The XD-15 bottom bracket is the fastest and toughest bottom bracket in the
XD-15 High Nitrogen Steel Alloy is 3.5 times more corrosion resistant than
440C Stainless Steel. In the past, ceramic hybrid bearing manufacturers were faced with a choice in bearing
race material: 1) The longer fatigue life of SAE52100 bearing steel when
paired with the extremely hard ceramic balls, or 2) The corrosion resistance of 440C stainless steel for use in harsh environments. If they opted for the longer fatigue life of 52100 bearing steel, the intrusion of water would
always be a threat to the races. If they opted for 440C Stainless, corrosion would become less of a threat
at the expense of longevity. The XD-15 steel not only combines the benefits of both, but EXCEEDS them on both
counts. Yes, much greater corrosion resistance than 440C and longer fatigue life than 52100 bearing steel.
Nitrogen Steel Alloy has a 40 percent higher load rating than SAE52100 bearing steel. Ceramic
hybrids made with 52100 steel races, while having a longer fatigue life than stainless, were still subject to premature
wear when used with ceramic balls. Of course the main claim of ceramic hybrids was less rolling resistance, resulting
in greater speed and a more efficient transfer of the rider's output to actual forward momentum. Wouldn't it be great
to get this superior rolling quality while actually increasing longevity of the bearing? Now you can. XD-15 has
an extremely fine grain structure which dramatically reduces the risk of failure under mechanical loading, lowers
noise and vibration, and makes a perfect interface with ceramic balls. Weak spots in bearing races due
to grain structure flaws in traditional bearing metals are not present in XD-15, which has a homogeneous structure of finely
dispersed carbonitrides, as opposed to large carbides concentrated at grain boundaries (which are vulnerable to corrosion
and mechanical stressing).
Grade 3 pure silicon nitride (SI3N4) ceramic balls are the best available.