Cytronex are a UK company based in Winchester, and ebiketips have already reviewed and been impressed with their standard kit. Cytronex are highly unusual in being one of the few UK companies who not only design, but manufacture their own e-bike system. The motor is the only part not made by them at their Winchester base.
An early Cytronex model appeared in around 2008 featuring a Tongxin motor and NiMH batteries; but 2017 saw a major new upgrade - the C1 - featuring a host of new patented technology. This included new lithium ion bottle battery including all of Cytronex’s own-design control circuitry, and their new handlebar control button.
Now comes the Brompton specific version of the Cytronex retrofit kit. Like the existing C1 it uses a geared front hub motor - though it’s lighter and narrower to suit the Brompton forks - but this is really the only conventional ‘off-the-shelf’ aspect of the system. There have been a number of enhancements to the C1 since eBikeTips’ review of the first ‘standard’ kit, all of which are included in the new Brompton version, plus some new features designed specifically for Bromptons.
The first thing that stands out is the sheer quality of the system. The alloy casing of the bottle battery (apparently tested in a metre of water), the lovely engineering on the marine-grade stainless steel lever-operated bottle release catch, and the single handlebar button that controls all the functions are impressive feats of engineering.
Closer inspection of the rear dropouts reveals how the power is delivered in response to pedalling, in the form of the Cytronex designed and patented sprocket movement sensor. This counts the sprocket teeth as they pass it; and because it’s so much more accurate than most of the cheap and cheerful PAS sensors found on more basic kits, it can deliver power accurately and smoothly over a good range of speed when allied with the constant current controller.
All the cable runs are neat and discreet, with the wire from the rear cog sensor to the bottle battery running through the inside of the chainstay. The bottle battery that also houses the controller unit sits on top of the Brompton ‘mainframe’, and so sadds to the height of the folded package slightly.
The Cytronex Brompton is also a very lightweight system, adding around 3.2kg to our test model (with hardwired mini-LEDs adding around 170g) making it a competitor for the lightest Brompton retrofit kit out there. The main opposition for light weight comes in the form of the Nano kit which adds around 3kg, but that weight includes only a 98Wh battery.
Other competition comes in the form of the Swytch (read our review of the original version here) which adds around 3.4kg on a recent version I tried, and whilst this is a very cost effective and lightweight solution it lacks the quality and sophistication of the Cytronex. Cytronex packs a 180Wh battery so it’s ahead of the small battery option Nano in a pound-for-pound fight is at least on a par with the Swytch. It also trumps the very high quality and sophisticated ARCC system in terms of battery capacity, weight and cost.
The non-Brompton Cytronex kit is very popular with road cyclists, other cyclists with lightweight bikes and a grateful minority of those with ‘hard to electrify’ bikes like tandems. I found the Brompton system came into its own being ridden in a sporty fashion, as keeping up a decent cadence in the lower power settings keeps the power coming steadily and efficiently, while conserving battery life; having said that, there was a surprising amount of torque available for the steeper 15% slopes on my Pennine test course, when I occasionally needed to dip into the highest power setting of the three available modes.
The motor is very quiet in operation and the power delivered smoothly around a second after you start pedalling, as the sprocket sensor kicks into action. Cytronex say the system could have been set to come on immediately on pedalling, but the delay is a safety feature to stop you accidentally applying power whilst carrying out a U-turn, to give one example. The sensor is a wonderfully unobtrusive and effective part of the system and looks relatively simple to fit, compared to crank motion and bottom bracket torque sensors which require either crank removal or bottom bracket removal respectively.
Initially I had the power profiles set in the software to 20% in the lowest setting, 50% in the middle and 85% on the highest ‘red’ setting to give a wide range of assistance. This gave just a tiny bit of assistance for modest hills and headwinds, moderate power up rolling hills in medium and lashings of power for the steepest hills when my legs might be fading fast. It also seemed the most sensible compromise between using the assist where needed and preserving the valuable power on such a moderately-sized battery.
I only very occasionally felt I lacked the raw power of a top-rated mid motor up the very steepest of hills on my Pennine test course; while the rest of the time I sailed along in exhilarating fashion, the system allowing me to match human input and motor input exactly as I required.
On flats and downhills I could knock off the power with a single tap of the control button (it’s pretty easy to pedal without power too), while keeping the power button on for a couple of seconds meant I could toggle through the three power levels pretty quickly to achieve just the right blend of human and motor power.
OK, there’s no data display but this is a wonderfully minimalist approach that suits the Brompton for that very reason... after all, if you really need a bank of performance stats you have your smartphone for that!
Keeping the control button pressed down for a few more seconds turns on the small but very powerful Busch & Muller LED lights, keeping everything under the control of a single button. The strength and direction of the front light beam is testament to how LED bike lighting technology has come on leaps and bounds in recent years; not that long ago it would have required a unit twice this size to produce an equivalent beam. There’s plenty of light here to ride on unlit roads, and the light pivots to let you concentrate the beam just where you want it.
What is equally impressive about this system is what it’s missing compared to its competitors. The clever and accurate sprocket movement sensing mechanism means that power cuts out in about 15cm of the bike’s forward movement. Apparently the technical requirements only stipulate brake cut-out levers if the system will not cut power within 2 metres of forward movement, so there’s no need for troublesome brake cut-out levers which only add complication and clutter. The single button control is also an elegant and simple piece of design.
There will be riders who prefer the immediate response from a torque sensor system; though this adds cost and complication in the case of retrofit kits, and the Cytronex system is still pretty responsive with power kicking in quickly and cutting out equally fast once you stop. If an effective walk assist function for hill starts could be easily integrated into the single button control, it would be a near-perfect power delivery package in my opinion.
After toning down the power delivery from the above settings by a few percent in the middle and top power levels, I calculated I would get a range of about 25 miles on my rather hilly Pennine test course, which also featured a brisk headwind for most of my rides. I’m a 68kg/10 stone 10lb rider and I’m not that fit, so probably felt the need for the motor more than a properly fit rider.
Mark Searles, designer of the system and owner of Cytronex, seems to have confirmed this mileage estimate in his test ride up the challenging Mont Ventoux in Provence (above), where he covered 45 miles using two 180Wh bottle batteries, but with capacity to spare at the end:
“To give our Brompton kit the ultimate test, I decided to cycle up the one of the toughest hill climbs in the Tour de France - the famous and relentless 13.5 mile climb of Mont Ventoux from Bedoin with an average incline of about 8%”, explained Searles.
“I completed it successfully in a Strava-recorded time of just 1 hour 24 mins. This time is close to Tour de France pace but on a bike with 16 inch wheels, plus I cycled to the start from Carpentras railway station and back covering 45 miles and over 7,000 feet of ascent in total. I achieved all this with just two C1 bottle batteries.”
You can check out Mark’s ascent in the Youtube video here.
Charging and the Control Software
Battery bottle removal and fitting is smooth and easy, and left me with the impression that the bottle is very securely plugged into the multiway connector on the ‘bottle top’ area. If there is an area that can be prone to water ingress and poor connectivity this is it - I have a Brompton Electric on long term test and this has suffered from occasional cut outs, most likely due to movement in this ‘interface’ area.
The Cytronex bottle system looks very firmly located and I never heard any rattling or suffered any cut outs with it, even over some less-than-perfect rural roads. The only slight downside is that it can get caught with your feet when mounting and dismounting, but on the plus side it leaves the luggage block entirely free for luggage, unlike the ARCC system or indeed Brompton’s own electric model.
The bottle features a neat LED light system that indicates the state of charge; green for 100-75%, blue for 75-50%, purple for 50%-25% and red for the last quarter. A flashing red light indicates you are approaching empty and the system recognises this and winds the power delivery down in an attempt to conserve some power to get you home. It’s all very minimalist and logical like the rest of the system.
There are two charging options, a 2 amp and a physically bigger fast 4 amp version (the latter costs £43 extra) and is achieved by sitting the battery into a charging base known as the ‘Charge Shoe’. The Charge Shoe also acts as a USB connector, allowing you to connect the bottle to a PC or Mac for useful tasks like altering the power levels or running diagnostic software. A smartphone app that did a similar thing would be the icing on the cake.
For such a high quality system the battery guarantee of a minimum 60% capacity after one year or 300 charge cycles (whichever is the sooner) is the only slightly disappointing aspect, possibly a reflection that smaller batteries just have a harder life through more charging and discharging than larger ones. Cytronex say that the same warranty is still applied to the original Cytronex system and there are batteries in use today that are 12 years old. Cytronex also say that since the lifespan of the new battery packs looks to be very good, they are likely to increase the warranty to at least 2 years.
Fitting Options and Cost
There are both self fit and shop fit options, plus two options for fitting the battery bottle to the frame. My test bike was ‘factory fitted’ with the mount attached to the frame by drilling into it with rivnuts, making for a very solid connection. Alternatively there will be fixings available that essentially clamp the mounting onto the frame.
The 15mph top assisted speed version is available in both the UK and the US. The price quoted is for the self fit option with water bottle mounts where a bike shop would fit the mounts. My factory-fitted version with lights included would set you back £1,390, while a full installation without lights would be £1,295.
To summarise, this is probably the lightest and most efficient retrofit option out there for Brompton owners who want to take the plunge and go electric.