Kellys Theos F90 E-MTB first ride review – Is this carbon revolution?

While carbon has long become the material of choice for many mountain bikers, it also has its disadvantages. With the innovative Feather steel-carbon composite material, Slovakian brand Kellys wants to exploit all the advantages of the black gold while at the same time minimizing its disadvantages. We tested the Kellys THEOS F90 eMTB with Shimano EP8 motor and 725 Wh battery.

We’ve already presented the THEOS in this exclusive announcement almost two years ago. Now the bike has finally made it to our office, straight from Kellys’ HQ in Slovakia. With their new THEOS, which means “god” in ancient Greek, Kellys want to appeal to the sporty gravity rider who’s looking for an indestructible, long-travel mullet eMTB for demanding trails but, at the same time, doesn’t want to renounce the perks of carbon such as the harmonious frame lines and a low system weight.

The Kellys THEOS F90 in detail

The Kellys THEOS relies on a Shimano EP8 motor and 725 Wh battery, which is permanently integrated in the downtube, protected by a generously-sized TPU plate and can be removed from the bottom of the downtube. The motor is tilted by approx. 45° and neatly integrated into the frame, which at first glance, looks a lot like a conventional carbon frame with its harmonious lines. However, the Slovakians employ a thermoplastic steel-carbon composite material a.k.a Feather, which was developed in close cooperation with Belgian tech company REIN4CED. What makes Feather so unique is that the carbon is reinforced with micro steel fibres, which are claimed to distribute forces more evenly and over a larger area in the event of a crash or impact and thus prevent delamination or cracks. As a result, the frame should be more impact-resistant and more durable compared to a conventional carbon frame – and without additional weight penalties! Despite the big battery and robust components, the THEOS tilts our scales at a very reasonable 23 kg (size L). However, unlike its name suggests, it’s not exactly a featherweight, but still one of the lighter bikes in its category.

The frame has a sporty silhouette, which the Slovakians combine with a moto-style swingarm. The top tube runs parallel to the shock and merges seamlessly into the seat stays, ensuring a clean and modern look together with the asymmetric shock mount. Unfortunately, the harmonious frame lines are spoiled by the cluttered cockpit. This is mainly due to the countless cables, which aren’t arranged as neatly as the rest of the motor system. The brake lines and dropper post remote cable disappear into the head tube and run straight into the frame. However, these aren’t clamped at the ports properly and held in place by flimsy rubber inserts, which dislodge from the ports very easily. The Acros headset with integrated BlockLock limits the steering angle and thus prevents the fork from hitting and damaging the frame.

The spec of the Kellys THEOS F90 in detail

Like all THEOS models, the Kellys THEOS F90 flagship model relies on a mullet wheel setup with a 29” wheel at the front and smaller 27.5” wheel at the rear. Our top-spec test bike retails for €8,999. Unlike most brands, Kellys pair suspension components from different manufacturers, combining a FOX 38 Factory fork and RockShox Super Deluxe Ultimate shock that control 180/170 mm travel at the front and rear, respectively. The fork’s high-quality GRIP2 damper provides four-way adjustability with high- and low-speed control both for the rebound and compression circuit. The air shock offers low-speed rebound and compression adjustments and features a two-stage lockout lever for the climbs. That being said, we never had to reach for the climb switch. While our test bike comes with a 150 mm FOX Transfer Factory dropper post, the production bike will be delivered with its long-travel 175 mm counterpart, which should improve freedom of movement.

An electronic Shimano XT-Di2 drivetrain ensures precise and reliable shifting and runs on a cheaper 11-speed 11–46T SLX cassette. Shimano XT four-piston brakes with big 203 mm ice tech rotors front and rear do stopping duties. The braking torque is transferred to the ground by aggressively-profiled Schwalbe tires, with a 2.4” Schwalbe Magic Mary at the front and 2.6” Hans Dampf at the rear – both in the Super Trail casing. The front tire employs the soft and grippy ADDIX Soft rubber compound while the rear relies on a harder rubber compound for lower rolling resistance. The tires are paired with a robust DT Swiss H1700 Hybrid alloy wheelset.

More Kellys THEOS spec variants

The THEOS range consists of 3 models – we tested the THEOS F90 flagship model. If you’re looking for a more affordable bike, you should take a closer look at the THEOS F70 and F50, which retail for €7,299 and €5,499, respectively. The F70 mid-range model comes with a very reasonable spec, including a Shimano XT-12-speed drivetrain, RockShox Zeb Charger R fork and RockShox Coil Select R coil shock. The F50 entry-level model is the best option for the price-conscious eMTBer and offers slightly less travel, combining 150/140 mm travel, at the front and rear. Moreover, it features a cheaper Shimano Deore 10-speed drivetrain and basic RockShox 35 Gold RL fork, which offers hardly any adjustment options.

The geometry of the Kellys THEOS F90

The Kellys THEOS F90 is only available in 2 sizes, M and L, offering a suitable option only for riders between 168 to 200 cm tall. The relatively steep 76° seat angle positions the rider centrally on the bike. Although the short 430 mm seat tube (size L) suggests plenty of freedom of movement, the 150 mm dropper post of our test bike restricts this significantly. The 459 mm chainstays are pretty long for a bike with a small 27.5″ rear wheel but don’t have a negative effect on the riding behaviour of the bike.

Size	M	L
Top tube	617 mm	643 mm
Seat tube	400 mm	430 mm
Head tube	105 mm	120 mm
Head angle	64.5°	64.5°
Seat angle	76°	76°
Chainstay	459 mm	459 mm
BB Drop	12 mm	12 mm
Wheelbase	1.269 mm	1.298 mm
Reach	463 mm	482 mm
Stack	619 mm	638 mm

The Kellys THEOS F90 on the trail

The pedalling position is comfortable and upright and puts hardly any pressure on your hands, making the THEOS F90 a comfortable touring companion. Uphill, the THEOS displays excellent climbing qualities, allowing you to negotiate even steeper climbs without having to actively weight the front wheel. When negotiating technical climbs, the rear suspension swallows small impacts and offers decent traction, even with the shock in “open” mode.

When gravity takes over, the THEOS integrates its rider you nicely between its wheels. The weight is evenly distributed between the front and rear wheel, allowing you to generate traction, even through open corners on loose terrain. Even on narrow trails, the Kelly responds to steering input willingly, making it easy to negotiate tight switchbacks. The rear suspension offers good support and allows you to pop off ledges without too much effort, contributing to the agile character of the bike. Despite this liveliness, the Kellys always feels composed, allowing you to commit to your line without too much effort, even in technical sections. Should the trail suddenly slope up, forcing you to drop a few gears in a hurry, it may take a while to find the shifter, because it’s positioned too far from the grip. On steep descents, the 150 mm dropper post restricts freedom of movement. The innovative Feather frame made it through this test without drama and did exactly what it’s supposed to do, withstanding all the knocks and stresses of an in-depth testing session and making it back to our headquarters unscathed. That being said, we can’t tell you whether it’s strong enough to survive more extreme situations, like a nasty crash in a rock garden – luckily, we didn’t have to find out for ourselves!

The Kellys THEOS F90 – our conclusions

The Kellys THEOS F90 has a comfortable riding position that makes it suitable for extensive trail tours. Downhill, it impresses with lively handling and good composure. The weight is evenly distributed between the wheels, allowing you to generate good traction through fast, open corners. The team at Kellys has designed a visual eye-catcher out of the Feather material. Only a long-term test will reveal what the pros and cons of the innovative steel-carbon composite material are.

For more information, please visit the Kellys website.

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Words: Mike Hunger Photos: Robin Schmitt