You should not use weight distribution hitches with a regular surge brake coupler that moves in and out when the tow vehicle stops and restarts . The pressure from the torsion bars , bind up the slide system in the coupler . If you have the newer style , electric over hydraulic brake system , you could use weight distribution , but you need to add a pole tongue adapter to the tongue . This bar bolts on , cross ways , so the torsion bars can clamp to a support structure , out on angles from the hitch ball . Weight distribution is really designed for a ''A'' frame trailer tongue , not a straight tongue . You can buy hi end kits that have sway control built into the design of the bars , and better load bar clamps . If they rate the hitch at only 4000 lbs without weight distribution , it must be a light hitch or the tow vehicle is on the light side , which they would use a lighter rated hitch . This happens with short wheel base , sport utility vehicles . When i was in the business , i always said " if you think a 1/2 ton will do , buy a 3/4 ton , if you think a 3/4 ton will do , buy a 1 ton . The longer the wheelbase the better , and buy the highest weight rated , tire you can for your towing vehicle .