Powertrac Elliptical Chainring for SRAM DM

Their proprietary design has ovality of 10% and timing of 112° after TDC (top dead center). These values provide the benefits of an oval ring without the drawbacks of greater ovality or more aggressive timing.  

The simplest way to explain how they "feel" is that where your pedal stroke is weakest it feels like you have a 2 teeth less on the chainring and where you have the most power it feels like you have 2 more teeth.  They feel this way because with the radius of the chainring constantly changing, the torque needed to turn the cranks is constantly changing to better match your power output.  Example: a 34t chainring feels like a 32t in the weak part of your pedal stroke and a 36t in the part of the stroke where your legs have the most power.