London Fixie Bike Cog
There is no doubt that from a pure engineering perspective, the traditional screw on fixed cog and reverse-thread lockring setup is not ideal in situations where there is back pressure applied. …Like a bicycle drivetrain. Bolt on cogs simply make sense, even if the traditional setup works well the vast majority of the time when installed correctly. London Fixie Bike out of the UK makes not only a very high quality cog, but spacers and custom rebuilt mountain hubs for street use.
The basic cog design comes from mountain biking, with an interface that matches the 6-bolt disc brake standard. Simple, and conveniently a mountain rear hub, flipped over with a cog such as above bolted on, provides a near perfect chainline. This provides a solid interface that simply can’t unscrew, and is better suited to the low gears (and high torque) of mountain biking. The bolts themselves are plenty strong, pro downhill racers have been known to ride with only three of the six bolts installed to save brake weight without any dire consequences, though I wouldn’t advise it. The London Fixie Bike cog is machined from a solid piece of chro-moly and then heat-treated before getting a shiny hand polish, yielding a fine piece of bicycle componentry. By the specs, these should last quite some time without showing much wear. Due to the interface, the minimum number of teeth is 16, available in one-tooth increments up to 19.
London Fixie Bike has some other bases covered too, like 1 and 2mm thick aluminum 6-bolt spacers to tune in chainline, and extra long chro-moly bolts to tie it together. About those converted hubs mentioned earlier, and pictured at left – it’s a Shimano XT front mountain disc hub with a solid axle swapped in, respaced for 110-120mm track bike rear ends for street use and a 41mm chainline before spacers. ‘Cross or mountain bikes could just use a mountain rear disc hub, no need for the custom spacers and handiwork. Check their site for instructions on how to respace your own hub.
For a true test, this cog needs a few offroad miles logged. While at one point I was logging some fixed trail miles, I pretty well retired after Team Mondo Guano a few years back. I’ll occasionally dip into the woods fixed, but not anywhere near as much as Mondo teammate Joe Whitehair of Single Speed Outlaw. So the cog is off, with updates to come as miles are logged.