Fixed Gear New Gen: the 6-bolt Cog

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There’s a new idea for fixed gear riders that’s just so devastatingly simple, I can’t figure out why this isn’t a standard already. Instead of relying on the traditional thread-on fixed cog and lefthand thread lockring, why not use a 6-bolt disc brake mount for the fixed cog? Of course the old style is faster for swapping gearing in between races at the velodrome, but the vast majority of street fixie riders hardly ever change their cog tooth count. For them, the greater worries are either the cog loosening during frequent skids or seizing to the hub after long term use, or the threads of the hub being stripped out. A 6-bolt, using good quality hardened steel bolts (allen head; forget about torx head) eliminates those worries.

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While other hub companies are racing to develop their own proprietary splined cog systems (Sugino, Miche, and Chub apparently), the 6-bolt is a simple design that is open to anyone. Enterprising individuals have started creating cogs to fit disc brake hubs already. You can talk to Daood at Metro Track Goods about getting some from his last batch.

One limiting factor for 6-bolt cog use is the lack of specific track hubs (120mm spacing) to fit these cogs. The current hot mod is to use a recent Shimano XT front disc hub (not Centerlock splined mount). That hub uses a 10x1 axle that is machined down at the ends to 9mm. One need only replace the original axle with a 10x1mm solid rear axle while keeping the stock cones and locknuts with the addition of 20mm total axle spacers. Voila! Works like a charm. The flange width is wider than some conventional track hubs (though narrower than others), and the chainline is almost perfect too.

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11 Comments

These definitely fall into the “why didn’t I think of that?” category. For PRO six-bolt cogs, check out: http://tomicog.blogspot.com/

It’s an idea that has been around for a while.  Kogswell made a couple batches of them in 2007, and I ended up snagging one back then.  There were also a bunch of folks drilling out cogs.

I fail to see why the standard Shimano spline can’t simply be popularized here too.  I’ve always been happy with my short-splined cassette systems for singlespeeding, it seems like somebody could make a pretty burly hub with splines for SS cogs and just omit the freewheel system.

that’s 6 more things I need to worry about coming loose really… splines make way more sense from a mechanical standpoint I think.

I have to agree.  This isn’t new.  It’s a great idea but not as tasty fresh as you might think.  On the flip side, if someone actually did make a cog to fit a current gen Shimano splined disc hub that would be new and different.

Lyle Vallie just designed some track specific 6-bolt hubs and cogs. I believe it is the first one that can run a 15 tooth…

http://valliecomponents.com/

@Lantius

I bet your SS cog rides on a steel cassette body.  Quality hubs are made aluminium.  Also, your Shimano Hyperglide splined cog is only pulled in one direction, not both like a fixed. Actually Easton’s EC90 track wheels use that system, but their stuff is made to pretty high tolerances and is not intended for street or trick riding.  If you want to see how bad a steel cog can bite into aluminium, you should take a look at my old road wheelset.  The 10sp cogs had to be removed from the cassette body with two chainwhips, a flathead screwdriver, and a mallet.

@flaherty

6 more things to loosen? Maybe, but each bolt is less likely to loosen. Why? Because cogs and lockrings loosen on fixed gears because the force of the chain pulling is tangential to the cog. The force on the 6-bolts is from the cog itself, and the force is radial (aimed at the center of the bolt), not tangential. Am I making this up? No. Take a look at the sprocket on a rear motorcycle wheel: bolts. They don’t loosen up…probably not even on a Ducati.


@Raiyn

No, 6-bolt is not entirely new, but there hasn’t been much push from the street and trick fixed riders, who are really driving the market, especially at the lower end.  Would Centerlock splined disc mount work?  Maybe, but I have my doubts.  You see, if there is any room for play on the cog/hub interface, the harsh alternating forces of fixed riding will eventually cause the cog to ruin the spline interface.  I’m not sure Centerlock is up to the task, since it was engineered for it in one direction.  You’ll notice that the splines are almost 10mm wide to absorb the forces of the discbrake rotor, which is riveted to an alloy carrier.  Steel cogs would need to be machined that wide at the interface and very precisely.  I can’t see that being inexpensive.

I have heard reports of Miche splines suffering from this, and Sugino went through the trouble of designing wave-shaped splines to endure this stress.  But for these designs, the splines are sometimes proprietary and always make it more complicated to manufacture the cogs and the hubs.  That’s why the 6-bolt system rocks…because it is simple to manufacture hubs and cogs and still have a durable, dependable product. If a bigger manufacturer decided to make a real production run of these things, cogs would cost less than $5-20 each and hubs could be pretty cheap without worry of the cog ripping through low strength alloy threads.

Mark - didn’t you show me the Easton catalog at one point where they used the Shimano splined cog type design for their track wheels?  It makes a lot of sense for trading gears out at the track for various events.  Problem is - most people need to trade out the chainring for small changes, not the cog.

please explain why the Metro cogs are less pro..

Please explain why the MTG cogs are not as “pro” as tomicogs? Also, tomigogs are great cogs, but as far as i know do not offer 1/8” pitch.

Also, the reason why we like this design, is it gives the user MANY hub options.. Isn’t it fun to tinker?

Basically what this would do is give you 6 more bolts that WILL loosen. One reason why a cog and lock ring work so well is the cog locks against the ends of the threads on the hub then the lock ring locks against the hub. And as for a spline system, I would love to try one but I have a feeling those designs can’t handle the torque of skid stopping. As far as bolt on the cog is going to want to pull one way when pedaling but the direction of the power would change with every push of the pedal. Crank bolts are spaced out for a reason as to relief some amount of pressure. The bolt on cog on the other hand wouldn’t have time to spread the immense pressure around since your hub spins a lot faster then your cranks which would either result in broken, stripped or self loosening bolts which would piss you off to a point that you resort to Loctite. My last point is stiffness. Again, I’m not sure how a spline system would work for fixed gear due to the back and forth pressure but I’m guessing since it’s not threading onto the hub it’s a rather tight fit on the hub’s spline. Even on the best cassettes you have back and forth play so how exactly could you eliminate that on the spline system. As far as the bolt on is with stiffness I would guess not well. Say it’s held together with 5mm bolts. So you have 6 bolts flexing back and forth and if they don’t flex they would most likely strip or just break. Then look at all the extra weight besides the hassle of having to actually maintenance your cog that much. Might not sound like a lot but tightening 6-bolts and making sure they stay tight is a bit of responsibility when you are commuting every day to work. I mean if you install a traditional cog the correct way it won’t slip unless you have a crappy cog/hub. I’ve ridden my Phil Wood hubs with a Phil cog for many many miles without ever slipping. Overall the hubs have 4,000+ miles on them and i replace my chain and cog twice a year. When I install the cog I grease the hub threads well and I’ll get the cog tight but leave the lock ring off. I’ll then take the bike for a sprint up a steep hill so I get the cog as tight as i can. For me the cog is spaced perfectly for the hub so my lock ring doesn’t bottom out, which is one of the main causes of slippage. If your drive train is slipping you should remove your lock ring and see if it’s resting against your cog, or your hub. If its on your hub you need to put a spacer behind the cog so the lock ring tightens against the cog. I have never had to tighten my lock ring or cog on these hubs and have never had any instance of slippage and I run 50/17 brake less in urban traffic. (Yeah I skip and go through about a pair of armadillos every two months)

-Wow, just read what I had written and I think I might be slightly less sober then I thought I was but anyway I guess this is a rant. Leave well enough alone and use a cog and lock ring.

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