In this article, we chat with Marcellus Putschli. A life long and well accomplished cyclist, Marcellus heads up product development for SEIDO Components and the Bombtrack Bicycle Co. Today he will help us to shed some light onto what goes into the design of all-terrain capable bikes, especially with regard to the progression of seemingly ever increasing tyre width.
So let’s begin with a bit of background into the rubber side of the coin and how things have developed to where they are now…
The days of finding 23mm stock tyres on road are long gone; we now see the trend of wider and wider tyres racing ahead. Bike manufacturers are kept constantly on their toes as professional gravel racers push the clearance on their frames to the limit, winning races on tyres of 50mm and upwards, often squeezed into frames designed only for 45mm. And outside of the race circuit, the cycling community is looking for wider, more supple tyres on all types of bikes.
Larger volume tyres have many advantages, particularly when it comes to momentum and how they roll over rough terrain. There are further advantages, such as comfort, their absorption properties due to the higher volume, low pressure aiding grip, and increased suppleness coping more effectively with high frequency vibration. These vibrations are also known as ‘suspension losses’, and reduction of these losses makes for more efficient power transfer, as well as this greater comfort. Additionally, when a higher volume is factored into a tyre’s design, manufacturers can confidently employ a lighter weight carcass construction due to the reduced risk of punctures associated with higher volume tyres. This nearly always leads to a suppler tyre that rolls quicker when compared to a tyre of smaller volume with its more robust casing. However, one trade-off to consider is the implications on aerodynamics that the greater frontal area of a larger tyre presents (more surface area = more material to push through the air). But in general, the speeds here are less than those encountered in an out and out road race or time trial scenario, where the aerodynamic drag is exponentially higher as the speed increases. So in an off-road situation the aerodynamic trade-off is more marginal, though still a serious consideration to the competing pro counting every watt.
Now for an insight into the bike design bit…
So why aren’t we seeing more off-the-peg gravel bikes with room for tyres 50mm and upwards? There could be many reasons, but frame design and component compatibility have large parts to play. Many gravel bike frames are made to function with road and gravel specific components. They have bottom bracket shell widths that fall under the road category (i.e. 68mm - 86.5mm wide) and trying squeeze everything together when working with lightweight materials such as carbon fibre, challenges can arise. Maintaining adequate chainstay thickness, leaving room for a wider tyre, plus ensuring there is enough space to accommodate a double chainset that will work with a road chainline are all parameters that must be factored together. All these factors need to be taken into consideration. But simultaneously, we have another tricky challenge to design a machine with a chainstay length short enough so that the frame’s sporty ride characteristics won’t be compromised.
Let’s now ask Marcellus to join up the dots…
SEIDO: “When designing a gravel frame with more tyre clearance, what considerations do you take into account, and how do you test the iterations of the design process?”
Marcellus: “Designing any product is always a compromise between several constraints. For the consumer, the most obvious are weight, cost and stiffness, but of course there are a lot of other aspects to keep in mind. Some of them are the result of others, some are of less priority than others. Finding the right balance and devising solutions to achieve the best possible final product, considering these unavoidable compromises, is the core challenge of designing.
Generally speaking the chainstay/ bottom bracket intersection is the hardest part to design on a hardtail, as a lot of different constraints apply to this area. I always start with writing down the main parameters. Important factors to consider for the rear triangle are (amongst others) drivetrain and chainring clearance and spec, chainline, frame material, frame geometry, BB specs, tyre clearance, target weight, and bike accessory specs like racks or mudguards.
In the next step I collect exact specs, drawings and sample parts, to make sure that my reference measurements and tolerances are correct. In particular, tyre measurements are often significantly different from their nominal sizes and also have huge tolerances. After I set those boundaries, I try to realise my planned geometry. I also aim to keep the frame versatile and plan for specs other than the ones we use on our complete bikes. For example, different cranksets or chainring sizes, bigger tyres or the use of mudguards.
After finishing the drawing, we make several sample frames that we use for ISO testing, production photo shooting and real-world testing. A bicycle is one of the most lightweight machines in relation to the forces that pass through it. All other vehicles, be they cars, aircraft, rockets, trains or boats, have many more redundancies and safety values designed into them. They are therefore much heavier in relation to the forces that pass through them. A bicycle must always be checked against the maximum dynamic forces, as a fully loaded bike will behave much differently to an unloaded bike in a bike stand.”
To the untrained eye, at first sight the bicycle first appears to be a simple machine. But, as we see here, once we delve into what really goes into designing a bike frame that will perform the way we want, we find that this is far from the truth. During high-intensity scenarios such as racing, we find variables that influence many different properties such as efficiency and safety. These factors mean that creating the perfect do-it-all machine is not quite as simple as designing a gravel race bike that will work with mountain bike wheels and run on a road-spec drivetrain. Because of this, we see riders making some weird and wonderful set-up modifications, intended to tick as many boxes as possible. Sometimes these DIY modifications work fine, sometimes they don’t. When they don’t, the consequences can be far from ideal, especially regarding safety. One of the professional bike designer’s key objectives is to make sure ALL the safety boxes are ticked.
For some race events, the limitations of the prescribed stock bike standards have pushed some competing cyclists to get creative with bike setups. For races such as the Leadville 100, a handful of riders have opted to equip cross country mountain bikes with drop handlebars. Given the nature of the course, with it sharing a significant number of similarities with many gravel race routes, this set-up has proven to be an effective choice. But what about the vice versa? Will we see gravel racers reverse assembling cross-country mountain bikes into more stripped-back machines, with carbon forks and drop handlebars? Some manufacturers may have foreseen this trend, and are already producing ultra lightweight ‘flat bar gravel bikes’ which are essentially rigid XC race bikes. We are yet to see these types of bikes of being sold with a drop handlebar as standard, but there are plenty of aftermarket parts available to help racers fine tune their bikes into the ultimate machines for specific courses. SEIDO Components are producing forks such as the TAZA and MGV to help facilitate the bridging of the gap between gravel bike and XC race bike. There are also some drivetrain options out there to enable the use of drop-bar shifters with wide-range mountain bike cassettes, both mechanical and electronic. To complete the package, we now have available ultra-low weight carbon wheelsets with their new super wide, deep section rims. These open up the exciting possibility to equip all types of bikes with more voluminous tyres, whilst still being lightning fast. If you want an absolute rocket ship of a bike that will make mincemeat of most types of terrain, chances are there is component upgrade out there for every part of the bike.
SEIDO: “Forks like TAZA and the MGV allow the rider to push tyre clearance, trim the weight and boost overall versatility on many different types of bike. When designing components like these, do you pull inspiration from your own experience as a cyclist?”
Marcellus: “Yes, definitely. I am also in close contact with our teamriders and try to benefit from their experiences and read a lot of reviews. But being able to draw from my own first hand experiences is extremely helpful. While studying engineering, I also worked as a bike mechanic, so in addition to riding bikes I can also relate to the real-life daily challenges of repairing and maintaining bikes which is unfortunately an often overseen and undervalued aspect of bicycle design. The choice of specs like external cable routing, threaded BB shells, round seat post, easy to source and replace cartridge bearings or external seat clamps are strongly founded by our time in the workshop.
In relation to the forks, the option to mount racks, allow for bigger diameter brake rotors and internal hub dynamo cable routing is mainly motivated out of selfishness, as we were looking in vain for such forks for a long time. I also often end up using multiple setups on the same bike, so this versatility is the key property that allows me to choose my preferred components for my personal rides.”
Thanks a lot to Marcellus, for enlightening us into the processes of designing bikes and components, true alchemy, what a great insight! To the uninitiated, a bike is simply two wheels bolted to two triangles, but this is clearly light years from the truth. The reality is that the devil is truly in the detail. The deep dive analysis and meticulous preparation required to develop us a bike that really does the job is a real eye-opener.
We hope you enjoyed this snippet, and we hope that this article helps to highlight considerations in bike design that might otherwise have remained out of focus.
Thanks for reading and ride safe!
SEIDO Components
June 2025
By Peter Skelton