# “ are rfactor2 physics broken” video

Discussion in 'General Discussion' started by GTClub_wajdi, Dec 29, 2020.

1. ### ComanteRegistered

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No, gauge measure "0" because pressure is a differential measure, it measure a pressure AGAINST another pressure. 0 Kpa ,Psi,Bar, just mean that the two pressures are equal, this can mean that the tire is punctured or that just there is the same pressure, and the tire is still sealed tight. I think a lot of people get confused here. So, when your gauge measure a pressure of 1 bar. that is 1 Kg/sqcm ... (thats quite a lot of pressure already), OVER the environmental pressure.

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2. ### Pawel44Registered

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It depends what you're according to, but ACC tire model seems more complete. It's probably more realistic as well atm. Some people think more complex means better, but it's plain wrong. PS. You should be aware by asking such question it can lead to flame war. Furthermore, it's completely off-topic.

3. ### mantasisgRegistered

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Thats crazy, definitely must be as low as it goes. Could we somehow tell what that pressure could actually be inside that tire ? 14kpa ? 12kpa ? 11 kpa ? 10 kpa ? I bet it couldn't be bellow 10kpa, and I wonder how much the pressure inside will increase once it gets hot, and I wonder if by then the performance of this tire will increase. Naturally, cold pressures has to be a bit underinflated, so the cold pressures get to be optimal, thats somethign we don't have to bother about in rF2, and that is weird.

Maybe, but doubt it. The tires at the bottom still deflects into reasonably large flat contact patch, which will give rolling resistance, also they have big wings, which must put some downforce I suppose.

How is that a no ? Thats exactly same thing which I meant. If tire is going to be flat it will have atmospheric pressure inside. It will show zero on gauge, then it means zero on gauge is actual atmospheric pressure.

4. ### ComanteRegistered

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Maybe is language here, but I've got the impression that many people think that tire pressure should be >1 bar to not be "deflated". While it just need to be >0 . I sounded strange to me that this was your case as I get the impression you have a fairly high degree of instruction.

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5. ### David O'ReillyRegistered

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I disagree.

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6. ### YzangardRegistered

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It seems to me that it is exactly what he meant, when he said it is zeroed at atmospheric pressure, it exactly means that at 0 there is no pressure delta between interior and exterior of the tire.

I'm afraid you are both saying exactly the same thing...

7. ### mantasisgRegistered

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@Yzangard Yes, I do think that we say the same thing.

However, there is one thing that complicates the matter, what if 0 in rF2 is actually not zero, but the difference to the atmospheric pressure. I have not thought about that before. It probably is so lol So anything I have said about vacuum in the tires in the past might be (very likely) nonsense, but nobody has corrected me about that. However no difference to atmospheric pressure is still kind of "nothing" putting all the stiffness and load bearing solely on the construction of the tire, which obviously couldn't be usable for any PNEUMATIC tire IRL.

There are pressure gauges that measure absolute pressure too https://www.precisionmass.com/what-are-the-types-of-pressure-gauges/, but probably in motorsport and simulations it has always been about differential pressure gauges, strangely never though about that before, nor have noticed others speaking about it.

Last edited: Feb 13, 2021
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8. ### YzangardRegistered

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I think in motorsports we always use differential pressure but might be wrong.

EDIT : all sources I've found are dealing with differential measures and actually it is the only one that really makes sense in our situation, what good would bring absolute pressure or even with a fixed reference ? What really matters is the pressure inside the tire compared to outside, isn't it ? So i think we surely always use differential pressure.

Last edited: Feb 13, 2021
9. ### Bruno GilRegistered

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Watch f1 and listen to the casters, watch the tech talk videos, watch that video posted in last page
Number for dragstwrs is also correct, albeit on the lowest range
Now you're getting it. Yes pressure is pretty much always measured as a differential to ambient pressure

I did always get confused about the vacuum thing lol

10. ### RaintyreRegistered

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Ok, lets's check the facts. Roll resistance RF2 test. ( Sorry for the ugly graphics, it's not easy to install some cars in Developers Mode, but physics are not altered...)

160 kilopascals:
Top speed: 291.50 kilometres per hour

0 kilopascals:
Top speed: 290.58 kilometres per hour

So running four deflated tyres (totally deflated, punctured) translated into a loss of 0.92kph !!!!

In the video you can observe both runs. There is minimal difference on tyre footprint, minimal difference on tread temperature spread. Minimal difference in average temperature (56ºC for the inflated, 63ºC for the punctured.... the punctured tyres should be melting and smoking)
I forgot to show ride height difference: only 2.44 centimetres (naturally the punctured tyre should lose at least 13cm, the sidewall height)

With the help of telemetry I show that the tiny difference in speed is not even caused or atenuated by engine rpm difference, since engine power is virtually the same, and also aerodynamic drag Cx is the same for both runs, despite the change in ride height.

Of course I am not interested in running cars at 0 kilopascals. With this test I just try to say: How do you want to convince me that rolling resistance or any other force or energy is correctly represented for slight subtle pressures changes when even using a extreme pressure difference the impact of this change is so absolutely tiny?

The 'low pressures' issue is very important, because it is not something isolated from the rest of physics. If the ideal pressure to be fast is too low, this has an effect on tyre temperatures, on tyre wear, on car suspension rate, and in the HANDLING. Some people complains that some cars are too forgiving, can slide too much, almost drift, their response to steering input is too slow, bumps are almost not felt.
If sim racers could finally use higher pressures that would change a lot of things for the good. Not only telemetry data and setups would be closer to the real model. Also the feeling of the cars would be stiffer, more alive, reaction times would be stretched and in overall they would be more exciting, and of course, more realistic.

I don't attack the mistakes. I attack the fact that they are ignored, not admitted or, even worse, accepted as correct!
I post this with the hope that developers introduce a change in physics that might improve this subject, or that might introduce more freedom to define the pressure windows for roll resistance, grip, temperature and wear.

Last edited: Feb 13, 2021
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11. ### YzangardRegistered

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1) I'm not sure the tire model is made to "allow" O Pka pressure so I don't hink it is a good example.
2) 13 cm (was 23 before, maybe a typo ?) ???????? What are you using, a truck ? I'm sorry but 2.44 cm is still huge on this kind of tire (I mean Pirelli P Zero, it is the one we should test actually)
3) can you please test with OFFICIAL content and not a failing mod nobody knows anything about ? What tires are you using, what the hell is this ?

Last edited: Feb 13, 2021
12. ### RaintyreRegistered

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It is official content, mate.

13. ### LazzaRegistered

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I'm not overly familiar with ttool, but I couldn't find any evidence of rolling resistance in either the realtime or quasi testing.

I'm surprised because from memory (uh oh!) rolling resistance was a simple curve built from parameters in the TBC, so if rolling resistance doesn't exist in rF2 it's one heck of an ommision.

Still, as I said a couple of pages ago, I don't think the model should be made to cater for such extremes as 0 or 2 kPa. @Raintyre we've agreed in the past that some extra parameters would help complete the tyre situation, without the need to actually rework the base physical modeling. I still agree FWIW.

What I don't agree with is the premise that the lowest legal pressure (say, 110-130kPa) in a given car/mod shouldn't produce the fastest laptimes. (ie making a low pressure unusable in a competitive sense, is more nonsensical than the lowest allowable pressure always being fastest)

And @mantasisg yes, F1 use the lowest allowed pressures at least for qualifying, including Monza. Of course these days there is so much downforce that those minimums are higher than they used to be (because of added tyre stresses), I'm not sure how things were when PSI in the teens was possible. But I wouldn't make any assumptions, if you can manage it.

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14. ### RaintyreRegistered

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15. ### YzangardRegistered

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What car is it ?

What track is it ?

What tire ?

Last edited: Feb 13, 2021
16. ### YzangardRegistered

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You seriously think this is a GT3 or GTE tire ?

Here is, for example, the 488 GT3 EVO :

See any difference ?

17. ### RaintyreRegistered

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Who said that? You say it is a P0, you say it is a GT3, you want things are what you want to be, but they aren't, I am sorry, the Earth is not flat, don't kill the messenger.

18. ### YzangardRegistered

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7°C in straight line difference and you think it is MINIMAL ? Really ? After less than 2 minutes test ?

Should be melting ? Just driving straight ahead ?

Do you have any real data to provide that are confirming this ? Or just personal opinion ?

19. ### ComanteRegistered

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.damn you rai tyre, 0 kpa is not a punctured tire , is just a tire that happen to have zero delta pressure with the atmosphere. This tire can be perfectly capable to sustain his share of car weight. The tire deformation reduces the internal volume, this can allow the tire to keep the rim off the ground. Because, again, the tire is not punctured.

20. ### YzangardRegistered

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Oh, he didn't said "puncture" thinking it will destroy the tire then, he really thought it was just a flat tire ?

I understand why he wanted the RH to be way lower...and why he thinks temp should be much more.