Riding Dirty Reiver on the BMC Kaius 01 One - A high-end gravel bike made for racing

The trees loomed high as we drove through the fog deeper into the forest. The clock had not yet struck 7am, it was an early wakeup call in the heart of Northumberland to get us to the start of the Dirty Reiver gravel event on time. Ahead of us lay a long day in the saddle: 130km of dirt roads under grey, stormy skies. The vast landscape of Kielder still looked stunning, but it had taken on a sort of intimidating quality as the wind blew leaves off the trees and the clouds descended lower and lower as we approached the start village.

2023 was the ninth year of the Dirty Reiver, regarded by many as the UK’s biggest gravel event. Skirting through English and Scottish borders, Kielder Forest, where the event takes place, is the largest man-made woodland in England at 250 square miles, and over three quarters of it is covered by tall imposing trees. This means the views can only be found by following the gravel tracks high into the clouds until they eventually break through the woodland and reveal breathtaking, expansive countryside and reservoirs. Over 1600 riders took on the Dirty Reiver this year, with some opting for the longest 200km distance, others, like myself, settling for the 130km, and the shortest option being a 66km loop.

While there are those who want to secure a good result or complete the route around Kielder in a particular time, there are others who are just looking to enjoy the experience. Part of the beauty of gravel events is that they are open to all and the Dirty Reiver is no exception. Any off road bike can be used to complete the route, and for 2023 an e-bike category was created for the first time. A team of eight disabled bikers, working with the national Experience Community group used specially adapted bikes – mostly hand pedalled – to take on the 66km route in torrid conditions.

As I stood on the line, surrounded by the one thousand other participants and the rain began to spit down on my shoulders, I began to feel a pang of nerves ahead of the start of the event being given. I fell firmly into the category of people looking to just enjoy the event and make it to the finish, but there’s something about waiting for the whistle to be blown that still ignites a bit of anticipation. To help me make it over the wet gravel and 1550 metres of climbing that lay ahead, I was riding the BMC Kaius 01 One, BMC’s premium, race-focused gravel bike that was used by the likes Pauline Ferrand-Prevot in last year’s UCI Gravel World Championships. The varied terrain of the Kielder Forest served as the perfect test bed for this fast, interestingly road bike-esque gravel whip.

About the bike

The BMC Kaius 01 One aims to take inspiration from the brand’s Teammachine SLR 01 road bike and combine it with the URS (UnReStricted) adventure range to develop a gravel bike which is capable and fast both on and off-road, striking gold for the middling surface conditions that gravel racing often throws up. While the URS range seemed to take inspiration from BMC’s cross-country mountain bikes as an answer to gravel, the Kaius 01 One is a clear move the other way, with its aggressive geometry and clean design looking distinctly similar to the iconic road bikes that BMC has produced over the years.

BMC says that the Kaius aims to strike the balance between being both stiff and lightweight, with the truncated aerofoil tube profiles mirroring those seen on the Teammachine. The Kaius also carries features such as the Teammachine’s ‘Aerocore’ bottle cages whereby the cages are shaped to integrate smoothly with the bike's seat and down tube.

At the front and of the bike, the focus on aerodynamics continues with the use of BMC’s ICS cockpit design to create a neat look and integrated finish. The ICS routes cables inside the cockpit and down through an enlarged upper headset bearing via spacers. In another attempt to make the bike glide smoothly through the air, the Kaius features narrow bars which measure 36cm at the hoods, allowing a rider to have a smaller frontal area. Even if a rider opts for a larger frame size, all of the Kaius 01 One builds will come with the same width bar – great if you’re looking for aero gains, but something that could take some getting used to if you don’t normally ride a bike with narrow bars.

Despite this heavy focus on aerodynamics, BMC claims to not have forgotten that a gravel bike needs to be robust enough to deal with the knocks and rough terrain that gravel throws up. The brand says that despite the light 7.4kg weight (in a size 54cm), the frameset has been reinforced in particular areas that are vulnerable to damage on the trails. A long, D-shaped seat post aims to introduce flex and improve comfort when seated, too.

When it comes to tyre clearance, the Kaius 01 One can take up to 700c tyres and the bike can either be set up 1x or 2x, allowing for versatility and use on a variety of terrain. The Kaius also features a PF86 bottom bracket standard which features large tube widths which should aid pedalling stiffness. The bike I rode came equipped with SRAM’s Red eTap AXS XPLR groupset which included a 10-44 cassette and a 40t front chainring, a well as a Fizik Vento Argo 00 saddle, Zipp’s 303 Firecrest wheels and Pirelli’s Gravel H tyres.

Ride feel and performance

When you first lay your eyes on the BMC Kaius 01 One, the aesthetics of the bike jump out. An all-white paint job is perhaps a little impractical for the mud that off-road riding can throw up, but it certainly looks sharp out of the box. My only gripe with the BMC branding was that the ‘B’ and ‘M’ on the logo slightly blurs in with the bottle cages. It’s a small detail, but something you can be picky about on a bike with this sort of price tag. Otherwise, I loved the clean looking front end of the bike and the pops of green on the forks. Keeping the integrated bar and stem white to match the frame is also a nice touch from BMC, it really makes it look sleek and aero – this is a bike which got lots of attention while out on the roads.

BMC’s decision to sell the bike with such narrow handlebars when the majority of gravel builds these days seem to come equipped with ever wider bars is an interesting move. I was a big fan of them, though, given they feel much closer and more familiar to those I use on my road bike. The flare of the drops means the bars are much wider at the base, something that definitely helps handling on technical descents. The narrow bars are paired with a big bottom bracket drop in order to give a bit more stability and slow down the fast handling which is much more desirable when riding on gravel.

I found the BMC extremely controllable on rough terrain, it is responsive without being twitchy and the built in compliance does a good job at smoothing out bumps which makes the bike comfortable enough to ride on even the longest days out. While it gives comfort, the Kaius doesn’t compromise on stiffness, however, still feeling responsive when I was out of the saddle putting pressure down on steep ascents.

The main reason for the narrow bars on the Kaius, naturally, is the aerodynamic benefits that they give a rider. BMC has taken an impressive attention to detail throughout the entire Kaius 01 design to optimise airflow: the lack of cables at the front end and the aero shaping of the handlebars alongside the Aerocore Bottle Cages and a hidden bolt on the seat post binder, plus an aero top cap for the steerer tube and cover for the stem bolts, as well as the thru-axles being limited to a single opening with the other side being completely smooth. When the roads are undulating, the Kaius feels good, but the aerodynamic details don’t really feel like they are making a difference. It is on wide, flat sections of gravel that the Kaius comes into its own. When it is time to get into a long effort on the drops and chug away, the Kaius is the perfect choice with the narrow bars helping you to get low and the aerodynamic benefit of the bike meaning you can glide quickly through the wind.

Zipp’s 303 Firecrest wheels were a great supporter of the aero-focussed Kaius frame. They felt incredibly accurate and composed even in wet weather conditions, while also remaining smooth and controlling speed impeccably well. The Dirty Reiver wasn’t an extremely technical course so the 40mm rim depth worked well, though this might be too much for more technical gravel as a low-profile rim could offer more compliance. For the terrain I was handling though, which was relatively light gravel mixed with tarmac sections, the 303’s did a great job. Pirelli’s Gravel H tyres did well too, holding grip on some wet sections where other riders around me found themselves slipping while also rolling fast on cleaner surfaces.

The braking power on SRAM’s Red eTap AXS XPLR groupset was impressive, it felt sharp and gave me peace of mind that I was fully in control of the bike’s speed. Even in the wet weather, the gears shift smoothly and despite using a 1x set up, the jumps between the gears weren’t too severe and I felt like I had more than enough range for tackling some steep climbs – although I did find myself spinning out slightly on long descents. With the derailleur’s Orbit Fluid Damper, I didn’t have any issues with the chain jumping around and the shifts were extremely precise. Saddles are, of course, extremely subjective but I found the Fizik Vento Argo 00 to be very comfortable, not feeling much different from the Specialized Power saddle I use on my everyday road bike.

Verdict

Retailing for €11,499, the BMC Kaius 01 One is a bike made for those looking for performance gains on the gravel. The price tag isn’t out of this world when compared to what some of the other leading bike brands are charging for premium builds, but it is worth bearing in mind that you could opt for some fully-custom bike options in a similar range. The Kaius 01 Three that BMC offers sacrifices on build which in turn affects weight, but does almost halve the cost of the One model.

The Kaius 01’s closeness to a road bike made it one of my favourite gravel bikes I’ve ever ridden, but the deeper wheels and racey geometry don’t render it the most suitable for extremely technical sections. On fast moving, light gravel and long stretches of road, the Kaius 01 One is one of the fastest options out there, it’s just the bike I’d want to be riding if I was on a long solo attack or having to ride for extended sections on the flat on my own. It’s great to see BMC embracing the fact that gravel racing is slowly getting closer to the road as many famed gravel races do challenge riders with lighter gravel which is far from mountain bike territory. It’s impressive that they have managed to tick the boxes on aerodynamics and speed while also maintaining comfort and keeping the Kaius 01 suitable for long races and all-day adventures.