i:SY SKYFLY E5 ZR F

Back in 2020, I began my Cube Compact Hybrid review with the line, “Just in case you haven’t heard about compacts…” reflecting the relative novelty of such a design at that time. Six years later, we have a host of small-framed, large-tyred, 20in-wheeled e-bikes featuring non-folding frames but sideways turning handlebars and folding pedals for easy storage. The i:SY Skyfly E5 ZR F is one of the more advanced – and also one of the priciest.

Whilst it looks remarkably similar to the aforementioned Cube, the Skyfly employs more up to date tech, such as a carbon frame, a lightweight Bosch Performance Line SX motor and dual beam front lights. This results in a high-end, premium-priced take on what is becoming an increasingly congested corner of the market.

i:SY is a German firm and appears to have set itself the mission of offering a bewildering array of compact mid-drive options, alongside a handful of other designs, including some very innovative looking e-cargo designs.

The Skyfly E5 ZR F is billed as, “the lightest i:SY ever,” with a claimed weight of, “considerably less than 20kg.”

On my scales, the loan model came in at 21.1kg – though it did feature an optional front rack with Klick-Fix attachment, so perhaps it does weigh less than 20kg… just.

As you might expect on an e-bike making lightweight claims, i:SY has opted for Bosch’s lightest mid-drive, the Performance Line SX, which weights around 2kg or so – roughly 800g less than the latest and most powerful Bosch mid-drive, the Performance Line CX (Gen 5).

Of course that lighter weight comes with a comparative performance penalty. The SX is rated at 60Nm max torque and 600W max power, whilst the CX has a peak power rating of 750W and offers an incredible peak torque of 120Nm.

In most circumstances, this wasn’t really a limitation for me, but I’ll cover the more extreme conditions where the motor (and gearing) did fall short a little. Suffice to say on a bike like this – built for urban chores, commuting and leisure rides, and kept as light as possible to aid portability – the SX is a spot-on choice.

It looks both a beautifully finished and practically designed e-bike. The oversize carbon frame – like so many e-bike frames these days – looks like it has leapt off a CAD designer’s computer screen and into the real world.

As luck would have it, I had an older Cube Compact model to hand to compare both bikes. Whilst the designs are strikingly similar, the Skyfly has a carbon frame against the Cube’s aluminium alloy and its geometry is a little steeper, but other than that they look almost identical. That’s good – it’s a small yet extremely strong and simple design that is well on the way to becoming an e-bike classic.

Other elements are similar too: a removable Bosch battery tucked behind the seatpost, hardwired front and rear lights (the positioning is different but works well on both), full length mudguards (much sturdier on the Skyfly), a sturdy rear rack and optional front one, a kickstand, and – a highlight for me – grippy, balloon-style Schwalbe Supermoto 20in x 2.4in tyres. The only notable difference was the Gates CDC Carbon belt drive transmission on the Skyfly and the presence of a chainguard.

The Skyfly of course uses Bosch’s most up to date mid-drive architecture in the form of the Smart System. This is more about software than hardware and allows for features like electronic locking and over-the-air updates, though there is a limited amount of actual performance upgrading too, in terms of increased torque and other performance metrics on newer compatible mid-drive motors. It also features a zappy and very easy to read large format removable Kiox 500 display.

However, when it comes to the basic design tenets of this compact model, i:SY has clearly stuck with the old maxim, if it ain’t broke, don’t fix it.

The ride

I was surprised at how comfy and stable the ride felt for such a small and relatively light bike – certainly it is a step up in terms of smooth handling compared to smaller wheeled bikes like the Brompton and even compared to some other 20in wheeled models. The latter fact may be down to a combination of those huge 2.4in wide tyres and the frame geometry.

The Performance Line SX is a great little motor – smooth and responsive yet lightweight for a mid-drive, it suits the quick manoeuvrability of the Skyfly perfectly. Its performance measurements (60Nm torque and 600W peak power) compare favourably to the 50Nm and 600W offered by the 2020 Cube’s older Active Line Plus motor given that it is considerably lighter.

I wouldn’t be surprised to see Active Line motors phased out completely in favour of the much newer and smoother performing SX.

The e-bike specific Shimano Nexus 5-speed is one of my favourite hub gear systems, providing reliable and easy twist grip shifting. My only quibble was that the gearing on the Skyfly was too high for really steep climbs. It struggled up my regular ultra-steep test climb and I had a feeling the motor would have helped me up far more easily in a lower gear.

I tested the Skyfly mainly over rolling terrain, as I was away from my regular super hilly Pennine scenery recently, and I found using the lower two levels on the Skyfly that 50 miles was possible. I reckon if I loaded it up and took it around my usual hillier haunts, 25-35 miles would have been more realistic.

The Schwalbe Supermoto tyres are fast and grippy on tarmac and very comfortable. With the tyre pressure dropped a little, they made passable off-road tyres too, allowing me to explore good quality bridleways and the like.

The 2.4in width of the tyres combined with some super plush ergonomic grips to give a really comfortable ride and the fact that the Schulz Speedlifter gives tons of quick-release handlebar height adjustment means that comfort can be enhanced according to your height and reach. i:SY says the one size frame should fit riders from 1.5-1.85m. The firm also manufactures XXL compact models for much larger riders.

Weight and portability were very slightly disappointing. While the bike came in a couple of kilos more than promised on the website, this was still superior to many other similar models thanks to that carbon frame and relatively small mid-drive.

The strengthening bar between down tube and seat tube was a little bigger than some aluminium alloy designs, which made it a little harder to grip one handed. Still, it’s a tremendously portable and storable design thanks largely to the quick and easy Schulz Speedlifter stem that allows you to turn the bars sideways in a jiffy.

The fact the pedals fold too mean it’s easy enough for an averagely fit and strong person to lift this bike up a small flight of steps and store it out of the way, even in most apartments.

The rear rack is rated to carry up to a hefty 27kg and apparently uses a ‘click and go’ type technology called Monkeyload for compatible accessories. Whilst this looks very capable, it’s a pity it is not MIK-HD ready as that seems to be rapidly becoming the standard ‘click and go’ system for heavy duty carrying, in Europe at least.

There also looks to be plenty of space around the rear non-drive-side axle nut to mount different designs of trailer hitch.

Unfortunately, the carbon-framed Skyfly compact bikes are not rated to take child seats, though it appears that other i:SY compact models are.

A final word on the digital features available on Bosch’s Smart System. I do find the app-controlled nature of it increasingly fiddly to use. I’ve used it several times now, and whilst it’s easy enough to use Bosch’s eBike Flow app to connect to any compatible bike, there always seems to be quite a few minutes of button pressing and waiting around for over the air updates and the like and – for my riding purposes at least – it doesn’t seem to add a tremendous amount of functionality.

The Skyfly was a case in point. It took me 15 minutes of googling and phone button pushing to figure out that not only the app software but also the bike motor software needs updating at regular intervals – all to upgrade from 55Nm torque to 60Nm torque.

Bosch seems to be having a big push on security features such as electronic locking and giving your bike and battery separate digital IDs so that they can be traced in the event of theft, and several other features are also now available on a subscription basis. I value bikes and e-bikes partly because they are usually simple and convenient to use and I don’t like anything that runs counter to that. Others may disagree of course.

Software rant over and back to the main point of this review: the hardware. In summary, the i:SY Skyfly E5 ZR F is a great example of the classic compact design. It’s high quality, fun and practical to ride and – as far as I know – the lightest mid-drive compact out there. That last point really plays into the compact design’s raison d’être – portability and storability.

Competition – other mid-drive compacts

i:SY itself offers a huge range of compact designs. The Skyfly is its carbon-framed range and the derailleur equipped S10 claims a weight of around 17kg. If true, that’s fantastic for a fully equipped e-bike with a mid-drive, a large capacity battery and large volume tyres.

Elsewhere, Cube is still going with the Compact Hybrid (£2,499), though this is several kilograms heavier than the Skyfly.

If you want more mid-drive options, check out Velo de Ville’s KEB Classic range from £3,099, which has tons of customisation options, including a choice of different Bosch mid-drives and even an off-road optimised option.

Benno produces the stylish looking RemiDemi range that sacrifices lightness (it’s much heavier than your average full-sized mid-drive e-bike) to be the mother of all cargo-carrying designs, but with definite compact-influences on its design.

Clearly – for now at least – i:SY appears to have carved its own niche in the lightweight, mid-drive compact e-bike area with the hugely appealing Skyfly range.