MOBI > Roval Fusee Star Wheels

Roval Fusee Star wheels have closely-spaced large-diameter flanges.

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They are advertised as "aerodymic" wheels:
Aerodynamically superior Star hub design reduces frontal area by 50%, minimizing wind drag as of 2009/08/03

"The key to the Star wheel concept of a narrow hub flange for improved aerodynamics is the short spokes. The shorter and stiffer spokes, combined with the super stiff hub allows us to balance aerodynamics with lateral stiffness and ride quality. The result is a 50% reduction in frontal area compared to a standard wheel. It's a truly unique hub, unlike any other on the market." - Chris D'Aluisio, Advanced R&D

[X] as of 2009/08/03

The maker's diagram shows a shorter "spoke length", but the flange is also elastic, and so behaves as a spoke and changes length under changing load. Conventional hub flanges also behave the same way, but since conventional flanges are short compared to the spoke length, their elasticity is small enough to ignore when computing wheel elasticity/stiffness.

The aerodynamics of the "Star" flanges are probably worse than the aerodynamics of flanges and spokes in a similar conventional wheel. The "Star" flanges are thicker than a spoke where they hold spoke and also appear to be thicker than a conventional spoke along their length. Although there are only five inboard "spokes" per side, each has a large surface area, increasing "skin" drag. Thus, total drag for one "flange spoke" likely exceeds the drag of a pair of conventional spokes.

The claimed aerodynamic benefit appears to come from narrow flange spacing, not the hub itself.

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Narrower flange spacing is also sometimes used with conventional hubs, and results in worse bracing angles against lateral loads, thus a weaker and more laterally flexible wheel.

The claim above appears to be that the "Star" flange design helps make up for the loss of lateral bracing, because an ordinary spoke is replaced with a shorter spoke and a length of flange; and that together they are stiffer than an ordinary thin spoke.

An alternative would be a conventional hub with narrow flange spacing, and heavier spokes. The Fusee Star's large flange is heavier than equivalent length of ordinary spoke, and probably has more aerodynamic drag than ordinary spokes, but allows a lighter spoke at the periphery, where the spoke velocity and thus air drag are greatest.

Thus, a more comparable system might use a two-gague spoke built using two short conventional spoke segments using a threaded coupler between them. That would allow a thick spoke section inboard and a thin or aerodynamic profile spoke outboard and would mimic the stiffness of the "Star" wheel. The two-gague spoke would likely weigh less and have a better aerodynamic profile than the "Star" wheel.

These wheels are not widely used, but at least one review finds little benefit:

[W]e noted some brake rub on uphill gradients, so they aren't as stiff as they look.

[O]n poor road surfaces these wheels feel extremely harsh. as of 2009/08/03.

The use of a shallow-section rim reportedly reduces problems with crosswinds.

According to as of 2009/08/03, the wheels are 1750g/pair not including quick release skewers.

The Roval Fusee Star flange spacing is not listed, but is likely on the order of 30-40mm, compared to 60-80mm for a conventional front hub.

For comparison, consider conventional wheels built with 425g Velocity Aerohead andAerohead OC rims, 85g front/235g rear Campagnolo Record hubs, and 40 aluminum nipples at 0.3 g/each. Without spokes, these wheels would weigh 1182 g, leaving 568 g for 40 spokes, or 14.2 g/spoke. For comparison, Sapim CX bladed aerodynamic spokes are about 6.75g/spoke in 260mm ( as of 2009/08/03), or 270g for 40x spokes. Obviously, the Campagnolo hub does not have the narrow flange spacing, but this gives an idea of the weight of the Roval Fusee Star hubs, and that other designs which do use a conventional hub with narrow spacing would have a wide weight margin for "inner" spokes and so on.