A panhard bar is a lateral link that locates the rear axle side-to-side under the chassis. Its height sets the rear roll center, so raising or lowering it changes how fast the car transfers load in a corner.
It’s a simple part — JOES Racing calls it “a bar with a rod end on each side” — that does two jobs at once, which is why small moves feel big. It “locates the rear end laterally,” centering the axle on the straight and taking lateral load in the corner. Height is the tuning knob: “a high bar transfers load quickly” for a sharper, more direct reaction when grip is up, while “a low one takes longer” and smooths the car out on a rough or low-grip surface. A J-bar is the same part with a bend in it, common on dirt race cars, where the offset clears the driveshaft and the bar mounts inclined rather than flat. Move it in small increments and write down where it was.
Panhard height is one of the biggest swings you can make with a single adjustment, so an unlogged change is a setup you can't get back.