Wait, What's a Triplizer?

A triplizer (or "tripleizer," if you prefer) is a special-purpose second chainring that lets you add a small third chainring to a traditional double crankset.

Here's how it works: On a dedicated triple crank (top photo, left), the large outer and smaller middle chainrings are bolted to the crank spider with one set of bolts and hollow nuts. A second set of bolts secures the small inner ring to a series of threaded holes further down on the spider.

Traditional double cranksets don’t have mounting holes for a third ring. But by replacing the conventional second ring with a triplizer ring--which incorporates  an inner circle of mounting tabs and bolt holes--it becomes possible to bolt a small ring to the triplizer itself (bottom photo at left). The triplizer is then bolted to the crank as for a standard double.

As with any double-to-triple conversion, a longer spindle or bottom bracket cartridge will be needed to provide clearance between the new inner ring and the drive-side chainstay.