Tyre physics question

LesiU

I have a question about LoadSens parameter.

I have some real world data curves lateral vs vertical force (few curves for different angles) - that's cornering stiffness and I think that's the most important for my needs (also have lateral load vs slip angles for different load curves)..
Lateral forces are rising slower with increased loads. That should be simulated by LoadSens and only there?
In real world, we finally get to a point where the cornering stiffness curve is flat - no increase in lateral force, with increasing load. That is our "final" point in LoadSens, after which no further drop occurs?
For which slip angle I should take values from the graph? From the highest known, for which there is still increase in ratio "lateral/vertical force"?

Thanks in advance
 
LesiU said:
>"no increase in lateral force, with increasing load"

Are you certain of this?
This defies the physics I learned.
 
That should explain more:

CS%20vs%20Fz2.gif
 
I'm not a tyre expert but I'll say cornering stiffness is the initial slope of a lateral force vs slip angle graph. If it is this way I can't see a clear relation between cornering stiffness and rfactor's LoadSens, but it *might* have something to do with LatPeak. I couldn't say any more without some latforce/slipangle graphs at different loads.

AFAIK LoadSens final point is where [peak] friction coefficient does not drop anymore, ie when any increase in vertical load increases [peak] lateral force by a proportional amount. [For a given slip angle, sure there may be no increase in lateral force with increasing load, specially if the angle is below the peak]
 
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LesiU, I've been thinking about this and probably we both were somehow right (or wrong). LoadSens, LatPeak and Stiffness are actually related and you can derive a fairly good approximation of any of them if you know the two others. I'm not sure about the latter but I'll try to figure it out and post it here when I'll have some time - I believe it's not going to be easy.

The problem is that we usually don't have detailed loadsens nor latpeak info available when working with real data.
 
My impression is that Loadsens is a fudge factor to simulate tires working better under higher loads over and above the increased friction generated by higher load. E.g. dirt or ice tires working better under higher loads as they are able to dig into the dirt surface more.
 
I think that LoadSens was intended to simulate the drop-off in grip that occurs on dry asphalt when load increases. You can use LoadSens to model tires working properly on soft surfaces as well but I don't think it is possible to make a single tire behave correctly on both hard and soft surfaces.

I strongly recommend Bristow's tbc file explanation, it was lost in the old RSC forums but there's a copy right there.

Back on topic, let's assume we know stiffness and peak slip variation and we want to know LoadSens, here goes my attempt:

Maximum Lateral force a tyre can provide is Cornering Stiffness (CS) times a slip angle. This slip in rfactor is a constant fraction (c) of peak slip angle (ie slip where peak forces occurs, let's call it Sp):

Fy = CS*c*Sp

Sp and CS are both functions of load (Fz). Sp(Fz) is defined by LatPeak parameters.

Fy = Fy(Fz) = CS(Fz)*c*Sp(Fz)

LoadSens (LS) is 1 if load is 0, otherwise:

LS = LS(Fz) = 1/DryLatGrip * Fy/Fz = 1/(DryLatGrip*Fz) * CS(Fz)*c*Sp(Fz)

and same applies for longitudinal force.

So if I'm not wrong somewhere, technically we can get LS from CS and LP (plus a reference slip curve to get c). But in real world it's far from easy to have reliable data available and over a wide enough range of loads.
 
R U KIDDING! After all of your Genius I have to say- This is very Impressive!

rogdini said:
I think that LoadSens was intended to simulate the drop-off in grip that occurs on dry asphalt when load increases. You can use LoadSens to model tires working properly on soft surfaces as well but I don't think it is possible to make a single tire behave correctly on both hard and soft surfaces.

I strongly recommend Bristow's tbc file explanation, it was lost in the old RSC forums but there's a copy right there.


Back on topic, let's assume we know stiffness and peak slip variation and we want to know LoadSens, here goes my attempt:

Maximum Lateral force a tyre can provide is Cornering Stiffness (CS) times a slip angle. This slip in rfactor is a constant fraction (c) of peak slip angle (ie slip where peak forces occurs, let's call it Sp):

Fy = CS*c*Sp

Sp and CS are both functions of load (Fz). Sp(Fz) is defined by LatPeak parameters.

Fy = Fy(Fz) = CS(Fz)*c*Sp(Fz)

LoadSens (LS) is 1 if load is 0, otherwise:

LS = LS(Fz) = 1/DryLatGrip * Fy/Fz = 1/(DryLatGrip*Fz) * CS(Fz)*c*Sp(Fz)

and same applies for longitudinal force.

So if I'm not wrong somewhere, technically we can get LS from CS and LP (plus a reference slip curve to get c). But in real world it's far from easy to have reliable data available and over a wide enough range of loads.
Click to expand...
 
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