Randbezirk 4100

This page is dedicated to the Randbezirk 4100 frame. Here you will find all information and updates surrounding the frame. Also you will be able to place an order here once the time comes.

Behind the Scenes: Creating the Randbezirk 4100

The Randbezirk 4100 is slowly coming to life. It’s an attempt of mine to create a frame that encompasses my views, passions and experiences of the fixed gear scene. It’s a project that has been marinating in my mind for a while and that I am now attempting to put into action, but what exactly is it? The project has many sides and intricate details to it and I have reflected the project alot, but you are obviously not able to read my mind. Therefore, I will try to put all my thoughts, motivations, inspirations and anything surrounding the frame into writing in this article. This way you can hopefully get a glimpse behind the scenes and into the 4100 frame.

Table of Content:

  1. Three Pillars of Inspiration
  2. The 4100 Frame
  3. Mistakes, Success and Prototypes
  4. Price and Availability
  5. Final Comments

1. Three Pillars of Inspiration

To start things off, the inspiration for the 4100 frame was accumulated
in three separate areas. These being:

  • The Love Letter Turbo event
  • My preferred style of riding
  • Past and current frames

- LLT

My personal “starting gun” for the project around Randbezirk and the 4100 frame was fired during the Love Letter Turbo event that happened beginning of 2024. Feeding off of the energy and creativity that was displayed there, I gathered the courage on the train ride home to deicde, that I wanted a similar outlet to funnel my creative energy into. Seeing other people chase their dreams and create wonderful things always creates a drive inside of me to atleast give my personal aspirations a real attempt aswell. By extension I also need to mention SlowSpinSociety here. Paul and the community that he has built has enabled me to even be in a spot to take part in these events and get to know all the great people doing their thing and building crazy bikes. So after arriving back home in Berlin, I naturally fired up BikeCad and started working on the geometry that I want to share with the fixed gear scene and which could enable people to feel the same joy riding that I often feel. This is also where the second pillar comes into play.

- My preferred style of riding

Egoistically speaking, the 4100 frame is an attempt to put my personal fixed gear experience into a physical item that I can share with people. It’s based solely around what I enjoy and what I value in a bike. From starting out on a Pure Fix Keirin Pro frameset with 25c tires and a 130 BCD FSA Gossamer crank with the chainring mounted on the inside to improve the chainline, my taste and riding has changed and evolved over the years. It has resulted in me today, loving wide tires, having a fetish for long stems and enjoying running brakes to have some peace of mind when it comes to the police. I will dive into the specifics of how these things transfer into the frame later. Furthermore, I currently prefer riding offroad in the forest, on gravel right in the middle of nature. It can either be fast and hectic in a cyclocross / tracklocross race or peaceful along a wide gravel road through the forest. Yes, I still love working on my Wandrer and joining the occasional night ride, but I knew the frame needed to support both riding styles. Also, I knew I had to take commuting into consideration as well. The frame had to be suitable to comfortably commute to and from work, as well as be able to run errands.

- Past and current frames

It’s undeniable that part of the inspiration for the 4100 frame was drawn from my past and current frames that I have owned and ridden. It all started on my girlfriend’s green fixie inc. that I decided to ride to work one day and I was hooked. After getting my own fixie inc., the first bike I fully built from the ground up was a Pure Fix Keirin Pro. Did I have any previous experience building bikes from scratch at that point? Absolutely not, and I still do not know what compelled me to order that frame. Funnily enough it was the last frame that was sold via the european Pure Fix website before it shut down. I have ridden many kilometers on that frame, it was also the frame that I was riding when I had my first introductions to fxd.bln at the time. The frame itself has seen many builds. It had the honor (or displeasure) of having my first self-built wheels mounted to it.

I sadly cannot find a picture of the very first wheels, but the rear was basically radial on both sides with a random spoke going the opposite direction here and there, because I didn’t know you had to calculate spoke length at the time, used whatever spokes I had and just tried to make it work. Surprisingly, I did ride around on them for a bit until I learned more about wheelbuilding and relaced the wheels. I wouldn’t say any specific aspects of this frame were transferred to the 4100 except that they are both fixed gear frames. It was and still is however, the foundation on which my passion for fixed gear is built and I still own this frame today. Over time many frames have come into and left my “collection” if you can call it that. I would like to mention a few notable frames and features that have contributed and found their way into the 4100 in one way or another. First off my Surly Steamroller, which was my first contact to wide tires. Originally brown, I rattle canned it a green / yellow color which is still has today. I did Berlin-Mannheim on it on 38c and realized how wonderful wide tires are. Next on the list is my blue Orlowski. The first ILTB Tracklocross races were planned and ridden on this frame. Through a stroke of luck, it fit wider tires than I had originally anticipated. This is the frame that made me seriously appreciate steel frames, their ride quality and the craftsmanship behind them. A final frame that I cannot leave out here is the a-frame track prototype that I own. Next to a-frame being a huge inspiration himself, the first prototype that he graciously sold me was my first introduction to high bottom brackets. For me personally, a match made in heaven. Ever since I’ve discovered and ridden the high bottom brackets, I have not been able to let go. The Vapour Cycles frame that I rode at the last last wo/man standing also incorporated a high bottom bracket. The feeling that it gives you is fascinating and an essential pillar of inspiration for my own 4100 frame.

2. The 4100 Frame

Now let’s get to the juicy part. The Randbezirk 4100 itself.

First things first: Steel frame, carbon fork.

The beauty of steel. Few things compare to the ride quality of a steel frame, which is why I chose steel for the 4100. Paired with a carbon fork the total package is hard to beat. Stiff yet comfortable. Ready for basically anything you throw at it. Complemented by a timeless aesthetic of steel and carbon together on a frame you can’t go wrong.

Sizes I’m working on: 50, 52, 54, 56, 58, 60.

Getting into the details, the frame is designed around 3 key features. While trying to envision the frame, I tried to think of what I would want if I had only had to ride a single frame for the rest of my life. The results of my inner discussion were:

  • I had to be able to fit long stems without being too stretched on the bike
  • The frame had to fit wide tires
  • It needed a high bottom bracket

These 3 features dictate most, if not all the design choices that are incorporated into the frame. I feel so strongly about these features, that it resulted in the development of a custom carbon fork, but more on that in a bit. Two other features that were important to me in the design process are the sloping top tube and the zs/ec headset. With my riding time of geared bikes increasing recently, my eye has enjoyed sloping top tubes more and more. There’s something about it that I can’t quite grasp yet but enjoy very much visually. The same goes for the zs/ec headsets and by extension 44mm headtubes. The modernity in combination with steel tubes is wonderful. Visually I enjoy the headset cup that serves as a separator between the headtube and the fork. Keeping all these features in mind, this is the resulting frame:

If you are wondering about why I’m so excited about the high bottom brackets I’d like to put it into a graphic description. Riding a high bottom bracket feels like being a kid, riding on the top deck of a double-decker bus, sitting all the way at the front with your parents / grandparents. Being high up and looking over everything gives you a wonderful sense of control, an overview and a feeling of security.

- The Fork

A frameset is not complete without a fork though. Designing the frame I faced an issue: which fork do I use? It needed to match the tire clearance of the frame without sacrificing the riding characteristics and aesthetics of the frame. Coming back to my previously listed inspirations of LLT and the a-frame prototype, these two wonderful people behind the respective projects come into play. Without spoiling any of their plans, all I can say is that both Corentin and Anthony faced similar issues as I did. We needed a carbon fork that fit wide tires, had a lower rake and a short a-c. So, what was the logical decision in our situation? Yes, we decided to develop our own carbon fork to fit the specifications that we need. The result? A beautiful and unique fork that fits 40/42c tires, has 35mm rake, 378a-c and can still fit a front brake / rack. Seeing this side-mission of a project develop and come to fruition is a wonderful feeling. I am 100% excited with the fork we have created and it’s the perfect fit for each of the respective projects.

No one has asked me this yet, but I will explain it anyway. Why is the frame model named “4100”? TLDR: It’s inspired by numbers that the Feuerwehr gives to their individual stations.

I decided that my frame needs a model name. I did not want it to just be the Randbezirk fixed frame and I am working on a gravel frame at the same time, therefore the frames need to be differentiable from one another. Leaning into the whole Randbezirk & Berlin thing, I loved the idea of using the fire station numbers. Unsurprisingly 4100 is the fire station located here in Zehlendorf close to where I live. In my eyes it was the perfect match to name my frames and the Randbezirk 4100 was born. Next to my Grunewald topography top caps, I had a special one made for the frame. It depicts the streets around the fire station itself. I’m still debating whether these should be available for sale or if it’s going to stay a 1/1. I’m always open to feedback so do let me know!

3. Mistakes, Success and Prototypes

The pictures of the frame you have been seeing are of my first prototype. Since such a project is not without its hiccups and mistakes, I want to discuss the things that have happened and I have learned along the way until now. First off, what is the current situation? With the final fork having arrived, I can say that I am happy with the geometry, features and ride feel of the frame. I do not feel the need to improve the geometry of the frame and am extremely pleased with it. It feels the way I had envisioned it in my mind and conveys exactly what I wanted it to when starting the project.  The next step that I am awaiting currently is receiving my second (and hopefully final) version of the frame. What has changed? There are 2 main things that did not go as planned with the first prototype. The worst one is that the brake bridge was limiting the tire clearance and dropout usage. The brake bridge too low, resulting in the tire rubbing against it, before it would reach
the end of the dropout. It limited the frame so severely that I had to cut it out, to be able to test the frame with the tire sizes it was intended to use. The following two pictures should explain the issue:

  • Tire touching the brake bridge

  • Dropout position while the tire touches the brake bridge

  • Removed the brake bridge

The final version needs a brake bridge for two reasons though. I want to be able to run a rear brake, or at minimum have the option to. And secondly, the frame features fender mounts, one of which should be at the bottom of the brake bridge. Fenders have been something I have enjoyed more and more recently. Especially in these cold rainy fall and winter months, having dry feet and a dry ass are wonderful. Therefore, I could not resist featuring fender mounts on the frame. The fender mounts lead me into the second issue that the first prototype has. Even if the brake bridge was not blocking the rear tire, it did not have the required fender mount. To still use fenders, I zip tied the fender to the frame to keep it in place, but this is obviously not a viable final solution.

Generally regarding fenders there’s an interesting fact about the frame. I attempted to design it in a way, that the use of a disc gravel fork will not impact ride quality too severely. No impact is impossible, since gravel forks are longer with more rake, but the benefits might be worth the small sacrifice. The fork mentioned above does not feature dedicated fender mounts. I started out riding the frame with a gravel fork, a front disc brake and a front fender. The frame still performed nicely and I am happy that the option exists without making the frame look or feel odd. Especially interesting for those really gloomy deep winter days when it’s dark, cold and wet basically all day.

There are a few more changes between the first and second version. The current frame is made of Reynolds 520 tubing. The second prototype will be made of Reynolds 725. I oftentimes follow “learning by doing” and by using Reynolds 725 for the second version I wanted to compare the difference in ride quality and feel to then make a final decision. The next change has to do with decals. The current decals are all stickered on. I had purposefully chosen to keep the first frame without decals so I could experiment with size and positioning of the decals. Now that I am happy with the result, the headtube logo, downtube Randbezirk and the 4100 on the toptube will all be painted. The small logo on the right seatstay and the 4100 on the back of the seattube will remain as decals. The color of these two decals can be customized or they can be removed completely if they do not fit your style. Lastly, I decided to remove the rack mounts at the top of the seatstays. Although they helped me to zip tie my fenders, I feel they don’t serve a real purpose and impact the aesthetic of the frame too negatively to just keep them.

While these issues might feel big, not everything is bad though! As a whole, the frame and fork are wonderful. Aesthetically they look amazing. Ride quality is great and I can’t wait to put many more kilometers onto it. The paintjob turned out wonderfully and I can’t wait to see it with the painted decals! The slope of the top tube is just the right amount and how I envisioned it to be. 40c clearing fork and the 45c clearance in the rear are a chef’s kiss. Riding the frame with risers or drops have both felt very natural to me, which enables the frame to be used in many different ways. All in all, I would consider my first prototype a success and will use the opportunity to improve it even further.

4. Pricing and Availability

I want to use this part of the article to talk about an ever-present and very important part of the project. The pricing and the things that go along with it. To not beat around the bush too long I am aiming for a price of 750€.

Currently this price will contain the frame, fork, headset and seatpost clamp.

While pricing the frame I faced a few issues. On the one hand, a goal of Randbezirk is to enable people to support local businesses like me, without having to pay the local business “tax”. Keep the prices fair for the customer and a great price-performance ratio, so that buying something can still feel fun and exciting without the feeling of blowing a huge hole into your wallet. On the other hand, I logically must make sure that I am not losing money on every sale. The pricing is a decision I have weighed all my options on and ultimately ended up at the price mentioned above. I’m always open for discussion and feedback so do let me know what you think!

Regarding availability: I face the issue of the unknown. My current plan is as follows: Assuming my second prototype arrives soon and fulfills everything I want it to, I want to open a pre-order for the frames. Ultimately and transparently a pre-order system benefits mostly me as the seller. I will not keep it a secret, that I can avoid the risk of ordering the wrong sized framesets / selling out of some sizes while being “stuck” with the others. It will also require patience and trust from you, the customer, as it will take longer to get the frames into your hands ready to ride.

On the other hand, a preorder enables something extremely important. I can offer a wide variety of sizes (50-60cm in steps of 2). This ensures that you will not have to compromise on sizing and will get the perfect frame you desire! As a customer for many bike-related things myself, I always appreciate it when a pre-order does not require the full amount upfront. My plan therefore was to ask for a 450€ payment upfront with the final 300€ being paid on completion before I ship the frames. Also, shipping is oftentimes a mood-killer for me personally, which is why I am planning to include free shipping on the pre-orders, as thank you for the trust and patience!

5. Final Comments

This article ended up way longer than I had initially anticipated. I hope you are still reading and if you are, have enjoyed it so far. It even ended up having chapters! It’s important to me to try and convey all my thoughts, plans and decisions that surround the 4100 framesets to share with you. This includes everything from the good to the bad.

I feel the 4100 encapsulates everything that I wanted it to be and am very proud with the results so far. I am really hoping I can excite other people for the frame and the ideas behind it aswell. None the less I am having a great time working on the frame and on Randbezirk in general. I can’t wait to see how everything progresses. Originally I was planning to have a booth at the Kolektiv bike fair, but have recently read that it is cancelled this year for 2025. On the other hand this opens the possibility for me to fully enjoy the last wo/man standing weekend. I have managed to get a spot on the start line and will be racing on the 4100. It’s going to be a crazy weekend and a wild race!

Thank you for reading my article and don’t hesitate to message me if you wanna talk about it / certain points or give any feedback!

-Pepe