Van Bikeradar: Skarper’s revolutionary ebike conversion kit uses a disc-brake rotor to drive your bike

British start-up Skarper has unveiled a new e-bike conversion kit that uses a specially designed disc brake rotor to provide power to your bike.

Most electric bike conversion kits are not easily removable because of the effort involved in switching out a wheel, cables, batteries and fittings.

However, the new Skarper system eliminates that issue by containing everything within a compact single unit that has a unique and patent-protected design to drive your bike’s rear wheel.

We’ve spent an afternoon using the system for an exclusive first-ride review and, so far, we’re impressed.

What you need to know about Skarper

  • The Skarper unit requires you to replace the rear disc rotor with its rotor/drive unit
  • It weighs in at a claimed 3kg
  • Skarper’s rotor works as both brake and drive, and adds just 300g to your bike
  • Once the disc is installed, fitting/removing takes seconds
  • Claimed range of up to 60km
  • Charge time of 2.5 hours

What is it?

Skarper’s patented DiskDrive rotor replaces the stock rotor on your bike.
Skarper

Skarper’s electric bike conversion kit is housed inside a one-piece drive and battery unit. The unit clips onto specially designed tabs that you fit to your non-driveside chainstay.

The motor then drives a purpose-built rotor, which the brand has dubbed the DiskDrive. Most electric bike conversion kits use a front-hub motor, a bolt-on mid-drive unit or rear-wheel motor to provide propulsion.

Like most ebike conversion kits, on Skarper’s system, a cadence sensor attaches to the cranks to control power output.

A simple fitting on the chainstay stabilises the Skarper.
Skarper

Who is behind the Skarper ebike conversion kit?

Sensors and the control system’s algorithm combine to deliver power when you need it.
Skarper

Skarper says it has a team of more than a dozen engineers and designers working out of its London base. Leading development is inventor Dr Alastair Darwood.

Dr Darwood already has plenty of innovations under his belt associated with his medical training. These include orthopaedic and anaesthetic medical devices developed while working in the NHS.

Supporting Darwood’s innovative electric bike conversion kit is a group of cyclists who’ve all backed the company privately.

Sir Chris Hoy helped with the R&D of the Skarper and invested in the project.
Skarper

The Skarper’s investors include six-time Olympic and 11-time world champion Sir Chris Hoy, who has also been heavily involved in the testing and development of the unit.

He explains: “I’ve always been an advocate of getting more people on bikes, regardless of their fitness, ability or age, and I’ve discovered that ebikes can play a huge role in making cycling more accessible to anyone.

“It opens up opportunities – whether it’s making a commute possible which would otherwise have been too difficult, keeping pace with a fitter friend for a challenging bike ride, returning to riding after an injury or illness, or just going further on your rides and seeing more for the same effort.”

The self-contained motor, battery and ‘brain’ of the system is remarkably compact and weighs in at just 3kg.
Skarper

What’s next?

Simple fitting and its compact dimensions could make the Skarper a true game changer.
Skarper

Skarper is remaining tight-lipped on the full details, but alongside the road/urban unit seen here, the brand has also been working with Red Bull Advanced Technologies on an off-road version.

Skarper claims this unit has “huge amounts of power and plenty of torque. It means you can clip-on the system to carry you to the top of the mountain, unhook it and stow it in your pack and then you’re free to ride the trails on your / without the added weight and expense of an e-mountain bike“.

When will it be available?

Skarper promises to make turning any bike into an ebike a straightforward process.
Skarper

Skarper has now committed to full production, with delivery intended for 2023.

No fixed price has been set as yet, but Skarper tells us that the target price is £1,000.

Skarper also claims it’s in discussions with major bike brands about the opportunity to fit the DiskDrive disc brake rotor as standard.

Skarper electric bike conversion kit first-ride impressions

Warren Rossiter, senior technical editor

At just 3kg, the Skarper unit makes your bike much lighter than most electric bikes.
Skarper

While at Skarper’s office, I fitted a prototype system to a modest Merida hybrid. This involved a switch of the centre-lock disc rotor for Skarper’s DiskDrive, attaching the Bluetooth cadence sensor to the cranks and then hooking the unit onto the rear chainstay, with its driveshaft plugging into the keyed slot on the rotor.

Taking the unit out of the box and getting it powered up and ready to ride took a matter of minutes.

I headed out onto the streets of Camden, in London, to try out the system.

The system provides assistance quickly from a standing start, progressively increasing the power smoothly and making for quick getaways from traffic lights.

We headed to Highgate hill, which rises around 60m in elevation. I came away impressed by how easily the Skarper coped with this short urban climb.

Unlike most electric bikes, the Skarper uses a combination of sensors and control algorithms to respond to the terrain and your input. Power delivery was smooth and predictable.

It’s akin to the level of assistance you get from lighter ebike systems, such as Mahle’s ebikemotion or Fazua’s mid-drive system. However, this self-contained unit, without a separate high-capacity battery, won’t have the same range as either of those systems.

The Skarper isn’t just for commuter bikes – you can fit it to your road bike, gravel bike, mountain bike or anything with a disc brake.
Skarper

While the Skarper is pretty much self-contained and self-controlled, the brand is also working on a smartphone app to allow the owner to tune the system and perform firmware updates and upgrades.

I asked about long-term concerns on driving the rear wheel via the brake rotor. Darwood explains that the force a rotor experiences under braking far exceeds any amount of power the Skarper system delivers. This, he says, means the system is said to operate well within existing standards.

With removal in seconds, compact dimensions and a 2.5-hour recharge time, the Skarper can truly be charged at your desk.
Skarper

Having spent 45 minutes riding the Skarper, and in prototype guise with a fabricated casing around the patented internals, I’m not ready to commit to a full-test opinion yet.

I was, however, impressed by just how good the system feels.

The unit even integrates a rear light into its locking lever.
Skarper

There’s enough power for urban hills and the power curve is smooth, progressive and instant in both turning on and off. The system also feels essentially drag-free when it’s not running (above the 25kph EU limit).

Skarper’s COO, Uri Meirovich, was quick to point out after my short test ride that the aim of the system is not to take on existing conversion kits, but to offer a viable alternative to expensive mid-drive and hub motor systems without the need to purchase a full-on electric bike.

The goal of producing a credible alternative to existing ebikes, while you can still use your own bike is potentially game-changing, but we’ll have to reserve judgement until we can get the Skarper on long-term test.

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