What Our Gearhead® Experts Are Saying:“This is the go-to EBB if you’re running a singlespeed Niner. It installs clean, holds tension reliably, and stays quiet once dialed. Just confirm your shell spec—55mm diameter and 68mm width—and you’re good to go. A great spare to have on hand if you swap gearing or travel with your bike.”The Niner BioCentric EBB keeps our singlespeed dialed by offering consistent, hassle-free chain tensioning that stays quiet and stable on long miles. Built for frames with 55mm x 68mm EBB shells, it’s a simple, precise upgrade or replacement for riders who prefer the clean efficiency of a geared-down setup. Easy adjustments let us fine-tune tension for different conditions or gearing choices, while the secure interface stays put through hard climbs and rocky washboards. Whether we’re refreshing a well-ridden frame or stocking a spare for the tool bin, the BioCentric II keeps the ride smooth and the drivetrain simple.