For +40mm lifted vehicle

This is where upper control arms (UCAs) come into play. A quality UCA needs to be able to allow the suspension to operate to its full extent, so it needs to be able to allow the wheel to go all the way down and all the way back up. But what happens when you hit a big washout or a big bump at speed off-road? Having a properly designed UCA that allows for that hyper-extension in an extreme off-road environment is a key part of the design of these UCAs.
If you're running a light-duty Hilux, the factory UCA may suffice. However, if you're using your 4WD in an extreme environment, like high-speed off-roading with a heavy load on the front end, the factory arms may not be able to cope. When you add a suspension lift, you also change the position that the UCA will sit at normal ride height. This means that a new zero position needs to be incorporated into the control arms so that the ball joint in the UCA is in the zero position at ride height.