The Bossi philosophy

Aerodynamics has become the buzzword for modern bike designs and that’s not entirely a bad thing. Wind tunnel testing and CFD (computational fluid dynamics) have taught us that aerodynamic drag at racing speeds (>50Km/h) equates to 90% of total drag, and as such has sparked an obsession with finding the path of least resistance through the air. Aerodynamically optimised components and frames have deep profiles to help reduce separation of airflow and subsequent turbulence. A common side effect of creating larger, more aerodynamic profiles, is an increase in stiffness – which is often unwelcome and creates problems for frame designers. This increased stiffness along with an aggressive aero riding position has given rise to the stigma of aero bikes being uncomfortable and uncompromising – not an issue if you’re a conditioned athlete with a team of physios working on you but can be problematic for the everyday cyclist. It’s with good reason that aero bikes are reserved for the short-course time trials and that different bikes are needed for different terrain. The real-world performance gains of aero bikes are further challenged upon scrutinising the standard models of wind tunnel testing: high simulated riding speeds of 48-64Kph (30-40mph), fixed bike and rider positions, flat terrain, riding in clean air (no other riders in front or behind). The real-world likelihood of this being recreated are about as slim as the chances of you being a pro-tour rider. So how important is an ‘aero’ frame? we know that a rider accounts for about 70% of wind resistance (range of 60-80% depending on rider position). Of the rest, wheels account for about 10%, and the remaining drag comes from fork, cockpit, and frame. Of course, all this goes out the window when we add the necessities of water bottles, lights, saddlebags, pumps, GPS and so-on. The reality is the frame only commands about 7% of total drag. An ‘Aero” frame is, at best, about 40% more streamlined than a non-aero type. Crunch the numbers and that means using an aero frame gives roughly a 3% advantage. And wind tunnel tests show this advantage only occurs at high speeds (>40km/h), in clean air, when riding on your own… That advantage is important if you are chasing a podium finish in the upper echelons of pro cycling. For anything else these stiffer and uncompromising bikes become physically draining to ride on anything other than a smooth, flat road. And that aero frame has little benefit in a group ride. So that begs the question, are these aero frames worth it? In our experience, bikes should be aero-optimised, not compromised: The cockpit, wheels, fork, and headtube create the ‘leading edge’ of the bicycle (those parts that contact the air first). These have the biggest effect on drag, so prioritising these parts for aerodynamic design leaves the rest of the frame to look after the rider’s comfort and efficiency. With aero bars, aero wheels, aero fork, and refined riding position - we can make significant aerodynamic improvements without the need, or compromises, of an ‘aero’ frame.

We’ve all been guilty of at least one of the following: Picking up your friends’ new bike as if our hands are digital scales. Buying a carbon bottle cage because its 6g lighter. Skimming through in-depth groupset reviews to find weight figures, or trying to convince ourselves (and others) that disc brakes aren’t worth the added grams – the list goes on. Everyone enjoys riding lightweight bikes because of the way they feel – they’re responsive, agile, and lively. However, there are lightweight bikes, and then there are ultralight bikes. As the old saying goes “Everything is poison, it’s just the dose that kills you.” As frame designers we’re constantly impeded by this annoying thing called ‘physics’. We desire to create indestructible featherweight frames that are stiff and flexible and corrosion resistant and aerodynamic and compliant and….. then ‘Old Man Physics’ calls the cops: every action has an equal and opposite reaction. To make frames lighter, you reduce tube wall thickness or diameter. The compromise of which is more flex and reduced durability. Intelligent engineering and material selection can help soften the compromise, but the compromise will always exist. Ultralight race bikes may give you marginal gains on steep climbs but to us the compromise is problematic. Symptoms include poor handling as increased headtube flex impedes wheel tracking, poor durability as paper thin tubes are susceptible to damage, and poor driveability as the frame fails to transfer large power loads. The real world performance value of such lightweight bikes is questionable, play with this calculator and you’ll find that the weight wheenie argument doesn’t ring true for the nonprofessional rider. For a pro-tour rider this may be the difference between a stage win and not being on the podium. Their bikes, however, don’t need to last more than a season so the compromise is tolerable. Unless you ascribe to the idea of living in a throwaway world, a true road bike needs to last in order to perform. They will be used and sometimes abused and, let’s be honest, s#*! happens. Your bike will be dropped, it will be mishandled in transit, it will be slammed into potholes – and that’s just part of life. The question is, how much of your passion (and hard-earned wage) is disposable?

In its simplest form, frame stiffness is generally tested in two areas - headtube flex and bottom bracket flex.  Headtube flex is linked to the trackability of the front and rear wheels and generally speaking appropriate headtube stiffness (in moderation) results in good handling. Bottom bracket stiffness is linked with the driveability of a bike.

Historically bike builders believed the stiffest frames were the fastest frames.  Whilst this concept still prevails in modern bike design the reality is starkly different. Recent studies have proven that not only are compliant bikes significantly more comfortable and energy efficient, but they help deliver the power more effectively throughout the pedal stroke. In compliant frames, the bottom bracket moves inboard when loaded and has energy ‘stored’ like a spring, when the load is removed (i.e. past 6 o’clock in the pedal stroke) the bottom bracket begins to move back to its natural plane and that stored energy gets transferred back into the drivetrain. This gives a smoother, less jerky, pedal stroke. 

Overly stiff frames suffer from poor handling causing tyres to lose traction on uneven surfaces and steep decents. Stiff frames are also notorious for transmitting road noise and chatter, the exhausting and spirit-crushing bane of bike riders. It’s ironic that frame manufacturers promote how super-stiff their frames are yet use all sorts of component gimmickery to make them more compliant.

So are highly flexible bikes better? Unfortunately it’s not that simple. What you to do to one area of a bike frame affects every other area of the bike. If you drastically reduce stiffness to make a frame more comfortable, you will inevitably impact handling. Apart from this, durability will decline and the most highly stressed areas of the bikes will inevitably fail. We design to create a state of equilibrium. We need enough stiffness to refine ideal handling characteristics and driveability, we need enough flex so that our bikes are comfortable and characterful. 

As a frame building material, titanium is king. Revered for its strength, character, durability, aesthetics, corrosion resistance, and ride quality – it’s the perfect material for real world performance. Unlike steel frames, the lower density of titanium allows us to use larger tube profiles with thicker wall sections to dial in frame stiffness without increasing frame weight. With larger profiles we can use oversized bottom brackets and headtubes to perfect power transfer and handling. This desired stiffness is further complimented by the natural compliance of the material resulting in bikes that are not only efficient but comfortable. Unlike unidirectional carbon fibre, titanium has a ‘crystaline’ structure that has powerful dampening properties to reduce road buzz and chatter, giving rise to its famed ride quality. The frame is the heart of the bike but it’s only one piece of the puzzle. In order to aerodynamically optimise the bike and maintain competitive weight, we use carbon fibre in the leading edge of our builds. Aero forks, bars and wheels are often used to break the wind and create a passage of lease resistance for the rest of the bike to follow. The lightweight rigidity of carbon fibre is a desirable quality in a fork as it helps create a solid front end with good feedback to the rider. Aerodynamic wheels are important to reducing drag on a bike as there are two rotating leading and trailing edges, creating vortices. Deep dish carbon wheels go a long way in reducing that drag and reduce rotational mass as a bonus.  

Our bikes have been designed with the perfect balance of stiffness and compliance to create a rapid and responsive ride that won’t leave you war torn the next day. Our lightweight builds utilise aerodynamic components to optimise performance without compromising the frame and ride quality. Our frames have been over-engineered to withstand the sustained long-term stresses of cycling and are backed by our 50-year warranty. Our designs blend the quantifiable notions of performance with unquantifiable values (character, ride quality, and durability) to create what we believe are the best bikes for real world riders.