Minumum k values are based on stopping sight distance, not the size (or clearance) of the vehicle. If you use the minimum k-values the tractor trailers will have no issues with clearance (if that's what you were asking).
If you are concerned with stopping sight distance, due to the slower deceleration of these vehicles, then you should determine the stopping sight distance of these vehicles and adjust you k-value accordingly.
And depending on your design speed, the miniumum horizontal curve radii may require that you widen the road surface in the curves to accommodate the larger turning movements.
