Jackyll the Tandem part 9: Tears for gears

Since originally purchasing our Jack Taylor tandem AKA Jackyll in March 2015, we have replaced almost all the worn out parts and restored the bike to working order.  Originally it came with oddball north road handlebars, a worn out drivetrain, wobbly wheels and rumbly bearings.  One of the last outstanding items to be fixed was also one of the most important, the rear wheel.  This is doubly important on a tandem as not only does it determine what gearing you can run but it also influences your braking choice.  Due to all these functions, building a new rear wheel and getting everything to work together was not so straightforward.

The original

In a nutshell the original wheel had seen much better days, the bearing cups were gone, the drum brake was ineffectual and caused a judder sometimes when engaged, the 7-speed freewheel was limiting and prone to cause axle breakage, the old worn rim was a hookless design which would prevent higher tire pressures being used and to top it off some of the spoke nipples had seized and prevented the wheel from being trued from it's wobbly state.

The replacement 

When I had replaced the rumbly front wheel I purchased a pair of the Velocity Atlas rims as 40h 650B rims are particularly difficult to come by and had to be specially ordered.  After I built the front wheel the other spare rim was sitting there alone in my storage until now... These are the specs of the wheels:


- Shimano HF08 hub respaced to 110mm with Wheels Mfg. solid cromoly axle
- Velocity Atlas 650b 40h
- DT Swiss Alpine III spokes and brass nipples


- Shimano FH-HF08 hub 140mm spacing
- Velocity Atlas 650b 40h
- Arai drum brake
- DT Swiss Alpine III spokes and brass nipples


The other big reason to change to a cassette hub was the large choice of gearing available.  The old hub only supported threaded freewheels which are limited to 7-speeds and a high gear of 13 teeth, which on a tandem can be quite limiting as flat ground speed can be quite high!  I had a slight dilemma with the cassette choice however, I wanted to keep using the Suntour retrofriction shifters, generally 9-speed with friction is the limit as it starts to get too finnicky with 10-speed.  In the end I bit the bullet and went for 10-speed and bought a pair of modern Dura ace bar end shifters which have indexing. The speed and convenience that you can shift gears with an indexed system is somewhat useful when barrelling down a steep hillside with a fully loaded tandem!

I took this opportunity to fit a smaller middle ring as previously it was a 53/42/26t setup which meant the middle ring was a bit too high and too big a jump to the granny ring. The next step was to see if the chain would get stuck between the chainrings.  The Spécialités T.A. Cyclotourist and other 50.4BCD cranksets have a unique way of attaching chainrings.  The outer ring attaches to the crank arm and the inner chainrings are bolted onto the outer chainring with another set of bolts and spacers.

This means that there are a myriad of configurations available, you just need the appropriate spacers and bolts for single, double or triple setups.  Previously when I fitted the 26t granny ring I used the slightly thicker spacers between the big and middle rings.  This caused the 7-speed chain to get caught between them.  I tested this with the 10 speed chain and it was worse, 10 speed chains are about 1.5mm narrower than a 7-speed chain so this was no surprise.

I already had a set of slightly thinner spacers and one set of thicker spacers (3.5mm).  These needed to be filed down so I only had thinner spacers (2.5mm).  As you can see in the picture below, now I had filed down the spacers, this meant the bolt that fixed the chainrings now sat proud of the chainring and didn't fix properly... this mean they had to be filed down too!

After all this I was finally able to reassemble the crankset.  Hopefully I won't have to come around to this again, but I'm confident now with the thinner spacers it should work perfectly.  The other part of the gears I had to fit was the Dura ace 10-speed bar end shifters.

Drag braking

One thing that I have learnt about tandems since I bought one is that they tend to go downhill very fast... they pick up speed very quickly and stay there because of the increased weight and insignificant increase in air resistance compared to a solo bike.  Because of this traditionally tandem bikes have had a drag brake, typically this was the Arai drum brake which was adapted from a delivery trike.

The purpose of this brake is to hold a constant speed down hills to prevent the tandem gaining too much speed and thus losing control.  The Arai drum threads onto the non-drive side of the hub which is the same threading as a standard English freewheel/bottom bracket, the axle pokes through that and the backing plate goes over that. Other than that it is very similar to other bicycle drum brakes except for the fact that it is huge (120mm diameter) and has a lot of cooling fins!

The first thing I had to do to fit the hub properly was to narrow the axle.  The rear axle spacing is 140mm, which is standard on older tandems, however the Shimano FH-HF08 hub was spaced to 145mm from the factory which meant I needed to respace and shorten the axle.  You might be wondering what that is over the hub in the above picture, not to worry I just put a glove over the hub to stop any shavings from coming anywhere near the bearings.

Now it fits nice and easy straight into the frame. This was somewhat of a relief as it took me quite a while and a lot of money to get the drum and the hub, both long out of production and somewhat niche being tandem specific.  

For those that might wonder why tandems have wider axle spacings, it isn't just to be able to fit a drum brake.  It also gives the wheel more strength as it reduces the amount of dish in the wheel.  Too much dish means that the hub flange (where the spokes attach) are too close to the centreline of the wheel and mean that they cannot give much sideways bracing.  A wider axle spacing allows the spokes to be at more of an angle instead of vertical which makes for a a stronger wheel.  

Now onto the next part where I actually build up the wheel... Thanks for reading


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