We are now stocking the Grintech (ebikes.ca) electric conversion kit custom made to suit Brompton folding bicycles!!
Electric Brompton Folding Bicycle
There are a few electric Brompton options around and most that we've tried have disappointed us. Although difficult to achieve on a Brompton due to its intricate and compact fold, our expectations are:
1 - minimally affects the fold of the Brompton and the accessories commonly used on Bromptons
2 - is a robust electric conversion that is suitable for daily use
From time to time there is talk of Brompton doing an official electric Brompton but I wouldn't advise waiting for that, it could be decades.
The status as of May 2016 is that we have ordered the Brompton electric conversion kit from Grintech (ebikes.ca) and we are installing it on a Brompton to be placed for sale. We have high hopes for this kit, as Grintech makes fantastic products! Please contact us if you'd like to be informed when it is ready for test rides. They have an exciting new airplane-legal lithium e-bike battery coming soon!
For information purposes we have some reviews and information from two other electric Brompton options we have tried in the past which are Freedom ebikes conversion kit from Israel and more recently the Hidden Power conversion kit from Korea.
Freedom ebikes conversion kit from Israel on Bromptons - our experience:
This was the first Brompton conversion kit that we tried. The website showed that they had sold many around the world and one of the company owners spent a lot of time in Sydney. It seemed worth a shot.
The kit itself was fairly unsophisticated, which is often a good thing for electric bicycles. The hill climbing performance was enough for most people and the battery range was quite good considering how small the battery was. The speed was fairly low (approx 20kph) which helped with battery range. The big drawback was that the motor often failed. Approximately 50% of the motors we sold were returned and repair was unviable. The basic cause is that it was a 'roller bearing motor' which is different to a conventional geared hub motor. It helped to make it more compact but it's problems under heavy use are well documented. It's likely the case that it isn't robust enough for a large proportion of Sydney e-bike riders (lighter people in less hilly areas will have fewer problems with this kit). While we have some customers happily using their Freedom ebikes electric Bromptons with this kit many years on, we had some customers go through three motors.
A kit that only works for some people isn't good enough for us to sell, but it might be just fine for your use. If you are considering purchasing this kit elsewhere, make sure you receive in writing how long your motor warranty is. Also check if the warranty is renewed each time you receive a free motor (generally not) and how long it will take to receive a replacement and whether the warranty also covers installation of the new motor. A review of the components is below.
User-controls: A simple throttle with 3 LEDs to indicate battery voltage was supplied. There was no pedal assistance. This is a sensible arrangement for a small folding bike
Battery: Any battery with an Anderson Connector works with the kit. It was supplied with a bare battery (the part that is usually inside another case) so looked fairly agricultural but was light and small. It fit conveniently into the back pocket of a Brompton front bag, such as the C-bag or T-bag. To fold your electric Brompton you simply first unplug the battery from the controllor - easy. The battery was just a little too big to legally take on airplanes, though many people report having successfully taken it on.
Controllor: An after-market Topeak saddle bag housed the controllor. The bag just happened to fit on the Brompton handlebar. The cables exited the bag through a hole they make in the bottom which eventually tears a seam in the bag. The nice thing is that by keeping the controllor attached to the inside of the handlebar, it folds down with the bike.
Motor: A slim and compact front hub motor already built into a 16" rim to suit the Brompton. Not quite narrow enough to fit without stretching the forks out. The fork drop-outs also had to be filed a little larger. The main downside is that it becomes slower and more difficult to fold the Brompton but that wasn't a show-stopper. The problem was the failure rate
Brompton Hidden Power Conversion (friction drive) Review - by Glow Worm Ali:
With minimum impact to the classic Brompton aesthetic, the 'Hidden Power' conversion is the perfect means to assist your commute without affecting the folding functionality. The light weight (2.6kg) conversion kit provides electrical assistance through a 250W motor driving the rear wheel. The level of assistance is controlled through a finger sized accelerator, located on the handlebar. At first this cruise control-like system seems unconventional compared to a spring loaded throttle or PAS, but after a few days riding I've come to warm to its accessibility. The friction drive motor contributes to a little noisier ride, however, this inconvenience is abated by the usability and performance of the conversion kit. This is not without its buts.
It should be noted that the literature and videos produced by Hidden Power seem overly generous on its functionality. All of the videos are filmed on a dead flat, dry surface. I live in Bondi and the climb out is stiff. Daily we use an eZee conversion kit on our Bakfiets cargo bike to assist the 45 minute commute. In one particular section has a steep gradient. People often dismount and walk up the hill. Our eZee conversion tackles this hill without a problem but the hidden power conversion on the Brompton struggles. One day, after forgetting to charge up, I had to grab my boyfriend's arm and hitch a lift from the Bakfiets. I found if only 2 bars remained on the battery, the electrical assistance would cut out as soon as it was under any load...meaning it would only provide electrical assistance down a gradient. Furthermore, the conversion provides no assistance in wet weather or when the roads are wet after rain, as the friction drive has insufficient friction and it slips (this is common to virtually all friction drive conversion kits).
If you are considering the installation of the Hidden Power conversion, you should be really clear on what your expectations are. It will not assist you up a gradient unless you're assisting the bicycle too. Unlike the video's portrayal, it would be unwise if you expected your legs could be dangling off the handlebars over a distance of 30 km in Sydney.