Slip ratio calculation when Vx reaches zero

Hi everyone, Does anyone know how CarMaker calculates slip ratio when Vx is close to zero?
I tried to calculate it as s=(-Vsx)/max(1,Vx) but the value is different from the one that Carmaker is showing me.

Good morning,

slip ratio is calculated as following (from the reference manual)


Hi there,
Thanks for your response. I’ve already seen that, but I’m looking for the CarMaker’s interpretation when the velocity (Vx) is below 1 and close to zero. As shown in the figure I’ve attached, there’s a difference between the value that Carmaker is showing and the value calculated based on the reference manual.

Good morning,

I calculated the slip ratio as following

Hello there,

I’m having a similar issue as Farzad.

I used the same method as you, Mr. Roberto, through Calculated Signals I’ve configured the following variable:


I excluded the multiplicative factor of 100 because I suppose you wanted to see a percentage value…

But when I compare with Car.LongSlipRL the data I get are quite different. See below:

So, Slip Ratio is the calculated signal I’ve configured and TCS_SR_RL is an user defined variable I’ve stated at my Simulink Model in a MATLAB Function, using WheelSpd * Nominal_radius / Vchassis - 1.

Can you enlighten me about this difference? I am aware it occurs due to the singularity in slip formula (when car leaves from standby and Vx is approx 0) but I am curious to know how does Carmaker comes up with such smooth data, and if it is more accurate then the calculated one.

ps: Slip ratio has such a high value here because I was trying to develop a traction control, and in this situation the maneuver is configured as "press acceleration pedal and never stop pressing it, proportioning an ideal situation to control the output torque and stop the wheels from spinning. It almost worked, but the oscilation of slip ratio is kind annoying.

Thanks in advance,


Good afternoon,

when using the Magic Formula Tire which documentation can be found here

there are limits that are set in the tire properties .tir