This article was produced in collaboration with BMC and first published in Rouleur Issue 144
As gravel racing has exploded over the past decade, the technology behind the bikes has entered an arms race of its own. With speeds increasing dramatically, aerodynamics now plays a far greater role. Terrain can be wildly unpredictable: traction and control over rugged ground at higher speeds necessitates higher-volume tyres. And thirdly, as with road racing, we're seeing a return to prioritising low weight – or at least placing it back on near equal terms with aerodynamics.
(Image credit: BMC)
Pauline Ferrand-Prévot won the first ever Gravel World Championships on the first-generation BMC Kaius in 2022. While the indomitable Frenchwoman made history, the Swiss brand's Kaius pushed the frontier in gravel bike design further than ever before by demonstrating that the DNA of a lightweight road race bike – its Teammachine SLR 01 – could work off-road, too.
But four years is a long time in gravel racing, and BMC's R&D team had something of a rock-strewn mountain to climb when it came to designing a new Kaius that would keep its elite gravel riders ahead of the pack. The impossible-sounding task they set themselves was to add aero, add clearance, add cargo capability, preserve stiffness – essentially imbue the new bike with more of everything but without adding any additional weight.
Inside the Impec Lab at BMC's Grenchen HQ, where all its innovation takes place, they met the challenge: the new Kaius was improved in all those areas that were identified and it did better than simply matching its predecessor for weight – it is 63 grams lighter. That's not a huge amount in the grand scheme of all things gravel racing, but it shows just how much of a numbers game the discipline has become in the pursuit of efficiency.
Aero, now with a rider on board
Aerodynamics, once regarded as a 'nice to have' offroad, is now central. The new Kaius borrows not only from the latest Teammachine SLR 01, but also from the aero Teammachine R 01 (as ridden by Tudor Pro Cycling), particularly around the front end. BMC calls this design AeroSynthesis, a system-wide design philosophy and technology that focuses less on the wind tunnel performance of the frame and more on how the complete bike performs with a rider at race speeds.
Head of R&D, Stefan Christ, says: "Making a bike faster is way more challenging than making a frameset faster. We're looking at the impact of the rider on the frameset, of the components on the frameset. That's why we always develop all of our bikes aerodynamically with a rider, with equipment including helmets and clothing. We have 3D scans of real athletes, and we make sure that whatever we come up with in terms of aero solutions, we validate for different athlete profiles."
(Image credit: BMC)
Room for 52mm
A major part of the front end redesign can be seen in the new Halo fork which is not only designed to improve aerodynamics but also to accommodate 52mm tyres. In order to reach and sustain the speeds over rugged terrain where aerodynamics becomes the difference between winning and losing in gravel racing, it was vital to increase the new Kaius's tyre clearance, explains BMC. Bigger rubber means not only more speed offroad but more comfort and better control, though it is still possible to run 32mm tyres for fast, smooth courses.
Compliance without the slack
The frame itself is designed to contribute to a signature ride feel that balances comfort with stiffness and low weight, and BMC achieves this with its Tuned Compliance Concept. The carbon layup, revised seat tube and redesigned seat stays are intended to create measurable vertical deflection without compromising power transfer. The AS10 aero seatpost, borrowed from the Teammachine range, plays a key role, allowing the rear end to absorb repeated impacts while keeping the rider stable in an aggressive position.
The reach, stack and bottom bracket height have been tweaked in order to deliver a bike that allows for a more aggressive riding position, but still has stable and confidence-inspiring handling. It's not just the higher average speeds. Elite racers are increasingly demanding that their gravel bikes react like road bikes to their input.
Built to be futureproofed
Bigger tyres are shaping the future of gravel race bikes – as long as it's not at the expense of the other performance metrics – but because the discipline itself is evolving so quickly, futureproofing the new Kaius was essential. BMC developed the new frame around a 1x groupset with the ability to fit gravel or mountain bike gearing so that riders can either boost ratios or tune them down according to the demands of the race.
(Image credit: BMC)
Taking this a step further, storage options have been added, including a bottle cage mount under the down tube, as well as a new top tube cargo plate mount.
Pro rider Clara Koppenburg's verdict? "Even before this update, it was clearly one of the best gravel race bikes out there. Jumping on the new Kaius, it immediately felt like home – same intuitive geometry and ride feel, but faster, more controlled, and even safer. And when you look at the numbers, with improvements in aerodynamics, stiffness, and weight, you know you're getting an extra edge. That gives you huge confidence heading into an intense race season with events like Traka, Unbound, and beyond."
(Image credit: BMC)
BMC sums up the new Kaius as a "no compromise gravel race bike". It's faster, lighter, it perfectly balances aero performance, stiffness, and low weight, while upping tyre clearance from 33mm to 52mm and adding smart cargo options. It's nothing less than the boundaries unbounded.
