GripTempPress calculation

Mee

Hi guys,

I'm the creator of CarStat, a program to get all kinds of stats of a selected car/mod.
I'm working on a new version of CarStat (sneak preview), but I'd like to include a graph that shows the effect of overheated or cold tires.
In the TBC-files there's one line that says:
GripTempPress=(2.50, 1.40, 1.00) // Grip effects of being below temp, above temp, and off-pressure (higher number -> faster grip dropoff)​

We now that at the optimal temperature the % of grip is 100 = optimal grip. But with the previously given parameters, how can you calculate how much grip (in %?) you've got when your tire is - for example - 10 degrees overheated?
What's the slope/function of the graph?

A picture says more than a thousand words (I hope):

carstat_temp_dropoff.jpg


So is this a linear fuction (1)? Quadratic (2)? Something else?

Does anybody (a developer or someone else? :)) know the answer to this?

Thanks!
 
I don't know if you are still interested, but here it goes:

The formula used is the following:

(1-(0.5*((GripTempPressValue1/(OptimalTemp+273.15))*ABS(RealTemp-OptimalTemp))^2))
Click to expand...

That would be if the real time temperature is below the optimal temperature. If it is above, you have to use the 2nd value

(1-(0.5*((GripTempPressValue2/(OptimalTemp+273.15))*ABS(RealTemp-OptimalTemp))^2))
Click to expand...

So, let's say you have a mod with the following values:

Temperatures=(100,70)
GripTempPress=(2.45, 2.1, 1.1)

And the real time temperature in game 90º:

(1-(0.5*((2.45/(100+273.15))*ABS(85-100))^2)) = 0.99784 (99.784% of grip).

2.45 was used because 90<100. If we had>100ºC, then we need to use the 2nd GripTempPress value (2.41). With that formula, you can plot a grip vs temperature graph quite easily.

Edit: the result would be something like this.
 
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That's great Domi, thanks for this!

But, just as a reference, could you tell me where you got this formula?
 
Thanks a lot for the insight on this one.

Can anybody shed some light also on the pressure side of this line (the third number in pareteses)?

What does the third number do and how?

Also, can you help to understand how the following line influence tire behaviour?

OptimumPressure=(100.0, 0.0215) // Base pressure to remain flat on ground at zero deflection, and multiplier by load to stay flat on ground

thanks!
 
The first value gives the optimal pressure at 0 load, the 2nd is a multiplier of load. Let's say you have 3000N of load on the tire, the optimal pressure would be at 100+(0.0215*3000)= 164.5 kpa.

What the third number of GripTempPress does is quite similar to the temperature graph.

=1-(0.5*(GripTempPressValue3*ABS(LiveTirePressure-OptimumTirePressure)/OptimumTirePressure)^2)

GripTempPressValue3 is the 3rd value of the entry GripTempPress=(x, y, z)
LiveTirePressure is the tire pressure (easy to check with Motec)
OptimumTirePressure is what we checked previously (let's say we have 3000N, then the value is 164.5)

So, doing a quick example:

Tire load of 3000N
OptimumPressure=(100.0, 0.0215)
GripTempPress=(2.50, 1.40, 1.00)
Live tire pressure 190kpa

=1-(0.5*(1*ABS(190-164.5)/164.5)^2) = 0.98798 = 98,789% of grip (or 1,211% of loss).

And you can plot easily a graph like this one
 
Last edited:
Domi said:
The first value gives the optimal pressure at 0 load, the 2nd is a multiplier of load. Let's say you have 3000N of load on the tire, the optimal pressure would be at 100+(0.0215*3000)= 164.5 kpa.

What the third number of GripTempPress does is quite similar to the temperature graph.

=1-(0.5*(GripTempPressValue3*ABS(LiveTirePressure-OptimumTirePressure)/OptimumTirePressure)^2)

GripTempPressValue3 is the 3rd value of the entry GripTempPress=(x, y, z)
LiveTirePressure is the tire pressure (easy to check with Motec)
OptimumTirePressure is what we checked previously (let's say we have 3000N, then the value is 164.5)

So, doing a quick example:

Tire load of 3000N
OptimumPressure=(100.0, 0.0215)
GripTempPress=(2.50, 1.40, 1.00)
Live tire pressure 190kpa

=1-(0.5*(1*ABS(190-164.5)/164.5)^2) = 0.98798 = 98,789% of grip (or 1,211% of loss).

And you can plot easily a graph like this one
Click to expand...

Thanks a lot! That's a really useful info.

I really like this forum! You guys are giving me so many useful info! :D
 
I finally got around to this, but are you sure you didn't misplace the ^2?
With your formula
(1-(0.5*((GripTempPressValue1/(OptimalTemp+273.15))*ABS(RealTemp-OptimalTemp))^2))
Click to expand...
the grip level really is about the same for 0°C (99,78%) as for 100° or 200°C (99,84%). I'm pretty sure I've got way less grip when my tires are at 200°C :).

Implementing your formula, I accidentally used it like this (notice the moved bracket):
(1-(0.5*((GripTempPressValue1/(OptimalTemp+273.15))*ABS(RealTemp-OptimalTemp)^2)))
Click to expand...

This gives me a graph like the one attached. If you'd ask me, that's waay closer to the truth. Could you check the reply yout got from ISI? Because like it is it's still guessing of course :).

Thanks!

View attachment 5388
 
Hmm, I just pasted the formula from an Excel spreadsheet, and it worked there :D

What optimum temperature (seems 100ºc) and griptemppress values were you using for that graph?
 
Anyway I have to clarify that this formula works fine to "isolate" the tire temperature effect, but it's not how does it work exactly. Both of them (temp and pressure) are combined, as well with the tire wear, to compute the tire grip loss. This is really the final formula:

Grip = TireWearGrip*(1.0-(0.5*offTotal^2))

Let's say we have the variable "offTemp" for the grip loss with temperature, and "offPressure" for the grip loss due to tire pressure, and "offTotal" the sum of both variables.

offTemp= ((GripTempPressValue1/(OptimalTemp+273.15))*ABS(RealTemp-OptimalTemp))
offPressure= (GripTempPressValue3*ABS(LiveTirePressure-OptimumTirePressure)/OptimumTirePressure)

Using the examples given in this thread, we have:

offTemp = ((2.45/(100+273.15))*ABS(85-100)) = 0.09849
offPressure = (1*ABS(190-164.5)/164.5) = 0.15502
offTotal = 0.09849 + 0.15502 = 0.25350

And assuming no grip loss due to tire wear (so 1.0), the result would be:

Grip = 1.0*(1.0-(0.5*0.25350^2)) = 0.967869 (96.79%).

If we had, let's say a 75% of tire wear, and at that point we have a grip multiplier of 0.85 (from the wear rates values), then the final grip would be drastically reduced to 82.27%.

I hope I was clear enough :D
 
Of course, you have to combine the different grip-reducing factors. But for what I want to do with it I don't need the combination :).
 
Ok :)

Remember that this is only for rFactor 1, though. I have no idea for rF2.
 
Need clarification

Domi said:
Ok :)

Remember that this is only for rFactor 1, though. I have no idea for rF2.
Click to expand...

That formula mentioned here was mentioned in 3 different forms. sometimes with ^2 sometimes without it or ^2 in strange places ...

So can somebody from ISI finally post the accurate formula?
 
Domi said:
Anyway I have to clarify that this formula works fine to "isolate" the tire temperature effect, but it's not how does it work exactly. Both of them (temp and pressure) are combined, as well with the tire wear, to compute the tire grip loss. This is really the final formula:

Grip = TireWearGrip*(1.0-(0.5*offTotal^2))

Let's say we have the variable "offTemp" for the grip loss with temperature, and "offPressure" for the grip loss due to tire pressure, and "offTotal" the sum of both variables.

offTemp= ((GripTempPressValue1/(OptimalTemp+273.15))*ABS(RealTemp-OptimalTemp))
offPressure= (GripTempPressValue3*ABS(LiveTirePressure-OptimumTirePressure)/OptimumTirePressure)

Using the examples given in this thread, we have:

offTemp = ((2.45/(100+273.15))*ABS(85-100)) = 0.09849
offPressure = (1*ABS(190-164.5)/164.5) = 0.15502
offTotal = 0.09849 + 0.15502 = 0.25350

And assuming no grip loss due to tire wear (so 1.0), the result would be:

Grip = 1.0*(1.0-(0.5*0.25350^2)) = 0.967869 (96.79%).

If we had, let's say a 75% of tire wear, and at that point we have a grip multiplier of 0.85 (from the wear rates values), then the final grip would be drastically reduced to 82.27%.

I hope I was clear enough :D
Click to expand...

Hello Domi,

Hope you are still around...
I had two questions regarding the constants used in the formula for the grip loss due tire temps.
- Where does the value '273.15' comes from?
- Where do you obtain the OptimalTemp of a 100?

Greatly appreciate your response and I wanted to thank you for all of these useful information!
Cheers!
 
- adding 273.15 is to convert the value from °C to Kelvin.
- Optimaltemp is in the car's TBC file, parameter "Temperatures". The first value is the optimal temp in °C.

This isn't relevant for rFactor 2 btw, only for rFactor 1.
 
Last edited:
Mee said:
- adding 273.15 is to convert the value from °C to Kelvin.
- Optimaltemp is in the car's TBC file, parameter "Temperatures". The first value is the optimal temp in °C.

This isn't relevant for rFactor 2 btw, only for rFactor 1.
Click to expand...

Thanks for the answer Mee.
It makes sense now!

By the way, I am finding the same variables and similar numbers in rFactor 2 under each car model tyres; I am using Motec and it seems like the data I am obtaining is quite on the right path.
I know that you mentioned that it is only relevant to rFactor 1, but it kind of is to rFactor 2 as well.

Thanks
 
It "kind of" is for rFactor 2, in a sense that the AI uses these values so they should be in the ballpark.
You can get those temps from the TGM-files now: search for the "StaticCurve"-parameter. From the TyreTool Quickstart:

StaticCurve = The static friction grip fraction relative to temperature curve in the format of (cold
temperature, static grip multiplier @ aforementioned temperature, peak temperature, grip
multiplier @ peak temperature, hot temperature and grip multiplier for said temperature). The
values are blended together to form a wide smooth curve.
Click to expand...

So the 3rd value of StaticCurve is the optimal temperature in Kelvin. So -273.15 for °C.
 
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