Solid axle vs. IRS

[68sixspeed]

One thing that hurts a 4 link in roll is hard to picture at first, but the easiest way to describe it I've found is to consider the pinion angle change-- If you have some 'up' angle in the lower link as you would want to plant the tire, then as the suspension is compressed the bottom brackets move rearward sligtly and the top brackets move forward slightly making the pinion nose down under compression. If only one side of the car is being compressed in this situation the axel will just lock up in roll and be force to compress both sides evenly. (as one side of the car is trying to hold the pinion angle constant and the other is trying to move it up/down - trying to rotate the rear end housing.) Rubber bushings help this by allowing some stretch, but it's a length of bar issue, not a swivel/rotation issue with the rod end or bushing. To help this, you can set a true 4 link to more of a 4 bar setup by bringing the bars more into parrallel which minimizes pinion angle change and twisting of the axel tubes. (for example, I've heard of pro-street cars actually break rear end tube welds from the tube stress of street driving.) I hope that makes sense... -Dan