I would think once it got to the point where it needed a bar (12.0 - 11.50s) it needs to have frame ties. Mid 13s and quicker it will certainly help. I wouldn't put a bar in without them. How you tie it up makes a big difference also. Bolt-ins are a waste of time. The 2x2 pre-fab weld-in kits are OK, but if you want it as stiff as possible, 2x3 sectioned into the floor is how it should be done.