Cover Assemblies with the ER2 Groove Design feature have a unique groove pattern CNC machined on the friction face of the Pressure Plate. The groove has been specifically designed to increase the Mean Effective Radius of the pressure plate and assist in heat removal. The increase in the Mean Effective Radius of the Cover Assembly gives an increase in Torque Capacity by up to 8%. Mean Effective Radius is directly proportional to Torque capacity.
By adding the groove to the Pressure Plate, the inside radius of the friction face has effectively been increased. The first 5/16 inches of the pressure plate has all but been removed and added to this, there is progressively less material removed as the radius increases. The net effect of this is to move the effective inside radius further out. When comparing the Mean Effective Radius (Rm) of the ER2 version to the non ER2 version you can see the ER2 version is further out. This increases the Torque Capacity of the clutch. Torque Capacity is directly related to Rm.
The formula for calculating the Torque is: Torque = Force x Distance or T = F x Rm For a Clutch the Force is dependant on the Coefficient of Friction: Force = Coefficient of Friction x Clamp load or F = μ x N.
(Note there are 2 friction faces so for a Clutch F = 2 x μ x N)
The Torque Capacity advantage of the ER2:
The Pressure Plate grooves increase Mean Effective Radius by 8%. As Torque is directly proportional to Mean Effective Radius this means the Torque Capacity is also increased by 8%. Using CI's in house Dynamometer the Torque capacity was measured for a Non ER² Pressure Plate vs an ER2 Pressure Plate.