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 an electric bicycle kit to a bike?

It was worth it – even though I spent a lot upgrading this bike and could have spent less.

Adding power to pedaling isn’t the lazy thing that it seems to be: whatever your fitness, you typically pedal an e-bike as much as you normally pedal! A motor now shares the work of pedaling. Your stamina is different to mine but the battery assistance allows me 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. The effort in a high gear is now like a low gear. A low setting, and more pedalling allows the battery to take me 30 miles.

And the bike will cut the power when you reach ~15 mph, so above this speed the effort is all yours. The word ‘accelerate’ has no use in today’s (2022) e-bikes – you will not be thrusted forward as you are on a motorbike. The motor power is a useful, not excessive 250W. You will be able to stop (or crash) just as a normal bike stops or crashes.

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

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

Brompton T5 cost £500 in 1999 which an inflation calculator estimates cost me £850 in 2022 money. For reasons unknown a similar model in 2022 is £1350.

If you don’t have a treasured bike, you can consider a ready-made electric powered bike and assume 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 bike-finder 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.
A sense of perspective: Left: Brompton Electric £3500 – the electric folding bike Right: Piaggio Medley 125 £3600 with auto gears, lights, mirrors, turn signals, speedometer, ABS brakes and a comfy seat for two.

A regular bike weighs like a 12-bottle case of wine. An ebike conversion kit makes your bike three bottles of wine heavier.

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.

* My Brompton bicycle weighs 14.7 kilograms or 32 lb – with all its trimmings. A Swytch e-bike kit added 3.5 kilos. A bottle of wine weighs 1.2 kilos. You only enjoy this extra weight if it’s wine!

Before you click ‘convert’, consider these few things:

  • A battery with more capacity is always 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. A 250W motor may be the legal on-road limit in some regions.
  • The placement of a heavy battery on the handlebars or the back rack will affect your ride.
  • Brake sensors that cut the power might seem like a good idea, but they add two more things to stop you moving at the wrong moment!
  • 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 is another failure point.
  • You might want a faster battery charger if say, you expect to recharge the battery during the day.

There are businesses that will convert a bike to an e-bike for you. ARCC in Cambridge make their own version of the Brompton Electric. You can also buy bicycle conversion kits online (ebay, Amazon, bike shops) and some of these receive good reviews. 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. As well as BAFANG see YOSE POWER. You’ll find dealers who will sell you a Bafang or Yose Power kit to convert a bike. Personally I need support to buy the parts to convert a bike and the next time I convert my bike I’ll be contacting local bike shops or local bike technicians. Since 2020 other brands of conversion kit have appeared – such as GEEKO – but much of what follows about snags and customer support still applies.

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.

compare e-bike power with other vehicles:

vehicleengine power – Wattspower to weight ratio – Watt / kg – includes 70kg rider
human 150 W2 Watt / kg
e-bike + human250 W + 150 W3 Watt / kg or 5 W / kg pedalling
ride-on mower12,000 W30 Watt / kg
125cc motorcycle13,000 W60 Watt / kg
VW Golf 1400cc90,000 W60 Watt / kg
family size car 2000cc150,000 W90 Watt / kg
There’s not a lot to learn from this table other than say that with this little power an e-bike probably doesn’t need enhanced brakes; nor is it providing too much oompf or thrills; nor is it using much of the world’s energy

how to fit an e-bike kit front motor wheel – feel the forks!

A Swytch kit includes a replacement 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

You might find that a custom printed bracket works for you. I initially used this model by FablabinaFlat but I needed to move the pedal magnet ring from the crank axle to the crank arm. To make up the increased gap I added some material to the sensor bracket. The ‘remixed’ model is here.

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 old Brompton handlebar grips are just a 100mm

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

See my thorough look at Brompton rear rack bags

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 ideas in this article

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

Swytch kit costs 2021 plus options£/ $my opinion
16″ wheel 36V 250W motor + PRO battery / charger£749essential
shipping fee to UK£30essential
torque arm fork strengthener (possibly generic)£15recommended
Brompton block – BRO-block luggage block adapter£60recommended
thumb throttle for handlebars (possibly generic) £25optional
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 = ‘half-price pre-order offer’£879

prepare my bicycle before converting it

This 20-year old bike had some issues and shabbiness so money – £222 – was spent as I waited for the Swytch kit to arrive. Your mileage will vary but I’d recommend a checkup, a new tube and a good tyre – paid as follows:

costs to improve the bicycle ahead of conversion£/$my opinion
Sturmey Archer gear service, gear cable and general service£45recommended
Schwalbe Marathon Plus – puncture proof tyre and 16″ tube£51recommended
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’ve supported people, like me, who hit snags. I did not expect to search for the info on my particular Brompton bike – but when I asked I got the help I needed. So that’s good as is the bike turned e-bike. But their approach to a mail order is a bit crappy. They need to lose that four month or so delivery time. Also the cables and cable ties have uglified my bike, so there is room to improve on the product. In 2023 the Swytch battery was made more sleek but everything else is still ugly. Indeed GEEKO, another e-bike kit company have stepped in to compete on some but not all of my points about SWYTCH.

After 2.5 years with my Swytch e-bike conversion I am impressed enough to recommend the concept to other Brompton owners. I might next try my hand with the more affordable Bafang or Yose power or Geeko kits – or I might see the 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.

it takes ages for a Swytch kit take to arrive

what happenedwait timedate
sign up for offer1 Sep
receive invitation to order after this many days:35 days4 Oct
order is now locked in for manufacture after:25 days29 Oct
order readies to go on a ship9 days7 Nov
order arrives at uk customs, the ship journey took:35 days12 Dec
arrives at UK warehouse – make ready for courier delivery5 days17 Dec
allowing for Xmas holiday, order was delivered within:7 days6 Jan
4 months since clicking the buy button plus 4 days to assemble4months

here’s a big ‘why I converted my Brompton’

We bought a second hand Brompton with a Swytch kit so that two of us could go some place, park and ride from there. Using my jigsaw puzzle skills I could set two bikes flat in the boot/trunk of the car, as shown below, and conserve a bit more space for other items.

two Brompton bicycles folded flat in the boot (trunk) of an estate car

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 or other Brompton projects

1 Response

  1. roger says:


    Does anyone have experience of pre-sales advice?
    A read of Swytch Bike Chat (facebook) ahead of placing an order might be helpful. While my Brompton kit was reliably tailored to my bike, I stumbled across a story where say, the bike forks fouled the motor hub (but luckily he found another bike where it didn’t); or another where the front wheel axle did not fit the forks. If I’d waited months for the kit to arrive and this happened I’d be miffed somewhat. I therefore wondered whether Swytch pre-sales advice was up to much.

    Swytch delivery time and order tracking has disappointed many
    A successful e-bike conversion is very happy making. My experience of excellent support from Swytch after delivery is echoed by many. But again reading Swytch Bike Chat people report that their order tracking, like mine, went slow when their kit arrived in the destination country. My kit was sitting somehow in my country (UK) for a month and when I raised a query with Swytch the problem was blamed on a global supply crisis. (What?!). When my kit arrived, the white van was filled to the top with Swytch kits suggesting to me that my (£30) delivery was delayed for other reasons. I posted the remarkable delivery timeline above on Swytch Bike Chat and the replies added up to ‘you’re lucky mate I waited … or I’m still waiting’.

    This post is unbalanced
    As you read e-bike conversion reviews in mainstream media, be aware that they are sought by the companies. The company with the most active marketing department gets the bigger press splash. That’s why I’m adding a footnote to my own post which unfortunately was not able to compare this kit with other kits. The Guardian newspaper similarly had one such single kit review. So did Which magazine. All of our posts unhealthily skew opinion.

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