The bevel benefit
The Velotegra hub is a unique planetary bicycle hub design. The Velotegra hub employs bevel planetary gears rather than regular planetary gears. This permits much larger planet gears with gear teeth large enough for engagement with rollers on the ring gears, thereby reducing wear and friction. To obtain the different ratios, the planet gears may be mounted at different angles around the circumference of the planet carrier, as shown on the right. The hub design is patented.
A compact chain line
The bevel-planetary configuration lends itself to higher gear ratios than conventional units. This means that the bike can have a smaller chain wheel and thus a more compact chain line, as shown on the right.
No more 1:2 ratio issues
In a conventional planetary hub as shown on the right, a step-up ratio of 1:2 is impossible in a single basic planetary stage since it would require infinitely small planet gears. Even gear ratios close to 1:2 are impractical due to the planet gears being too small. No such restriction is present with a bevel planetary configuration – a 1:2 step-up ratio is easily obtained.
More built-in clearance
Because the gear teeth are much larger, a larger clearance between meshing surfaces of the teeth can be built-in without any risk of the gear teeth skipping or marring, as demonstrated in the video clip on the right. This has multiple advantages: it permits the hub to be manufactured with enough initial clearance to avoid any requirement of a break-in period to reach full mechanical efficiency; it avoids any binding of the gears in the hub due to high applied pedal loads; and it allows more generous manufacturing tolerances and therefore lower manufacturing costs.
Stacked planet gears
Instead of being angled around the perimeter of the planet gear holder, the planet gears may be stacked vertically as shown on the left. This simplifies the geometry by giving a simple 90 degree intersecting shaft layout. As shown, the rollers may be located on the planet gears, rather than on the ring gears.
Bottom bracket installation and direct-drive
The high ratios and robust torque capacity enable adaption to direct-drive, where the hub is driven directly by the pedals rather than through a chain drive. Direct-drive permits the hub to be used as a bottom bracket gear and opens up new bicycle design frontiers, such as the direct-drive recumbent bike, shown at left.
Improved contact ratio
The smoothness of meshing between two gears is dependent on the average number of teeth engaged at one time – the more teeth engaged, the smoother the load is transferred. This is known as the gear contact ratio; the higher this ratio the smoother the meshing of the gears. A bevel-planetary configuration has a higher minimum contact ratio than a conventional planetary configuration. This results in smoother meshing.
Constant profile gear teeth
Bevel gears normally require a tooth profile that varies radially from the center of the gear outwardly (across the face width of the teeth). However, when the gear pitch is large, the gear face can be small for the same applied load. This means that the variation in tooth profile is small across the tooth face. As a result, the rollers can be cylindrical in shape, rather than frustoconical, and the sprocket teeth can have a constant profile to match the cylindrical roller surface. This simplifies manufacturing and associated costs.