Kelly’s Theos AX with Avinox: A high-performance enduro bike with a removable battery, from 3,999 euros

Opinion of the BIKE editorial team

Kellys is also jumping on the Avinox bandwagon, and the Slovaks are too, focusing on the lower price range. The entry-level model, priced at 3,999 euros, is exceptionally well-equipped for trail riding. Only a practical test will reveal just how well the bike really performs off-road. The move towards robust, affordable e-MTBs is certainly good news for e-mountain bikers.

Slovakian bicycle manufacturer Kellys is significantly expanding its e-bike range for the 2027 model year: with the Theos AX, the brand is announcing a completely new platform for the electric mountain bike sector – featuring the highly anticipated Avinox drive. Until now, the manufacturer had equipped its e-MTBs with motors from Shimano and Panasonic, amongst others. Four models will be launched at the same time, covering a price range from just under 4,000 to over 6,000 euros. The new bikes are set to go on sale from January 2027.

Two engines, one platform

The Avinox system is available in two versions at Kellys. The top-of-the-range model, the Theos AX 90, comes with the Avinox M2S motor (reviewed here), which delivers 130 Nm of torque in normal operation – in Boost mode, it even reaches up to 150 Nm – and a peak power output of 1,500 watts. Weighing around 2.6 kilograms, it remains comparatively light and compact. The three other models in the range – the AX 70, AX 40 and AX 20 – are equipped with the slightly less powerful Avinox M2 engine equipped with a motor that delivers up to 110 Nm (125 Nm in boost mode) and 1,100 watts of peak power.

The facts about Kelly’s Theos AX

• Motor: Avinox M2S or M2
• Battery: 800 Wh, removable
• Frame material: aluminium
• Suspension travel: 170/160 mm
• Wheel size: 29 inches
• Frame sizes: S, M, L – the top-of-the-range model is also available in XL

Battery: removable and fast-charging

The power source is an 800 Wh battery, which is fully integrated into the frame but can be removed at any time – both for external charging and for replacement. Weighing around four kilograms, the battery is slightly heavier than the permanently fitted version.

The fast-charging function is particularly noteworthy: the 508-watt charger (12 amps) specified for the AX 90 is said to be capable of charging the battery from zero to 75 per cent in 1.5 hours. The other models, however, are supplied ex-works with the slower 168-watt charger (4 amps).

Frame and chassis

All four models share the same frame design: an aluminium frame with a Horst-Link four-bar rear suspension system and 160 mm of travel, combined with a 170 mm fork, forms the backbone of the platform. The wheels are 29 inches in diameter and can accommodate tyres up to 2.6 inches wide. The bike is available in four frame sizes (S to XL) with integrated cable routing and a UDH dropout for compatibility with the latest SRAM rear derailleurs.

Four models, from 3,999 euros

With four trim levels, the range covers a wide price bracket. The top-of-the-range model, the Theos AX 90, costs 6,299 euros and combines the M2S motor with the DP100 display, a RockShox ZEB Ultimate suspension fork and the wireless SRAM GX Eagle AXS rear derailleur. The latter features a Smart Torque-Cut function, which briefly interrupts the motor’s torque during gear changes to protect the chain and cassette.

The Theos AX 70, priced at 5,299 euros, switches to the M2 motor and the DPC100 display, as well as a RockShox ZEB Select fork, but also retains a wireless SRAM Eagle AXS rear derailleur. The AX 40 (€4,399) does away with wireless transmission and instead features a Shimano Deore XT groupset combined with the ZEB Select fork. The entry-level model, the Theos AX 20, is available for €3,999. It features a RockShox Domain suspension fork and Shimano CUES groupset. All models are fitted with 200 mm Galfer brake discs across the range; depending on the model, the brake calipers are from the Shimano XT or Deore range.

Classification and availability

Kellys Bicycles is kicking off its 2027 model launch with the Theos AX. The new bikes are set to go on sale from January 2027. With the AX models, Kellys is expanding its portfolio to include a clearly performance-oriented platform, which is set to exist alongside the Panasonic AMXXPRO range. The broad model range, featuring four price tiers, suggests that the brand is positioning the new system as a long-term platform – rather than merely as a niche offering for the high-end segment.