"That just ain't right."
I was wheelie dropping off a skinny, a big log at the end of a series of ramps and teeter totters, on a rigid fixed geared mountain bike. But he wasn't looking that the fixie gear, or the rigid Ti fork, or the clipless pedals, or the "One f***ing gear" sticker, or the XC Ti frame. He was staring at the rear wheel - specifically the rear hub. It had started out it's life as a front hub - identical to the one bolted to his front fork.
Then he looked over the rest of the bike and shook his head.
"That just ain't right"
I've been riding with him for years - and what he meant was "You just ain't right".
I started riding fixed gear one winter during our first "Winter Solstice Ride", where we were purposely being silly on bikes in snow, prior to the all important post ride food & drink. I had a SS MTB frame that I wasn't using, and I thought riding it "fixed" would be "fun". And so it was, so much so that I started commuting and riding technical trails with it. However, I soon found out that a cheap track cog + a cheap fixie hub and a low gear ratio meant that a stripped cog threads were inevitable. I verified this a few time just to be certain.
I remembered an article I read on 63xc.com about converting a rear disc hub to fixie by bolting a BMX cog onto the disc mount - a great solution to stripped cog threads, I thought. But why not just replace the axle on a front hub with a solid bolt-on rear axle - you'd get a very clean looking rear track hub with no threads to strip. So that's what I did. That was almost 3 years ago, and I'm still using that wheel.
So, the plan was to take a cheap front Shimano hub, which has a 9mm threaded axle. Replace it with a solid rear 10mm Shimano axle (available for ~$10 with cones). Shimano front & rear hubs have the same ball bearing and cone dimensions (9 balls/side) so the cones on the rear axle will work just fine in the front hub-shell. Re-space the axle so the cog (17t BMX drilled and bolted to the disc mount) has the correct chain line, and build up the wheel and dish it to center the rim. Easy.
I verified that my rear shimano axle would fit one of my existing front hubs, and went to the lbs looking for something cheap to prototype. From a junk bin (We have this great shop that is loaded to the rafters - literally - with old/new/odd stuff - but that's another story) I found this old used Axiom front disc hub for $5. The clincher was that it already had a 10mm threaded axle, so I could just use the cones that came with it with the Shimano axle. However, when I took it apart, I found only one cone was threaded, the other was press-fit onto a flat on the axle. So I only had one cone that would fit properly onto the shimano axle (the shimano cones were different). That meant cannibalizing another $5 Axiom hub for the other cone (there was another in that bin...) - but since I was just prototyping, I though why not just build a flat on the shimano axle with some brass shim, and press the cone on?
OK, so I was too cheap to buy another $5 hub.
Here is a view of the original axle, and the replacement 10mm shimano solid rear axle with some of the cones and spacers attached. The brass shim has been rolled under the spacer, and its thickness was selected to provide a press fit for the cone - brass shims in assorted thicknesses are available from most machining or auto parts stores. When the brass shim wears into the threads, another layer of brass will have to be added. You could fill the threads with solder or brazing alloy first, but I was too lazy.
A comparison of the original axle and the replacement (with its brass shim), along with the necessary spacers, cones & seals.
Some of the spacers came with the new axle, and others were scavanged. The cone has been press-fit on the the brass shim wrapped around the axle.
The following sequence of images shows the axle going back into the hub...
Then the other side...
...care must be taken to keep the ball bearings from falling into the hub shell. If you use a Shimano hub, it's a lot easier since the ball bearings are larger.
At the time, I had a 18t shimano steel BMX cog, and a Spicer Ti SS cog, so I drilled some holes in the Spicer cog to match the disc brake mount on the hub. If you've ever tried to drill a hardened steel cog with a hand drill and cheap drill bits, you'll understand why I chose the Ti cog. I used a disc rotor as a guide. Surprisingly it was not hard to get the cog centered... either that or I was very lucky. There was minimal run-out on the first try.
or you can buy one of these things, like I did later.
Shimmed and greased, laced to a mtb disc rim (No Rear Brakes Here!) and respaced symmetrically, I ended up with this.
After two and a half years of commuting, trails, rain, snow and sun
The bike has not always looked like this, I had a suspension fork on it for a while (a rare linkage job that had a reputation of breaking...) but I discovered that it really was not necessary for fixie trail riding. Then I had a suspension stem (another vintage device), but in the end, the body english required to keep a fixie rolling on trails with obstacles just didn't need any supplemental suspension help. Its true! The front wheel is a 700c rim laced to a disc hub, and the Brooks saddle was just added recently.
If I had to do it again, I would start off with a shimano hub. The conversion would be easier and the bearings smoother, but the assorted pasts of the pieces that make up my fixe wheel shows no signs that it's going to want to be replaced soon. More importantly - no more stripped cog threads!
See ya, Tom.....Tom.Chow at hrcc.on.ca