convert a bicycle to an ‘e-bike’ or electric powered bike

when you want an e-bike and you don’t want another bike:

A cyclist told me that spending thousands more on a bike gets a bike that’s a pleasure to ride. Converting to an e-bike, got me a bike that’s like that (Roger Frost, casual cyclist).

was it worth fitting a Swytch electric bicycle kit to a bike?

It was worth it. Adding power to pedaling isn’t the lazy thing that it seems to be: a motor now shares the work of pedaling. Your stamina will be different but I can now do longer, once unthinkable journeys by bike. Even when I set the e-bike power level to its lowest setting, and pedal in top gear, I get help to take me up hills. This low setting also means that the battery can take me further.

Whatever your fitness, you typically pedal an e-bike as much as you normally pedal! The word ‘accelerate’ has no uses here: the effort on a high gear is now like a lower gear. And the bike will cut the power when you reach ~15 mph, so above this speed the effort is all yours.

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topics in this post:

• choose between converting a bike and buying a purpose made e-bike
• what to consider before converting a bike
• how does the Swytch kit fit?
  • fit the Swytch front motor wheel
  • fit the Swytch battery and controller ‘power pack’
  • fit the Swytch PAS pedal sensor
  • fit the Swytch thumb throttle
  • rear rack alternative to the Brompton bag on the front luggage carrier block
• how much does it cost to convert a bike to an e-bike?
• what do I think about the Swytch conversion process?
• learn about other approaches to converting to an electric bicycle

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choose between converting a bike and buying a purpose made e-bike

My decision was easy: I liked my Brompton folding bike. I would take it to far-off places and use it. I would often drive to a car park and ride it into Cambridge. If I converted it to an e-bike I could do that entire journey by bike. My decision was helped by the worth of this Brompton: a twenty year old bike is valuable when spare parts can still be bought

If you don’t have a treasured bike, you’ll look for a ready-made electric powered bike wondering if, or assuming that it’s better made for the purpose. For example, some bicycle parts need extra strength, or the cables and battery may be better integrated or the electronics will better adapt to your effort, or there’s a GPS bike-finding security feature. You might think that you need special brakes, but I think no. You need brakes to suit your speed of travel. Whatever your speed the brakes need to be as good as any brakes need to be.

A dilemma arises between choosing an e-bike with lots of tidy but proprietary parts (that may be expensive or difficult to replace) or choosing a bike with parts that look a mess, like a Frankenbike, but are generic and cheap to replace.

If you often transport the bike and go cycle, a folding electric bicycle may be your ideal. If the Brompton folding bike appeals, the Brompton electric bike is a ready-made equivalent. It’s price is ~ £3600. For technology which is unlikely to survive ten, nevermind 20 years, I pass at that price, though I suspect it will be infinitely re-saleable at a high price.

what to consider before converting a bike

With a motor and a battery your bike will be heavier. While this will hardly affect your effort (because you’re now powered), carrying a bicycle that weighs like a case of wine will feel three bottles heavier*. Your journey to the car or the street with a folding bike, may not be as short as mine.

* Brompton weight with trimmings 14.65 kilos or 32lb. Swytch kit 3.5 kilos. Bottle of wine 1.2 kilos. You’ll enjoy your extra wine though.

Before you click on ‘buy’, do get to know what’s right for your bike and you. A battery with more capacity is more desirable. A motor with more power seems more desirable but fitting a powerful front motor on a bike with soft aluminium or brittle carbon forks needs advice (furthermore a 250W motor may be the legal on-road max in some regions). The placement of a heavy battery on the handlebars might affect your ride. Brake sensors that cut the power quickly seem like a good idea, but they add two more things to stop you moving. A thumb throttle that turns on the power when you’re not pedalling helps if say, the pedal sensor fails. A Bluetooth connection to a phone is cute but another failure point. You might or might not want a faster battery charger.

There are businesses that will convert a bike to an e-bike for you. You can buy bicycle conversion kits online (ebay, Amazon, bike shops) and some of these receive good reviews. ARCC in Cambridge sell their own version of the Brompton Electric.

BAFANG for example is a respected industry leader and they’ve been making the hardware for eons. There’s an overwhelming choice of front, middle or rear drive motors and so on. You’ll find dealers who will sell you a Bafang kit to match your needs. Personally I need their support to buy the parts to convert a bike. See also YOSE POWER.

With these concerns I settled on Swytch who, for better or worse, kept the options available simple. SWYTCH is a brand that’s both marketing itself and winning respect. It supports customers who find that despite their best planning, their kit doesn’t fit as expected. For example, Swytch quickly attended to a couple of queries when my made-for Brompton kit arrived with parts for a later model. Swytch reliably dispatched the correct missing items. Overall that delayed my bike conversion by a week. Ultimately I’m happy but with the surprise that Facebook was a better source of information than the Swytch manuals and knowledge base. Swytch aim to make bike conversion look simple. But it’s more true that Swytch make a DIY bike conversion more likely, and with so many bikes in the world, that’s surely not simple.

how does the Swytch kit fit?

fit the Swytch front motor wheel and feel the forks

A Swytch kit includes a replacement wheel for your front wheel. You’ll make a few measurements when you place your order so that the correct wheel is made and delivered. I fitted the new wheel with a new tube and a puncture-proof Schwalbe Marathon Plus tyre.

The wheel has a motor at its hub where a wire exits on its way to a power pack (see photos). An axle at the wheel centre has two flats to help lock the axle in the front forks while the wheel around it turns. This locking idea is so important that a ‘torque washer’ is placed on each side of the fork. The torque washer spreads the turning force of the motor and helps lock the axle further. The motor can generate 40Nm of turning ‘torque’ – roughly that of a good cordless drill.

An optional (but recommended) ‘torque arm’ provides further safety against the turning force on the front hubs. As shown below, the torque arm fits over a wheel nut and restrains the axle against a fork. To install it you completely unscrew the jubilee clip, add a rubber lining, or ‘heat shrink’ and tighten it, but not insanely, with a socket spanner. There are different torque arm designs for different dimensions, but in most cases the result looks strong and ugly.

the Swytch battery and controller ‘power pack’

The Swytch battery and controller has a cute carry handle should you want to remove it from the bike for charging or when it is left unattended. This is easy and to be expected as the bike’s brains are precious. Under this ‘power pack‘ unit is a battery mount which connects wires that come from the wheel and the pedals. The power pack is normally mounted between the handlebars which allows you to press buttons to increase or reduce the power assistance – but in normal use I wouldn’t expect to fiddle with this. If you have a Brompton or Dahon or Tern bike you can buy an adaptor to mount the power pack lower down on what’s known as the luggage block. This was my choice as I didn’t want a bike that’s top heavy.

the Swytch pedal sensor or PAS

This last essential item ‘tells’ the motor that you’re pedaling the bike. After half a turn you’ll notice the motor lightening your effort. If you stop pedaling you’ll freewheel to a stop. The pedal assist sensor (PAS) fits over the crank axle that turns with the pedals. The PAS is a ring of magnets that wave past a sensor on the frame so telling the control unit you’re moving.

The Swytch pedal sensor is a split disc that fits over the crank in seconds and is kept in place by a metal clip. The sensor must be attached fairly close to the magnets, and in a way that it can’t move. The kit contains sticky pads and cable ties to experiment with different positions. In addition there is a good choice of rings of magnets to suit different bikes. Should even that fail you, I suggest calling Swytch technical support with a photo.

I found a variation of a pedal sensor online where a pedal crank must be removed to fit it. The Swytch split ring saves you the strength to remove this. A similar PAS sells on Amazon and delivers tomorrow – worth knowing should yours fall off somehow).

The installation can now be completed by routing the pedal sensor cable with the gear cable, along the frame, to connect the sensor to the power pack.

the Brompton pedal sensor bracket – 3D print

the thumb throttle works like the twist throttle on a motorcycle

I took the option to fit a thumb throttle on the handlebars. When you press its lever the wheel motor propels you along. Let go and the motor stops. Its advantages are minimal but with it the bike keeps moving without pedaling. Also should your pedal sensor fail ‘cos you knocked it, the thumb throttle offers a backup. BTW by some sources, having a throttle changes the bike’s vehicle class. Other sources say that having such a device is in no way ‘illegal’. I can’t judge this, but I can say that a thumb throttle is a safety feature to get you moving in a tricky moment.

The Swytch thumb throttle, like the generic thumb throttles widely available, slides along the handlebars and is clamped near a brake lever. I used a hair-dryer to soften and remove the handlebar grip. A hex screwdriver or Allen key removes the brake lever assembly as well as clamp the thumb throttle in place. The sensor cable terminates as a Julet male, and depending on your setup, might need a female-male extension lead to connect it to the Swytch power pack. On my setup the sensor lead fell short by 400 mm and needed 2 x 200mm sensor extension leads. A tour of ebay will find Julet male-female 3-pin extension leads of 500mm and 800mm and these work.

the brake sensors are very optional

A brake sensor fits inline with the brake lever and the brake cable. A wire feeds a signal to the control unit such that hitting the brake stops the power to the wheel motor. But I haven’t yet read a positive comment about brake sensors, indeed since these sensors ‘stop me going’ I imagined they’d be the cause of stopping me going at the wrong time. That said, there may be e-bike conversions where brake sensors really do have a role.

rear rack alternative to the Brompton bag on the front luggage carrier block

While the Swytch kit on the Brompton folding bike luggage carrier block loses the bestest, cleverest means of carrying stuff, you might now feel stuffed but no. The alternative bags I found use the KLICKfix UniKlip to attach to a rear rack – these include the Vincita Nash Bag and some of the Rixen and Kaul range. These bags fit the tapered Brompton rack when you align the side grips of the sturdy KLICKfix Uniklip and push two bag clips to lock it on. The Vincita Nash Bag (~£100) sold on Amazon, has drop down side flaps so you can carry things pannier-style. Unlike regular panniers these don’t foul your pedalling feet on a Brompton. From the KLICKfix Rixen and Kaul range choose bags with the Uniklip option. Despite their similar shapes, the R&K bags have different side panel and pockets. Prices hover around ~£100. The bag feels fancy. Of course there are many other strap-on bags for less money.

• Vincita Nash Bag 12 litres
• Rackpack Light UniKlip is 8 litres; Rackpack Sport UniKlip 12 litres
• Brompton official Rear Rack Bag
• More choices in a separate article

how much does it cost to convert a bike to an e-bike

Swytch kit costs plus options	£/ $	my opinion
16″ wheel 36V 250W motor + PRO battery / charger	£749	essential
shipping fee to UK	£30	essential
torque arm fork strengthener (possibly generic)	£15	recommended
Brompton block – BRO-block luggage block adapter	£60	recommended
thumb throttle for handlebars (possibly generic)	£25	optional
brake sensors – one sensor for each brake (possibly generic)	–	very optional
Julet extension cables (possibly generic)	–	very optional
total Swytch kit cost for a Brompton	£879

did you prepare the bicycle before the conversion?

Yes, this 20-year old bike had some issues and shabbiness so money was spent as I waited for the Swytch kit to arrive. Your mileage will vary etc but I’d recommend a checkup, a new tube and a good tyre.

costs to improve the bicycle ahead of conversion	£/$	my opinion
Sturmey Archer gear service, gear cable and general service	£45	recommended
Schwalbe Marathon Plus – puncture proof tyre and 16″ tube	£51	recommended
Brompton rear frame quick release clamp – a safety feature	£33
Brompton new mudguards and stay – were shabby	£47
Brompton elastic luggage cords for rear rack – worn	£8
brake pads and holders – worn	£28
Brompton replacement pedal – was noisey	£10

what do you think about Swytch?

Swytch are onto a good thing. Collecting my thoughts on this page they’ve kept it simple and they’re supporting people, like me, who hit snags. I didn’t enjoy scouring for the info to put my kit together – but when I asked I got the help I needed. So that’s good as is the bike turned e-bike. If I had any interest in business, I’d set up and compete because a four month delivery time may be easy to improve on. As I feel that the cables and cable ties have uglified the bike’s appearance, there is yet more to compete on.

After two weeks with my Swytch e-bike conversion I am impressed enough to recommend the concept to Brompton owners who can put it together. I might next try my hand with the more affordable Bafang or Yose power kits – or I might see some benefit from owning a second Swytch kit. As a technology reviewer myself, I’ve read about the negative aspects of all kinds of gear and know that not every complaint is worthy, nor is every feature (‘it’s got Bluetooth’) is worthy either. Swytch offers appropriate features at a time when I don’t need anything fancy.

how long does a Swytch kit take to arrive

what happened	wait time	date
sign up for offer		30 Aug
receive invitation to order after this many days:	35 days	4 Oct
order is now locked in for manufacture after:	25 days	29 Oct
order readies to go on a ship	9 days	7 Nov
order arrives at uk customs, the ship journey took:	35 days	12 Dec
arrives at UK warehouse – make ready for courier delivery	5 days	17 Dec
allowing for Xmas holiday, order was delivered within:	7 days	6 Jan
Time since my buy decision. Excludes 4 days to assemble	4 months

reviews of other conversion kits in the market

It’s at least educational to shop around and learn about other approaches, so this is a link to a video with wider experience. I owe some thanks, and thus this link to a YouTube by Dr James for helping my choice. I also owe thanks to Swytch Bike Chat on facebook for a good read during months of waiting for my kit to arrive. Wishing you an unfussed journey – do post anything useful below.

see the index to my other technology projects