Light, sexy, and sporty? The Bosch SX powered FLYER Upstreet SL 3.63 city ebike in review

FLYER present a new addition to their portfolio, the FLYER Upstreet SL. But what does the abbreviation SL mean? Does it stand for “Super Light”, “Street Legal” or “So Long”? We put the FLYER Upstreet SL 3.63 through the wringer and found out what it’s all about.

Premium Swiss brand FLYER lovingly refer to their latest family member as an Urban Lightweight, expanding their long-standing urban range with the Upstreet SL 3.63. We’ve already tested the s-pedelec and 20″ wheel versions of FLYER’s city bikes, and the Upstreet 7.10 even got a 2023 Design and Innovation Award. The new Upstreet SL is intended to close a gap in their urban offering. FLYER position the Upstreet SL 3.63 as a sporty city ebike that is made for zipping about, promising everyday usability and modern design. In terms of weight and versatility, the Upstreet SL even surpasses its award-winning predecessor.

In size XL, the model on test tips the scales at just 18 kg, which is a whopping 10 kg lighter than the lauded Upstreet 7.10, and it’s available for € 5,899. For this price, you get some state-of-the-art components, like Bosch’s latest compact SX motor, and a 2-speed Classified POWERSHIFT hub, more commonly found on high-end road bikes. Thanks to the smooth tires and a carbon fork, the Upstreet SL 3.63 looks a bit like a gravel bike. But you’ll have to read on to find out whether the light ebike also performs like a gravel bike in practice, and whether the “Urban Lightweight” title does it justice.

What sets this bike apart?

The FLYER Upstreet SL 3.63 boasts a modern design, and an elegant aluminium frame with distinctive, rectangular tubing. Although some of the weld seams look a little rough, like on the down tube, they don’t significantly detract from the overall picture. That said, the seam on the head tube could’ve been sanded down for a sleeker, more seamless look. The carbon fork was developed in-house by FLYER, and is simply referred to as Rigid Fork. The rather beefy looking FLYER ONE Carbon Cockpit SL is made of the same material. Evidently, FLYER deliberately specced weight-saving components made of carbon, which you would usually see on more race-oriented bikes. As mentioned above, this gives the urban ebike more of a road or gravel bike feel, emphasising the sporty character of the Upstreet SL 3.63.

Compact powerhouse – The Bosch Performance Line SX motor in the FLYER Upstreet SL 3.63 in detail

For the motor on the Upstreet SL 3.63, FLYER rely on the compact Bosch Performance Line SX drive unit, capable of assisting the rider with up to 55 Nm of torque, and cutting out at 25 km/h. Due to its weight, the still relatively new Bosch motor, which we’ve already taken a detailed look at in our big motor group test, is a popular choice for light eMTBs, though it also features in urban, gravel, and city ebikes. Looking at the motor, you will immediately notice the custom cover, which allows for top notch integration. As such, the motor blends seamlessly with the urban ebike’s frame. The sleek integration of the system doesn’t stop at the cockpit either. FLYER dispense with a conventional display on the Upstreet SL, relying on the Bosch System Controller in the top tube and the mini Remote instead. The wireless Bluetooth remote reduces the number of cables needed, which further optimises the bike’s overall look and functionality. Speaking of which, the cable routing on the FLYER Upstreet SL 3.63 is super clean and simple. Both brake hoses enter the frame via the headset and only re-emerge from the carbon fork and aluminium rear end where they’re needed. The cable of FLYER ONE HL-2 LED headlight also disappears discreetly into the headset, providing the necessary visibility with a 100 lux output and an automatic daytime running function. Incredibly neat and tidy cable routing!

The motor is powered by the 400 Wh Bosch Compact Tube 400 battery, which is integrated into the down tube of the Upstreet SL 3.63. As usual with FLYER, you can easily remove the battery via the side of the down tube. Therefore, the bottle cage bosses remain in place, which double as a mounting point for the optional range extender. The Bosch PowerMore 250 Range Extender ups the total battery capacity to 650 Wh, which should minimise range anxiety and increase the possible range significantly. Nice!
Thanks to a magnet on the valve of the rear wheel, the system can sense the speed without having to run a sensor to the brake rotor or the spokes.

The components of the FLYER Upstreet SL 3.63

The FLYER Upstreet SL 3.63 doesn’t have a lot of bells and whistles, focusing instead on the essentials. This is evident when looking at the drivetrain. Here, the urban ebike relies on a 2-speed Classified POWERSHIFT hub, which we’ve previously reviewed on a gravel bike in our sister magazine GRAN FONDO. As such, the drivetrain of the FLYER Upstreet SL 3.63 initially looks like a simple single-speed system with an ambitiously large chainring. However, the tech is hidden inside the hub and allows for a choice of two gears: one with a 1:1 ratio (so the sprocket rotates at the same speed as the hub body, as with a normal hub) and one with a 1:0.686 ratio (the sprocket rotates at a higher speed than the hub body, providing a lighter gear), making easier work of the climbs. Thereby, the geared hub combines the simplicity and ease of maintenance of a single speed drivetrain with the benefit of an extra gear, underlining the bike’s clean look and keeping the gears sealed from the elements. The hub is controlled via the Smart Thru Axle, which transmits the shifting signal wirelessly. To avoid the annoying lubrication, cleaning, and maintenance of a conventional chain, FLYER rely on a GATES CARBON DRIVE belt, which suits the bike’s minimalist, low-maintenance approach. The 700c wheels are fitted with Vittoria Terreno Zero Classic Skin tires. To keep your speed in check, you’ve got TEKTRO T280 brakes with a 180 mm rotor up front and a 160 mm model at the rear. To arm the urban ebike for city traffic and everyday life, the FLYER Upstreet SL 3.63 also comes equipped with a bell, Hebie IC kickstand, and a Lezyne Fender tail light to match the FLYER ONE HL-2 headlight. The 60 mm wide Curana fenders round off the overall package.

Model variants of the FLYER Upstreet SL

The FLYER Upstreet SL is available in two frame variants: a step-through version with a dropped top tube, and a classic diamond frame variant with a high top tube for sporty riders. Both are available in sizes S, M, L and XL. The most affordable model, the € 3,999 FLYER Upstreet SL 3.12 XC, relies on slightly different components, like a chain and derailleur based drivetrain, and it has to make do without a rack. True to the motto, “less is more”. You can also get the € 4,199 FLYER Upstreet SL 3.10 for € 200 more, which also uses a chain and derailleur, though it has a rack for improved everyday convenience.

Size	S	M	L	XL
Seat tube	440 mm	480 mm	520 mm	580 mm
Top tube	549 mm	576 mm	599 mm	617 mm
Head tube	154 mm	180 mm	207 mm	239 mm
Head angle	70°	70°	70°	70°
Seat angle	74°	74°	74°	74°
Chainstays	460 mm	460 mm	460 mm	460 mm
BB Drop	89 mm	89 mm	89 mm	89 mm
Wheelbase	1.078 mm	1.107 mm	1.131 mm	1.152 mm
Reach	380 mm	400 mm	415 mm	425 mm
Stack	590 mm	615 mm	640 mm	670 mm

What is the FLYER Upstreet SL 3.63 capable of?

What’s the use of sporty styling if the urban ebike hasn’t got the performance to match? That’s why we took it to the urban jungle and rode it along the asphalt and cobbled streets of Stuttgart, putting the brand’s promise to the test. The FLYER Upstreet SL 3.63 had a noticeably firm ride over cobblestones, since the Selle Royal Vivo saddle can only absorb small bumps, and the bike has trouble mitigating bigger impacts. That said, the urban ebike is still a lot of fun to ride, encouraging you to dart around obstacles. Quickly shoot through that gap in traffic? No problem! The motor rewards an active, high-cadence riding style with a lot of power, and you’ll find yourself drag racing against other cyclists at the traffic lights. When pedalling at a high cadence in Sprint mode, the motor can put out up to 600 watts, and the torque briefly goes up from 40 to 55 Nm.

However, the Bosch Performance Line SX doesn’t sound like it’s revving high, as the motor and the bike remain pleasantly quiet throughout. Despite its compact size and low weight, the Bosch motor provides the FLYER Upstreet SL 3.63 with powerful thrust. In our “Urban Hero” piece, we took a closer look at the advantages of the Bosch Performance Line SX motor for urban riders. You can read all about them here.

On steep inclines, however, the motor is brought to its knees, which is due to the limited gear range of the 2-speed Classified POWERSHIFT hub. The 2-speed hub serves as a reliable partner on flat terrain, enhancing the bike’s sporty feel by shifting gears almost instantly. Shifting under load also works flawlessly, and provides a pleasant riding experience. That said, the geared hub’s limits become noticeable the moment you enter hilly terrain. Even the easier gear isn’t designed for steep climbs, so you might just have to push, unless you have the legs of Lance Armstrong. If the FLYER dealer hasn’t already done this for you, the initial setup of the Classified POWERSHIFT hub is somewhat cumbersome. Once configured, however, the geared hub’s ease of use underpins the entire bike’s user friendliness, giving it a hop-on hop-off feel.

The concept of the motor harmonises well with the concept of the bike. Just as the motor demands a little more input from the rider before unleashing its full performance, the handling of the Upstreet SL is also rather demanding. Instead of gliding through the city with great composure and predictability, the Upstreet SL responds very directly to steering input, almost making it feel nervous. Manoeuvring it through narrow city streets at high speeds requires a steady hand with surgical precision. Beginners are advised to scrub off some speed before hitting the corners.

In city traffic, the integrated head and tail lights provide enough visibility to use the ebike safely even at night. We particularly like the daytime running LEDs, which help keep you visible during the day. When the weather takes a turn for the worse, the Curana fenders provide plenty of splash protection as they extend far down around the tires. However, the 1.7″ wide Vittoria Terreno Zero Classic Skin tires can be a little unnerving when crossing railway tracks or drain covers, and the slick tread offers little grip. However, the smooth, fast rolling tires allow the city ebike to get up to speed with ease, and suit its responsive handling.

The everyday accessories on the FLYER Upstreet SL 3.63 are discreet: clean, minimalistic, and tidy. At first glance, the urban ebike may not seem that practical for everyday use, but the Bosch Smart System offers many useful features. Thanks to the integrated eBike Lock, consisting of a mechanical lock housed in the motor, you can rest assured that your bike is safe while taking in the views or enjoying some refreshments. To avoid getting lost in city traffic, you can pair your smartphone with the Bosch eBike Flow app and use it for onboard navigation. It’s not often we find an urban bike with a rattle-free stand, but this problem has been addressed on the FLYER Upstreet SL 3.63 with the Hebie IC kickstand. Nice!

To round off the everyday accessories, the Swiss brand include a rear luggage rack with a maximum capacity of 15 kg, sourced in-house and made of steel. With the capacity of the rack fully exhausted, the FLYER’s handling doesn’t seem to be affected, though the acceleration feels significantly slower when pulling away at the traffic lights, almost doubling the weight of the 18 Kg bike.

Who is the FLYER Upstreet SL 3.63 for?

The FLYER Upstreet SL is aimed at riders who prefer speed and agility to comfort. If you’re generally pressed for time and looking to commute in style, the Upstreet SL 3.63 is the bike for you. The lightweight aluminium frame and carbon components result in a lively and fun bike. However, the Upstreet SL 3.63 doesn’t make longer journeys all that enjoyable. The lack of comfort, and the limited gear range of the 2-speed reserve this bike for zipping around the city. However, hip urbanites with a penchant for design will find a reliable and low-maintenance companion for the urban jungle.

According to our review, the SL in the name could stand for “Stealth Lightning” or “Stylish Lightweight”, but it definitely doesn’t stand for “Suspended Locomotion” considering the urban ebike’s lack of compliance. The FLYER Upstreet SL 3.63 might look like a gravel bike, but it’s best kept on the road with its semi slick tires. Despite the hefty price point, the value for money is reasonable if you take the overall spec and build quality into account.

Tuning-Tipp: For city dwellers without sporting ambitions: none
– However, if you live in a hilly area, you should go for the 3.10 model with a derailleur, offering a wider gear range.

For more info, visit flyer-bikes.com

Words: Benedikt Schmidt Photos: Antonia Feder