BMC Kaius 01 One review: A truly novel take on mixing old-school and new
Story Highlights
- What it is:BMC’s first gravel bike specifically made for racing.
- Frame features:Semi-aero carbon fiber construction, official clearance for 700×44 mm-wide tires, fully internal cable routing, PF86 bottom bracket shell.
- Weight:910 g (claimed, 56 cm frame only); 400 g (claimed, fork only); 7.48 kg (16.49 lb), as tested, 51 cm size, without pedals or accessories.
- Price:US$12,000 / AU$14,500 / £11,350 / €11,500.
- Highs:Super stiff and snappy, very light, semi-aero gains without the downsides, progressive frame geometry, great spec, utterly gorgeous.
- Lows:Narrow bars are very polarizing, tire clearance isn’t as good as claimed, fully internal routing is highly inconvenient, OMG it’s so expensive.
Bike brands conveniently label “gravel” as a single category. However, the reality is that it covers a wide range of riding and gear, and Swiss company BMC sure seems like it wants to cover all the major bases. First came the URS in 2019 with its innovative rear micro-suspension and super progressive frame geometry. Three years later, BMC followed up with the URS LT, which went further down the off-road path with a novel steerer-based front suspension fork. And now, BMC’s gravel pendulum has swung in the other direction with the more “racing focused” Kaius.
Much of the Kaius feels familiar, like its semi-aero shaping, the light-and-stiff carbon fiber construction, and yet another fully integrated one-piece cockpit. But BMC has also paired that with an only mildly diluted version of its hyper-progressive gravel bike geometry, and what results is one of the interesting bikes in the segment.
What is gravel “racing”, anyway?
Whereas the URS and URS LT are ostensibly intended more for general riding and exploring on unpaved roads, the Kaius is very specifically aimed at gravel racing: i.e. going as fast as possible on the sorts of unpaved surfaces you’re likely to encounter at various timed events.
Granted, the idea of what exactly constitutes gravel “racing” is up for debate, but BMC’s interpretation of the genre is clear. The carbon fiber Kaius is built with big tube sections that prioritize low weight and high stiffness, but much like the latest crop of do-it-all road racing bikes, there are also modestly aerodynamic cross-sections used throughout to help the Kaius move more efficiently through the (dusty) air. True to form, the claimed frame weight is very impressive at just 910 g for a 56 cm sample, plus another 400 g for the matching fork. Even the aero-profile carbon fiber seatpost is surprisingly light at a wispy 160 g.
Light, stiff, and aero do not a gravel bike make, though BMC seems to have covered those bases, too. The maximum tire size is officially rated at 700×44 mm – 2 mm more than the URS, in fact – and the frame compliance is supposedly somewhere between the road-going Teammachine and the more rough-and-ready URS. BMC also claims it’s engineered a greater-than-typical amount of impact tolerance into the Kaius’s carbon fiber lay-up schedule, which suggests it’s more than up for a little abuse.
Things get especially interesting in terms of frame geometry.
BMC pushed the envelope with the URS range, which features an extraordinarily long reach dimension with correspondingly stubby stems, similarly long front centers, and slack – but not crazy-slack – head tube angles. The result is one of the finest-handling gravel bikes I’ve ever used in technical terrain.
BMC hasn’t gone quite that extreme with the Kaius, but it’s still a lot longer than the norm. For example, as compared to a 56 cm Specialized Crux (which is probably closest in spirit to the Kaius than anything else currently on the market), the reach dimension on a Kaius of the same size is 8 mm longer. The difference is even more dramatic on smaller sizes. The 51 cm Kaius I’ve tested here sports a reach of 397 mm – a full 15 mm longer than the equivalent Crux.
Not only that, but the front end of the Kaius is also a lot lower. That Crux is hardly a lounge chair, but yet a 56 cm Kaius is 8 mm lower in stack for the same size, while a 51 cm Kaius is 17 mm lower than a 52 cm Crux. You did always intend to start a stretching routine again, no?
Other dimensions aren’t quite as polarizing. The chainstays are admirably short at just 420 mm, and while the 66-68 mm of trail is on the quicker end of things (and notably quicker than the URS), it’s still in the ballpark. Down below, the 80 mm of bottom bracket drop promises a stable and planted feel.
Far more controversial is the one-piece cockpit – and it’s not because the routing is fully internal through the bar and stem.
Naturally, BMC is varying the stem length with frame size, from 80 mm on the smallest size up to 110 mm on the biggest one. But regardless of the stem length, the bar width is the same throughout at just 36 cm, measured at the hoods. And nope, that’s not a typo.
Thirty. Six. Centimeters.
The drops are flared at 12.5°, though, so the bar is somewhat more generous at 42 cm at the ends for more control. What’s the motivation, you wonder? Simple: narrower is faster, at least as far as the wind is concerned.
Mounts fall on the minimal end of the spectrum, with two bottle mounts in the usual spots, a top tube feed bag mount, and… that’s it. No fenders, no rack, no anything mounts on the fork. And if you think you need a third bottle, BMC apparently thinks you should finish faster.
Other details include a PF86 press-fit bottom bracket shell, included aero-profiled bottle cages (really), a hidden wedge-type internal seatpost binder, and a removable front derailleur mount for 1x or 2x drivetrain compatibility. BMC doesn’t include an out-front computer mount, but there are two threaded holes in the standard locations on the underside of the cockpit should you want to add your own from a third party.
BMC only offers the Kaius in a single flagship-level frame construction, but in six sizes and three different build kits. BMC provided to me the top-end Kaius 01 One, fitted with a SRAM Red eTap AXS XPLR 1x wireless electronic groupset, Zipp 303 Firecrest aero carbon clinchers wrapped with fast-rolling 40 mm Pirelli Cinturato Gravel H tubeless tires, and topped with a Fizik Vento Argo 00 saddle.
Total weight for my 51 cm sample is just 7.48 kg (16.49 lb) without pedals or accessories, and retail price is a whopping US$12,000 / AU$14,500 / £11,350 / €11,500. If you’re willing to drop down to the Kaius 01 Three with its Rival AXS, more generic carbon wheels, and non-integrated cockpit, the price literally gets cut in half.
What exactly does it mean to go fast on gravel, anyway?
I should first preface my riding account of the Kaius with some clarification on what BMC apparently means when it says the bike is meant for gravel racing. “Racing” obviously implies speed, but speed on gravel doesn’t always mean the same thing as speed on tarmac. In other words, while less weight is always better than more (all other things being equal, of course), a stiff bike isn’t always a great thing on unpaved surfaces, and a rough ride can mean the difference between being able to keep putting down power vs. coasting through a section, or feeling fresh at the end of a six-hour day vs. feeling so beat-up that you can barely finish, period.
To that end, it’s clear to me that what BMC means here is that the Kaius is aimed specifically at the sort of all-day slugfests on unpaved roads that typify American-style gravel racing, not shredding singletrack or underbiking in general. And it’s in those sorts of environments where the Kaius excels.
Long-time roadies will probably feel right at home on the Kaius. It feels fast from the first pedal stroke with an ultra-efficient power transfer and noticeably low weight. There’s an immediate response when you mash on the pedals, and not surprisingly given its impressive performance on the scale, the Kaius is noticeably light both when accelerating on the flats or tackling a tough climb.
The Kaius clearly likes to build pace quickly, but it’s also adept at maintaining it. Is it actually aero? That’s hard to say exactly, but between the obviously fast-rolling tires, the aero wheels, and that super narrow bar, the Kaius is quite happy to get somewhere in a big hurry.
In many ways, the Kaius feels exactly like its appearance would suggest. It’s basically a high-end road racing bike fitted with fat tires, as opposed to typical gravel bikes that are somewhat softened for off-road endeavors. On the smoother dirt roads that litter my local stomping grounds, the Kaius is an absolute beast.
That’s not to say it doesn’t have its fair share of quirks, though.
As you’d expect given the oversized front end, there’s no noticeable twisting up front, and the handling is extremely precise. The narrowness of the bar took some getting used to, but I actually grew to like it for general cruising. However, I never grew to love it as there just isn’t as much leverage or stability as I often prefer.
Yes, the flared drops do provide a more reasonable 42 cm of width, and as it’s my preferred position for sprinting, that wasn’t a big deal. But there are also lots of times I want more leverage and stability without shifting my weight down and forward, and this just doesn’t provide that flexibility. BMC’s more traditionally shaped road cockpits look like they’ll fit if you really want to swap, but that’s hardly an easy or inexpensive option.
Keep in mind that I have fairly narrow shoulders and usually go no wider than 40 cm at the hoods with my road bars. While my experience here was reasonable, I’d imagine broader individuals might not be so adaptable.
The ride quality of the Kaius is also firmer than I expected it to be. It’s not as jarring as some other bikes we’ve reviewed here (the Evil Chamois Hagar and Bianchi Arcadex come to mind), but it still relies heavily on the tires for comfort, despite all that extension on the D-shaped carbon fiber post and those flattened tops on the integrated bar. It’s another indication of how BMC intends for the Kaius to be used. It’s still capable on rougher ground, but I can’t say it’s particularly fun to get bounced around in that situation for hours on end.
Speaking of capability, it’s an interesting mix here for the Kaius.
On the one hand – rougher ride and all – the generous tire clearance allows the Kaius to navigate an impressive array of terrain. Smooth-and-fast dirt and gravel is obviously where it’s happiest, but those big footprints still let you rip through some reasonably ugly singletrack, too. And while I didn’t spend any time with this setup, my guess is that a set of foam tire inserts would go a long way toward expanding the Kaius’s comfort envelope even further.
The bike’s handling helps a lot, too. Prospective buyers will naturally cross-shop the Kaius against the Crux, with them both being light-and-stiff gravel bikes with fairly traditional-looking designs. But while they might share somewhat similar profiles, that longer front end of the Kaius makes for a pretty different experience off-road.
Just like other bikes that have adopted similarly progressive geometry (like the Devinci Hatchet, Fezzari Shafer, and that truly wild Evil Chamois Hagar), lengthening the front center allows you to really push the front end of the Kaius through loose corners without a sudden wipeout, and it also provides more leeway to shift your weight around as needed. The shorter trail dimension also keeps things very lively in terms of initial turn-in, although it’s tempered by the longer wheelbase. That does keep the Kaius from truly tearing through a series of very tight-and-twisty corners, but let’s not forget this isn’t meant for that. As is, it works very well for the wide-open dirt and gravel roads on which the Kaius is designed to shine.
I personally would still prefer the more forgiving URS for the sort of gravel riding I do around here (more a mix of light-duty trail, poorly maintained fire roads, and dirt roads), but it’s hard for me to argue that BMC hasn’t accomplished its goal here. It’s an absolute ripper of a gravel bike – in the right conditions.
Lastly, I don’t want to ignore the Kaius’s aesthetics. Simply put, it’s a beautiful bike. The lines are super clean and elegant, the paint and graphics are bold yet tasteful, there are nice details like the painted-to-match headset spacers and cockpit, and even the blind thru-axle holes lend a distinctly finished look to the whole thing. It’s almost a shame to get it dirty.
Fast isn’t everything
What, you didn’t think I found the Kaius to be perfect, did you?
I know I keep banging on this drum, but I find the fully internal routing to be particularly grating here. BMC has also demonstrated that it can do concealed routing without running the control lines inside the bar and stem – a minor improvement, but an improvement nonetheless – so I struggle to understand why that wasn’t done here, particularly given the polarizing 36 cm bar width. It just isn’t going to work for everyone, and it’s going to be a massive hassle to swap it out. Prior experience with other similar one-piece BMC cockpits suggests those brake hoses won’t come out wholly intact, either.
The rear brake hose also rattled a bit inside the down tube.
Come on, BMC, you can do better.
I also get that BMC intends for the Kaius to be used for gravel “racing”, but I don’t see how a third bottle mount would detract from that purpose. If anything, that might let someone perhaps skip an aid station and gain a few minutes on the competition, no? Sure, a third bottle mount might tack on a few grams and add a bit of visual distraction, but this just seems like a silly decision to me.
Last but not least, I’ve grown accustomed to brands under-selling the tire clearance of their gravel bikes, but this is one instance where BMC’s claims might be just a tad ambitious. The “40 mm” Pirellis have an actual measurement of around 40.5 mm, but it’s already a somewhat close fit between the seat stays. Will a 44 mm tire fit back there? That depends on how much you value your paint, I guess.
Spec notes
There are no real surprises here for the most part.
I’ve written at length about the virtues of SRAM’s Red AXS XPLR wireless electronic groupset, and the same accolades apply here. The 10-44T 12-speed cassette offers plenty of range for this sort of gravel riding, and when combined with the stock 42T chainring, you’ve got all the climbing gear that most reasonably fit riders will need (and if that isn’t enough, chainring swaps are relatively cheap and easy). Shifter ergonomics are also very good – eTap is still my preferred style of electronic shifting – and the brakes continue to impress with their excellent power and control, even if the lever action could still stand to be a bit lighter and snappier.
Likewise, the stock Zipp 303 Firecrest wheels are outstanding: light, fast, durable. Tubeles setup is easy as pie, and while the hookless format limits tire selection somewhat, the choices are expanding almost daily. Speaking of which, the Pirelli Cinturato Gravel H tires are superb for harder surfaces. They roll super fast yet still offer good cornering grip on reasonably loose ground, and are an excellent pairing for the Kaius’s personality.
At least for me, the Fizik saddle was also a very comfy and supportive place to spend a few hours, and even those fancy profiled bottle cages worked surprisingly well. It’s easy to get bottles in and out, and the hold is impressively secure. Normal cages will attach to the standard bosses, of course, but I wouldn’t feel much motivation myself to bother.
Now, one more thing about this integrated bar/stem: I hate that the tops are untaped. I understand why bike brands do this on high-end, full-aero road bikes: marginal gains and all, and most people riding those bikes probably aren’t using the tops much, anyway. But the Kaius isn’t an aero road bike. Any time I used the tops, I was struck by how slippery the painted surface was, and how challenging it was to get a secure purchase – with or without gloves.
My bike was provided fully assembled, but BMC dealers have informed me bar tape is installed at the shop, not the factory, and there’s plenty of tape to wrap the bars normally. I know it doesn’t look as cool, but when you consider the primary function of a handlebar is to provide somewhere to securely put your hands, I’d strongly recommend going that route.
An intriguing beast
BMC historically has few qualms about rocking the boat and the Kaius is yet another example of that, combining the low weight, high stiffness, and moderate aerodynamic performance of a modern do-it-all carbon fiber road racer, but with excellent tire clearance and daringly progressive frame geometry.
It’s eye-wateringly expensive and that whole bar-stem business is just so polarizing, but if you can tolerate the quirks (and stomach the cost), this is one heck of a good time.
More information can be found at www.bmc-switzerland.com.
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