Crankset based bicycle power measurement

An input torque measuring device for a drive train of a bicycle, the drive train including a first crank arm and a second crank arm configured to be engaged by a rider of the bicycle at an outboard end, an inboard end of each crank arm rotatably mounted to the bicycle at a bottom bracket of the bicycle, at least one generally planar chain ring oriented generally perpendicular to the bottom bracket and configured to rotate about the bottom bracket and to rotate a driven wheel of the bicycle, the device comprising:

• a spider connected to a first crank arm adjacent the bottom bracket, the spider including a plurality of spider arms extending out to and directly supporting and connected directly to the at least one chain ring, the spider configured to transmit force applied to the crank arms through the spider arms to the at least one chain ring;
• the spider including a plurality of sensors configured to respond to the force applied by the spider to the at least one chain ring and produce an electronic signal relative to the force transmitted by the spider;
• the plurality of sensors mounted to the plurality of spider arms and comprising a strain grid, wherein all of the plurality of sensors are oriented parallel to a plane of the at least one chain ring;
• an electronic circuit configured to receive the electronic signal and generate an output representative of the load on the spider parallel to the plane of the at least one chainring.