Anybody knows what are the optimal hot pressures for a race car? I'm using 32-33 PSI for GT3 cars, i think that's alright, but should i use that (for example) for low-tech car like Clio from ISI? That car uses Slick tires aswell, should i go for the same hot pressure as for the GT3 car? Or maybe i'm wrong and someone can explain?
Optimal tire pressures depend on lots of variables: 1) weight of car 2) springiness of sidewall 3) construction technique (radial or bias-ply) 4) friction of racing surface 5) ambient temperature 6) racing surface temperature 7) driving style 8) suspension setup 9) tire wear goal (endurance vs. sprint) So... you have to test to arrive at an optimum hot pressure and there are trade-offs to be considered. What is right for other drivers might be wrong for you. What is right on one track on one day might be wrong the next day.
I know that depends on lots of things, especially ambient and track temperature.. But which one to aim for? Which pressures to start? I also realised that in RF2 hot pressure is constantly rising, there is no "up to a point" hot pressure
Yes there is an "up to a point" pressure actually. You can check that in the picture of the telemetry I provide at the end of the post That value is between 1,8 - 1,9 bar for the Honda Civic. However, I do think that tire thermal model is the less accurate part of the tire model. You can check in the graph that tire temps reach equilibrium around lap 6-7. However it takes almost 10 more laps for tire pressure to reach its limit. 15 minutes seems a lot of time to me for air to reach its equilibrium temperature compared to the 10 minutes for tires. Unfortunately, I don't have data to check if such a delay of pressure with respect to carcass temperature is realistic or not. I would expect however that both pressure and temperature would reach their limits at the same moment approximately. If tire air volume is not in equilibrium I cannot understand how tire carcass temperature reaches its equilibrium. The should be both linked and hotter inside air should always provoke a higher carcass temperature. In any case since the above is not a proof, but a feeling instead, lets analyse the pressure increase... Tire temperature for FL tire goes from 20 ºC to 90 ºC. If you consider the pressure increase for a constant volume according to the ideal gas law you would get the following factor: (273+90)/(273+20) = 1.24 Multiplying the initial pressure by this factor: 1,3 · 1.24 = 1.61 bar However, in the sim FL tire pressure rises up to 1.85 bar. How is this possible? where is that pressure coming from? Someone explain it to me please. It should be noted that I made a very conservative approach of a tire being constant volume which is not true. Tyre grows in volume when inflated and therefore the obtained pressure should be lowered by the volume increase factor. In this case I am the one who is saying that rF2 physics are not OK. I have always stated that tire thermal model has a big issue. Maybe some will learn to provide some data when they say something is wrong.
Buddy, you are absolutely right about everything you said! I highly agree that tire thermal model has a big issue.. I'm racing with RF2 for a long time now, almost a year and i didn't drive a single race with a proper tire setup (tire temperatures spread). I just can't make it done.. Yes, somehow the camber settings are alright, but tire pressures (the middle tyre temperatures) are always the same in readings ( in Rfactor 2 garage or in my motec project) I was hoping that CPM on cars would solve this, but.. well, it isn't.. P.S. So the tire needs around 25-30 laps to get it's optimal pressure? is that right?
I also expected that CPM could partially solve this. I have the same issues you mention with center temps. I am now driving corvette C6R which was updated with CPM and thermal model seems to have changed somehow. Interesting results... I just extracted the same graph as for the Honda Civic (non CPM) and I can now see the expected correlation between tire temps and pressure. Now they do follow the same trends throughout the stint. View attachment 18511 If we now check pressure and temperature increase for hottest FR: 1.45 · (273+130)/(273+30) = 1.93 bar In the sim the value is 2.03. Now we are not as far as we were before but remember that 1.93 should be lowered somehow due to tire volume increase. So IMO still needs some work. Other aspects cannot be so easily addressed as this. I have the feeling that tires heat up too much because of an improper heating/cooling effect simulation. I have pòsted about this in the past but never received any answer. I have asked several times what fraction of the heat created when sliding is going to the tire. I have also pointed that the much higher cooling effect of rain compared to dry asphalt is not perceived and tire temps go higher than when it dries out. The thermal effect of locking seems excessive IMO. It seems as 100% friction energy is used to heat up the tires which would be wrong for sure since part of it goes to the track.
I think that CPM is only about how tire sits on the road properly... Temperatures spread only slighthy changed (for example new clio 1.6) The temperature spread is another thing they should solve and update, it's already over 3 years of this game, right? You can check in the main folder of RF2 in KnownIssues file, it says: "Contact patch load distribution model is not final, which means tire pressure does not have the full effect that it should." I'm just wondering will they ever update that?
Maybe the extra pressure come simply from tire load? I mean the constant weight of the car when stopped, and also load from weight transfer and downforce. I'm no an expert, just guessing. Enviado desde mi GT-I9505 mediante Tapatalk
No. It shouldn't be caused by the weight. It is also present when tires are cold. Besides since the tire is stiffer at higher pressure, I would expect a lower global deformation and volumen decrease compared to lower pressure. Hence tire load should provoke a higher pressure increase at low pressure. The effect should be the opposite to the observed one. Enviado desde mi SM-G130HN mediante Tapatalk
I agree, as league racer, pressures always were strange to work with in rF2... As temps under wet conditions. Would be nice to see more information by ISI about this.
If you talk with a real driver, he will tell you that they can read 110C when the car reach the pits after a few laps. So, while the car is on the track the temp should be higher for sure. RF2 seems to have this range of temps wrong, because tyres usually loses lot of grip over 120C.
I'm talking about RF2. You start to lose grip over 120C when the tyres become yellow, and tyre wear is more noticeable. Optimal tyre temp on RF2 seems to be below 100.
in rF2 tyre model, the InternalGasHeatTransfer (heat transfer coefficients to internal gas cavity is = base + mult*Vel^3. It is extremely depend on speed of the tyre. I believe, in your chart, this is reason why temperature is relatively higher (90 degree C in your chart). So pressure will be higher too. The equation, you used, may not hold in this case. In other words, the entropy is not a constant from point A to B (from 20 to 90 degree points in your chart).
My chart shows tire carcass average temperatures. When tire temps reach equilibrium (no variation between consecutive laps) internal gas will get the temperature of the inner layer of the tire. Never higher than that since gas can only exchange heat with it. A poor conductivity could explain the delay of the first graph but you need to note that with C6R this delay does not exist any more. The first graph is quite old but the second one is build1008 and C6R v1.62. More research would need to be done to see if this is car or build related. Regarding ideal gas law. It can be used for "low pressures". Up to 5-10 bar if I can recall correctly. Entropy has nothing to do with this. Enviado desde mi GT-I9505 mediante Tapatalk
I did not mean to the ideal gas law. I meant to the "Isochoric process", of which the formula you used. We know the tire deforms dynamically (shape, and volume). Hence there are delta W (work) dynamically consumed through all the way (from point A to B). The inner wall is no longer as hardest solid (as for ideal gas). It maybe treated as "thermal equilibrium" between the inner air and the inner layer of tire, but may not a in "thermodynamic equilibrium", as a close system for inner air enclosure. This is what I tried to say. If nothing "new" going on, they simply can use a restriction condition PV/T = constant in their model. But you showed about 15% off in pressure or temperature. That makes me think..... Or you might be right, ISI screw up big time on this..... Update: I do not know what means of tire carcass average temp you mentioned. I looked at the ISI plugin code, here they gave: fprintf( fo, " TireLoad=%.1f GripFract=%.3f TirePressure=%.1f\n", wheel.mTireLoad, wheel.mGripFract, wheel.mPressure ); fprintf( fo, " TireTemp(l/c/r)=%.1f/%.1f/%.1f\n", wheel.mTemperature[0], wheel.mTemperature[1], wheel.mTemperature[2] ); they do offer three "surface tire temperatures" I think, called "wheel.mTemperature". Also, "wheel.mPressure", I will think it is patch area pressure. I assumed the data you got are TireTemp and TirePressure(?)
Tire deforms with pressure and that increases volume. I already stated that the pressure obtained by the ideal gas law should be decreased by this factor which would increase the claimed difference. However I cannot figure out how to account for that. I'll think about it. The amount of elastic energy involved in tire deformation will be very small compared to the heat generated at the contact patch. This energy is not provided by the internal gas but by varying tire load. The main effect in pressure adding (subtracting actually) to temperature effect will be volume variation not elastic energy or whatever delta W you mentioned. Thermodynamic steady state is being accounted. There is no such equilibrium since conditions vary all the time. But the overall heat exchange with air within a lap becomes "zero" at this steady state since temperature and pressure cycle around a mean value. I will tell you tomorrow what temperature and pressure channels I used in motec. Enviado desde mi GT-I9505 mediante Tapatalk
Just a quick reminder, the temps you see in-game while on the track are surface temps of the tires. The core temps can be seen in the garage once you leave the track. Again this is just in-game. Motec is probably the best way to investigate the tire temps for sure. Also, the new CPM is still evolving and has come a long way from when it was first introduced to us. I do agree the heating of the new CPM still needs some TLC but it is way better than it used to be.
I love the way RF2 is showing the tire temperatures.. Surface and Core temps.. i knew that before and always was looking in my motec project for temp.. But never had success to find the proper tire temperature spread cause somehow the tire pressure change never changed my mid tyre temp.. I guess that still needs work..
You'll find it easier to refer to the definition of TelemWheelV01: double mTemperature[3]; // Kelvin (subtract 273.15 to get Celsius), left/center/right (not to be confused with inside/center/outside!) double mTireCarcassTemperature; // rough average of temperature samples from carcass (Kelvin) double mTireInnerLayerTemperature[3]; // rough average of temperature samples from innermost layer of rubber (before carcass) (Kelvin)
