Kuroshiro ensō685 carbon fat bike rims — First look

World's lightest and most expensive carbon fat bike rims

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.

Kuroshiro: the italian start-up with a japanese name is introducing the ensō685, an 85mm-wide carbon fat bike rim with a claimed weight of just 415g: kuroshiro: the italian start-up with a japanese name is introducing the ensō685, an 85mm-wide carbon fat bike rim with a claimed weight of just 415g
Kuroshiro: the italian start-up with a japanese name is introducing the ensō685, an 85mm-wide carbon fat bike rim with a claimed weight of just 415g: kuroshiro: the italian start-up with a japanese name is introducing the ensō685, an 85mm-wide carbon fat bike rim with a claimed weight of just 415g

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 single-walled rim gets its strength from a raised spline that connects the offset spoke holes: the single-walled rim gets its strength from a raised spline that connects the offset spoke holes
The single-walled rim gets its strength from a raised spline that connects the offset spoke holes: the single-walled rim gets its strength from a raised spline that connects the offset spoke holes

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.

From the inside, the zig-zagging channel allows tire sealant to coat the nipples making the rim tubeless without the need for a rim strip: from the inside, the zig-zagging channel allows tire sealant to coat the nipples making the rim tubeless without the need for a rim strip
From the inside, the zig-zagging channel allows tire sealant to coat the nipples making the rim tubeless without the need for a rim strip: from the inside, the zig-zagging channel allows tire sealant to coat the nipples making the rim tubeless without the need for a rim strip

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.

Josh has been riding and racing mountain bikes since 1998. Being stubborn, endurance racing was a natural fit. Josh bankrolled his two-wheeled addiction by wrenching at various bike shops across the US for 10 years and even tried his hand at frame building. These days Josh spends most of his time riding the trails around his home in Fort Collins, Colorado.
  • Discipline: Mountain, cyclocross, road
  • Preferred Terrain: Anywhere with rock- and root-infested technical singletrack. He also enjoys unnecessarily long gravel races.
  • Current Bikes: Trek Remedy 29 9.9, Yeti ASRc, Specialized CruX, Spot singlespeed, Trek District 9
  • Dream Bike: Evil The Following, a custom Moots 27.5+ for bikepacking adventures
  • Beer of Choice: PBR
  • Location: Fort Collins, CO, USA

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