New FLYER Uproc SL:X on test – The swiss clock amongst Light eMTBs?

With the new FLYER Uproc SL:X, the Swiss bike manufacturer takes the plunge into the light eMTB segment. The Uproc SL:X introduces itself to the world with some promising stats: 130 mm of travel (f/r), 29″ wheels and a Bosch Performance Line SX motor paired with a 400 Wh battery. FLYER’s very first light eMTB wants to impress above all with a natural ride feeling – but how does it fare in real life?

The Uproc range has long been an integral part of FLYER’s portfolio. At the beginning of the year, the Swiss manufacturer launched the FLYER Uproc X, a full-fat eMTB with a powerful Bosch Performance Line CX motor, that took part in our huge 2024 e-mountainbike comparison test. The Uproc X is now being complemented by the brand’s very first light eMTB, the Uproc SL:X, which generates 130 mm of travel (f/r) – 20 mm less than its full-power counterpart. It rolls on 29″ wheels and comes equipped with a Bosch Performance Line SX motor, which delivers up to 55 Nm of torque and draws its power from a 400 Wh battery. All of this is built around a carbon frame. The 8.70 variant we tested tips the scales at XX kg and is expected to retail for € 7,499. The Uproc SL:X was designed to deliver a natural ride feeling and deliver tons of fun with its agile handling.

The FLYER Uproc SL:X in detail

The FLYER Uproc SL:X relies on a rectilinear, sharp-edged frame silhouette, with the shock transitioning seamlessly into the flexible seat stays. These are designed to offer more compliance and essentially replace a pivot point in the chainstays, saving weight and minimising the bike’s overall complexity. FLYER swim against the current, routing the cables through conventional cable ports in the frame rather than through the headset, which makes it far easier to service your bike.

The full carbon frame comes in a stylish silver paint finish, and the more vulnerable areas are covered with protective film. A generously sized seat and chainstay protector prevents chain slap and paint chips, while a rubber flap between the main frame and swingarm prevents small rocks from getting stuck in the gap. Other clever details include an integrated multi-tool in the headset (included on the 8.70 and 9.50 variants) and a stem-mounted MonkeyLink interface, which allows you to clip on a light that draws its power directly from the bike’s main battery.

The Bosch Performance Line SX motor is neatly integrated into the carbon frame and fully enclosed in a plastic cover. It delivers 55 Nm of torque with 600 W of peak power, and draws its power from a 400 Wh battery, which is permanently integrated into the down tube.

However, this means that you’ll have to schlepp the bike into your flat or house if you don’t have a plug socket in your garage – or a garage at all. That said, the charging port just above the motor is easily accessible and feels good to use. For more range, you can expand the battery with Bosch’s 250 W PowerMore Range Extender, which comes standard with the more expensive 8.70 and 9.50 spec variants. Whether you pay for it or not, the range extender can be secured to the bottle cage mounts, which means that you’ll have to carry your water bottle in a hip pack or backpack if you need the extra power.

The wireless Bosch Mini Remote and minimalist Bosch System Controller are a popular choice for sporty eMTBs. They only show basic riding data, but this is perfectly fine and matches the sporty orientation and clean look of the FLYER Uproc SL:X. If you need more information while riding, you can connect your bike with the Bosch eBike Flow app via a smartphone.

The spec of our FLYER Uproc SL:X test bike

For this review, we tested the FLYER Uproc SL:X 8.70 variant, which comes equipped with a 34 mm FOX Performance fork and matching FOX FLOAT Performance air shock. However, neither of the suspension components can keep up with their top-tier Factory counterparts.

Shifting is taken care of by a cable operated Shimano XT drivetrain, which has long been a popular choice thanks to its smooth, precise shifting. Shimano also supply the four-piston Shimano XT brakes and 200 mm rotors, which provide powerful and reliable deceleration, even on long descents.

A brand-new OneUp V3 dropper post offers 180 mm travel in size L, ensuring sufficient freedom of movement on the trail. The cockpit consists of a Satori Ursa stem and Hayes ProTaper carbon handlebars in a whopping 810 mm width. For the wheels, FLYER combine a DT Swiss HX 1700 LS alloy wheelset with shallow-profiled Schwalbe Wicked Will tires, both in the hard Speedgrip rubber compound and puncture-prone Super Ground casing. We definitely recommend upgrading the tires to a more aggressive model like the Schwalbe Nobby Nic – and while you’re at it, go for the more robust Trail casing and grippier Soft rubber compound.

Tuning tip: tire with a more robust casing and aggressive profile

All spec variants of the FLYER Uproc SL:X

The FLYER Uproc SL:X is available in four different spec variants, 4.10, 6.50, 8.70 and 9.50, all of which come standard with 29″ wheels and a Bosch Performance Line SX motor with a 400 Wh battery. The FLYER Uproc SL:X 4.10 entry-level model retails at € 5,799, for which you’ll get X-Fusion suspension and TRP Slate Evo brakes. Shifting is taken care of by a 12-speed Shimano DEORE drivetrain. Retailing at € 6,999, the Uproc SL:X 6.50 comes equipped with a FOX 34 Rhythm fork, FOX FLOAT Performance air shock and a robust, electronic SRAM GX Eagle Transmission groupset, which delivers the same outstanding performance on the trail as its top-tier XX Eagle Transmission counterpart. The FLYER Uproc SL:X 9.50 flagship model sets you back € 9,999 and features a prestigious, high-quality spec, including a bling SRAM XX Eagle Transmission drivetrain and fancy FOX Factory suspension. The Uproc SL:X 9.50 flagship model is also the only one to come standard with a DT Swiss HXC 1501 carbon wheelset.

The geometry of the FLYER Uproc SL:X

The FLYER Uproc SL:X is available in 4 sizes, S to XL, offering a suitable choice for riders between 155 and 195 cm tall. Overall, FLYER’s very first light eMTB relies on a moderate geometry. Our test bike in size L combines 485 mm reach and a 65° head angle, which is neither particularly slack, nor particularly steep. At 440 mm, the seat tube is on the short side and, together with the 180 mm dropper post, ensures sufficient freedom of movement. Chainstay length is 453 mm across all frame sizes. A flip-chip on the shock mount allows you to switch between a low and high setting. When set to low, the head angle is slightly slacker and the bottom bracket lower.

Size	S	M	L	XL
Top tube	571 mm	605 mm	629 mm	664 mm
Seat tube	380 mm	400 mm	440 mm	480 mm
Head tube	100 mm	110 mm	125 mm	135 mm
Head angle	65°	65°	65°	65°
Seat angle	77.3°	77.1°	77°	76.8°
Chainstay	453 mm	453 mm	453 mm	453 mm
BB Drop	38 mm	38 mm	38 mm	38 mm
Wheelbase	1,199 mm	1,234 mm	1,258 mm	1,294 mm
Reach	435 mm	465 mm	485 mm	515 mm
Stack	605 mm	614 mm	623 mm	637 mm

What is the FLYERFlyer Uproc SL:X capable of on the trail?

As soon as you swing your leg over the saddle, the FLYER Uproc SL:X places you in a compact yet comfortable pedalling position, which is gentle on your back even after a long day in the saddle. When cruising on level ground, there’s a slight pressure on your hands, but this comes in handy as soon as the gradient steepens, as it helps to keep the front wheel planted. The Bosch Performance Line SX motor packs a punch, pushing significantly harder than other light motors in the strongest support level, making it easy to negotiate even steep climbs – provided the terrain is dry and grippy. In wet conditions, the firm rear suspension and shallow profiled tires generate poor traction and struggle to transfer the motor power to the ground.

When you drop into a trail to shred your way back down into the valley, you’re nicely integrated with the bike. The weight is evenly distributed between the front and rear wheel, meaning that you don’t have to actively weight the handlebars to keep the front wheel tracking, even in fast, open corners. The Flyer Uproc SL:X is particularly fun to ride on flowing trails, where the firm suspension allows you to generate speed by pumping through rollers and berms. However, the rougher the trail gets, the more demanding the FLYER becomes, requiring good riding skills and a cautious, proactive riding style. The firm suspension passes on feedback to the rider almost unfiltered, requiring a high level of concentration from inexperienced riders. The nimble, agile handling, on the other hand, encourages experienced riders to play with the terrain and makes it easy for them to spontaneously change their line. This all goes out of the window in wet conditions, however – the shallow profiled tires quickly reach their limits, at which point you become more of a passenger than a pilot. If you spend most of your time on technical trails, you should upgrade to more aggressive tires with a more robust casing and softer rubber compound.

Who should take a closer look at the FLYER Uproc SL:X?

The FLYER Uproc SL:X is a good match above all for sporty riders who want an agile trail bike with motor support. On dry, flowing trails, it slaps a massive grin on your face, regardless of whether you’re a newbie or a seasoned trail warrior. If you spend most of your time on technical trails, you should have a good level of riding skills to ride the FLYER Uproc SL:X!

Our conclusions about the FLYER Uproc SL:X

The new FLYER Uproc SL:X Light-E-MTB looks stylish and features some very clever details, like the integrated multitool in the head tube and standard protective film. It shows its strengths on the ascents, especially on steep climbs that aren’t too technical. Downhill, it’s particularly impressive on flowing trails, where it slaps a massive grin on your face. When the going gets rougher, however, it requires an experienced rider to keep it in check.

For more information, visit flyer-bikes.com

---

Did you enjoy this article? If so, we would be stoked if you decide to support us with a monthly contribution. By becoming a supporter of E-MOUNTAINBIKE, you will help secure a sustainable future for high-quality cycling journalism. Click here to learn more.

Words: Mike Hunger Photos: Mike Hunger, Hersteller