# Hot (optimal) tire pressures

Discussion in 'General Discussion' started by romano2603, Nov 9, 2015.

1. ### JoeRegistered

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I see.

So those two sets of data actually could be not sync in the same way as sampled in time:

double mPressure; // kPa (tire pressure)
double mTireCarcassTemperature; // rough average of temperature samples from carcass (Kelvin)

Could this result in 15% off when applying to the Isochoric process as Euskotracks found?
Does the tire pressure output as spot value? (seems suggest as I read). that says its physics is OK, just data representation may lead a such "error".

2. ### EuskotracksRegistered

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Some pictures which I think are very clarifying and answer about which motec channels I was using.
They are from yesterday's race. Corvette C6R at home track: Gotham Hills (DR)

As you can see I have plotted three different tyre temps.
1. Tyre Carcass Temps
2. Average (I,M,O) Rubber Tyre Temps
3. Average (I,M,O) Tyre Temps

It can be seen that Tyre Temp is surface temperature. It is the one that fluctuates the most by a lot. It cannot be used for pressure calculation
It can also be seen that Rubber Temp and Carcass Temp have a very small difference (<1ºC). Carcass Temps fluctuate less and "follow" Rubber Temps. Hence carcass will represent the inner part of the tire.
Another proof of this is checking how accurately and with almost no delay, Pressure follows Carcass Temp pattern.
Hence air and tire carcass can be considered in a permanent quasistatic thermal equilibrium.

Checking expexted pressure with respect to temperature increase show very good match in rear tires (less than 1% difference).
In front tires this difference is around 3%. In this case the difference is smaller than in both previous analysis.
I have plotted the calculations directly in the image in the pressure graph.
I have used the same colours as for the channles to identify different tires.
As stated some small additional pressure loss would need to be accounted due to a non purely isochoric system.
I would expect a less than 5% pressure decrease but still havent figured out how to calculate this so take it as a reference/guess.

I made a mistake in my previous posts. Laguna Seca Telemetry is from Build 998. This one is from B1008.
Considering that the oldest build showed the worst results and latest build is more accurate.
It appears that some progress has been made with pressures.

View attachment 18534

3. ### JoeRegistered

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so what is standard deviation of ratio P to T (P/T)? Can you plot P/T vs time? It shall hold steady constant in time. Your previous results suggested it was not, there were about 15% off between two points as you found. So are those 15%-off still there in your new charts?

Last edited by a moderator: Nov 12, 2015
4. ### EuskotracksRegistered

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I don't see how that will help.
It is clear that the error in the latest graph is much smaller compared to the older pictures.
Comparing both graphs the similarity is very high.

It is curious that front tires show bigger difference. What I will do is compare all 4 tires in the three graphs to check if the error was big in all of them and now has gone down. I will also check other old telemetries to see if this error is in fact something that can be considered solved.

Enviado desde mi GT-I9505 mediante Tapatalk

5. ### romano2603Registered

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With the new update i realized that "KnownIssues" folder no longer contains Tire pressure problem.. Does that mean we finally have proper tire temperature spread after doing aligment setup?

Somebody have time to test this? I'll try it too

6. ### coopsBanned

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why is this info not available from the mod builder in a readme ??????
if it does not have to be how is a person with no motec or any other plugins to find out what these temps should be ???????

7. ### EuskotracksRegistered

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As I said I made a more complete review by checking all 4 tires in each case.
I made an excel file in order to save some calculation time with a nicer look.
It is curious to see that the only non ISI car is showing pressures below expected ones but also with the smallest error.
The oldest telemetry seems to have serious issues with huge differences. I wonder how much is from the build and how much from the car.
Newest cases show a 5% average difference between calculated and measured pressures.

I have to clarify that I made a mistake in the last graph of Gotham Hills when I said things seemed to be OK.
In the new chart the values are the correct ones. Now they are not OK.
If you check, you will see that instead of using final pressure to compare with the calculated one, I took the average pressure from the stint.
Hence I maintain that something seems to bre wrong in the way the rF2 calculates tire pressure.
I still wonder where is that extra pressure coming from.

If someone is willing to check other ISI cars, he can upload his telemetry of a full stint.
It takes me 2 minutes to type the values in the chart.
View attachment 18559

8. ### NielsenRegistered

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rFactor 2: No relation between tire pressure and temp

Just posting some data to support the conclusion that there is a missing relation between tire pressure and tire temps in rFactor 2.

Comming from iRacing where there is no usefull relation between tire pressure, camber settings and tire pressure I have become a bit disappointed that the relation in rFactor 2 is just as bad(= non existing).

To check it out I just made some test laps with the same setup where I only changed the tire pressure.
Note: The camber values was F(-3.1) R(-1.8) and the track was Suzuka in the FR3.5.
I did run 3 test sessions each about 7 laps changing the tire pressure from 90/90(min) to 130/130(mid) to 170/170(max).

Via Motec I calculated the average tire temps for the 3 sessions(outher, mid, inner) for Front and Rear wheels.
And to make it a bit easier to get an overview I also converted these absolute temp values to Split values for the tires.

Hehe. If you check the Split FrontL middle temp it looks like it goes down(29>27) when you raise! the pressure from 90/90(min) to 170170(max).
On the RearR the middle temp goes likewise down(24>22) when you raise the pressure!
Using some common sense the change in temp should be the opposite.

You can download the Motec outputs for the 3 sessions from my Dropbox.
https://dl.dropboxusercontent.com/u/29587629/Motec RaceRfactor Suzuka 2013.zip

9. ### WiZPERMember

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You do realize that there are several tyre-temps ?

Tyre (surface), Rubber and Carcass.

10. ### Juergen-BYRegistered

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Not sure, if the tire temp is working, but tbh, comparing e.g. (pressure) 130 and 170 seems to me more as senseless. The temperature window, where a tire is proper working, is usualy very small, maybe (depend on the car/tire) not much more than 5-10°.

And yes, when you raise the pressure from 90 to 170, the temp could be lower with 170. The surface contact area becomes with 170 bar much smaller as it is with 90 bar...

Last edited by a moderator: Jul 18, 2016
11. ### NielsenRegistered

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If you read what I did write then I also said that I did measure the temperature between these 2 extremes.
But you could allways postulate that the "window" where the tire pressure-temp actually is existing is so small that I cannot find it
But as a further information I can say that I have also made the same measurement using the same setup with tire pressures of 110110, 125125, 135135..
And all of these displays the same picture of the completely missing relation between tire pressure and temp.

The reason I didnt post all these tests is only because I wanted to make this posting of data simple and understandable
- hehe and because I did predict from similar discussions that there are always some who try to argue that completely different measurements are needed.

12. ### stonecMember

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That statement is not a general truth in rF2. rF2 simulates a real tire with all construction, which will dynamically alter shape and size as you increase/decrease pressure. So already by basic physics principles it should have some effect on temperatures. It's well known though that you need to run a car with CPM (contact-patch-model) to get the latest and most realistic tire model. All cars released/updated after May 2015 (listed here) have CPM tires.

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14. ### NielsenRegistered

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Just a thought that could (could!) contradict this explanation of lower temp with higher pressure.
If we suppose that the laptime (and therefore grossly the forces transfered) is the same for the session with pressure 90/90 as with 170/170 then the same forces (and friction) will be transfered through a much smaller area.
And maybe my sense of common sense is wrong but I would suppose that the laps using the 170170 pressure should also give the highest tire temps.
Probably much higher if the sim was simulating the tire pressure to tire temp relation.
But thats probably only me.

Note: The laptimes are pretty comparable between the 3 sessions by the way.

15. ### EmeryRegistered

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Tire with minimal air pressure will work the carcass more due to flex and that adds heat to the carcass.

So which car did you test? Ah, nevermind, now I see it was the Formula Renault.

16. ### AndregeeRegistered

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The tyre Modell of Rfactor 2 is still beta, even with the latest Cpm. The track temperature still doesn't affect the tyre temperature. But all new Sims are lacking of tyre functions which worked well in Gmotor 2.0 and thats really poor so the best complete working tyre is that from Automobilista for me

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17. ### NielsenRegistered

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Hopefully thats the explanation of the complete missing relation conserning the FR35 - eventhough this car is a dream to drive(IMO)
I have no intention of having absolute or megalomaniac knowledge of rF2

18. ### unknwnRegistered

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Is there an app/option to see both surface and core tire temperatures while in game?

19. ### TJonesRegistered

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That's not correkt, track temperature has an affect, you can see, if you choose a car with pre heatet CPM-tyres, F-ISI foe example. Drive slowly out of the box, and you should see that those part of the thread which is in contat with the tarmac (inner part of the front's) cool down a bit. Reason is track surface is colder (around 20°C.) then pre heatet tyre (60° c. at start). You could also stand still a few seconds, then move very slowly and you see colder flats on the tyre.

At the moment the track surface is bound to air temperature, and that on the whole track. Hope this change in the not so far future.

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