By now, we’re all familiar with the claims made for ceramic bearings. Harder, rounder, smoother, and lighter than traditional steel balls, ceramics have the potential to reduce rolling resistance and angular momentum, run cooler, and last longer. These attributes are generally accepted to provide noticeable–if pricey-benefits on wheels, derailleur pulleys, and bottom brackets. But in a headset? In keeping with their no-compromises approach, German master machinists Acros have built a set of their very own angular contact hybrid ceramic bearings into a 50g (actual, 1 1/8 IS integrated) headset. Can its performance live up to the hype? Hit the jump to find out.
In many climates, headsets have largely evolved to fit-and-forget parts. Seals are ever smoother and more robust and, especially in the case of integrated models, weights are all fairly reasonable. Still, a market remains for handsome and well-made models- often as the piece of bike jewelery that completes a build.
The thought that has gone into Acros’ IS headset is apparent. The slotted crown race makes installation (and fork swaps) a tool-free affair. The clever top cover slides up and down an inner sleeve, minimizing the gap between frame and headset. Unusually, the top and bottom bearings are different: while the bottom uses a pair of 45-degree tapers to interface with the frame and crown race, the top uses a tapered frame interface and a straight (or very nearly straight) interface with a Delrin steerer sleeve. This has the benefit of keeping the fork in place after a stem is removed and, one would think, helping to keep the headset snug. Both bearings use low-friction metal reinforced seals to keep the crud out without interfering with the balls’ smooth motion.
Mounted on both 120mm cross country and 150mm trail bikes, the AI-24R1L has been both a quiet pleasure and a slight embarrassment. 
A pleasure because I know that the headset was made by perfectionists in their own factory in a first-world country. A pleasure also because the Acros has done nothing but go back and forth, quietly and smoothly as God intended. The slight embarrassment comes from the Acros’ ceramic-ness–which is advertised by the word etched into the stem and headset caps–and to which I can’t attribute any real performance gains. Its light weight and exacting manufacture are evident and the 1o year guarantee adds some peace of mind- but the pricey bearings’ benefits just aren’t obvious through the handlebar.
In exchange for a $70 lower asking price (closer to $110), Acros’ stainless bearing model loses half the guarantee and adds a claimed 15g. The 100% German construction remains, as do the XC, enduro, and freeride blessings. Though the metal balls may not spin as freely as their ceramic cousins, knobby tires conspire with brake, shift, lockout, and dropper post cables to have a far greater impact on steering feel. Every bit as attractive and (presumably) as well made, the steel model would make a great finishing touch on any integrated frame- without awkward trailside discussions about the ceramic bearings’ limited benefits.
marc
