Topolino's Spokes

Hybrid-Fiber Spokes

The optimum use of composite fiber.

Topolino’s unique hybrid-fiber spokes consist of continuous Kevlar and carbon fibers within a thermoplastic resin matrix. The carbon fiber core provides strength and stiffness, while the Kevlar outer layers provide strength and toughness. Each Kevlar and carbon fiber extends through the hub and across the diameter of the wheel. This continuous-fiber construction makes the most effective use of our advanced composite material allowing a hybrid-fiber spoke to weigh 60% less than a 15 gauge steel spoke of identical length, while retaining exceptional stiffness and tensile strength.

Our hybrid-fiber spoke material has a linear density of approximately 7 grams/meter (nearly 1/3 of a 15 gauge steel spoke). This low linear density equates to low weight -- not low strength. In fact, our hybrid-fiber spoke material possesses more than three times the tensile strength of a 15 gauge steel spoke.

Not only are our spokes light and stiff, but they damp vibration as well...

Conventional steel spokes transmit vibration very efficiently – a quality that makes for great guitar strings. But a steel spoke’s inherent sustain means it is also more effective at transmitting road vibration to the rider.

Topolino’s unique composite spoke material has much lower sustain and damps much of that harsh road “buzz” before it reaches the rider. From the graph below, one can see that vibration decays (is dissipated) much more quickly in composite material. Thus, road vibration is damped much more effectively with Topolino’s composite spokes.

All the stiffness and half the weight...

Up until now all bicycle spokes have been made from metals. Each metal type has inherent material properties of tensile stiffness (Young’s modulus, or the materials’ “stretchiness”) and density (the materials’ weight). As it turns out, the ratio of tensile stiffness to density is virtually identical for steel, aluminum, titanium, magnesium. This is an important concept in the understanding of bicycle spoke construction. This means that, for an aluminum spoke to have the same tensile stiffness of a steel spoke, it must have a larger cross-sectional area, thus negating any weight savings. With these metals any weight savings can only be accomplished by reducing spoke thickness which results in correspondingly reduced tensile stiffness, which results in a flexier wheel.

The beauty of Topolino’s composite spoke is its ability to break free from these constraints associated with metallic spokes. Composites do not have to fit in the stiffness ratios of common metals -- a composite’s performance characteristics can be tuned to best suit its application. Thus, a Topolino spoke will have a substantially lower density while retaining the tensile stiffness of a standard steel spoke. Simply put, the Topolino spoke provides significant weight savings with no sacrifices in stiffness or responsiveness in the final wheel.

We go all the way...

In composites, longer fibers are always better and continuous fibers are best. By maintaining continuous uncut fiber length throughout our spokes the mechanical properties of the composite material is optimized

Our hybrid-fiber composite allows our spokes to pass through the hub flange, on to the diametrically opposite side of the rim. This through-the-hub construction also allows the spoke to reinforce the hub flange while becoming an integral structural element.

Virtually all other wheel designs utilize a single span spoke that terminates at the rim and the hub flange. This requires the hub/spoke interface to support the absolute (complete) spoke tension. In contrast, the Topolino continuous spoke is actually two spoke spans in one. With this arrangement, the hub merely supports the difference in tension between the two spans of the continuous spoke. Whereas the absolute tension of a bicycle spoke may range from 170-220+ pounds, the difference in spoke tension between the opposed spokes of a Topolino wheel is but a small fraction of this amount. One need only to look at the deformed spoke holes of a used aluminum hub to recognize the tremendous stresses introduced between the spoke and hub flange of conventional wheels.

Further, our through-the-hub construction eliminates any high stress areas on the spoke such as the J-bend. The attachment point of a J-bend spoke is laterally offset from the line of tension of the main body of the spoke itself. This lateral offset causes a bending moment in the spoke. While riding, cyclic flex is introduced at this bending moment, adding to the spoke’s fatigue stress. The spoke will eventually fail when enough fatigue stress is introduced.

In contrast, Topolino’s composite spokes have no J-bend and pass through the hub -- with Topolino wheels, breaking a spoke is thing of the past.