EBB & Belt Tensioning

An eccentric bottom bracket (EBB) is one that allows the normal bottom bracket, which is screwed into the EBB, to be moved forward or back so as to tighten or loosen the chain or belt. After the desired tightness is achieved it is necessary to fix or lock the EBB in place. This is done by a pair of wedges that slide up two ramps and bear against the inside of the frame shell. Turning the 5mm hex-head bolt clockwise tightens it in position. Torque of 5Nm-8Nm is sufficient to lock it in place.

Left: End view (the left end is marked with an L and must be on the left side of the frame). Right: Side view Before assembly the entire surface of the unit, including the ramps that the wedges slide on and all sides of the wedges, and the inside of the frame BB shell, should be coated with light grease.

Left: End view (the left end is marked with an L and must be on the left side of the frame).
Right: Side view
Before assembly the entire surface of the unit, including the ramps that the wedges slide on and all sides of the wedges, and the inside of the frame BB shell, should be coated with light grease.

Loosening the EBB Unit

Use the long 5mm hex key with the copper pipe extender as in the picture below. To unlock the position the hex-head is turned counter clockwise. After one-two turns you notice there is a point where resistance rises. This is where the wedges are being dislodged. Your unit is not yet free to rotate until you turn another few turns, through this resistance. Now, providing there is sufficient grease on all of the internal surfaces, the unit will be free to move sideways or to be rotated slightly in each direction.

Setting Correct Belt Tension

Correct tension is important. However, carbon belts, unlike chains, do not stretch or elongate so only lose their tension over a very long time as slight sprocket and belt deterioration develops. With a life expectancy of 25-30,000 km this is indeed a very long time. A new VWR bikes comes with this preset and you are unlikely to need to touch it. If you do ever need to there are two things to know.

    1. how to rotate the EBB unit in the frame, and
    2. how to measure the belt tension before tightening.

Once you have loosened the screw, given that the EBB is properly coated with grease, the EBB unit can be freely rotated in the frame. Due to the range of positions and directions possible It is hard to make one tool to rotate it. Pin spanners can be used as in the picture below but it is not easy to get sufficient purchase with them. If you are stuck without tools, an arrangement of zip ties can be used, as in the picture below.

Another very simple method is to hold the hex key firmly and turn the crank to get leverage against it, with some cloth between the crank and the tool. To measure the tension Gates makes the Krikit Gauge, small enough to fit in the tool bag. It sits on top of the belt and allows for single-finger tension testing through the click of a button. There is also a phone app that you can download to check you have achieved the recommended range of 35-50 Hz.

Pin Spanner Method

Zip Tie Method

Note: unlike another type of EBB that uses “grub screws” through the frame to tighten the unit in position, the internal expansion type used on your VWR can be adjusted as often as you like and in as tiny increments as you like.

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PH: +61 2 7900 6734  
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PO Box 156, Summer Hill, NSW 2130, Australia
 


Vivente Bikes is a venture of Gemini Bicycle Centres Pty Ltd, ABN 32 003 102 538

Address: 1/201 Marrickville Rd, Marrickville, NSW, 2204, Australia

Designed by Joshua McFarlane

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