How is Trq_T2W calculated in MotorcycleMaker?

I am trying to implement a custom powertrain. In order to calculate the rotational speed of the wheels, the engine torque/brake torque is added/subtracted with MC.TR.Trq_T2W and MC.TF.Trq_T2W. What exactly is Trq_T2W and how can I calculate it manually?

Trq_T2W is the torque to wheel, if you see the reference manual or user guide it shows what it can be like
Car.Tire[0].Trq_T2W = Resistance Torque Wheel FL or Vehicle.FL.Trq_T2W=Front Left Wheel Torque.
In a user powertrain if you want to calculate the engine torque you can use a 2D look up table with Engine RPM, Throttle position and Torque. You enter the table with real time RPM and real time Throttle position and will give you the Torque output. You can use the UserPowerTrain.mdl in CM4SL as a reference.
Hope this clarifies your doubts.