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Dual tire issue

Hi everyone,
 
I would like to know how to properly define dual wheels in acar. There is no problem when I create single wheels(left and right) and simulate them. The wheels remain stationary on the ground with the reaction force equal to the weight of the wheel. But whenever I create dual wheels either in a single template or by assembling single wheels from two individual templates and simulate them, the force on the wheels is shown as 1e6 N in the postprocessor and in the animation too, I can see the wheels flying off vertically upwards at tremendous speed. I am using PAC2002 tire property file for defining the wheels. In the simulation, I simply create a generic assembly using only the wheel subsystem that I created, There are no constraints (not even fixed joints between the two wheels) except the contact force with the ground that is created by default by acar (til and tir) ). Then I simply run a general actuation analysis for 2 seconds and 200 steps) and get the result as described earlier.
 
Can anybody give me any pointers as to what I might be doing wrong?