Josh’s Custom Big Forest Frameworks ATB

I recently learned about the concept of affordances. In design, it refers to the action an object allows you to take or the action possibilities that are perceived. Lacking the deep mental bike catalog of the pro reviewers on this site, it seemed like an interesting lens through which to evaluate the custom ATB I built at the framebuilding course offered by Big Forest Frameworks in nearby in Potsdam, Germany. After assembling the bicycle—project name Sandskimmer—over the winter, I took it for a few easy day rides around home, but it would take a longer trip in more challenging terrain to reveal the new possibilities enabled by this capable bike. With a return to Spain coming up, I wondered how riding it would affect my journey.

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One year ago, I pedaled my Pelago Stavanger from Berlin to Barcelona and then spent three months touring around the interior of Spain. As one of the few road-oriented gravel bikes that fits beefy 2.2” tires, it was ideal for traversing the variety of gravel roads I encountered while being zippy and fun on pavement, too. This year, I had a shorter window of about a month and took the train to the Spanish border, eager to revisit some landscapes and people I got to know last year. It was perhaps a more conventional bikepacking trip, though I left my itinerary wide open so my route and events could serendipitously unfold like they did last year.

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But before we get back to Spain, a few words on the Sandskimmer. My goal was to build something significantly more off-road-capable than the Stavanger and equally versatile. A bike that could carry me in comfort and efficiently over rough tracks, come what may. I wanted a true ATB.

My starting point was a Surly Krampus I’d borrowed for a weekend and greatly enjoyed. Based on that classic, I bounced back and forth between different poles of the hardtail genre, taking cues from touring-friendly mountain bikes such as the Nordest Sardinha and Brother Cycles Big Bro. After a whole lot of fiddling in BikeCAD and countless internet rabbit holes, I arrived at a design resembling a Kona Unit X. In his review, Logan called the Unit X the “ultimate gravel bike,” which resonated with my design intent and charged my expectations.

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Among many other subtle facts about frame design, I learned that handlebar geometry varies greatly and has a drastic effect on fit, so I lengthened the top tube for the SQlab 3OX 16° bars I wanted to use. I relaxed the seat tube angle slightly for comfortable all-day pedaling. Then, I lengthened the top tube some more to compensate for the reduced reach I thought a longer suspension fork would incur, which, in hindsight, may have been unnecessary. In the end, given my lack of experience, I had to accept that the design was a hypothesis. It could never be more than an imperfect prototype.

• Highlights
• Angles: 68.5° Head tube, 74° Seat tube
• Reach/Stack: 475/610mm
• Bottom Bracket: 73mm Threaded / 70mm drop
• Hub specs: 135mm QR (rear) / 15x110mm (front)
• Chainstays: 455mm
• Max Tire Size: 29 x 3.0/2.6 (front/rear)

With the rigid fork, the Sandskimmer has a 750mm front center, a 1200mm wheelbase, and a 655mm effective top tube. The long front center maintains the 1.63 rear/front weight balance of the Krampus despite long chainstays. In combination with the swept-back bars, the front wheel is also kicked out further in front than the 68.5° head tube angle suggests, hopefully without compromising steering on dirt roads as much as a slacker head tube angle would. That’s the justification in my notes. Later, I realized the geometry is almost exactly a Revel Wayward size L with a 10mm longer top tube. I’m 178cm/5’10” with short legs (30” inseam), a long torso, and gangly arms.

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I selected fairly light steel tubing for the frame, with a 35mm Reynolds 853 DZB downtube, 34mm seat tube, and 32mm top tube. I peppered the frame and off-the-shelf fork with rack mounts, added ports for internal dynamo wiring, and included a portage handle. As my departure date neared, I worried that I’d built the bike too long and light for bikepacking. There was only one way to find out.

Picking up the trail

Crossing into Catalunya at Portbou, I veered off the busy coastal tarmac onto the first gravel road that wound its way into the Pyrenees. Sweating in the intense sun, I climbed toward snow-capped peaks. The gravel road turned into a hiking trail, and when that got too steep to ride, the portage handle made it easier to heave the bike over the razor slate. The situation kept escalating, but I kept going. The next day, I found myself nearly stranded on an exposed rocky ridgeline, and that’s how I learned the hard way that all-terrain is not meant literally. I was more cautious about giving in to the allure of unknown dotted lines after that.

After recovering in Girona, I took another train down the coast to Sagunto, from where I rode north into the Sierra Calderona of Valencia. It’s a low karstic range with steep hills isolating small valleys. Roads are rivers of chunky limestone rubble. The long bike was a bit of an armful to wrangle on double-digit grades, but my gears were low enough to winch my way up while my leg muscles roused from hibernation. Cresting the bare summits, the Sandskimmer was a rocket on the descents—flying stones, watering eyes. With the front wheel way out there and the saddle dropped, I never felt like I was going over the bars. It was astounding. On my gravel bike, I would have been walking and looking for the next paved road.

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Riding up the Turia valley into Teruel Province, the wavelengths lengthened and the surfaces mellowed. Limestone gave way to familiar red clay. As luck would have it, around the equinox, I re-united with Ernesto Pastor and joined his friend group ride and traced with them his new route Of Hope and Resilience. The route is a mix of flat farm roads in the Jiloca basin with plenty of climbing in the surrounding mountain ranges. Everyone else was on “faster” gravel bikes, but I had no issues whatsoever keeping up since we weren’t racing.

For me, the feeling of efficiency is more important than theoretical watts. With the fast Mezcal tires aired up, the Sandskimmer was in its element rolling in mixed terrain. The confidence afforded by the wide rubber, long wheelbase, and flat bars allowed my attention to wander from the path directly in front of me. I had the capacity to contemplate the facts and stories related by Ernesto and began to see the challenges written into the landscape. Unlike my last trip, I wasn’t distracted by wrist pain this time.

Everyone who gave my bike a go commented on its length, which again had me wondering whether I’d overshot the mark. The contours are a bit radical, but it felt good except on the steepest of climbs. I rode many hours on rail trails and paved roads on the “hoods” position provided by the SQlab Innerbarends, which felt very familiar coming from drop bars. Leaned-forward and stretched-out is more comfortable for me than an upright fit. It’s odd how hard it sometimes is to trust my perceptions.

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After two weeks of cruising on caminos, I regained my appetite for hiking trails and singletrack. I’d packed fairly heavy for this trip, and fully loaded with water and food for multiple days, the relatively light steel frame flexed noticeably in response to chunky features and abrupt steering inputs. Since nearly every bike I’ve ever ridden has been drastically overbuilt for my weight, I was concerned that I’d messed up the tubing selection until I realized I’d actually succeeded. This was that much-vaunted compliance—appropriate stiffness. I didn’t want to build a heavy expedition crawler. In that case, I’d simply buy a Tumbleweed and call it done.

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Despite the sunny start to my trip, mixed weather and early sunsets reminded me that it was still the unpredictable spring season. On my gravel bike, I tend to avoid riding unknown rough terrain in darkness for safety reasons, but now I had zero reservations and indulged in the subtly mind-bending experience. Less-than-ideal road conditions no longer deterred me, either. I hit a few patches of dreaded concrete mud in the badlands north of Calatayud but didn’t get stuck. Crossing capricious Mont San Lorenzo in the Sierra de la Demanda, I found myself knee-deep in a winter wonderland. Riding, then pushing, the Snowskimmer’s wheels kept turning—barely—and I made it to the other side. Ultimate gravel bike.

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Back in Berlin, the few local MTB trails are short, harsh, and steep, seemingly built by and for enduro riders looking to get their fix—not exactly my style and punishing on a rigid bike. But a bit further south in Czechia, smooth cross-country trails snake through the Sudetes Mountains. Last weekend, I took the Sandskimmer down there, and ripping around rigid with friends, I burned every last drop of dopamine—no suspension needed. The idea of a fast-and-light bikepacking trip connecting MTB trail networks with gravel roads, following forested hill chains and summiting peaks sustains me as I type this through a vicious bout of post-weekend blues.

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High-low build

This ATB was designed around the Rohloff Speedhub internal gear hub. I paired it with a matching SON 28 Boost dynamo hub up front to power SON dynamo lights. I had the hubs expertly laced to Ryde 35 Disc rims by SES Sandmann. I have got to thank the folks at Rohloff and SON for the generous industry discounts on this endgame wheelset. Even if I move to another frame at some point, these high-quality components will live on.

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I saved on the rest of the build by going with affordable commodity parts that just work really well. The square taper triple crankset from my parts bin matches the hubs and slender fillet-brazed frame, lending a classic flair. They also provide a relatively narrow pedal stance while meeting the Rohloff 58mm chainline, or close enough. Shimano Deore hydraulic brakes stop as well as XTR. The three-finger T6000 Trekking levers enable one-finger braking with the bulky Rohloff grip shifter. The lightweight Allygn Diamond Rack is essentially integral to the bicycle, and the custom Gramm framebag in the lovely Challenge Ultra material fills out the frame quadrangle perfectly.

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Big Forest Sandskimmer Build Kit

• Frame: Big Forest Frameworks custom ATB
• Fork: Nordest Sardinha, modified
• Rims: Ryde Disc 35 29″
• Hubs: SON 28 15 110 Dynamo (front) / Rohloff Speedhub 500/14 CC DB OEM (rear)
• Tires: Vittoria Mezcal 29 x 2.6″
• Handlebars: SQlab 30X 16° with SQlab Innerbarends
• Grips: Ergon GP1
• Headset: Cane Creek 40
• Crankset: Sugino XD triple clone
• Chainring: Shimano Ultegra 34T
• Pedals: Shimano PD-M540
• Rear cog: Rohloff 17T
• Brakes: Shimano Deore BR-M6000 + BL-T6000
• Rotors: Hope 180mm front, Rohloff 160mm rear
• Shifter: Rohloff grip shifter
• Saddle: Fabric Line Elite 142mm
• Seatpost: BikeYoke Revive 2.0 160mm
• Stem: Ritchey Toyon 60mm
• Front rack: Allygn Components Diamond Rack
• Lights: SON Edelux II (front) / SON Rear Light (rear)

I half-expected the dropper post to be a gimmick but was quickly converted. It’s constantly useful for micro-adjusting saddle height on climbs, dismounting in city traffic, carrying the bike up tight stairwells and over obstacles, and, of course, for descending safely. It’s a social component, too, allowing shorter people to experience my ride. The BikeYoke Revive 2.0 is by far the nicest dropper post I’ve had the pleasure of using. Their extra-long dropper lever works well with the inboard three-finger brake levers.

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I’m still figuring out my handlebar situation. The straight-ish 16° SQlab 3OX handlebars are great for control on singletrack. Back home, I swapped to a shorter 50mm stem for trail riding, which seems to give me the right amount of reach so I’m not pulling on the bars on steep grades. For general touring, I’d like a bit more backsweep to keep my wrists happy, perhaps Soma Dream Lowdown Risers? I have to remind myself that it takes a while to get acquainted with a new bike and dial in fit and that those preferences are dynamic, too.

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After a few months of riding the Rohloff on tour and on the local trails, I think it’s a great fit for the mix of riding I do. Between the hike-a-bike misadventures and banging in and out of trains and buses, I probably would have torn off a derailleur somewhere along my first trip. The staggering 530% range meant I never ran out of gears in the mountains, but the inability to shift under load still trips me up sometimes. On singletrack, it requires a little more mindfulness; there, I ride it like a multi-singlespeed. The noise is less of an issue than I was led to expect, and I find it mostly unnoticeable after wearing in. The added weight doesn’t register with a bikepacking load.

FRAME SPECIFICATIONS

• FRONT TRAVEL: Rigid (100mm suspension-corrected)
• WHEEL SIZE: 29″ F&R
• COLOR: Pearl Copper (RAL 8029)
• FRAME MATERIAL: Steel
• FORK AXLE TO CROWN: 483mm
• FORK OFFSET: 51mm
• HEADSET (TOP): ZS44
• HEADSET (BOTTOM): EC44
• BB SHELL: 73mm BSA Thread
• DROPOUTS: Paragon Rocker w/ Rohloff OEM insert
• SEATPOST DIAMETER: 31.6mm
• SEAT CLAMP: 34.9mm
• MAX TIRE SIZE: 3.0″ front / 2.6″ rear

While it wouldn’t be my choice for a pure mountain bike, arguably no drivetrain except a fixie or singlespeed can match the Speedhub’s reliability and user simplicity for all-terrain, multi-modal travel. Compared to dinner-plate cassettes and motors, it looks pretty sleek, too, almost like a singlespeed setup. I do wonder where I’ll go from here as I’ve seemingly attained retired German cyclo-tourer energy earlier than anticipated, but I guess there’s still butterfly bars.

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For Spain, I packed extra warm layers, an iPad for navigation and work, a monocular for bird spotting, and reserved one of the two mini-panniers for groceries. As such, I ran a rather capacious bag setup consisting of an Ortlieb Handlebar-Pack with Accessory-Pack and Ortlieb Fork-Packs mounted to their Quick-Rack. I had a pair of Outer Shell Stem Caddies for my camera and a water bottle, as is my usual. As mentioned, the bike is probably at its best with a lighter load than pictured. No doubt, the next trip will see refinements to my packing.

Unforeseen affordances

Returning to the concept of affordances, in Spain, I got the sense that I more readily departed from the typical lines of drift and headed farther into the mountains—sometimes even a little too far, which I’ll chalk up to my newfound all-terrain excitement. You could trace the route I took with a gravel bike. But in open-ended touring mode, it’s all about likelihoods, and I suspect I wouldn’t have chosen some of the rougher tracks or kept going in the off-seasonal conditions if not for the enhanced capabilities of the all-terrain bike. Returning to a region and tracing parallel lines—perhaps nudged by the unique affordances of a different bike—can offer an alternative perspective and depth in a kind of parallax effect.

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This affordance to wander isn’t solely down to the objective off-road capabilities of the bicycle, substantial as they are. Perception of affordances is also culturally informed. For example, I’m conscious of BIKEPACKING.com ATB mythology, which I’ve manifested in my bicycle, priming my mind with particular narratives and images of adventure as I ride along. More mysterious likelihoods that play into the decision when I get to a fork in the trail. Millions more are probably at play, the vast majority below the conscious surface.

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My hand twitches, and the bike veers. A chain of action potentials shoots back up my nervous system, scattering through its layers in reverse, refocusing attention, modulating movement, and finally generating a plausible justification for the new path that was—in all likelihood—beautifully, complexly, subconsciously chosen. Or something like that.

Perhaps that’s another awesome affordance this bike has in store for me. It’s a vehicle for embodied thinking beyond the beaten track, for letting my mind and body wander until they find back together on the way to melding with all else.

Further Reading

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