The only way to do this is if they are different. So the core model HAS to take into consideration that it is under a surface layer. There is no other way to do it. Similarly, the surface model has to take into consideration that it is on the surface. There is just no way around that otherwise both would give the same results.

As I understand it. The temperatures that the sim are reporting are consistent with temperatures taken deeper in the tire and insulated from high fluctuations in the surface temp.

Oh, I see what you're saying. When set to simulate the core temp it likely just uses a different thermal profile, so that you get temperatures read off of it which are more consistent with what you'd see on a real tire when you stick a pyrometer into it. Those temperatures deeper in the tread change more slowly. If you set it to surface then it'll likely use a different thermal profile, one that changes more rapidly.

That's just simply not the same thing as simulating both at the same time. If you're suggesting that the core temp couldn't be derived without also simulating the surface temps then I would refer you back to the half dozen or so sims I worked on which did exactly that, as well as rFactor 1 and most every other from the last 20 years.

 

[Matt Sentell]

I tried to tweet both @KunosStefano and @Aristotelis about your posts, but so far no response. If either of them could comment it would be so cool!

This very technical discussion the last few pages has been a pure joy to read, especially considering who is posting.

EDIT: Maybe we already have an answer from over a year ago... http://www.racedepartment.com/forum...ne-of-assetto-corsa.53467/page-2#post-1201969

I remember reading that post but had completely forgotten about this bit, which is really intriguing:

This is not our "NTM" that I mentioned in that tweet you've posted. That's an even more advanced tyre model that we are not going to use on v1.0. That one theoretically has some even more impressive potential, but we haven't even driven it, it's just equations and graphs for now (but very impressive hehe).

Long time ago. I wonder how things progressed with that.

 

[Goes To 11]

That's just simply not the same thing as simulating both at the same time. If you're suggesting that the core temp couldn't be derived without also simulating the surface temps then I would refer you back to the half dozen or so sims I worked on which did exactly that, as well as rFactor 1 and most every other from the last 20 years.

That's not what I'm suggesting at all. Sorry, I have to go back to an equation. Let's make it really simple. Let's say that G = 2a + 3b + c. But let's say we also know that b = 3a. So we can rewrite the first equation G = 2a + 3(3a) + c which simplifies down to G = 11a + c. My whole point is that even though you never explicitly calculate b, it is essentially taken care of in your equation. The AC tire model includes everything that would be needed to calculate the surface temperature. Even if they don't calculate it explicitly, it is possible that it is taken care of in how they model the tires. It all depends on how they fit their model to the data. Apparently they went with core temperature as a driver because it fit the data better. In statistical modelling, you can calculate how much adding a variable helps your model. If you have already included all the variables that account for surface temperature, actually adding surface temperature might not be of any benefit at all.

 

[David O'Reilly]

That's not what I'm suggesting at all. Sorry, I have to go back to an equation. Let's make it really simple. Let's say that G = 2a + 3b + c. But let's say we also know that b = 3a. So we can rewrite the first equation G = 2a + 3(3a) + c which simplifies down to G = 11a + c. My whole point is that even though you never explicitly calculate b, it is essentially taken care of in your equation. The AC tire model includes everything that would be needed to calculate the surface temperature. Even if they don't calculate it explicitly, it is possible that it is taken care of in how they model the tires. It all depends on how they fit their model to the data. Apparently they went with core temperature as a driver because it fit the data better. In statistical modelling, you can calculate how much adding a variable helps your model. If you have already included all the variables that account for surface temperature, actually adding surface temperature might not be of any benefit at all.

Without being very good at equations and therefore not postulating a counter equation I would ask the question.
Do both models model time?
As the surface temperature will react in a much shorter time frame as it is the first contact point for energy (slip) and cooling (air). So surface temp will fluctuate quickly and the deeper structures more slowly but they will have a realationship as they influence each other.

 

[theserioussam]

I thought Xavier's post was very interesting so shared it on a comment on virtualr. Then it got deleted =/

 

[Frederic Schornstein]

I thought Xavier's post was very interesting so shared it on a comment on virtualr. Then it got deleted =/

Do you know why?

 

[theserioussam]

Do you know why?

No idea. Not a big deal to me but just thought it was interesting that happened.

 

[Matt Sentell]

That's not what I'm suggesting at all. Sorry, I have to go back to an equation. Let's make it really simple. Let's say that G = 2a + 3b + c. But let's say we also know that b = 3a. So we can rewrite the first equation G = 2a + 3(3a) + c which simplifies down to G = 11a + c. My whole point is that even though you never explicitly calculate b, it is essentially taken care of in your equation. The AC tire model includes everything that would be needed to calculate the surface temperature. Even if they don't calculate it explicitly, it is possible that it is taken care of in how they model the tires. It all depends on how they fit their model to the data. Apparently they went with core temperature as a driver because it fit the data better. In statistical modelling, you can calculate how much adding a variable helps your model. If you have already included all the variables that account for surface temperature, actually adding surface temperature might not be of any benefit at all.

I still don't think you understand that the rate of change is radically different in the core temp than it is in the surface temp. That's the key difference. At any given instant the CoF is calculated based on a bunch of variables, one of them being temperature. If you have surface temp available then you use that value. If you only have core temp available then you use that value. If you're using the core temp then CoF is going to be less affected by any variations in load or sliding at that moment than it would be if the surface temp were being used.

That's why I said previously that using the core temps will result in tires that are less thermally sensitive.

 

[Birddogg66]

The sore loser above started to dislike my (older, unrelated) posts too for some reason...is it puberty hitting you hard ?

Maybe he just does not like you and the great level of intelligence you express in your posts.