Leaf springs have improved alot over the past several years but are still old technology .Coilovers however have several advantages over leafs . Coilovers can be adjusted easily for different conditions ,where leafs can't. The ride is better with coil than leafs for the same stiffness. When using a 4 link (like suggested in the above post) ,the pinion angle does not change like the leaf spring suspension, so the torque is more constant when being applied to rearend and the ground . The leaf spring normally gets in the way when you want to use wider wheels and tires ,where the lower control arm on the 4 link isnt as intrusive. The leaf is heavier and increases the unsprung weight because it is carried with the axle ,where as the coilover is lighter and the control arms are not carried with the axle . The coilover leaves more space under the rear of the car for more exhaust options ect.ect. There are few types of 4 link coilover rear suspensions , The trianglated 4 link (like the RMS street lynx I have in my car) does not need a panhard bar because the upper control arms are mounted at a angle from the body to the rear housing .
