Heavy Duty I.R.S. Mounts And Trailing Arm Bushings. For high performance work, the standard E-Type Independent Rear Suspension (I.R.S.) and trailing arm mounts are a bit too soft. (And, conversely, some of the available polyurethane mounts are far too hard.) These mounts are made in England by folks with decades of experience with modified E-Types. They provide far more positive location of the I.R.S. unit for improved handling but without undue harshness.