roynyc

Thought I'd share this as I've seen a couple of folks discussing/asking about the possibility of making a fixie belt-driven bike.

The answer is yes! It took a bit of time, money, patience, and ALOT of research. In the end, I'm pretty happy with how it turned out.

A quick bit of background... I recently got a new bike so I was retiring my old Kilo TT daily commuter. I have no metal working experience (and it shows) and somewhat limited bike assembly experience (I perform maintenance on my bikes and some minor upgrades) so I spent a lot of time researching how to do some pretty basic things (like how to remove a BB). Luckily I didn't make any major mistakes or have to redo anything. And before you ask, I'm not going to get into nor explain why I wanted a fixed gear belt driven bike... it tends to be a polarizing topic (especially on this forum) so if you're interested, please read on.

As all of you know, the belt in a belt drive system cannot come apart or "break" like a chain, so in or order to slip the belt inside the rear triangle, the frame itself has to "break". After some research, I decided on a coupler made by Paragon Machine Works. The coupler came in the diameter I needed for the seat stay.



With coupler in hand I proceeded to cut the seat stay (right one). I measured from the outside edge of the coupler (the exposed parts that do not slot into the seat stay) and cut a section of the tube a hair shorter so that I can file it down to the exact measurement later. Since the coupler has about 1/4 inch of a smaller diameter section that sits inside the seat stay tube, I knew I had to bend the seat stay at the cut-out to actually fit the coupler in. Given that the Kilo is steel this wasn't much of an issue.

Next comes the joining the coupler to the frame. After learning the difference between brazing and welding and the equipment necessary for it, I decided to braze the coupler onto the seat stay. At first I tried a propane torch but the flame was not hot enough to melt the bronze filler rod I wanted to use, so I bought some MAPP gas and that did the trick. After filling the gaps (and letting the molten metal do it's capillary action work), I was left with this:



At first I was quite worried at how ugly the joins were with the excess filler material bubbling up like that. I took an angle grinder and hand-file and very very very slowly ground away the excess material. Resulting in this:



I then finished off the joins by using a steel brush mounted on a hand-drill, which resulted in the final joint:



After painting and assembling the various new parts I bought, here are some pics of the finished product:

The joint:



The rear cog:



The front "chainring": Note about this, I initially bought an installed a 55 tooth chainring (belt teeth count the same as chain teeth) but later upped it to a 60 tooth. The smallest rear cog that Gates makes is the 21 tooth fixed gear cog, due to the belt not being able to bend as much as a chain without affecting the strength of the belt. Since this was going to be my rain/icy roads bike, I wanted a lower ratio than what I normally ride but didn't want the ratio so low as to affect my top-line speed. The 55 tooth left me spinning like a crazy person even on flat roads; the 60 tooth feels just right.



Final product:



Hope you enjoyed reading my post. If you're interested in doing this yourself and have any questions, please feel free to ask! While I'm no expert at any of this stuff, I'm happy to give it a try.

Oh I do want to caveat that this is potentially dangerous if the brazing is not done properly.
While I have no idea if I myself did it properly, I'm willing to accept that risk and I stress-tested the finished bike by abusively hitting every pothole I can find and going up and down curbs and then inspecting the bike for damage. I've ridden this bike for about 2 months now with no issues.

nripin

Wow thats a well done mod !!

carleton

Wow! Nice job. I expected a hacksaw job with some half-assed welding. I am impressed.

orangeology

awesome.
been wondering about it since i saw the paragon machine works product awhile ago
—it was pro'ly a previous version that's supposed to go right next to the DO + seat stay joint.
and you are the very first one actually sharing such a neat conversion process via online.

other than the gear ratio stuffs, how does it ride?
do you see/feel noticeable difference between the chain and the belt?
is there any flex difference due to the joint in the middle of the seat staty etc?
just curious.

not having to maintain the chain mess seems a big advantage.
thanks for sharing.

GuitarBob

Nicely done!

stryper

Grats on a job well done. I'd like to add a belt driven bike to my stable before too long. Nice to see an average joe able to do it without issue

Leukybear 

Looks great! I bet it sure rides that way too!

Philasteve

Damn wtf dude, that's pretty sick.

howeeee

tooooooooo sweeeeeeeeeeeet

hairnet

Nice work. Did you practice your brazing on some scrap tubing before going at the frame?

europa

Well done mate, and good on you for having a go.

I personally don't understand the hate for belt drive (which accepting that it's not for everyone) and would be interested in your reasons.

IAmSam

I would like to also extend my kudos to the OP on job well-done and admit that I will be stealing his idea to include on my own bicycle bucket list

heymatthew

Damn... Can I send you my frame and have you convert mine, too!? So well done!!!

heymatthew

Duplicate post. My bad!

roynyc

Thanks all for the kind words!

It rides really smoothly and quietly. I also have a belt driven fat bike that I commute with in heavy winter snow. That bike, while smooth, is definitely not quiet due to the tire noise. The Kilo by comparison is quietly... eerily quiet.

As for the flex, there's none that I can tell... I've tried to bend the seat stay with my hand and I can't budge it at all (by comparison, I can nudge the left uncut seat stay a very tiny amount). From what I can tell, the coupler actually made the seat stay stiffer if that's possible.

While I haven't washed the Kilo yet, I can tell you when I commuted the past 2 winters with my belt driven fat bike it was great! My bike would be caked with road salt and when I get home I just hosed down the bike with the garden hose and let it dry. Not having to worry about chain lube was one of the main reasons I wanted to do this conversion in the first place.

roynyc

I thought about it but given that it was my first time I wasn't sure if I had enough MAPP gas to finish the job so I just kind of winged it... I figured that if I messed up I would just melt off the filler and try again or if I applied too much filler (like I did) then I would just have more work grinding/filing it off.

roynyc

For me, maintenance was the main motivating factor. Since I commute through all weather conditions, my bikes get pretty dirty (riding in NYC doesn't help either) so I found myself having to clean and lube at least one bike per week. I've read about folks who could clean/lube a chain in 5 to 10 minutes but for me it always takes 20 to 30 minutes for some reason. Not to mention that I don't have a lot of space in my garage so I would have to set up my maintenance stand and put it away once I was done. All in it was about an hour each week.

roynyc

Not a chance! I wouldn't dare deprive you of the experience. It was an eye-opening experience and I learned a lot from it. The fact that I have a functioning bike to show for it is just bonus.

orangeology

@roynyc

thanks for the answers. charming, i'd say.
less maintenance hassle, quiet and smooth ride + no compromise in terms of the frame integrity.

sounds quite brave that it was your first brazing job,
but hey we all need the first timer, right? respect that a lot.
enjoy. i might bump to see your cool bike on the nyc street one day—i'm in the vicinity too.

time to look for a donor/tester SS frame to try it myself, i guess.
i just need a reason to buy another frame, in fact.

one more quick question if you don't mind here:
how did you determine/tweak the belt size when you bumped up the ring from 55 to 60?
did you just follow the Gates' suggestion?
if i am not mistaken, the belt is not flexible at all for different gearing
so it has to be deliberately calculated from the beginning, right?




** kinda surprising. we rarely see a post and responses going so overall 'positive' mood here.

nindustrial

excellent post! and congrats on a great looking conversion. i'm nowhere near this level of modding (anything metal related) but i appreciate the detailed overview of the process, and the professional-looking outcome.

i like the front wheel disc-brake conversion too, how difficult was that?

TejanoTrackie 

Awesome ! Once in a blue moon something really noteworthy appears on this forum.

heymatthew

Gee... How can I express my thanks? Nah... You did a beautiful job. Looks really, really great!

roynyc

Yes I used their online gearing/belt length calculator. It does a pretty good job and assuming you have a horizontal drop-out there's a bit of play so that you can gear up/down 1 or 2 teeth without having to get another belt. For reference, when the gear ratio was 55/21 I used a 113T belt and when I upped it to 60/21 I moved to a 118 belt. This of course entirely depends on the size of your frame (my Kilo is a 54cm) which impacts the distance between the BB and the center of the horizontal dropout which is how Gates instructs you to measure.

roynyc

This was pretty easy but does require buying a new fork. I went with a fork from Dimension which already had disc brake mounting points. I chose it for the similar rake to the original Kilo fork (IIRC I think original is 43mm and this one is 45mm). I did originally look into the possibility of welding mounting bosses to the original Kilo fork, but from my research, brazing was not good enough for this type of joint and welding equipment is too costly so I just decided to replace the entire fork.

As for the brake itself, I chose TRP's HyRd which fits my needs nicely. It's a cable actuated hydraulic brake which allowed me to run a TT brake lever on the bullhorns and a cross-top interrupter style lever. The hydraulics in my opinion works better than mechanical (I have Avid BB5s on my fat bike) in that it never needs adjusting as each brake pull re-centers the brakepads.

europa

I reckon it's because he knows it was beginners luck and he'll probably cock up his second attempt

Onya mate, I'm still impressed.