Bolt on cogs.
 

I've thought about playing with a bolt on fixed cog on my SS 29er since it has disc hubs and had a few questions.

- Any recommendations of a good cog to try? Looks like Velo Solo has a ton of options.

- Chainline... Probably one of those things that I'll just have to bolt up and see how it goes, but if you have input on it, shoot.

I'm thinking about going for a tiny ratio and learning some tricks for kicks. 32T chainring + big ass cog? I think yes...

My friend did this and just fabricated a cog from a 34 tooth cassette cog to get a fg with one insanely low gear so he could pull a trailer.

If I had a drill press and a better spare parts bin i'd give it a whirl but I think I'm going to have to get a pre-fab one.

after stripping two hubs, i decided to lace up a front disc hub and bolt a cog on. drilled out a ss cog myself and the chainline worked fine. havent had a single problem with the hub in 4 years. originally the holes werent perfectly drilled, but because the splines on the cog were slightly smaller in diameter than the hub flange, it was easy to sand around with a dremel quite evenly to avoid eccentricity

http://i11.photobucket.com/albums/a1...2/DSCN2397.jpg

From Velosolo site:

From my understanding you can fine tune the chainline a couple of mm outwards with spacers if necessary.

^most helpful first post I've seen, thank you

tomicog...tomicog...tomicog

have used one for fg mtbing (32x18)) for several years, chainline may not be quite perfect but never a single problem yet

I'll repeat it: Tomicog, Tomicog, Tomicog!

+2. I have two tomicogs (16t amd 17t) that I have been using with a surly front disc hub for several years now on an old Monocog 26er.

Don't just bolt it up and see how it goes. Use a ruler and your brain to figure out what the chainline will be beforehand. Chances are it will be close enough and/or you'll find ways to adjust it. If fixed off road is something you are into, it would be a good idea to build a second wheel. Then you don't have to muck around with removing the rotor and all that everytime you want to go fixed.

If you have canti studs on your seatstays, remove the disc brake and install a V-brake in the rear. Then you can built a flip flop out of a SS disc freehub and still have the rear brake for when you flip to the freewheel side.

I use Tomicogs on my fixed gear mtb, 34:18 or 34:19 depending on the trail.

Shimano XT-M756 front hubs are awesome on fixed gear road bikes with track bike chainlines and 120mm spacing. It's a front hub but it uses a 10mm axle (instead of a 9mm axle that a normal Shimano road hub would use), so you just have to replace the axle with a solid threaded axle long enough to fit your frame (Wheels Mfg stainless axles are great and super affordable) and add two 5mm axle spacers and you've got a nice, bolt-on specific fixed-only rear wheel for your track bike. The only downside is cog sizing for bolt-on cogs, which is limited by the bolt circle diameter of a 6-bolt disc mount. I think 16t is the lowest you can go.

Is a 9mm axle on a front disc hub pretty standard. I am looking into using an american classic front hub but it seems they don't make one with a 10mm axle. Is this something you can convert (9mm to 10mm) easily?

Not, it's not something you can convert easily. You'd have to find bearing cones that fit the same bearing size and layout on the cup on the hub, but are drilled and tapped for 10x1mm threads. There might be something you can cobble together with bits and pieces of several different hubs, but I've never sat down and tried. I think all of the Shimano mtb disc front hubs that you'd be doing this to in order to run it as a fixed rear hub are like the M-756 and use a stepped 10mm axle or cannot be converted as all because they use larger alloy axles, like the newer XT and XTR hubs.

9mm is the standard for quick release or track hubs for front axles/dropouts. The M-756 is interesting because it uses a 10mm axle that steps down to 9mm where it enters the dropouts (if it were 10mm straight through, it wouldn't fit in a fork).

Of course, all of this axle swapping and what-not is unique to cup-and-cone (loose-ball) hubs, like Shimano. I have no idea what your American Classic hub is like.

I think you could get away with using the locknuts/cones/axle from a Surly rear hub with a 10mm axle in a Surly front hub if you're into Surly hubs and wanted to run a Surly Disc Front Hub as a rear fixed bolt on hub. I've not seen the guts of a Surly hubset in a while, so I can't be for certain.

Side note: you can replace the "adjustable" cartridge bearings (that don't hold their adjustment) in a Surly hub with a normal non-adjustable cartridge bearing and turn it basically into a Formula-type non-adjustable hub that won't loosen up and annoy you (which is the biggest complaint of Surly hubs I've heard). An alternative solution for people who already have Surly hubs and hate that they loosen/tighten themselves over time.

Edit: 6901 bearings are standard 12x24x6 non-adjustable cartridge bearings that are a direct replacement to Surly bearings and will make your Surly hub hold its adjustment.

after reading this http://www.fixedgeargallery.com/arti...mson/surlyhub/ it seems that the Surly front disc hub is the easiest way to go.

Exact same principle as the XT-M756 conversion, except you don't need any hub locknut parts. You only need the 10x1mm axle and spacers to get you to 120mm.

I use Velosolo cog on a 26" mtb rear wheel with the casette side converted to singlespeed for a diy flipflop (very easy to match chainline to the disc side). with v-brakes. The chainline is a bit skechy for now because of mismatched cranks/bb width (too wide in front even with two 1mm spacers under the cog and chainring in middle position). I intend to fix the bb width, but so far I've had zero problems, running 1/8" chain on 1/8" VS cog and 3/32" middle ring from an mtb triple, 32/17 for winter gearing.

What's the advantage of Tomicog over Velosolo? The seem a bit more expensive, even with international shipping for VS included. For extra 2 pounds VS is also available in 15t and 22t. The quality of VS seems very high and if you wear one out you get free replacement:

Not saying Tomicogs are not of high quality, just not familiar with them. My experience with VS is very good, but I'm not an expert, this is my first fg conversion :)

Seems like they're both about the same price. It would be hard to make a blind call without trying both of them. Those Velosolo Disc-hub mounted cogs look pretty sexy, in general. That, combined with a Salsa Vaya w/ eccentric BB would be interesting. I spent too much time thinking about this **** sometimes.

Phil
 

be patient on ebay, and pick one up cheap!

http://www.ebay.com/itm/Phil-Wood-1-...item256be74de1
http://www.aspirevelotech.com/images...Cog-18-17t.jpg

I don't think there are any advantages or disadvantages.
My tomicogs look a bit more "raw", like some dude made then in his garage. In that respect, they fit well with the whole jerry rigged vibe of bolting a cog onto the rotor mount of a front hub. They function flawlessly however. There is no notable eccentricity, and mine show no signs of premature wear after several years of use. The teeth on the tomicog look really tall to me, although I haven't made any real measurements to confirm that, its just an impression. Taller teeth (if that really is the case) may reduce risk of derailment (?).
Bear in mind my tomicogs are a few years old and bought very shortly after they first became available. Perhaps the newer Tomicogs are more refined looking like the velosolo cogs, but in any case, they are well made cogs.