Weight-distribution hitch (WDH)
A weight-distribution hitch uses spring bars to move part of the tongue weight from the tow vehicle's rear axle to its front axle and the trailer axles.
How this site uses it
Ford and GM towing guides state a trailer weight above which a WDH is required for a given configuration; where the guide gives it, the site stores it per row and the widget applies it. Otherwise the site recommends a WDH when the trailer exceeds 50% of the vehicle's curb weight.
Related: Tongue weight · Hitch · Towing calculator