Custom Klunker Challenge: The Leafcycles Trail Digger

As a trail worker, cyclist, and product developer at Schwalbe tires, Michael Rudolph knows better than most that heavy, and often sharp and pointy, tools don’t make for the most convenient bike cargo. And, coaster brake klunkers don’t often make the most capable cargo bikes. But, with the announcement of Leafcycles Custom Klunker Challenge, Michael was on a mission to reconcile these incompatibilities. Read on for the backstory and build process for his winning custom klunker submission: the Leafcycles Trail Digger.

Even though Klunker bikes have always appealed to me precisely because of their simplicity, it was always this simplicity—and it’s narrow range of use—that kept me from buying a klunker. But when Leafcycles called for a custom contest to re-purpose one of their Klunker bikes, the opportunity was too irresistible to pass up. I immediately had this image in my mind of how I would rebuild the klunker to make it usable for my purposes. Specifically, my trail-building purposes.

Visualization: The Trail-Digger-Commuter-Bike

I wanted mounting options for attaching all my tools, so that they would ride without wobble for safety but also so they’d rest quietly on the bike until I’d reached my work site for the day. In addition, it should be possible to transport different tools, regardless of whether I’d be building straight jumps or steep turns. Shovels, pick, rake should all be quick and easy to attach to the bike. I live in a hilly region in Germany and, including myself and tools, I had reservations about the coaster brake setup (singlespeeding would be hard enough!). The coaster would have to yield to something more capable and versatile. Finally, I wanted the appearance of the Klunker to be discreet, so as not to attract unnecessary attention in the forest.

Felix Kley, MTB rider and trail builder, helped me with the first visualization and represented all my ideas in the form of a drawing. Having a real picture in front of you makes a huge difference in planning for a dream bike. His sketch (pictured above) was an incredible motivator throughout and was something I could come back to for reference as different strains of the project came together.

Parts Procurement

For the parts procurement, I rummaged through my own parts boxes and, after asking friends, acquaintances, and work colleagues for anything expendable, it came together quite nicely. A worn-out and scratched SRAM Decendant crankset was stripped of its paint and treated to a gleaming polish refresh. A pair of lonely DT 29″ rims finally found a home. Bernie Kammel provided me with rotors and pads so a discarded TRP Quadium 4-piston brake system could be made viable again. In short, as the component box filled more and more, and it was time to move on to the assembly.

Admittedly, a job in the bicycle industry makes the procurement of some parts immensely easier. I work as a product developer at Schwalbe in the field of trekking & commuter tires, so I barely had to mention the project before my work colleague, Carl Kämper, was on board. As mentioned earlier, it was my intention for the appearance of the bicycle be as discreet as possible. There are few circumstances where a completely black tire isn’t in line with a bike’s design but Carl had other ideas for my klunker. A few prototypes later and we had our tire: a SCHWALBE Nobby Nic with a custom sidewall in olive green. Cool look, good grip and low rolling resistance made this the perfect fit for the project! Onto the next!

But tinkering with such a klunker shouldn’t just be limited to the exchange of individual components, at least in my opinion. Which leads me back to the coaster brake dilemma. It didn’t take long for me break out in a cold, fearful sweat when imaging trying to brake on trails with the current system while astride a veritable rolling tool box. In combination with the singlespeed coaster-brake-hub in the rear, rhe front side-pull brake seemed to work about as well as a poorly adjusted cantilever brake.

To make this a true trail worker’s dream ride, the solution was obvious: gears and a solid disc brake system had to come. Timo Brakowski offered me a SRAM i-Motion 9 hub with Grip Shift lever and disc brake mount. It was, indeed, the perfect solution, aside from the minor issue of the klunker’s rear triangle frame dimensions of 110mm. The SRAM hub required 135mm. True to the motto: “what does not fit, is simply made to fit” I decided it was time for rougher interventions.

Bending up the Rear Triangle

Somehow the hub had to fit into the frame, but there was the small matter of finding an additional 25mm or room. Without further ado, I decided I’d just have manually update the rear dimensions. This was done with the help of a threaded rod, washers and nuts. During the bending process, the affected zones at the rear end were heated by a soldering torch. Somehow, I managed to stretch the rear end evenly to 135mm without any problems. The hub was ready to be installed, but I was still missing the disc brake mount on the rear triangle. That was the moment when I started sweating a bit again. Although I have some soldering experience, that was years ago and I’d practically forgotten everything.

Time to Sizzle: Disc Brake Mount and Braze-ons

Now came the heat. After a few YouTube tutorials and the purchase of a 85 € soldering set from the hardware store, I was motivated enough to solder the brake mount to the frame. The disc brake mount was sawed out of an old screw clamp using a flex and file. The main task was now to position the disc brake mount correctly on the frame without a frame gauge…I proceeded as follows:

Step 1: Mount the brake disc rotor onto the hub and insert it in the frame.
Step 2: Screw the disc brake mount to the brake caliper.
Step 3: Slide the caliper over the rotor and move the disc brake mount to the correct position on the frame. Then keep the brake lever on tension by belt, so that everything stays in position.
Step 4: Now the brake caliper can be fixed to the frame by soldering points.
Step 5: Remove the rear hub and unscrew the brake from the disc brake mount. Then the mount can be completely soldered on.

Admittedly, I was a bit afraid of screwing up the frame, but the result was surprisingly good. A piece of leftover tube was then used as a support between the chainstay and seatstay. Numerous M5 blind rivet nuts were also threaded into the frame and fork so that the tools could be attached with an adapter. For added strength and a tidy look, I also soldered the blind rivets. Since the frame had neither mounting points for the brake or shift cables, these got soldered, too. This was my chance to make sure that all the cable housing would route sensibly along the frame and fork. Of course, since the soldering fever had completely gripped me, I decided to make my own head badge. What was closer to this trail-building-commuter-bike project than a shovel? A piece of copper tubing left over from renovation, a bit of manual labor and the head batch was ready to attach.

The bright idea with the holders for the tools, on the other hand, took a while. It was important to me that all tools could be easily attached to the bike without scratching the paint. In addition, I also wanted the holders themselves to be removable.

With the help of Artur Becker I was able to have beautiful holders lasered out of 3 mm stainless steel sheet. Additional tension locks with rubber straps behind the seat tube help keep the tool in place.

Color Confession and Fine-Tuning

I had the frame, fork, and handlebars powdercoated to match the olive green color scheme established by the tires. The brown C17 saddle and the brown grip tape from BROOKS added another natural tone to complement the rest. For inspiration in how to maintain a clean look around the handlebars, I was reminded of Phillip Ebener, who many years ago equipped his slopestyle fully with Grip Shift around the seat post. I thought that this would fit perfectly with my concept for the project so I borrowed this same idea for my Leafcycles build. TRP brake levers in silver and the original Kartell stem (partially sanded to expose the bare aluminum) rounded out the cockpit. The bright stainless steel tool brackets and silver spokes added the final flare to the otherwise subdued look. The last step was to add the original Leafcycles klunker frame sticker set. You’ll also find a few NT dirt stickers on the bike—shoutout to my homies in Zurich, I miss you guys! #therealzüritrails

Last Words

For me there have always been two reasons to build something. Either what I wanted didn’t exist, or I simply couldn’t afford it. And because my father also shared this mindset, I started to learn craftsman skills from him quite early. First with wood, but then also with aluminum and steel. Over the years I developed a third reason to build something. The joy of creating something real out of a wild idea. A cool idea for a trail? A custom piece of furniture? A crazy bike? Build it! At the top of my bucket list is still a completely homemade frame. Due to lack of machinery, frame gauges, etc., I haven’t dared to do it myself—yet. However, through the Custom Klunker Contest, I was able to at least modify a frame enough to fit my wild idea of having a bike that could safely carry my trail-building tools.

With just a rough memory of a brazing course from over 20 years ago, a few Youtube tutorials gave me the courage to really get started on this project. And what can I say? It’s so much fun to bring an idea to life. I find brazing, especially, to be such a satisfying way to modify a steel frame. On the one hand, brazing is a simple and quick way to attach something to the frame, but on the other hand, the process totally decelerates me. And if you sit on your bike at the end, then it is pure satisfaction, at least for me. That’s enough to start a new project this winter again. This time no klunker, but definitely a bike on which I want to spend a lot of time.

At the very end, I would like to clarify again how grateful I am. First of all, thanks to Frank Heinrich from Leafcycles for the contest. Alone, I probably would have never come up with the idea to start such a crazy project. Thanks also to everyone who helped me to complete the project: My employer Ralf Bohle GmbH a.k. a Schwalbe Tires and, by extension, my colleagues Carl Kämper, Artur Becker and Stefan Franken; Felix Kley; Timo Brakowski; Bernie Kammel; Phillip Ebener from Zweiradsport Ebener; Andri Hafen from Bike Hub Zürich; Alex Clauss from Portus Cycles; Pietro Tomasella and Alice Icardi from Selle Royal; Sergej and Waldi Lind, the homies in my home country who have faithfully built dirt and berms for 15 years; and, of course, my shovel family NT-Dirt in Zurich. Finally, the biggest thanks go to my wife Karin and daughter Noelani, who patiently had to do without me for many hours. During the whole rebuilding time I realized once again how much fun you can have together with other people to create something special out of an idea.

Meanwhile, my klunker conversion has already several hundred kilometers of forest roads, trails and bike paths under its custom tires and I can look forward to the fact that this bike will not collect dust as a decoration in the corner! By the way, Leafcycles has already announced a second and final round of this klunker custom challenge. If you are interested, check out their website

Parts List

Frame: Leafcycles Klunker | 4130 CroMo
Fork: Leafcycles | 4130 CroMo
Stem: Kartell BMX stem
Bar: Leafcycles Motobone | 4130 CroMo
Grips: BROOKS Microfiber Bar Tape
Brakes: TRP Quadium
Rotors: Miles Racing SS3
Pads: Miles Racing semi-metallic
Drivetrain: SRAM i-Motion 9 hub with Gripshift around the seat post
Cranks: SRAM Decendant | hand-polished
Pedals: Crank Brothers Stamp 7
Tires: SCHWALBE Nobby Nic | custom colored side wall
Saddle: BROOKS C17 Cambium
Seatpost: Race Face
Rims: DT-Swiss (leftovers)
Tool-brakets: Selfmade
Beer: Erzquell Pils (excellent taste)

Text by Michael Rudolph/Translated by Frank Heinrich/ edited further by The Radavist for clarity.