A Series of Tubes: Ferguson City Bike with Carbon Belt Drive
Posted Nov 24 2009 10:01pm
The latest custom Ferguson city bike with Carbon Belt Drive
“Bike building is a lot like the Internet. They both involve a series of tubes.” Elliott McFadden,Violet Crown Cycles
This fall, I was contacted by a customer wanting a Ferguson city bike as a possible replacement to his car. He lives and works downtown and was ready to give car free living a try. The problem was he works in an office where he has to wear a suit so he needed a bike that would allow him to ride in different weather and not stain his clothes as well as allow him to run everyday errands.
We initial looked at a regular Ferguson with a full chain guard (as opposed to the half guard I’ve normally been putting on them.) While in the Netherlands full chain guards are sold in department stores, they are near impossible to get in the U.S. market. I with research, I found an importer, but in the meantime, the customer had grown interested in a Carbon Belt Drive after test riding a Trek Soho.
Trek was one of the first companies to use the Carbon Belt Drive technology in a stock bike. Replacing the conventional chain drive with a belt system similar to belts in a car engine, the Carbon Belt Drive has many advantages including a substantial weight savings, no greasy chain, and increased efficiency. On the down side since the belt is all one piece, you are pretty much done with your ride if the belt ever breaks. No shorting the chain or popping in a link here. It is also a couple hundred dollars more expensive for the system and replacement belts run in the $60 range. Still in an urban cycling environment, the system makes a whole lot of sense.
One other issue with the fact that the belt is all one piece is that you have to have a frame that can break apart to install the belt. This limits retrofits to steel or ti frames in the hands of knowledgeable frame builders. The design choices to make this work are either breaking the frame at the drive side dropout or on the seat stay with an S&S coupler. I found breaking the the frame at the dropout to be the simplest, structurally strongest, and least obtrusive option.
Before getting to the frame breaking, I built up the frame to the customer’s dimensions as I would any other bike. Again since the Carbon Belt cannot be broken, I had to pay extra close attention to chain stay length and double check work along the way with the belt, crank and hub. The Carbon Belt Drive folks have you use a calculator with the cog and crank sizes as well as desired chain stay length to determine which belt size to order. There is a little wiggle room with horizontal drop outs, but I had to take care that everything fit well.
Closeup of Carbon Belt Drive and rear dropout. Stainless steel reinforcement plate holds the required split dropout together.
One difference from previous frames is that I switched to backward facing horizontal dropouts. This track style design, as opposed to the forward slanting touring style dropouts I’ve used on earlier frames, worked better with my frame break design. It also allows easier chain tensioning (or belt tensioning in this case). On the down side, it is a little more difficult to insert the rear wheel with fenders in this setup. All in all, I do think rear facing dropouts are a better match for these bikes, and I intend to make them standard on future versions.
Once the rear triangle was done and everything checked for alignment, I used a thick stainless steel cover plate to create the needed reinforcement for the soon to be made frame break in the dropouts. I drilled and taps four points on the plate and dropout for a secure fit. Out came the hack saw next, and I created a nice clean break between the seat and chain stays.
New VO saddle with copper rivets and very nice Brooks Brick Road pannier bags.
Once the bike was back from powdering coating in a nice high glossy black, I built up the bike with its new Carbon Belt Drive. I was pleased with the smoothness and quietness of the belt drive, and it added a nice modern feature to the otherwise classically designed bike. I did keep a half chain guard just to keep the odd pant leg from getting caught, but this system should provide grime free riding for the foreseeable future.
The Carbon Belt Drive does seem to be a real step forward in drive train design and certainly an option I’d recommend for future customers.