Wednesday, April 26, 2017

Avanti Inc 3: Installing Eccentric BB + Dura-Ace Crankset

Time to assemble the new components onto the Avanti Inc 3 bike! The new components are the Bushnell eccentric BB, the Dura-Ace 7900 crankset, the 46T Gates front sprocket and 118T Gates belt.

After I had changed to Alfine 11 Di2, the chain line has been moved inwards. Now, since the crankset will be changed, I will need to ensure that the chain line is maintained more or less the same. To make the job easier, I checked the clearance between the right side chain stay and the 42T Gates front sprocket, while still using the Deore crankset. The final clearance should be around this value after changing to road crankset and 46T front sprocket.

2.5mm clearance between 42T front sprocket and right side chain stay

As shown in a previous post, the stock eccentric BB was removed, and replaced by the new Bushnell eccentric BB. A shim was used to reduce the internal diameter of the frame BB shell from 55mm to 54mm, in order to be able to use the Bushnell eccentric BB.

Bushnell eccentric BB installed, with the shim visible around it

A road BB should be used since the width is 68mm and a road crankset is used. Shown here is the SM-BBR60 bottom bracket.

New road BB installed in the eccentric BB

New crankset, front sprocket and belt installed!

Good clearance between the right side chain stay and the 46T front sprocket

This clearance is measured to be about 3.5mm. Chain line is straight.

Black coloured Bushnell eccentric BB blends in well with the black frame

Shiny Dura-Ace 7900 crank arm, with 46T Gates front sprocket and 118T Gates belt

Final picture of the Gates drivetrain

The crankset after some wet weather usage

The modification has been completed, and the Q factor has been reduced from 182mm to 146mm. This means a Q factor reduction of 36mm which makes a big difference in pedaling feeling and comfort.

At the same time, the gear ratio has been adjusted due to the changes in sprocket sizes. With the 46T front sprocket and a 28T rear sprocket, the gear ratios of the latest Alfine 11 setup can be seen below. On the Alfine 11, the lowest gear, Gear 1 has a big 29.2% difference from Gear 2, which some people like while some people don't. I personally don't mind having this big step, as it gives an extra low gear for climbing.

Range of Alfine 11 gear ratios with 46T front and 28T rear

With that, the objective to reduce the Q factor has been achieved. At the same time, the adjusted gear ratios means that most gears will be used most of the time, with a top and bottom gear reserved for slope riding.

Saturday, April 15, 2017

Avanti Inc 3: Dura-Ace 7900 Crankset + Gates Belt and Sprocket

In the previous post, the Bushnell Eccentric BB was used to replace the stock eccentric BB on the Avanti Inc 3. This changed the BB width from 73mm to 68mm, allowing the use of a road crankset.

The road crankset that I can use should have a 5 arm design, and 130mm BCD. I would have preferred to use the new 4 arm road crankset, but Gates does not make their belt drive sprockets in that specification. Therefore, I have to select the crankset to match the available belt drive sprocket from Gates.

The smallest 5 arm, 130mm BCD front sprocket from Gates is 46T. This is smaller than the stock 50T, but still larger than the 42T that I was previously using. Together with the 28T Alfine Di2 rear sprocket, the gear ratio will be changed again.

46T, 5 arm, 130mm BCD Gates front sprocket.

Weighs 81 grams

The road 5 arm cranksets that I can choose from are the Ultegra 6700 (on Dahon MuEX), and Dura-Ace 7900 (removed from Merida Scultura 5000). In order to maintain a full Ultegra 6700/6770 groupset on the Dahon MuEX, I decided to use the Dura-Ace 7900 crankset on the Avanti Inc 3. Only the crankarms will be used, while the chain rings will be removed.

Since the Alfine 11 Di2 hub has a blue accent line running around the hub shell, I was thinking if I should use some blue chain ring bolts to match that.

Blue accent line on the Alfine 11 Di2 hub

Blue chain ring bolts. However, too many colours on the crank arm (blue, black, dark grey, silver) makes it difficult to showcase the beauty of the Dura-Ace crankset. 

Using black chain ring bolts makes the crankset look less busy, giving a more stealthy look

Gates 46T front sprocket mounted on Dura-Ace 7900 crankarm

Front sprocket needs to be mounted behind the tab to maintain straight chain line with rear sprocket

409 grams for right side crankarm plus 46T Gates front sprocket

A comparison picture of the front single sprockets. Crankarm on the left will be installed on the Avanti Inc 3, while the Dura-Ace 9000 crankarm + Wolf Tooth chain ring on the right has already been installed on the Wheelsport Fantasy mini velo.

Next, due to the change in sprocket size, a new longer Gates belt is required. I have no choice but to order a new belt.

Gates carbon drive belts come in a large box to prevent mishandling (twisting, bending) of the belts

118T, which is the next step up in size from the previous 115T belt.

118T Gates belt weighs 90 grams

With all the components gathered, the next step is to install all of them on the Avanti Inc 3. This modification will allow the use of a road crankset, which will have a narrower Q factor for more comfortable pedaling. This is quite a lot of work and modification required just to change the Q factor! To be continued...