Since the original post didn't include a lot of technical details, I wanted to address some of that here for anyone wondering about chainline, specs, spacing, etc.
If you're looking for a step by step on converting your bike, here's the quick and dirty version!
If you're looking for a good belt drive bike, single speed, geared or fixed, there's a plethora to choose from. Currently there are a few fixed geared options on the market, but when I converted this one there were only CDC options and there was also some debate regarding the CDC verses CDX system being used fixed, with some people arguing that the CDC system could slip and had to be run at too high of a tension. While I don't know if this is fact, I have both systems and have never had a belt slip, so I would assume that like every bike, proper care and maintenance probably makes a big difference. In short, I mostly went with the CDX system because of the part availability.
Anyway, lets get to it.
|I've been asked if this is my drift charm.|
Chainline: My District is a bit of a special case. The rear spacing is 135mm, but the original wheels were made to work with a road chainline of 47.5mm. Although I replaced the cranks, I kept with the road spacing and decided to maintain that throughout. With the CDX system, chainline has to be precise. Belt rings are also not available in 144 BCD, so bear in mind that if you have a track crank with a BB many standard track bottom brackets won't work unless you change out the axle.
|The dropout system.|
Rear Wheel: Since I have wonky spacing and wanted wheels that matched my bike, I had to lace a Surly Hub to a Velocity B43 rim. Instead of using a 135mm Surly Hub which would throw off my chainline, I used a 130mm fixed/free hub with some spacers and a bit of tweaking to the dishing to get what I was looking for. I'm sure this isn't the best method, but it was such a slight adjustment and this was initially only a test. So far, it's working fine and my chainline is perfect, so for the time being I'll stick with it.
Frame: The Trek District was originally meant to be more of a relaxed road frame, so it's by no means a track frame, nor is it a fixed gear for the road frame. Nonetheless, it's a nice ride that isn't overly aggressive and does well on longer jaunts, but doesn't have geometry that's entirely set back so I can still ride a bit aggressively if I want to (I believe the angle of the seat tube is around 73.5 on this model). My caveats are the longer top tube that I need to compensate for with a shorter stem and I'd prefer the frame to be steel over aluminum, but that's a different story. The frame itself separates at the dropouts, which is how the belt is changed out.
|No more rear brake. I decided to keep this one solely fixed.|
Wear and Tear: I don't hit many extremes here in California, but I do ride about 20 miles daily along the bay, which includes salt, sand, and some lovely road grime. I have yet to need to replace a belt...in fact, I've yet to have to do more than routine cleaning and maintenance to the bike, and I think the only thing I've done to the belt at all is a quick wipe down. It hasn't stretched, and consequently the cog is also still in good shape. Things are still fairly new, but by this time on any other bike I'd have re lubed the chain more than once. Also, this bike survives a daily beating on Caltrain, which includes everything from kids with spikey BMX bikes to ladies with massive Dutch style tanks that all get basically thrown against each other. This bike has seen some things, and has survived.
Part Availability: If you're dreaming of a Phil Wood belt driven bike, you might want to reconsider just a bit. Though Phil did make these parts, they aren't making them right now, and the backorder is months long. If you already have the parts in hand, then you're lucky, and your bike will be fantastic - and also CDC. Gates and White Industries are the main suppliers, and generally stock is good on all of the parts needed, though the 21T cog was quite popular for a while and took me a few weeks to track down. It's not like hunting for an ultra rare group though, so getting parts isn't a hassle - though they are a bit pricier than a standard drivetrain. All parts that I have come across have been high quality and well made, so for the time being there really isn't the chance of getting a low end belt group.
Overall Parts Changed: I changed out the entire CDC system to the CDX system, which was a huge overhaul (cog, belt, belt ring). The crank was also swapped, as were the handlebars for my more preferred pursuit bars. With the handlebars I also changed the brake levers to SRAM TT levers (or a SRAM TT lever, I should say). The saddle was switched to something nicer (Specialized Ruby, which I highly recommend to all you ladies out there), but it's rare that I keep a stock saddle anyway. I had to lace the rear wheel in order to get something that would work with the thread on fixed cog, so there was the rim, hub, and the spokes. And, of course, cables, but that's easy.
There was also the vinyl addition of both reflective striping and the Caltrain Tag, but that was a minor upgrade.
Ride Quality: Smooth. Buttery smooth. And quiet. Rides like, well, a fixed gear, but a fixed gear with a perfect chainline. The belt really doesn't feel any different from a chain as far as stretch goes, but I do find it just a bit nicer. I'm also probably quite biased. Anyway, it accelerates just as fast as a chain, and resists just as well. I don't generally skid stop, because I enjoy my knees, but it does seem to lock up fairly well during the rare times I do (actually, this is really where the CDC vs. CDX debate came head to head - if you primarily skid, go with CDX just for the extra security). It truly is a fun ride, and lots of people ask about the belt, so you get to have some good conversations and meet new people, if you're into that.
Conclusion: If you came here looking for info on a fixed gear belt drive because you're curious, here's my two cents: if you were planning to get a fixed gear for commuting/the road and want to spend a little extra, go for the belt. If you have a current bike that you're perfectly happy with and have no problems with a chain whatsoever, it's probably not worth it to switch unless you really have a harsh environment (or, if you really want to!). If you want a fun project and have a frame that would be capable of taking a belt though, it is pretty cool to learn a new system and have a belt driven bike. Basically, it's not for everyone - certainly not for the velodrome or someone who likes to change ratios frequently. But, if you want something fixed and durable (and perhaps want to eliminate a chain snapping or the Cat 6 Tattoo) I really do think it's worth it.
I'd be happy to answer any other questions or point you in the right direction if needed!