Biopace was a system developed by Shimano in the 90s to enhance the power delivery to mountainbikers on difficult terrine. It was intended to optimize the power transmission of the mountain biker on uneven terrain. Due to numerous complaints from riders with knee pain and other difficulties like an inability to really generate smooth pedaling Shimano stopped the production and came back to round chainrings.
How are absoluteBlack and its oval chainrings different from Biopace? First of all, Biopace chainrings were not oval, absoluteBlack chainrings are oval. The timing of oval chainrings is the position of the oval in relation to the crank arm. This timing is what creates the real benefit of oval chainrings. Back in the 90s, Shimano did not find the correct timing and instead of improving the power delivery Biopace did the opposite. absoluteBLACK has precisely optimized and tested the timing over many years, now the chainrings offer an undenyable advantage to the biker.