An anti-roll bar keeps the chassis AND the body square to the ground. I am sure you have seen cars that launch with the left front tire way higher in the air than the right......an anti-roll drastically diminishes that keeping the front end pretty close to level....(On "my" car....the driver's side front tire comes up about an inch, the passenger side just gets the majority of weight taken off of it, yet it still touches the ground....{69 Notch-back Mustang, all tube chassis, fiberglass front end, doors and hood.....runs 5.70's in the 1/8th}
Another thing to check and make sure of....is the air pressure the same in both rear tires???......THAT will make one wiggle around on ya too.