The manufacturing process
A glimpse behind the scenes

We work in the aviation industry. We are used to thinking in larger dimensions.

Our bikes’ exceptional handling qualities and numerous well thought-out design details reveal our quest for perfection. Our core strength lies at the heart of the bicycle and its frame: in the tube set. We use the most advanced available, comprising tapered and butted tubes – no plain or ovalised round tubes, nothing that is sold by the metre. Steel is the cleanest and most ecological material in frame-building, for the lowest amount of energy is used in its production.
Our success is the result of the coming together of two things. Firstly, we are a small, dynamic company. This gives us flexibility, vibrancy and freedom to innovate – and means that our products have a personal touch. But what makes us different is the fact that we have direct access to some of the most advanced design and manufacturing facilities in existence, and the skills to make use of them. Because all our frames are built in-house and surface treatments are applied at state-of-the-art facilities just up the road, we are in a position to keep a very close eye on things: our quality control is second to none.


Our comprehensive knowledge isn’t only created indoors.

We also selflessly give up weekend after weekend to conduct demanding test rides through the local countryside. In all seriousness, this aspect of our research allows different tube sets to be precisely investigated in terms of the loads created at the various points of force application. This means that we are able to refer to a large range of data drawn from this real-world research, in order to keep pushing things forward – both in terms of our bikes, and 21st century bike design in general. But it’s not just field research. Development at this level requires the use of cutting-edge modern design technology. We use a breath-taking array of virtual and physical tools to support the investigation of wide-ranging parameters of stiffness, shock-absorption and strength as we work through the prototype stage. In addition to Computer-Aided Design images in both 2D and 3D, strength calculations using Finite Element Method are always undertaken. Only in this way can we best address the various interdependencies between different elements of a design, and find the sweetest of sweet spots in terms of balance between weight, durability and stiffness.





The manufacturing process


  • The first stage is to define the desired handling characteristics for the category of bike (tourer, racer, etc.) and the specific model, and establish the optimal frame geometry, and then tube lengths, tube diameters, wall thicknesses, braze-ons, cable routing and appropriate dropouts.


  • In accordance with these calculations, the tubes are cut to length and with the correct angles, air and water vents are drilled, and water carrier ‘braze-ons’ and cable guides are welded on. Once all the preparatory stages are complete, the next step is to align the tubes of the frame’s main triangle. All lengths and angles are then rechecked on the frame table.


  • Now the main tubes can be spot-welded together and then checked for accuracy back on the frame table. The joins of the rear triangle are welded in a parallel work stage, untensioned and off the frame table. The order in which welds are made plays an extremely important role within the overall manufacturing process. The aim is to produce a triangle with the smallest possible amount of distortion; titanium frames are very difficult to realign, as titanium has the tendency to drift back to its original position. When the rear triangle welding is finished, a test-wheel is used to check it for vertical and horizontal alignment. Finally, careful checks are made to ensure that the head tube – and with it the front wheel – is aligned with the rear triangle and rear wheel. The result: the superb handling characteristics for which our frames are known and repeatedly praised.


  • A side note: our frames are produced with exceptional weld seams, but are only welded once. This contrasts with some manufacturers, who use a second welding stage in order to create joins that are visually attractive. This second stage is done merely for aesthetic reasons, and has the disadvantage that the metal in the welding areas is subjected to enormous stresses, which leads to brittleness. Most of our frames have a wall-thickness of only 0.6 to 0.9mm at the tube-ends. For this reason, we don’t have a second, aesthetic welding stage: we are not prepared to compromise on quality for appearance.


  • Finally, the bottom bracket thread, brake mount and head tube threads are recut and milled, ready for components to be attached later on.


  • Before Rennstahl steel frames are painted, they receive a comprehensive pre-treatment known as cathodic electro deposition. This involves creating an electric circuit where the frame holds a negative charge and the coating (suspended in a liquid) holds a positive charge. This process results in the frame being exceptionally resistant to rust, both inside and out. This extremely complex treatment is unique within bicycle frame-building, and comparable with modern production methods for top-quality products in large-scale industry. It’s a detail that makes the main difference in whether a frame rusts in later years, or not. All other cavity sealing processes (e.g. wax) don’t have anything like the same durability, and in terms of corrosion protection don’t even come close. Think about older cars’ susceptibility to rust, compared to cars nowadays… Rennstahl forks are of course pre-treated in the same way, which means they are also protected against corrosion inside and out – including the steerer tube. This is important, because our touring bikes have an electrical wire routed through the fork and frame. This means that with Rennstahl bikes, rusty water is a thing of the past. There is a price to be paid, however: our bikes are and will only ever be available in black, because the electro deposition coating is black and black only.


  • After the electro deposition stage, the frame is given a coating of gloss paint. Once that has dried, the decals are added, followed by a top layer of lacquer.