Originally Posted by Matt Howard
The 6mm droop is measured by a droop gauge, the 4mm is the ride height. Or you can set the ride height to 4mm and if you can lift the car 2mm before the tires lift off the ground then you have 6mm of droop.
If you lift your chassis 2mm and the tires come off the ground, you have 2mm of droop. If you measure 6mm to the lowest part of the arm/knuckle on blocks, you have set your "downstops" to 6mm. Hudy, Serpent, and most of the industry have used this nomenclature for years.
I see from the HPI guide they have decided to interchange the two terms like many I see online.