Designed with Purpose
The driving force behind the design of the rear hub was to further equalize the spoke tensions between the drive and non-drive sides of the wheel. Several engineering decisions were made to accomplish this design goal, among others to make a solid total package.
The most noticeable difference in the rear hub is the large drive side flange. We call this the R-Symmetric Flange, short for Right-Symmetric Flange. Unlike the front hub, which has symmetric drive and non-drive flange spacing, the rear hub has limits on how wide the drive side flange can be spaced due to the cassette. There are a few ways to equalize the spoke tensions on the rear hub with equal flange diameters, such as narrowing the non-drive flange width to that of the drive side. This makes a wheel with equal spoke tension, but the narrow flange width creates a very unstable system. In order to keep the widest possible non-drive flange width, we increased the diameter of the drive side flange to make a wider effective drive side flange width as shown below. With the spokes leaving the rim at similar angles, the force vectors acting in the direction of the spokes are more equal, thus creating a more balanced wheel. Keeping the base triangle as wide as possible makes the wheel more laterally stiff, because the spokes are creating a wider bracing angle that opposes lateral flex.
What’s the point of having a stiff wheelset if it always needs maintenance and eats through bearings? With our design, we elected to create an adjustable axle to ensure proper wheel alignment and preserve bearing life. The axle adjustment allows us to ensure that there is no slop in the wheels due to manufacturing tolerances. Companies that use shouldered axles run the risk of having slop in the axle relative to the hub shell if the shell is undersized in bearing width -- or worse, binding the bearings if they are oversized. The adjustable axle lets us dial in the bearing contact, so they roll smoothly without side-to-side play. Our axles are a one piece construction to prevent deflection of the bearings under load. No axle deflection means that the inner race of each bearing is free to spin in a single plane (as they are design to do) as opposed to being torqued and damaged every time you hit a pothole.
To further prolong the life of the bearings and lessen the amount of friction within the hub, the shells and axle end caps were designed in unison to create a labyrinth seal that keeps water and other contaminants out. By using tight manufacturing tolerances, we were able to overlap the hub shells over the end caps to make it difficult for dirt and water to make it too the bearings, because they would have to enter the shell parallel to the axle and on a rotating surface. This design can be seen below.
While others might cut costs with lower grade bearings, we have opted to use quality NSK ABEC7 stainless steel bearings and Kogel ceramic bearings. These bearings are precision ground, ensuring less rolling resistance and greater longevity.
Keeping with quality products, we spec Sapim CX-Ray spokes and locking nipples. Sapim designs their products to work together, so we are keeping them paired. The secure lock spoke nipples help prevent the wheel from coming out of true by preventing the nipples from untightening.
Design for assembly
By starting from scratch, we were able to overcome the challenges presented by our new innovative design. After running several lacing patterns through a program we wrote to calculate spoke tensions based on the lacing pattern, we decided on the 2x non-drive and radial drive pattern. To be able to use the alternating spoke lacing pattern we wanted, small design changes needed to be made to allow the non-drive spokes to be fed into the flange with the heads, while still clearing the enlarged drive side flange. The ramped spoke holes shown below allow us to do just that, and highlight our philosophy of designing with purpose.
Throughout the theoretical design process, Numerical calculations were ran to determine the optimized flange widths and diameters. From this starting point, the hub was subjected to Finite Element Method analysis to determine things like the thickness of the flange, the amount of material needed to minimize deflection of the large drive side flange under load. Versions of the flange deflection (left) and stress analyses (right) are shown above.