Reduction of energy required for acceleration
Compared to WH-R9170-C40-TL, the new WH-R9270 series requires less energy for acceleration at all rim heights. The energy required for acceleration is largely related to four factors: inertia, total weight, air resistance, and shaft rotation resistance.
The total weight plays an important role in running fast, but it is also true that the contribution to acceleration differs between 1 g in the center and 1 g on the outer circumference. If the outer circumference weight is reduced, the moment of inertia (i.e. inertia) becomes smaller. The smaller the moment of inertia, the less energy will be required for acceleration.
As a concrete example, let's compare C36-TL with the conventional product C40-TL. To accelerate from 35 to 45 km/h in 7 seconds, 788.5 W output is required on the conventional model. On the other hand, the new model requires only 781 W, enabling a 7.5 W reduction. As for the breakdown of 7.5 W, the outer circumference weight accounts for as much as 60%. In other words, the reduction of the outer circumference weight greatly contributes to the reduction of the energy required for acceleration.
We aimed to develop a wheel with good acceleration by reducing the inertia while ensuring the required drive rigidity. As part of such efforts, we sharply reduced not only the weight of the hubs and spokes as mentioned above but also the outer circumference weight (≈ rim weight).
Output required to accelerate from 35 to 45 km/h in 7 seconds
Breakdown of decreased contents
HG Spline (Road 12s dedicated) was newly developed exclusively for DURA-ACE components. We succeeded in making the entire FREEHUB body and ratchet structure from aluminum and achieved a weight reduction of about 45 g compared to that of the current FREEHUB body.
Furthermore, on C36 and C50, we have achieved a weight reduction through adjustment of spokes and nipples while ensuring the required rigidity. Specifically, this was made possible by optimizing the spoke size and tension. (WHR9170C40TL vs WHR9270C36TL ⇒ -106.7 g/set)