The thinner the individual wire the higher the flexibility of the whole tension member! This interrelation led us to develop BRECO® BRECOFLEX® and SYNCHROFLEX® TIMING BELTS with E tension members.
In the E tension member the tension member cross-section is distributed to a lot more thin individual wires and, therefore, the bending fatigues are markedly lower in the individual wires. The advantage of the E tension members is a higher flexibility.
This is especially important, when smaller mounting dimensions for pulleys and tension rollers are required. The minimum number of teeth and/or minimum diameter of the pulleys can be fallen below up to 30% compared with standard tension members.
Timing belts with E tension members are recommended for multi-shaft drive with frequent bends.

Summary:
thinner individual wires in the steel cord
higher dynamic capabilities
extremely high bonding and bending fatigue strength
smaller pulley and tension roller diameter
no correction of the synchronising pulleys are necessary