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jujunosuke

Pacejka tire model question

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Hi everyone.

I have some questions about the famous Pacejka tire model for a racing sim.

Does most of the racing games nowadays tend to implement this tire model ? (I know that very arcadish games implement there own system but what about games that are in between ?
By in between i mean cars that have a kind of realistic behavior but does not take into account all the details of a very strong simulation. more freedom.

Is Pacejka formula is a kind of standard ?
Does a Pacejka implementation (with the good settings) will always lead to good driving behavior ?

I have read many thread on gamedev with many guys trying to reach some accurate driving physics and then become crazy with it.
Like they spend months and months working on the physics and fail because the driving behavior is just not good...

I would like to hear your point of view on this please.

Thank you in advance for any help/contribution.
Regards.

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Like any tyre model out there, Pacejika is just a "formula" with some parameters. The formula part is the easy part, it doesn't matter how convoluted the formula is, you just need to translate it to C++ (or whatever language you work with) and you are done.
The real headache comes from the parameters... mark my words: You will _NEVER_ find a complete pacejika parameter set for a tyre you are trying to model. It is not something you google for.. they are rare even in the high end of professional simulation.
Most of the times, you'll have some partial set of parameters, more often you start with some curve graph, sometimes you start with nothing.

The essential thing is that, whatever tyre model you are using, you get familiar with each and every parameter in it, what it does to the result and how this translates into the vehicle dynamics in the game. This is, by nature, a trial and error process.. experience plays a huge factor into this picture that is why developing a proper driving sim is a very loooooong process and you can count the main "actors" in the business with one hand.
There is no "plug and play" tyre model.. you'll have to fiddle with it for months (even years) with it, it is a never ending quest.

The general trend in sim racing software right now seems to be to give up "empirical" tyre models (like pacejika's) and move to a more physically based model. These tend to favor consistency and easiness ( they tend to have far less parameters than empirical models) by giving up the possibility to match a given experimental curve 100% . These are usually some derivation of something called "Brush Model".

To recap. a direct answer to your questions:

[color="#1C2837"]Does most of the racing games nowadays tend to implement this tire model ?
[color="#1C2837"]
[color="#1C2837"]netKar PRO, iRacing, rFactor, RBR, LFS, CARS, Shift.. no
[color="#1C2837"]Forza and GT .. perhaps in some simplified version
[color="#1C2837"]
[color="#1C2837"]Does a Pacejka implementation (with the good settings) will always lead to good driving behavior ?
[color="#1C2837"]
[color="#1C2837"]No. It will get you half way there (provided you find these "good" settings).. but it's quite a general consensus that pacejika way of modeling the levels of grip after your peak has been reached (eg. drifting) is not appropriate for interactive usage.
[color="#1C2837"]
[color="#1C2837"]
[color="#1C2837"]

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kunos, thank you for taking time to answer. This was very informative.

Last question but quite important for me, i never heard about another tire model. (Maybe that is why i asked if Pacejka was a standard).
Is there any simplified way to calculate, longitudinal and lateral slip ratio ?

Thanks again !

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