With a three week break staying at my Dad's place in North Carolina, I've been able to give the Llama a much needed overhaul (the dust from the Carretera had penetrated every tiniest nook and cranny). I also took the opportunity of having access to a well-equipped workshop to upgrade to an internal gear hub.
Originally the Llama had been fitted with an 8-speed cassette, and it required a long-cage derailleur to accommodate the low gear (32T) I need for fully-loaded touring. With a 20" rim this meant that the bottom of the derailleur and the tension pulley sat only a centimetre off the road surface, making it overly vulnerable to rocks and dust. Luckily the derailleur survived up until now, but I did have to bend it straight a couple of times, and I was constantly having to clean the chain, especially on unpaved roads.
One option to overcome this problem would have been to change to a short-cage derailleur, which would provide more ground clearance, but would have meant using a narrower-range cassette and eliminating my lowest gears. I decided instead to convert to an internal gear hub. These have become quite advanced in recent years, offering low maintenance and and an efficiency similar to that of a derailleur system, albeit with increased weight.
My first choice would have been a Rohloff Speedhub, a marvel of Germanic engineering with 14 evenly spaced gears and a whopping 526% range. However, at $1,100 it was more than I could afford. I opted instead for a Shimano Nexus 8-speed hub. It has received good reports and is a lot more economical, but the gears aren't so evenly spaced, and the overall range is only 307%, meaning I needed to retain the front derailleur, which in turn meant I needed a chain tensioner to take up the chain slack.
The first step was to get a new rear wheel built. For this I chose a Velocity Taipan BMX rim (my existing Alex rim had only 32 holes and the Nexus has 36) and ordered appropriately sized DT spokes from Bike Friday. I also ordered a Shimano Alfine RadidFire shifter (a regular 8-speed shifter won't work), a set of no-turn washers for vertical dropouts, a Shimano Alfine chain tensioner, and an 18T sprocket (providing a range equivalent to an 11-34T cassette).
Fitting the hub to the bike and connecting the shifter was a relatively straightforward case of following the instructions. The main difficulty was in fitting the snap-ring that secures the sprocket.
On fitting the chain tensioner, I found that I couldn't align the pulleys with the sprocket, even using the supplied spacers and with the sprocket dished inwards. I ended up fitting a Shimano Sora short-cage derailleur, which has similar dimensions to the chain tensioner but, being a regular derailleur, has a wide range of lateral movement so it can be correctly aligned. It is a bit heavier though. I'm surprised that an Alfine chain tensioner isn't compatible with a Nexus hub, as these are sibling products in the Shimano range.
The final problem to overcome was that, because there is no rear derailleur shifter/cable in this set-up, I had to use the H adjusting screw to position the derailleur in line with the sprocket. This screw wasn't long enough to bring the derailleur far enough inward, so I had to replace it with a longer one (Dad's pot of old screws to the rescue!).
The next step will be to convert from a triple (30-42-52) to a double (30-42) chainring, as the short-cage derailleur can't handle a jump from 30T to 52T, and anyway I found the 52T mostly redundant, only being able to use it going downhill when I prefer to coast and conserve energy anyway. This will give a chainring to sprocket ratio of 1.66:1, a bit lower than the 2:1 that Shimano recommends to avoid pushing too much torque through the Nexus's mechanism. Time will tell if this is an issue or not.
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