E-bike kits are an often overlooked option. If you have a bike ready to fit one, they can certainly be an economical option - but there are also some remarkably sophisticated kits out there too. These may be pricier, but they can give you a higher quality of e-bike than if you had just splashed the same cash on an off-the-peg e-bike.
There might be other compelling reasons to think about retrofitting. Your old bike might fit you like a glove or you might just be sentimentally attached to it but feel an electric boost will get you out and about on it more.
Although there are now electric versions of most genres of bike, some of the more rarefied designs still don’t offer a huge choice and the ready-made options out there can either cost many thousands or be rather crude and heavy. Recumbents, trikes and fat bikes spring to mind.
Easier to fit kits can also be used to swap between bikes if you feel like a change or can simply be removed if you feel like going back to the ‘analogue’ bike experience (we are generally talking about front hub motor kits here).
Once upon a time lightweight e-bikes were unheard of but nowadays there are quite a number of sub-15kg e-bikes around. However, these tend to be pretty pricey or single speed machines with very modestly sized batteries. With some electric kits adding not much mor than 3kg, a high quality e-bike weighing 10-12kg may now be within your financial reach.
Or you might just enjoy tinkering with bikes and want to come up with an electric creation that no one else has!
This article concentrates on hub and mid-drive kits, but there are other options too, such as friction-drive motors.
Practicalities and legalities of converting your bike into an e-bike
Here’s a quick checklist of the main practicalities you might want to consider when fitting a kit:
How much weight will it add?
E-bike conversion kits range from around 3.2kg (Cytronex and Nano are good examples of lightweight systems - more detail below) all the way up to 9kg or more for a very beefy motor with an extra large battery.
Will it fit your bike?
Hub motors not only need the correct width dropouts but also the profile of the forks in the area of the hub motor should not foul its smooth running. The better kit providers have motor templates or measurements, so you can check before purchase if the kit will fit. Will the battery fit where it is supposed to? Sometimes things can be modified to fit - e.g. fork dropouts or motor axle filed down slightly to ensure fitting - but some kits just won’t fit to some designs of bike.
How complicated and time consuming is it to fit?
All kit fitting requires at least basic bike DIY skills such as swapping out a wheel and refitting a tyre. At the more complicated end are mid-drive kits that require you to remove the bottom bracket, perhaps to fit a torque-sensing bottom bracket or even a mid-drive motor.
Check how many separate, interconnected wired elements there are. Some of the more budget kits may come with brake cut-out levers (though often it isn’t necessary to fit them) and both cadence and speed sensors (simpler kits feature cadence or movement sensors only). You may even see older kits that feature a separate controller that involves a spaghetti junction area of wired connections. Most kits nowadays incorporate the controller within the motor or battery housing.
You also need to ensure the cable runs between components will reach to where they are supposed to, so again if this info is not available, check how how many cables there are and what their lengths are.
Simply put, the more interconnected elements there are, the fiddlier the kit will be to fit, the more potential problems there will be and the less ‘clean’ the converted bike will look.
Some kits, like ARCC, Vekkit and the Go Outdoors Ultra, rely on wireless elements and/or other sensors hidden within the motor to keep the need for wiring to a minimum (we haven’t tested the Vekkit or the Ultra so they are not included in the list of recommended kits below).
Note that a minority of e-bike kit producers will only allow their kits to be fitted by themselves or accredited bike shops. These are usually the higher end, high tech kits. Examples include Cambridge’s ARCC and the German Pendix system, available in the UK via Velobrand’s IBDs.
Sounds obvious, but kits are one area where it’s possible to build an e-bike that doesn’t conform to the definition of a road legal machine. It’s also quite possible to unwittingly fit a kit that produces an illegal e-bike. Before buying you should ensure the kit is UK compliant. That means a 15.5mph maximum electric assist speed and a 250W continuous power rating (maximum or peak rating can be several times more and no legal limit is specified on this). The pedals of your e-bike must also be turning for the power to kick in.
Also be aware that it is the responsibility of the fitter - whether that's yourself or a bike shop - to ensure the kit is fitted properly, and just as importantly that the recipient bike is in good mechanical and structural condition to stand up to daily use with the kit on board. Spindly forks, poor dropouts or weak brakes on older bikes may rule them out as recipient bikes.
Front hub motor v rear hub motor
Front hub motors are generally the most popular and the easiest design of kit to install. This is for the simple reason you don’t have to touch the drivetrain, which will be a consideration with rear hub motors.
Both front and rear hub systems usually add the batteries to the frame somewhere, perhaps using existing bottle cage mounts or clips or clamps supplied by the kit manufacturer that tighten onto the frame. They may also go on the handlebars or rear rack (Swytch are a good example of a successful company that have used the handlebars for mounting the battery).
Again, checking all critical measurements with the manufacturer beforehand is the best way to avoid problems later. Comprehensive ‘template’ type instructions are best. Cytronex provides outstandingly clear compatibility information, including several templates, demonstrating that even one of the simplest kits to fit involves checking quite a few important elements. Kits that claim to be ‘universal’ may fit many, many designs of bike, but certainly not all. (To give just one example, only Grin from Canada produce kits that fit thru-axle bikes as far as we're aware, and they are US, not European spec).
Rear hub motors are said to provide more traction and reduced likelihood of wheelspin as there will be much more weight on the rear wheel, so off-road types who want to fit a more powerful hub motor might consider them. Similarly, if your front wheel features something that you don’t want to or can’t remove, like a hub dynamo or drum brake, then clearly a rear wheel hub is a better option.
Very often a rear hub system will mean at the very least tinkering with the gear system and possibly more. You may have to change hub gears for a derailleur system and if you want to keep your existing sprocket, you need to know if the hub allows either freewheel or freehub (cassette) gearing. Usually a hub motor is of the geared type (i.e. there will be some kind of gearing inside to reduce the speed it drives the shell of the hub as motors generally spin faster than wheels). Of course make sure the wheel is the same size as the one you are replacing and that it accords with the 15mph limit. Gearless hub motors aren’t as common – the Heinzmann and Zehus are the only ones that make our list.
UK legal hub motor kits – front and rear – will come with some kind of cadence sensing mechanism that means power only arrives when you are pedalling. Some kits have a throttle option. As already noted, these are illegal if they operate independently of the pedals turning as ‘twist and gos’. However, throttles are legal if they can only be operated while the pedals are turning.
Mid-drive e-bike conversion kits
These offer all the advantages of a pricey mid-drive e-bike – getting great motor power at all speeds and using the motor at its most efficient too - without the big price tag.
Again, pay attention to compatibility issues - mid-drive kits need the correct width of bottom bracket housing and the correct threading pattern. More recent bikes are more likely to have a newer non-compatible type of bottom bracket frame housing. As kits are often fitted to slightly cheaper or older bikes that may not be an issue. As these motors put considerable twisting force on the frame in the pedal axle area, some kind of bracket or locknut fixing may also be supplied with the kit, so again check if your frame design will accommodate it.
9 of the best e-bike conversion kits
This is not a comprehensive list. It concentrates on systems we have either tested or have had good general review feedback on.
The internet is awash with cheap hub motor kits from sellers you are unlikely to have heard of, but Australian-based Dillenger sell in a number of countries and have done so over a number of years, building up a good track record in the process. Their website also offers good info on compatibility and fitting and they offer a clearly set out one year warranty.
Dillenger’s Samsung Power 2.0 front hub motor kit packs a lot of value in given the budget price so it’s perhaps not surprising they claim to have sold over 10,000 worldwide.
It ticks all the boxes: it’s disc brake compatible (standard 6 bolt mounting), comes ready spoked into a wide range of wheel sizes (20”, 24”, 26”, 27.5” and 29”), has a decent sized 468Wh battery with cells from a recognised maker (Samsung) and also has the option of a throttle.
Swytch has a headline-grabbing low price, but that is for the ‘Eco’ version with a modestly-sized 180Wh battery. The slightly larger ‘Pro’ version packs a 252Wh battery and costs an extra £95. It is disc brake compatible and has a throttle option. Its most distinguishing feature is the handlebar mounting battery that removes at the click of a button. As these are relatively small batteries, they don’t appear to affect handling too much – you can read our original and follow-up reviews of the Swytch kits - the latter based on the new and more adaptable bottom bracket mounting cadence sensor. There is a Brompton-specific version too.
The light weight is attractive too (3.2kg for the Eco kit and 4.45kg for the Pro version). The real downside is the wait; Swytch wait until they have enough orders before they order direct from Asia which is a low risk strategy for them but can mean several months' wait for customers who have signed up.
Bromptons have narrower front forks than most bikes and Nano’s Brompton-specific kit is based around a brushless, front hub 36v, 250w, 290rpm motor with a weight of 1.6kg. This comes already built into a new Brompton 28-hole double-walled rim. Nano have long experience of providing e-kits for Bromptons and the latest iteration of their popular kit adds around 3.3kg total to the weight of the recipient Brompton. It features a single 144Wh clever and practical ‘in bag’ battery. Larger batteries are available.
With Brompton’s own electric version (not retrofittable) starting at almost £3,000, and weighing in at 17.4kg, the Nano option fitted to a second hand titanium-specced Brompton (typically around £1,500) looks a very tempting option.
Bafang BBS01 - £949 from Dillenger (widely available elsewhere)
Undoubtedly the most popular mid-drive kit in the western world - where mid-drive kits are rare indeed. The BBSO1 is rated at the UK/Euro motor output level of 250W whilst the BBSO2 is rated for the US market at 750W. The Dillenger version comes with a 522Wh battery so the sub-£1,000 price tag looks attractive. Like Dillenger’s front hub motor kit, the battery has a 5v USB socket handy for recharging.
You need to be happy removing and reinstalling components in the bottom bracket area of the bike of course, but if you are, you should get all the benefits of a much more expensive mid-drive e-bike (currently most mid-drives cost well over £2,000).
The kit weight is stated as 7kg, which is pretty heavy for a kit, but the weight is nice and low down and produces a well handling bike that’s also easier to pick up than you might think. The motor position also means your front and rear wheel setup can remain just as it is.
‘All in one’ kits – with all the elements required to add electric assist to a bike in a single wheel hub – were a growth area a decade or so ago, with new designs regularly coming along. However, many have faded from view.
The Zehus system appears to be going strong though. It is a gearless rear hub system that can be purchased both as a retrofit kit and on certain ‘off the shelf’ e-bikes - we have tried it on both the incredible Hummingbird Electric and the Quella.
So far models available in the UK have all been single-speed models but the Zehus website suggests versions that can take 4, 7 or 9 derailleur gears also exist. Stated battery capacity varies from around 155Wh to 173Wh depending which website you look at. Testing conclusions from our experiences suggest a very clever system and one that should be easy to fit if you don’t mind a single speed e-bike, but maybe one that lacks raw hill climbing power.
The higher price of the Cytronex kit reflects the fact that it is designed from the ground up to produce a lightweight and high tech solution that will feel extremely bike-like to ride and which will offer groundbreaking range from the 198Wh battery. Our tests on earlier versions of the kit (here and here) show the British company has largely succeeded.
A recent redesign of the battery means you can take the bottle on a flight or send it anywhere by courier without it being classed as dangerous goods (classification for exemption being two batteries of up to 100Wh installed in equipment– so the bottle itself classifies as it contains both the batteries and the electronics). Cytronex are also about to introduce a travel charger that will fit into a bike's seat pack.
The front hub motor may look conventional enough but a plethora of original design features include a quick release bottle battery, a simple but highly functional handlebar mounted ‘boost button’ and a sprocket movement sensor mounted out of the way on the chainstay.
Along with the ARCC and Pendix systems this is probably the highest quality system featured and includes impressive details such as a marine-grade stainless steel mounting mechanism and Bluetooth functionality that, via the app, lets you not only alter the power profiles of the five motor assistance levels but also monitor the charge of the battery even when it is off the bike.
At 3.2-3.6kg depending on spec it is also one of the lightest retrofit options out there.
In addition to the kit, Cytronex offer complete bikes from the likes of Bobbin, Cannondale and GT. There is also a Brompton specific option and a tandem option.
This longstanding German manufacturer produces electric drives for everything from tracked snow vehicles to electric boats, so e-bike motor technology should pose few problems for them.
The only motor kit currently available in the UK (via exclusive supplier EV Solutions) is the DirectPower gearless motor. This is a quiet and very high quality motor with a good amount of power but at 4.5kg for the front wheel version, this is certainly going to be one of the heavier kits out there. This is motor weight only too – the standard 500Wh battery will add several more kilograms. But if solid construction and high reliability (and the possibility of regenerative braking) are high on your list, and you don’t baulk at the very high price, this certainly could be an option.
This German-designed high quality kit places a gearless motor in the non-drive side of the cranks. It’s a very pricey but very high quality system. There are three options of increasing battery capacity, starting at 300Wh.
It is a very neat, minimalist looking system that requires minimal cabling. Control is via a knob on top of the cleverly designed 48V battery. It’s pretty heavy - the lightest version adds around 8kg. There are folding bike versions as well as options for regular bikes.
Pendix don’t give out detailed fitting instructions as they insist their kit is fitted at a dealer. It is distributed in the UK by Velobrands and there is a dealer page on their website.
ARCC, like Cytronex, produce a small, lightweight and high tech kit based around a geared front hub motor. Like Cytronex, they actually UK manufacture many of the components they have designed themselves.
They use small capacity Bosch powertool batteries which are mounted in the ‘Intelligent Drive Unit’ that is permanently fixed to the head tube, minimising the cable run to the front wheel motor (though it does all make the bike rather front heavy). An extra battery can be frame mounted using ARCC’s own bespoke battery holder. Perhaps the most impressive element of the kit is the wireless handlebar unit used to control power settings.
There are Brompton specific options, disc and rim brake options and the system comes with a five year warranty on the ARCC system and a one year warranty on the batteries.
ARCC do not allow ‘home fitting’ and you need to send or take the recipient bike to ARCC in Cambridge. If you want a complete bike then ARCC sell a small range of these too, including Moultons and their own-manufactured Abington and Rosemont town bikes. Ebiketips has already reviewed their electric version of the Abington.
The kit itself adds just under 4kg to the overall weight of the bike, including a 144Wh battery (216Wh batteries are also available from ARCC and 324Wh ones from third party sellers).
ARCC say early 2022 should see the launch of a new app (on both iOS and Android) and a new version of the handlebar control unit with a screen and more ride data.