Sunday, August 26, 2018

Dahon MuSP: Crankset and Cassette

On the Dahon MuSP, a front single setup will be used. This means a 1x11 speed drivetrain, which is sufficient for everyday casual riding. My preferred front single crankset would be a Shimano road crankarm with Wolftooth Drop Stop chainring.

From my experience, the 105 5800 crankset is a great choice for setting up a front single crankset. The 105 right crankarm (340 grams) is just slightly heavier than an Ultegra right crankarm (325 grams), but is quite a bit cheaper. However, I want to install a full Ultegra groupset, and not mix the components. Therefore, I still decided to use the new Ultegra R8000 crankset for this setup, even though it is more expensive.

Ultegra R8000 crankset, with the chunky right crankarm as seen here. Similar to the Dura-Ace R9100 crankset used on the Canyon Endurace.

Right crankarm weighs 325 grams, which is only a little bit lighter than the 105 version.

Wolftooth Drop Stop chainring, 46T. This is larger than the 44T chainring which I used on the 451 Wheelsport Fantasy and also Java Freccia mini velo.

Comparing the 46T narrow wide chainring to the original Ultegra R8000 50T chainring

However, with the new chunky crankarm design, it is not a straightforward swap to the Wolftooth chainring, as there is some interference on one of the four arms. Therefore, some cutting and filing is required on the Wolftooth chainring, in order to make it fit on the Ultegra R8000 crankarm.

Special curved profile on the original Ultegra R8000 chainring, to clear the crankarm.

First we need to know which area on the Wolftooth chainring to remove. This can be done by placing the Wolftooth chainring onto the Ultegra chainring, which fits neatly on the chainring bolts.

Once placed together, the area to cut off can be seen here. Need to match the profile on the original Ultegra chainring.

Mark the area to remove with a marker, and either cut or file off the interference area. It was quite a bit of workout, as the chainring is made of heat treated aluminium which is quite hard.

Blue coloured Litepro chainring bolts to match the overall blue theme of the bike. It comes in a set of 5, but only 4 is needed.

With the Wolftooth chainring and blue chainring bolts installed! The blue chainring bolts really stand out.

Right side crankset weighs 426 grams.

Left side Ultegra R8000 crankarm weighs 194 grams.

This gives a total crankset weight of 620 grams, which is considered quite lightweight. Note that the crankarm length for this R8000 crankset is 165mm.

Moving on to the cassette, we will use an Ultegra R8000 11-30T cassette. Previously, when building the Crius AEV20 folding bike, I used an Ultegra R8000 short cage rear derailleur with the 11-32T cassette. The maximum recommended cassette size for short cage rear derailleur is just 30T, not 32T. Therefore, it was difficult to get the rear shifting tuned properly, although it can be done.

This time, I decided that it would be better to stick to the recommended specifications, which means a maximum sprocket size of 30T for the Ultegra Di2 R8050 rear derailleur.

The gear sprocket sizes for the 11-30T cassette is 11-12-13-14-15-17-19-21-24-27-30. This gear range should be sufficient for casual cycling, with more gearing details shown later in this post.

24-27-30 teeth sprockets are mounted on the same aluminium spider

19-21 teeth sprockets are mounted on a carbon fibre spider for lower weight.

In total, the Ultegra R8000 11-30T cassette weighs 270 grams. This is a big increase from the Dura-Ace R9100 11-30T cassette, which weighs only 206 grams.

Cassette installed on the Wheelsport rear wheel! All new and shiny.

With the 11-30T cassette, the gear range is quite wide, and sufficient to handle most conditions. Using the different sized chainrings will just shift the gear range higher or lower.

From my past experience, a 44T chainring is good for 451 wheels, while 48T is used on 406 wheels. Both gives a top gear of 88 gear inches, which is sufficient most of the time. The only time when this top gear is lacking is when we want to pedal down a slope.

This time, I decided to shift the gear range slightly, by using a 46T chainring instead of a 44T chainring for the 451 wheels. As shown below, this yields a higher top gear ratio, at the expense of a higher low gear.

Gear range of 46T chainring with 11-30T cassette, on 451 wheels is 33.7 to 92 gear inches.

At the top gear ratio of 46/11 teeth, a cadence of 100 RPM will move you at 40km/h, which is more than sufficient for a folding bike.

For sustained efforts, if you can maintain 90 RPM at the top gear ratio of 46/11 teeth, your speed will be 36km/h, which is not easy even on a road bike. In other words, this gear range is surely sufficient for the folding bike for casual riding.

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