Work in baby steps ... if you average cadence is around 75 ... then work on staying around 85 to 90 for 2 to 3 minutes at a time. Take some breaks and ride at 75rpms. Do this ... and over time, increase the rpms. Try and get to the 90's compfortably. Just takes time.
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-\Brian
18' Landshark Tandem - Custom
15' Wabi Special Single-Speed Road
06' Cannondale Six13 TeamOne
06' Cannondale Prophet 3 "Lefty"
92' Trek 5200