As the fat bike market grows so too do the number of riders seeking to keep the benefits of their massive tires while shedding pounds. We saw several companies, NoTubes, HED and Borealis among them, introduce carbon fat bike rims at Interbike 2013.
When it comes to rotating mass — of which there is a great deal — carbon rims are only half of the fat bike weight loss equation. The other half is tubeless compatibility. The average fat bike innertube weighs around 450-500g. Ditch the tubes and one can easily shed close to 1kg (2.2lb) of rotating weight.
A small Italian start-up is seeking to outclass its competition by taking fat bike weight savings one step further, for a price, for course.
Kuroshiro is a new brand created by the Italian bicycle parts distributor Raceware. Its first product is an 85mm-wide carbon fat bike rim that has a staggeringly low claimed weight of just 415g per rim.
Dubbed ensō685, the rim is produced by the Italian carbon component manufacturer Alchemist
The ensō685 is not a simple single-wall rim, nor does it have a box-section design. It gains its rigidity from a raised spine, called "SP-line" by the company, that crosses back and forth across the exterior of the rim, connecting the offset spoke holes. Company founder Mauro Bertolotto claims the SP-line design increases rim stiffness by more than 18 percent with a limited weight penalty.
The spoke holes along this raised zig-zagging channel are reinforced to deal with the high spoke tensions needed to effectively run ultralight spokes, such as Sapim CX-Rays. When assembled with ultralight spokes and hubs this could result in a complete wheelset weight in the neighborhood of 1,600g.
The ensō685 retains a bead hook design in order to improve the seat between the tire and rim and minimize the likelihood of burping air when riding over hard terrain at very low pressures. According to Bertolotto, the goal was to great a high performance carbon fat bike rim that was capable of performing on any terrain and any season.
Tubeless and tapeless
The final piece of this new light and wide rim is what the company calls “40 Below Technology.” According the Bertolotto, the conical interface between the nipples and the rim is built to such precise tolerances that the user does not need to use a rim strip in order to set the rims up tubeless. By removing the need for a rim strip the user sheds approximately 20g per wheel, or 40g total.
The company claims that the interior portion of the SP-line channel lubricates the spoke nipples with enough sealant to prevent air from escaping between the nipples and the rim.
As one might expect, all this technology comes with a premium price tag; the ensō685 retails for €899. (Other pricing TBD.)
Kuroshio ensō685 rims and complete wheelsets are available now. For more information visit www.raceware.com.