Special rear wheel hub

Different Rear Wheel Hubs

In comparison to a conventional derailleur bicycle, gearbox transmissions have certain advantages. These vary according to current transmission technology, and may, depending on the field of application be of different value. However, some of these advantages can only show their full potential if changes are made at the rear wheel hub.

Illustration 1.1 shows the configuration of a conventional rear wheel hub used with derailleur bicycles. A hub body with spoke flanges, a left-side retainer for a rotor and components for the bearing and freewheel are illustrated. By positioning the freewheel at the rear wheel hub the chain stands still when the rear wheel turns, therefore friction is reduced while cruising. Only the friction of the wheel itself, the bearing and the freewheel have to be surmounted. Additionally, in conventional rear wheel hubs the freewheel holds the cog set or a single sprocket in singlespeed instances. In the following it always has to be differentiated between hubs with or without freewheels.

  
Pic 1.1 (rear hub with wide freewheel body)



Pic 1.2 (rear hub with narrow freewheel body; used for singlespeed bicycles)



Pic 1.3 (narrow freewheel body, BMX type rear hub)



Pic1.4 (COR rear hub)

Rear Hub Advantages and Disadvantages

Existing hubs can be used with gearbox transmission bikes, according to applied transmission technology, the positioning of the freewheel on the rear wheel hub affects the switching operation differently. Transmission concepts that are based on conventional derailleur technology (Petespeed, Honda) are dependent on a running chain while shifting, these transmission concepts should be run with hubs that do not have freewheels. The freewheel inside the gearbox allows the transmission to shift when cruising as the sprockets are rotating. Three different cases can be distinguished:

- Shifting whilst pedalling

- Shifting whilst cruising

- Shifting whilst stood, no cruising or pedalling.

Table 1.5 depicts these three cases in connection with the design of the rear wheel hub and

the positioning of the freewheel.

To sum up, a rear wheel hub combined with transmission should show following characteristics:

• Optimum chainline
• Optimum fitting width (the largest width possible between supports of the bearings)
• Easy mounting and dismounting of the rear wheel
• Easy tensioning of the chain
• Reduction of weight (decreased suspended rotating mass)
• Disc brake compatibility.

An optimum chain line runs at 90 degrees to the output sprocket of the gearbox. The width of the transmission therefore influences the width of the rear wheel hub. More information regarding chainlines can be found at question 8.

Through removing the conventional free wheel body located on the rear wheel hub rigidity of the rear wheel construction can be maximised. This is due to the symmetrically aligned spokes. Larger build-in width and axle diameters, as well as symmetrical spoke angles increase the stability of the bicycle wheel.

The change in strength and performance when having wider spaced symmetrical spokes is a gigantic leap and a massive improvement.

Chain Tensioning

Depending on the rear swing arm pivot point location change in chain length can be eliminated; resulting in no chain tensioner being required. The following systems can be used when mounting the rear wheels.

- simple horizontal dropouts

- Dropouts with circular shaped slots which are offset from the front sprocket. This tensions the chain when the wheel is mounted to the correct position and only needs to be set once. The chain tension is also unaltered when mounting and dismounting wheels.

- COR rear wheel hub for transmission bikes. View the film ( nabe.swf )

The Nicolai COR rear hub design shown in the video above has the chain located to the left of the frame and the brake to the right. This was the 2005/06 model and these two elements are swapped for the 2007 COR hub.

In comparison to conventional rear hubs, the COR rear hub is divided into several segments:

1. Sprocket mounting unit with inside spline (left)
2. Hub body with flange and double-sided splines (Middle)
3. Disk brake mounting unit with inside spline (right)

The sprocket, chain and disc brake stay attached to the frame when the rear wheel is mounted or dismounted, once adjusted the chain tension stays unchanged. The hub parts are connected with the spline and fixed through a shaft. Due of this form fit the drive and braking torque of the two sections are transferred through to the middle part.

The following steps are required to change the rear wheel.

Dismounting:

1. Loosen and turn out the shaft,
2. Loosen the left wedge bolt,
3. Loosen the sprocket mounting unit from the hub body and pull to the left,
4. Loosen the hub body from the right-sided mounting unit.

The rear wheel is dismounted and leaves the brake rotor and sprocket on the frame.

Mounting: