Back in November, 2008, I discussed the possibility of converting one of our carrier pigeon box bikes to an externally geared machine, in an effort to gain greater flexibility in the drivetrain compared to an internally geared hub. While I have enjoyed the Sturmey-Archer XRD-8 hub a great deal, it –like its internally geared brethren– presents a number of less-than-ideal behaviors and characteristics that could be easily resolved with traditional external gears:

• Gearing flexibility: whatever you do to expand its gear range, the internally geared hub will always present more limitations than its external cousin. External hubs provide the opportunity to efficiently and inexpensively change gear combinations to best suit your performance desires and cost limitations. The XRD-8 exacerbates this issue by the mere fact that it’s a relatively tall-geared hub. 1st gear in the XRD-8 is 1-to-1 (regardless of the chainring/rear sprocket combo), making each successive gear that much higher. Added to this, the jump from 1st to 2nd is a fairly steep increase of 28%. This means that if you wish to lower your gear range, you have to focus on the number of teeth on your crank and your rear sprocket. The rear sprocket is limited to a maximum size of 25 teeth on the XRD-8, and if you go too small up front, you risk over-torquing the chain or the hub –internal hubs have very specific limitations on chainring/sprocketcombs. For the purpose of comparrison, the Shimano Nexus internally geared hub doesn’t hit the 1-to-1 ratio until 5th gear. On the plus side, the XRD-8 has very close gearing in 2nd through 8th gears, but they’re just too tall overall to be terribly useful with the box bike. I rarely move past 3rd gear when hauling just about anything.
• Maintenance: technically, internal hubs are supposed to be maintenance-free, and so far the XRD-8 hub has lived up to this claim. Regardless, if there ever is an issue, it takes a degree in mechanical engineering (or at least a very good mechanic) to deal with it. As it is, under regular, daily use it’s advisable to have someone take the hub apart at least once per year and ensure all the seals are intact and that the gears and pawls are well lubricated and in good condition.
• Wheel maintenance: quite simply, an externally geared rear wheel can be removed and managed very easily, so fixing a flat is not a problem. An internal hub presents additional challenges in this regard as you need to be cognizant of how to remove the shift cable in a manner that it can easily be reattached.
• Sturmey-specific performance: the XRD-8 has been a great hub, but it requires that you understand the nature of SA hubs and how they operate. Their preferred course of operation is not necessarily in line with what people expect after riding externally geared hubs. And if you don’t use the SA hub exactly as specified, you may encounter performance that is less than beneficial (e.g., pawl slip). SA hubs are not well suited to cyclists that spend a lot of time out of the saddle or shift quickly as there always exists the potential for slip during shifting if you don’t perform the shifts as demanded by the hub. This tends to make the rider lose some confidence in an otherwise good hub.
• Efficiency: it is a known fact that internally geared hubs are simply less efficient than external hubs due to the nature of their design. It’s one of the simple trade-offs encountered when choosing between the two.
• Weight: internally geared hubs are traditionally quite heavy compared to an external hub, where you have the option of choosing individual components that can help reduce weight.

All this being said, here’s what I have loved about the XRD-8 hub:

• The SA roller brake: quite simply, this is one of the best roller brakes I’ve ever used. Modulation is perfectly balanced and stopping power comes on evenly and strong.
• Smooth, quiet rolling: compared to my Nexus hub, this thing doesn’t even elicit a purr. Regardless of what gear you’re in, the ride is smooth and ultra-quiet.
• Feel: the Nexus hub translates the feel of its internal mechanism back to your pedals far more than you may expect. This is especially true in 4th gear, where most all the gears are engaged (the least efficient point of the hub). Conversely, the XRD-8 is smooth in any gear, without the feel of inefficiency. While we know that internal hubs are less efficient than external hubs, the SA hub doesn’t translate this feeling of inefficiency to your pedals. This actually makes quite a difference in the riding experience.
• Shift while stopped: internal hubs offer the opportunity for you to shift into any gear while sitting at a complete stop. This is handy when you are forced to come to a stop but don’t have enough time to shift down. With an external hub, your chain has to be moving in order to shift, which means you have to be pedaling.

After researching various hub and transmission options for the box bike, I came up with the following list of issues with a potential conversion to an externally geared transmission:

• Brakes: if I got rid of the XRD-8 hub, I’d lose my much-adored rear brake. Replacing it wouldn’t be an easy task as the box bike doesn’t have any rear brake mounts. This is the reason I sought out the Arai drum brake, a well-tested and well-loved drum brake designed for touring tandem bikes.
• Hub width: unfortunately, there are only a handful of hubs that will work with the Arai brake, and the most narrow hub available is 145mm, whereas the box bike’s rear stays are spaced at 135mm. This would require a 5mm spread on each side –not a huge deal with a high-ten steel frame, but still something to consider.
• Cost: unfortunately, the Arai brake and associated hub would have pressed me well into the $300+ range for a new rear wheel (the Arai brake is $70+ alone), before I ever even considered the other necessary components (shifter, derailleur, etc.).

As I stated last week, I was quite excited to discover the Sturmey-Archer XRD 8-speed freewheel with roller brake, as it provided the option of ditching the Arai drum brake + Shimano hub combo in favor of a SA hub with roller brake. The only issue I had with that setup was that the XRD is a freewheel hub, relying on a somewhat limited set of available freewheel sprocket sets –an older, proven technology, but not as expansive as freehub cassettes. While not the perfect option, it seemed worth pursuing. With all of this in mind, I decided to discuss this with the fine chaps at Joe Bike to get their take on my idea for an externally geared conversion.

I called the gents at Joe Bike and they informed me of the new XRD-C freehub with roller brake. Thanks to the fact that they have their finger on the pulse of rear hub options, Joe’s mechanics were able to get an early read on this excellent new freehub. Like the XRD freewheel hub, the XRD-C freehub incorporates the lovely SA roller brake with a Shimano-compatible freehub body that can accommodate an 8 or 9-speed cassette. Again, I was happy to consider a freewheel, but the idea of having access to a freehub was even more enticing, as it would enable a wider array of gearing options. As if to add icing to the cake, the new XRD-C freehub is 135mm wide, making it a perfect fit for the carrier pigeon box bike. This essentially solved the brake and chainstay width issues, and it also solved the issue of cost, as the XRD-C is quite affordable.

Together with Joe’s mechanics, we spec’d out a combination that took advantage of the new XRD-C hub. I spec’d a number of parts that met a good balance between cost and performance, and Joe’s gents helped me hone down these options based on their experiences with certain components. Once we came to consensus, I turned over ‘Goliath’ (my wife’s box bike) for the big conversion.

In addition to the freehub conversion, I also decided to take advantage of the new wheel by swapping out the crank for a new setup that leveraged a high-quality, super-rigid FSA mountain bike crankset, thereby giving me the option of two different chainrings up front. Nope, there isn’t a front derailleur on the bike and I have no desire for one at this stage. You simply don’t need quick, ready-access to all those gears, but it’s nice to have the option of a mid-range and a super-low range, based on your particular needs for any given use-case. For example, the small chainring is 22T (and can be swapped with 24T or 26T rings quite easily), transforming the bike into a fast-spinning, climbing beast. In fact, the range is so low, I’m now referring to the bike as the ‘mountain pigeon’.

This being said, if you’re interested in a taller gear and higher speed –perhaps you live in a flat area or don’t have plans to carry a ton of cargo– simply use your finger to easily move the chain up to the 32T chainring. As I spec’d it, the rear wheel features an 8-speed SRAM cassette with a range of 11-32T, so when combined with the 32T front chainring, you’ve got an excellent, everyday gear range for most any relatively regular-grade and/or low-weight use-case.

I picked up the bike from Joe yesterday and tried out both chainrings –each provides a fantastic experience. The small ring is definitely well-suited to the task of carrying two little girls through our somewhat hilly neighborhood, or packing a bunch of groceries home. Using the small ring, I could easily take my girls up to Mt. Tabor without issue.

Regarding the conversion, the process was excellent. Joe’s team handled this ‘beta’ project extremely well –their attention to customer service was outstanding, as it always has been. Joe’s team sourced the parts (except for the rear derailleur, which I already had on-hand) and built the wheel from scratch –and they did a great job. Really, I’m very pleased with the results and I’ve only had the bike in my hands for one day after the conversion.

Truly the offspring of a stock box bike and a mountain goat, this conversion transforms the excellent, stock box bike into a whole new breed of urban transporter, very well-suited to Portland’s hilly terrain.  If you’re interested in purchasing a box bike with these specs, contact Joe directly as I believe he’s going to start offering this as an option for new buyers as well as existing box bike owners, further expanding the drivetrain options that he already offers for this excellent bike.

For the gearheads reading this, here’s the parts list for the ‘Goliath’ conversion:

• Sturmey-Archer XRD-C freehub with drum roller brake
• SRAM PG850 8-speed cassette (11-32T)
• SRAM PC850 p-link 8-speed chain
• SRAM X.5 8-speed twist shifter (rear only)
• SRAM X.3 long-cage rear derailleur
• Sun CR-18 26″ rims built with 13g spokes
• FSA Gamma Drive ATB Crankset 175mm 22/32/44T (includes the Gamma bottom bracket)

I’m so pleased with the results that I’m going to convert my second box bike (‘Big Beef’) using nearly the same specs. The only difference is that I’m going to use an X.5 rear derailleur and I’ll probably swap out the 22T chainring for a 24T. A big thanks to Joe, Tom and Larry at Joe Bike for their fantastic service, quality work and attention to detail.