Does a GT6/Real World Tire Conversion Chart Exist?

[Griffith500]

The main issue with tire/surface modeling is the floaty ghost-like movement of the car, with the handbrake pulled, in some uphill/downhill area's of some track's. Off the top of my head Sarthe (just as you're going downhill after Dunlop).
If someone has experienced this before, please post a video. When that gets fixed, then we can talk about other tire physic's/modeling problem's.

GT, like many sims in the past, uses a different low speed tyre model. As the road speed approaches zero, the Pacejka-like models, that used to be almost universal, result in divide-by-zero. So you have to catch that "divergence" at some arbitrarily low speed (10-15 kmh for GT, if I recall correctly) and switch the model. It was always tolerated, because the interesting stuff occurs at high speed in most driving games.

The switch from low speed to high speed is conspicuous by the sudden halt of the creep you mention, a sudden change in tyre sound, and a little kick in the FFB.

 

[VBR]

@ALB123 - Someone did this with GT5, as a rough guide (original thread here).

The tyres in GT6 seem to be one level more grippy than in GT5, so SH in GT5 are the same as CS in GT6. Adjust the tyres in GT6 to suit & you'll have a very rough guide.


👍

 

[MatskiMonk]

The switch from low speed to high speed is conspicuous by the sudden halt of the creep you mention, a sudden change in tyre sound, and a little kick in the FFB.

I always wondered why I go so much vibration through the wheel when I was crawling.

Also, this thread is great. Thanks for the info.

 

[ALB123]

You have all been providing some fantastic information. Thank you. I really hope that PD is spending a good amount of time in bringing a 21st Century tire model to Gran Turismo 7. With the advanced processing power and memory of the PS4, I can't understand that there should be any viable excuse why we should be stuck with this generic model. To me, a physically accurate and materially accurate tire model is probably the second most important issue after the overall physics model implemented into the game.

 

[Griffith500]

Caution: the model is not generic. All the Pacejka type models are, however, general. Quite a different notion, despite the obvious etymological link.

The real difference is that Pacejka relies on measurements alone and does not work well if at all outside of those measurements (and its bizarre parameterisation, at least for non engineering uses), whereas all the interesting work is being done on physical models these days. Just like sound!

 

[MatskiMonk]

Caution: the model is not generic. All the Pacejka type models are, however, general. Quite a different notion, despite the obvious etymological link.

The real difference is that Pacejka relies on measurements alone and does not work well if at all outside of those measurements (and its bizarre parameterisation, at least for non engineering uses), whereas all the interesting work is being done on physical models these days. Just like sound!

I was going to say something similar, just in a far more derpy fashion. I think it's fair to say that much of what most people say about the physics calculations in the game is speculation.... however at least this gives us an idea of what the variable are, even if not how they work with them.

I'd have like to have seen some examples of these tyre parameters.

 

[Griffith500]

I was going to say something similar, just in a far more derpy fashion. I think it's fair to say that much of what most people say about the physics calculations in the game is speculation.... however at least this gives us an idea of what the variable are, even if not how they work with them.

I'd have like to have seen some examples of these tyre parameters.

I think I've seen some, but that may only have been visual data. Doubt if I can find the info again, though.

Regardless, the thing to watch out for is whether the game actually uses the values in the database. Perhaps, at the very least, PD have a use lined up for them in the future.

 

[ALB123]

Please forgive my ignorance on this subject. I have not done much research into tire dynamics... Let's assume, for a minute, that Gran Turismo is indeed using the Pacejka magic formula - is that to say that other sims, like iRacing, Assetto Corsa and rFactor are they using something different? I can understand that the Pacejka model runs into problems at low speeds, so let's just disregard that for now. Let's only assume higher speed situations right now - why is there so much praise thrust upon the sims I just mentioned compared to Gran Turismo? I haven't played those sims, so I'm only going based on what I've heard. Are you saying that it's NOT the tire model at all that's necessarily responsible for the differences in performance?

 

[MatskiMonk]

Please forgive my ignorance on this subject. I have not done much research into tire dynamics... Let's assume, for a minute, that Gran Turismo is indeed using the Pacejka magic formula - is that to say that other sims, like iRacing, Assetto Corsa and rFactor are they using something different? I can understand that the Pacejka model runs into problems at low speeds, so let's just disregard that for now. Let's only assume higher speed situations right now - why is there so much praise thrust upon the sims I just mentioned compared to Gran Turismo? I haven't played those sims, so I'm only going based on what I've heard. Are you saying that it's NOT the tire model at all that's necessarily responsible for the differences in performance?

I'm no expert either, but the way I see it, it's the the difference between expectation & approximation, vs. true simulation. <snipped my own rant> At the end of the day, these are games, at some stage they will stop accurately representing actual physics, and default to to constants and coefficients. The assumption is that the PC kinda sims take it further, though only one person in this thread has attempted to quantify that with much more than their own opinion.. and now he's banned

 

[Griffith500]

Please forgive my ignorance on this subject. I have not done much research into tire dynamics... Let's assume, for a minute, that Gran Turismo is indeed using the Pacejka magic formula - is that to say that other sims, like iRacing, Assetto Corsa and rFactor are they using something different? I can understand that the Pacejka model runs into problems at low speeds, so let's just disregard that for now. Let's only assume higher speed situations right now - why is there so much praise thrust upon the sims I just mentioned compared to Gran Turismo? I haven't played those sims, so I'm only going based on what I've heard. Are you saying that it's NOT the tire model at all that's necessarily responsible for the differences in performance?

I don't think any of those games use Pacejka models.

iRacing is a proprietary approach said to be based on things like energy balances on the work the tyre does, along with some semblance of structural modeling, coupled together. That coupling of models is an old Papyrus forte: Dave Kaemmer and his team basically looked at engineering-style finite difference schemes and figured out how to truncate / simplify them for real time / interactive use. As a semi-informed guess, based on interviews with them in their Papy days, anyway.

Assetto Corsa is built on the same magix that NetCar(Pro) used. I don't know what they did, but I suspect they started by throwing away the bogus parameterisation of Pacejka (fine for researching tyre design, as one component of a larger test scheme) into something more befitting of the wide range of situations possible in, and the dynamic / interactive nature of, a game. There is no doubt a dynamic structural element to it, based on the steering feel alone. It is mostly magic, though, in my uninformed opinion.

RFactor 2, don't care.
It's probably a third different approach again.


Which is actually a really encouraging indication of the innovative and exploratory attitude in the genre, at least at a technical level. PD, despite outwardly slow progress (ask iRacers how long Dave sat on NTM, though, and how it wasn't the revelation most had hoped for, at first), share that adventurous spirit.

 

[ALB123]

@Griffith500 Thank you for your comments. Like I have said, I have zero experience with ANY other driving/racing game/sim so it's hard for me to have these really in-depth discussions. I know there are many things I like about Gran Turismo and there are many things I dislike. There are things I think are fairly accurate in GT6 and there are things that I feel are not even close to being accurate in the real world.

I've been fascinated with the Tire Model because it is something concrete that any GT user can point to and say "Okay...My car does THIS with THESE tires on it..." and instead of the typical debates that usually pop up about what grade of tires to use in which situation, it's nice to really jump into the nitty gritty of why Gran Turismo's tires do what they do, or don't do what they don't do.

I actually just happened to read the thread about "Hoping We Get Better Sounds"... or whatever it's titled, today. I read, with great interest, your posts about what you believe is the next generation of sound development for Gran Turismo. I appreciate learning as much as I can about this game, from a technical standpoint, and hope that we are headed in a positive direction. I've been very satisfied with GT6 because I have nothing to compare it to. Yet, I can understand the frustrations some people have in regards to what GT6 is, overall...