Physic discussion thread

I still wonder why Niels doesn't want to mod the physical tire model. It's one of two reasons:

He refuses to move with the times and use a superior (physical) tire model
or
The empirical tire model is superior

Maybe just maybe.... and i am playing devils advocate here .... You cannot emulate a tire by constructing a virtual tire but rather a slip curve and pure calculations comes closer to the real feel of a car tire grip?? I mean i never wanted to be toxic this is why i removed my comments and replaced with "...." but this still really annoys me because is hard to get concrete answers seeing as they compared rfactor 1 to reality back in the day and it was exceptionally close to the lap time as well as driving feel so im confused and thus wondered if it was a marketing gimmick.

How close is close enough?
How close is close enough? – Part 2

 

I do hope the physical tire model is more realistic when comparing to real life lap times and car behaviour.

 

Summarizing to make thing overly simplistic, the empirical model has the upside that the developer can directly "design" the tire behavior to his liking or to the data they may have collected (I suspect this is what Niels may have liked particularly but who knows for sure). The downside is that it's a stiff model: its accuracy gets degraded fast as soon as the conditions in which the model operates are not anymore those under which the data were collected, which is an inevitable occurrence.

The physical model does not give a direct control of the tire grip curves to the developer, but it is rather an indirect product of tire properties set by the developer through certain engineering equations. This is obviously a nuisance for the developer, but allows for much bigger excursion from the data that may eventually have been collected ahead of time while remaining closer to the IRL tire behavior, which empirical models will not be able to do.

Which one is better depends also on the application: if you are an F1 team and all you want to know is which changes you have to apply to your already known setup on an already known track and track conditions and tires because you just finished your Friday Free Practice 1 & 2 you are probably unlikely to enjoy the pros of a physical model. Also you won't give a heck about FFB fidelity in your simulator. All you want to understand is the trend in lap times by making a change in setup.

If you want to sell a commercial simulator that needs to provide a realistic tire/car behavior for a very wide range of conditions and tracks for which data will be covering an extremely small portion of those conditions and you are after FFB fidelity, then probably the physical model is a much better choice in the long term if you are persistent enough to go after its tuning.

For the sake of clarity, lap times are not the ultimate test bench of fidelity of a model. You can predict laptimes for a circuit with knowledge of a car and its properties almost with a Matlab routine alone with a certain accuracy, but that doesn't make Matlab a simracing software.

 

I can't speak for Niels on the exact reasoning, but he sees shades of grey and would be first to say that he doesn't know everything - for certain anyway.

Philosophically speaking I think you're putting too much value on what a single person may or may not think about it. It's not good for everyone's own analytical thinking. You need a lot of it for such a subject as it is very multi-faceted.

Also to cut Niels some slack: it's not so black and white that I'd say he hasn't moved on with the times or anything snarky like that. At the end of the day he has a great system for reproducing cars and tires for the models that he is familiar with. But just because he has a great system for what culminated in AMS1, doesn't mean everyone has to follow him.

Yes the old faithful ISI engine as a whole is indeed a masterpiece in many ways (reminder: Madness physics are an extension of ISI engine). It's not just the tire model, but the sort of physical chassis and suspension model ISI came up with that AMS2 is also still using to great effect. All of it adds up to create a general framework for vehicle dynamics which gets close to real lap times if you tweak it the right way.

Putting aside the tire convo for a moment: it has to be said that it's also limited for consumer simulation without additions. Not to criticise it, it's from 2005 after all. AMS1 already had some important additions like the turbo model that rF1 was sorely lacking, and I'm sure Raceroom has added plenty. Madness added the SETA tire model, a thorough driveline model/solver, barometric pressure, Livetrack, dynamic weather, DRS, and a boost model for different needs and rules (P2P, ERS, turbo pressure override).

These are all things that you don't necessarily need to replicate a real lap time or race pace, because in the end it all works on averages. This is a bit of an extreme example just to underline how misleading accurate lap times can be as a metric for sim accuracy. The same is true when we talk about tires in optimal conditions and within limits and when you throw them into crazy scenarios - which tires go through in practice lap after lap to give us an end result.

In the end with consumer sims I like to think more along the lines of: yes it gets close enough to the real lap time. But it did it on a cold Sunday evening at historic Hockenheim on bias ply tires. What each person values in a sim (race car engineers have veeery different priorities for example) changes how we view each one available.

That is also why there isn't a concrete answer. It depends. You just have to live with that.

 

Live with it or use games with empirical model.

 

The karts at rain are totally disfunctional. The things will strongly aquaplane even within low speed (as 30km/h). Even with wet tires it is incontrollable, as if totally disconnected to the ground.

These folks were running over some big puddles way faster than I and their karts were barely disturbed by that. You need to be way faster to feel like hitting a wall like I did.

A lad racing with a faster kart. It's slippery, but not disconnected. Just see how the guy always had some control, the transitions are gradual and some big&deep puddles barely disturb the kart.

Maybe kart's tires still need some love.

PS: Just as a reminder because it's my favorite car ever (in RL, not the AMS2 version), but the McLaren F1 LM still drives as if it have tires made of glass. In the rain I would be faster driver a Polo and in the dry it just don't match the fame of being a friendly car to drive (in RL a lot of folks reported to use this car as an usual daily vehicle as it behaves as a death trap even if you drive it slow and stead (following real road rules).

Abração e obrigado pelo update!