Si Mountain Headsets

Cannondale's Si headtube system makes headsets easier. The Si headtube was designed around the Lefty and Headshok forks and the proprietary 50.5mm bearings used for those forks. You'll find the conversion headsets here for use with 1 1/8", tapered, 1.5" and Lefty/Headshok forks below. 

Note that the Si headtube is different than a 1.5" standard head tube which requires the use of cups for the bearings. The Si headtube allowed the use of Lefty/Headshok bearings to go directly into the frame and avoid the use of additional cups as was done on earlier generation frames.

The Si headtube has been used on most new mountain bikes since model year 2009 with a few models prior to then. These models include Rush Carbon, Rize, RZ120, RZ140, Habit, Trigger 26, Trigger 29, Trigger 27.5 (prior to 2018), 2nd and 3rd generation Jekyll, Taurine, Slate, and others. 
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