Tuesday, October 22, 2013

Short Cranks for Kids on Tandems

In my first post about my Bike Friday tandem from last year, I showed a picture of the Ride2 crank shorteners I first used for making the rear crankarms a more suitable length for riding with small kids on the back. Crank shorteners get the job done, but they are a bit expensive ($110 on Amazon right now), and they have the effect of spacing the pedals out further away from the bottom bracket (the so-called Q factor). I would assume this is more noticeable to riders with short legs, so I think it's a less than ideal solution. Since the Bike Friday was already set up with single side drive due to the DualDrive shifting, the rear cranks can be replaced with any standard crankset.

When we acquired another tandem last year, I put the crank shorteners on that bike and tried using a short crank on this one. The cranks pictured here are made by Sinz, who make parts for high-end BMX bikes. These cranks are available for both square taper and ISIS bottom brackets, in lengths from about 130 mm to 180 mm in 5 mm increments. They can be found online for about $60, and occasionally less. The ones in the picture are 145 mm ISIS cranks. (Note that the bike comes with square taper bottom brackets, but I found an unusually good price on an ISIS crank and happened to have an extra ISIS bottom bracket.) The cranks have a 110 mm bolt circle diameter, which matched the old cranks, so I just moved the original chainrings over to the new cranks.

I think this is a superior solution for tandem riding with kids. It's not adjustable in length like the crank shortener, which has three different lengths. However, it is possible to buy two Sinz cranksets in different lengths for not too much more than the cost of one pair of crank shorteners. If I did it again, I would do that, getting them in lengths of 145 and 155. Using this approach requires single side drive, but in this era of compact road cranksets and 11-speed gearing, one could theoretically convert even a standard double side drive tandem to use cranks like this without losing much in terms of gearing range.

Bike Friday Tandem Customizations

I already wrote previously about my Bike Friday Family Tandem. I used it for over 2 years in the configuration it came in: flat handlebars with Sachs (now SRAM) 3x7 Dual Drive shifting. I prefer drop handlebars, so last winter I decided to switch out the handlebars.

Switching to drop handlebars on this bike requires a few other changes. First of all, I needed a pair of 3x7 Shimano STI brake/shift levers, which various online sources claim are compatible with the older DualDrive hub/derailleur combinations. Shimano hasn't made a 7-speed shifter for a number of years, so these have to be bought on the secondhand market, but even then they are hard to find because Shimano had already gone to 8 speed on their high end drivetrains when they introduced STI in the 1990s. The one exception is the RSX shifter, which presumably was sold on some lower end road bikes in that era, and comes in a 3x7 configuration. I found these RSX shifters on eBay.

One problem these shifters had when I bought them was that the smaller levers (the ones that shift to a smaller chainring or rear cog) did not engage. This apparently is a fairly common problem with these shifters and it is caused by the old grease getting sticky. I can confirm the claims made by others on the internet that this problem can be fixed relatively easily by spraying degreaser into the shift mechanism a few times, followed by a light lubricant, which eventually frees up the mechanism.

The brakes on this bike (drum brake front, V-brake rear) expect a longer cable pull than STI shifters are capable of generating, so it is necessary to add the Problem Solvers Travel Agent. I've used them on another tandem already and they work great. They come in two varieties, one for V-brakes and one for disc brakes (or drum brakes), so I installed one of each type. Here's the rear V-brake with Travel Agent installed. It replaces the curved "noodle" normally installed between the cable housing and brake.

The disc brake version comes with a hole at the top so that it can be attached to the fork using a cantilever brake mount. This fork doesn't have cantilever mounts, so I attached it to the fork with zip ties and used a piece of inner tube around the fork blade to prevent scratching the paint and hold it in place. So far, braking performance both front and rear with the travel agents installed has been great.

The left shifter, which normally goes to the front derailleur, has worked fine operating the 3-speed internal hub. It takes some getting used to because when connected to this hub, its operation is backwards from a front derailleur: the large lever shifts to a lower gear rather than a higher gear. The combination of the right shifter and rear derailleur has been less than ideal so far. The cable pull for each click isn't quite enough for the derailleur. It's adjusted so that it works OK in the middle of the gearing range, but starts to miss shifts as I get out to the edges. It's possible the derailleur or shifter are just old, but the original grip shifter that came on the flat handlebars worked better.

DIY Winter Cycling Gear

Some time in the late 1980s, I bought this neoprene headband from the Performance Bike Shop in Boulder, Colorado. Since then, it's been used for countless miles of winter cycling, including two years of 12 mile commutes during college, and many other winter outdoor activities. It's been great for cycling in particular because it's quite thin and easily fits under a helmet while keeping my head and ears warm for any temperature above freezing. Colder than that usually requires additional headwear.

Its design is incredibly simple: a single peice of neoprene with a single seam at the back stitched together using a zigzag stitch.

As is evident from the first picture, it's starting to show its age a bit. Some of the foam material has started to break down so it doesn't feel quite as thick as it used to. I'd have bought a replacement years ago if I could find one, but have never seen anyone selling anything like it. Last year Heather and I started doing more winter rides and it became apparent that her fleece headbands were often not enough. It occurred to me that my headband should be quite easy to replicate. Neoprene fabric can be bought in small quantities online from various sources. I bought a 1 foot by 4 foot piece of it from an eBay seller for about $15. I estimated the thickness of the fabric used in the original to be about 2 mm thick, so I ordered the material in that thickness, but it appears to be a slightly thicker than the original. It's possible the original was actually 1.5 mm (I think the fabric is also available in that thickness), or that it's just thinner due to deterioration over time. In any case, 2 mm seems like about the right thickness for me, but others may prefer something in a different thickness.

I have a relatively large head, and Heather's is relatively small, so based on the original headband, I created two separate patterns, to fit large and small head sizes. In case this is useful to anyone, I created this PDF document with patterns for both sizes.

Note that the patterns reach relatively close to the edges of letter-sized paper, so check the print settings when printing it out. Some viewers by default will try to shrink it to add extra margin at the edges. In Chrome PDF viewer, uncheck the "fit to page" option. To make sure the printout is the right size, I've added measurements to the diagram so the size of the printed pattern can be checked before using it to cut fabric.

Here's the end result. It basically looks like the original, except that it's clear my pattern cutting skills weren't quite good enough to get the bottom of the seam to line up perfectly. Since I made them in two sizes, I stitched my initial into it in order to tell them apart coming out of the laundry. I made a total of 3 of these using about 1/3 of the neoprene fabric I bought, so for about $15 in materials (probably about what I paid for the original headband), someone could make 9 of these.