There’s nothing revolutionary about electric bikes. Ogden Bolton Jr. was awarded the first US patent for one in 1895. His battery-powered bicycle featured a hub motor mounted inside the rear wheel, with the battery attached to the cross bar. Two years later in Boston, Hosea W. Libbey invented an electric bike that was propelled by a motor tucked into the hub of the crank-set axle.
And while battery and motor technologies continue to evolve, those basic propulsion methods remain relatively unchanged—despite ebike sales reaching $41 billion in 2020 and expected to grow to $120 billion by 2030. Obviously Ogden’s patent is only a distant cousin to the latest high-performance peddlers, but even the most modern machines follow the same basic design principles.
In a shop tucked down a cobblestone street in Camden, north London, Alastair Darwood has invented a clip-on motor and battery pack that can turn any bike with disc brakes into an ebike. It’s an innovative, exciting proposition, and one that has caught the attention of six-time Olympic champion and 11-time world champion cyclist Chris Hoy, who has invested in the project and has been heavily involved in its development.
The Skarper requires you to replace your bike’s rear disc-brake rotor with its DiskDrive, which otherwise looks and works just like a traditional disc-brake rotor. Then a 3-kilogram (6.6 pound) unit housing the battery and a 250-watt-hour motor clips onto the bike frame. The DiskDrive rotor slots into the clip-on unit, where it engages with the gearing inside. The motor's internal gearing turns the special brake rotor, spinning the rear wheel. A small sensor also clips to the bike's crank, where it measures your speed and cadence as you pedal.
Once fastened in place, the Skarper offers a claimed 37 miles (60 km) of assisted cycling at or just below maximum legal speeds: 25 kph in the UK and EU, and 18 mph in the US. And once you get where you’re going, you can unclip the unit and stuff it in a bag, then recharge the battery in just 2.5 hours.
Take a Brake
Skarper’s story started during the first Covid-19 lockdown in 2020, when Darwood, a keen cyclist and inventor in the medical space, started looking for an ebike. He wasn’t prepared to spend enough to get a quality ebike, but neither was he convinced by current ebike conversion methods that retrofit a standard bike with a motor and battery.
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Looking at existing conversion kits, Darwood realized that almost all of them require you to either swap out your wheels for powered wheels or add a hub motor, both of which are drastic alterations. With new ebikes, he felt the brands were beholden to the motor manufacturers and had to build the entire bike around someone else's kit, while also stashing batteries on the frame and running cables all over. Darwood wondered if there was a less invasive way to power a bike, and he turned his attention to disc brakes.
“Look at any bike and the geometry around a disc brake is universal. The back wheel is an industry-standard design,” Darwood says. “I looked at the wheels and disc brakes and realized there was quite a bit of space between the back of the rotor and the wheel as it tapers into the tire, and I wondered if you could actually drive a bike wheel only using the disc brake.”
Darwood struck upon the idea that you could extrude material from behind the disc brake and fit a gear running around the outside in the recess. In this design, the disc still works to stop the bicycle when needed, and your bike otherwise rides as normal. But when the Skarper unit attaches to the rotor, two pins hold the disc securely in position while a third pinion gear drives the wheel. It’s an ingeniously simple solution.
Of course, this system requires replacing your stock rear disc-brake rotor with the DiskDrive. This conversion adds around 300 grams (10 ounces) to the weight of the bike. That might give a Tour de France racer some pause, but most of us won’t be inconvenienced by the weight. More significantly, the motor system creates no additional drag, and you can still freewheel while riding.
The other bonus is the fact that any bike frame engineered for disc brakes has already been designed to cope with any additional force applied by using the Skarper. This was crucial to the viability of the system, and it was only when Red Bull F1 engineers looked into the issue and confirmed their force calculations that the Skarper project was greenlit.
Initial Impressions
Before we talk about cost, competition, and implications for the evolution of ebikes, you might be wondering what the Skarper feels like to ride. I tried the system on two very different bikes: a top-of-the-line, ultralight Cannondale gravel bike, and a hefty sit-up-and-beg, super-comfy commuter.
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Connecting the Skarper unit to the frame is brilliantly simple. The rear section slots onto the DiskDrive at two points, and the tapered front end clips securely into a small bracket that you mount to the bike frame. Press the only button on the unit, wait for the status light to come on, and you’re ready to ride.
Riding the backstreets and gentle hills of north London, I was hugely impressed by the help offered by the Skarper and the instantaneous pull I felt as soon as I started to pedal. The assistance isn’t overbearing, and it won't freak out first-time ebike riders with inconsistent, aggressive acceleration. It simply works, just like a decent ebike should, helping when you need it but not making you feel like you’re on a moped.
I tried the Eco and Max modes, and while full power was more fun, both offered a solution to avoid getting sweaty on a daily commute. Given the compact size and simplicity of the unit, this is a huge accomplishment.
What surprised me most during the test, however, was the fact that the big, goofy step-through commuter bike was more fun to ride than the ultralight gravel bike. It bounced along with a real sense of joy, feeling like an infinitely superior pay-per-ride city bike. Maybe I didn’t enjoy the pro design because it’s the sort of bike that is fast, fun, and engaging to ride without electric power. In truth, it’s the bike you hurtle to work on, under your own steam, and then mosey home on, with Skarper taking the strain.
The prototype needs a bit of finessing. In my tests, the bearings made a bit of a racket (apparently caused by letting a BMX rider do jumps with it at a trade show), and it pulled a little too forcefully at times when turning through tight corners. But even after my short ride on this preproduction model, I could easily see the potential.
Puzzling Price Point
There’s no escaping the debate about cost. The Skarper is expected to retail for around £1,000 ($1,190), a sum most casual cyclists would rather just spend on a complete ebike. A quick search on Amazon reveals 577 complete ebikes for sale at a lower price. So how can the company justify such an outlay?
“There’s a real value fallacy in buying a £1,000 ebike,” Darwood says. “Battery and motor component costs are high, so you’re essentially paying for a motor, battery, and a bike built with unbranded parts that wouldn’t cost more than £100.”
“So you can find what appears to be a bargain of an ebike, but the truth is, if you’re buying from a leading manufacturer such as Specialized, Giant, or Trek, there’s almost nothing available for less than £2,000. So what we’re saying is, go to a bike shop, spend £1,000 on a hybrid commuter bike with quality components, and then buy a Skarper,” Darwood says.
On the face of it, that’s an awful lot of work and expenditure for the average bike commuter to be bothered with. But the fact remains that you don’t need to buy a new bike to use the Skarper; you may be able to install it on the bike you’ve been riding for years, as long as it has disc brakes.
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“It’s an entirely new system, and being able to clip it on and off is a unique selling point,” says Chris Hoy. “My dream is that in 10 years, in any major city, you’ll see people clipping a Skarper onto a bog-standard bike and enjoying the benefits of assisted pedaling.”
This vision is certainly appealing to more than just a superstar cyclist who's invested in the company. Anyone who's had a battery die on them while riding a heavy ebike, or anyone who lives in an upstairs flat and doesn’t want to lug an ebike up and down the stairs has yearned for something simpler and lighter.
As a regular non-Lycra-clad London cyclist, I can definitely see the appeal of the Skarper, and I imagine most people would enjoy a little extra help on the way home from work, at stop lights, or up a particularly nasty hill. But at the current pricing it will remain a brilliantly innovative solution for a small group of riders.
Trouble is, I'm one of them. For me, a stand-alone ebike doesn’t yet make practical or financial sense. But the ability to clip a motor onto a compatible bike I already own is a tempting proposition indeed, and a whole lot easier to sneak into the house than yet another bike.
Changing Gear
In my time with the team at Skarper, bike components and intellectual property came up a lot, and what became clear is that, aside from sales ambition, the company wants to become part of the cycling establishment. By making its DiskDrive disc-brake rotor universal, the company aims to be an industry-standard choice in the same way brands like Shimano and SRAM are.
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Manufacturers who fit a DiskDrive onto their existing bikes are essentially making the machine “ebike ready,” which slings the doors open for third-party motor and battery innovation. And, as Skarper COO Uri Meirovich alludes to, this will include a range of different-powered propulsion units, including an exciting solution for mountain bikes, currently in development with the help of Red Bull Advanced Technologies.
Skarper is by no means the only electric bike-conversion kit available, though it's the only one that doesn’t compromise the ride of the original bike and can easily be removed. Its closest cousin, the excellent Swytch, is lightweight, universal, and relatively simple to install—and boasts a 50-km range with a two-hour charge—but it still requires you to replace a wheel, run cables, and find a place for the battery.
Other worthy mentions include the Pendix eDrive torque-based mid-drive unit, which handily has a dealer network to help sidestep the complex installation, while you’ll find a wide range of hub-and-wheel conversion kits from Chinese e-mobility specialist Bafang, not to mention countless bargain basement, potentially terrifying unbranded options on the likes of eBay, Amazon, and Wish.
When it hits shops in 2023, the Skarper will be one of the simplest ebike conversion kits. The scope to be able to buy multiple DiskDrive rotors and give all your bikes the “ebike ready” treatment is a compelling one, and I can also see the benefit of having a shared Skarper unit at home. Yes, it's expensive, and explaining why it constitutes “value for money” will be a constant and tricky conversation. But with the rapidly changing landscape of urban mobility, and the obvious health benefits of regular cycling, it is a welcome change.