Hi, I’m Stephen from Stromm Cycles. I’m the mechanical design engineer here and do all of the main structural and mechanical design for our bike frames. After the success of our Trakk frame around the world at national and international levels of competition, we wanted to apply what we learned to a revolutionary road bike platform. There were a lot of interesting learnings and improvements throughout our development cycle, and I’d like to give you a little peek behind the curtain of our development and engineering.
At Stromm, we always try first and foremost to design the bikes that we want to ride. These bikes aren’t made to hit a pricepoint, niche, or trend. The three of us here at Stromm have raced on the road for a combined 50+ years. Plenty of time to know what we love and loathe in a road bike. Our non-negotiables were broad component compatibility, spacious tire clearance, a wide fit envelope, and ease of assembly, day-to-day use, and maintenance. The catch? To deliver all of that and more in the fastest bike on the planet. In aid of our, frankly audacious goal, we pushed the structure of the bike to the limits of physics and manufacturing. Let’s look into how that's done!
The first step in designing a bike is laying out the frameset, choosing not only the geometry, but also the general widths and depths of each tube section, and deciding on a steering system. To inform this process, we created a parametric physics model that lets us see how much the weight and stiffnesses of the bike will change given certain wall thicknesses or tube depths, in each area of the bike. This allows us to fine-tune the balance between aerodynamics and structural efficiency (stiffness to weight). Generally speaking, tubes that are great aerodynamically (long airfoils) are not efficient structurally, so we need to calculate the minimum cross sections for each section of the bike before we design the airfoils. Tube stiffness scales linearly with depth and wall thickness, but cubically (x^3) with width, so small differences in dimensions can make a big impact. Another corollary to this is that if a tube is very long front to back, it will have a ton of vertical stiffness (x^3 again!), resulting in a very harsh ride (anyone remember first generation aero bikes?). Some areas of the bike have more of an effect on horizontal stiffness (pedaling/handling) and less on vertical stiffness (comfort), and vice versa. We can pick shapes intelligently for each area of the bike to maximize both comfort and hit our stiffness goals.
But how stiff should we make the bike? Many brands brag about increased stiffness values, and it’s an easily measurable frame characteristic. Like bare unpainted frame weight, carbon fiber type (T1100 NanoAlloy anyone?) and other essentially meaningless characteristics, marketing departments love to glom onto stiffness as a marker of frame structural performance. In fact, frame stiffness has an unmeasurably low impact on power transfer, and overly stiff frames are unnecessarily heavy, uncomfortable to ride, and are difficult to control when cornering on rough surfaces. Therefore, we set out to design a bike that had only the stiffness needed to maintain good handling and ride feel for each frame size, while allowing us the maximum leeway to make the bike extremely fast. We determined targets for zonal lateral and torsional stiffness based on frames we had historically loved the ride feel of. Then we processed these values through our model to output tube dimension requirements for each section of the bike.
One of my favorite handling race bikes - a 1967 Gazelle Champion Mondial
Another thing about stiffness as a metric is it’s not really just one number. Many companies publish overall torsional stiffness, or bottom bracket stiffness from test jig results (commonly Zedler test protocol) as their yardstick, but while those tests are an industry standard for a reason, they don’t really capture the way a bike deflects and feels while being ridden. At Stromm, we have our own internal models for how the bike should flex in each section, and in each axis. One example - while the fork itself should be stiff to allow for precise handling inputs, having more compliance in the frame between the front and rear wheels can allow the frame to absorb impacts mid corner. Getting this right leads to a planted, carving feeling when cornering - as opposed to the jumpy, skittery understeer feeling you get when the bike is too stiff. There are areas like that all over the bike - toptube, seatstays, chainstays, etc. where stiffness in one axis is beneficial, and in another can cause a harsh ride, poor handling, shimmy, etc.
This is a Raktt in a Zedler type headtube stiffness testing jig. The bike is fixtured at the rear dropouts, and a point in the center of the headtube. You can then measure the torsional stiffness in N/mm deflection.
At Stromm, we are EXTREMELY hands on with every step of the process. 🙂
Once Ben designed the airfoils for each section of the bike, we then calculated their mass moments of area, and plugged those back into our model to evaluate the full system stiffness impacts. Iteratively, we approached our optimum structural design that balances weight and stiffness, while achieving maximum aerodynamic performance. Next, we brought the composite engineers at our production facility into the loop to make sure the layup could be physically made as specified, negotiating millimeters to improve manufacturability and part yield. Before cutting molds, we needed to validate our aerodynamic simulations in the wind tunnel. We brought several 3D printed versions of the Raktt to the tunnel to A-B test the aerodynamic impacts of different structural options, using interchangeable pieces and a bucket of modeling clay to fine tune the steering system, tube junctions, and transitions.
We use smoke to find areas to improve, not just for cool marketing shots.
After wind tunnel testing a variety of front end configurations, we ended up using a fairly conventional “hinge” style fork solution. Popular on time trial bikes, this design is fantastic for reducing frontal area while maintaining stiffness. On the Raktt, the headtube is 29 mm wide, almost exactly the same width as a standard 1.125” steerer tube (28.6 mm). By putting the steerer in front of the headtube instead of through the headtube, we can reduce the frontal area significantly while maintaining the same stiffness and strength as a traditional fork. In addition, since we also have a secondary “steerer bolt” going through the headset, the fork design is intrinsically safer, with no single point failure in the steerer assembly and easier inspection of the carbon steerer tube for damage in case of a crash.
Tour Magazin - the big leagues of race bike aero testing.
I’m a pretty opinionated person, and one of the positives, but also negatives to being in a small company is that there isn’t necessarily anyone to stop me from going wild. When I got the first riding sample in October of 2025, I was thrilled. I put miles on the bike and rode through every pothole I could find, bringing rave reviews to our team meetings. With only my size manufactured at that point, Ben and Dave trusted my judgement and we sent off the only other rideable sample frame to Tour Magazin for their famous road bike comparison testing. (To be fair, I’m a 95kg sprinter, so they weren’t insane for just taking my word for it.) If you weren’t already aware, we won that wind tunnel test and still have the fastest bike tested by that magazine. Tour was also complimentary about the ride and handling, but noted that it was not very rigid in their machine stiffness testing.
Reason #437 why we sponsor the most successful US team - if it's strong enough for Ella Sabo, we can guarantee it's good to go for your town sign sprint
While eagerly awaiting our Tour results, we continued qualifying the remaining frame sizes and sent them off to be raced by our professional team, Virginia’s Blue Ridge TWENTY28. The team immediately started winning big races on them, and generally had very positive feedback on the ride, handling, and aerodynamic performance. However, some of the taller riders reported that they felt very different to the bikes they were riding previously, and wished that the bikes were a little more rigid to feel more “locked in” while sprinting. Luckily, we work with a fantastic factory team, and we used this feedback to tweak the layups, locally change fiber types, and selectively add material in key locations to significantly increase the stiffness of the bike, while maintaining the relative stiffness ratios needed for the ride quality I was striving to achieve. The entire turnaround, including our proprietary fatigue and impact testing protocols, took about 2 months, and all frames shipped to customers have the new layups.
Zedler test results of the initial riding sample and the final customer versions shipping now.
In bike racing, the saying is that you either win, or you learn. In this way, making bike frames is even more rewarding than racing them; we won the Tour test, but we still learned a TON and were able to use early feedback to improve our product and deliver better results to our most important stakeholders, riders like you. I could talk about stiffness all day, so please reach out with any questions through our website or at support@strommcycles.com.