We have observed what we believe might be an error with ABAQUS SST. 

If we apply braking torque to a tire and plot the longitudinal force versus slip ratio, then we can match measured data quite well.

However, if we take the same tire model and apply driving torque to it and plot the longitudinal force versus slip ratio, then we have results that do not agree well with measurement. 

Why? Is there an issue with ABAQUS SST? Have other ABAQUS users reported the same problem?