Coupling 101.
When the rear of the suspension compresses, and the scissor touches the coupling block it couples the rear arm to the front arm, so they work together like a parallelogram. All our suspensions are coupling suspensions engineered with equal length arms so when coupled they are working together combining spring rate and compression in the shocks through the full travel. We have 4 settings of coupling, measured in the amount of travel of the front arm coupled with the rear arm.
The number 1 on our coupling block is about 20% of the front arm travel when it is coupled with the rear, 2 is about 40%, 3 -70% and 4 is 85-90% of the front arm travel. When coupled it is the rear arm trying to pull the front arm up in the vehicle, the more aggressive the coupling the more load on the skid and vehicle its mounted to. Some models need tunnel reinforcing because of the extra load.
Stock mountain suspensions are designed for the front and rear arms to work independently, the front arms are longer, and the rear is almost half as long. Spring rates are calibrated to work independently, so it is possible to couple a stock suspension up to about 20-25% of the front arm travel. Anything more than 25% will just lock up the rear so it won't compress any more, it will defiantly help hold the front end down but if the sled hits something hard enough to get it to compress then the weak link in the suspension or tunnel will show it ugly head as in bent parts or bellowed tunnel.
All the aftermarket companies selling couplers will work and look to be a good quality product, just do your diligence and mount it so they will not couple more than 20-25%.
Kevin