Nano Brompton Electric Bike

Nano Brompton

Review of: Nano Brompton

Reviewed by:
On 01/06/2007
Last modified:27/08/2013


It’s a delightful little beast. It does everything it’s claimed to do, plus a bit more, and it offers great value for money. If you’re looking for a folding electric bike, take a closer look at the Nano. We trust you will not be disappointed.

Brompton Nano Folding Electric BikeORIGINAL STORY FROM JUNE 2007. The Nano-Brompton later ceased production, but returned in revised form in early 2012, with a different battery and repositioned electronics. Prices are very different to those quoted here!

We’ve championed electric bikes since they first appeared, but somehow folding electric bikes have always proved a technological leap too far. Some are woefully underpowered, others have a limited range, all are bulky, and some are monstrously heavy. Our line has consistently been, don’t buy one. A good conventional folder is lighter, cheaper and more enjoyable to fold and ride, because by and large – the available electric machines add nothing to the capabilities of a good unpowered bike. This changed slightly with the arrival of the Dahon Roo EL, which showed what could be done with a good folding bike and quality power-assist system, but it was a bit weak and very expensive. Back to the drawing board. What is a folding electric bike actually for, you might ask? Some would consider it no more than something to throw in a car boot for a powered trundle round the park, but more usefully, it is (or could be) a priceless weapon for extending the door-to-door capabilities of public transport. For the average person on foot, the realistic range from a railway station might be a mile. On a folding bike, this increases to five miles – or perhaps ten in favourable conditions – but if there was a machine that most people could ride swiftly and with relative ease for twenty or thirty miles in an hour or two, almost any inhabited area of the United Kingdom would be in easy reach of almost any other. That’s the dream, and with the Nano Brompton – a kit produced by Tony Castles of EGO – it has become a practical reality.

Nano Technology

This machine has been a long time coming. We had some small involvement at the beginning of the project, talking through ideas and bringing a few engineers together, but the trail then went rather quiet. In the background, electronics boffin Tony Castles was working away, sourcing equipment and putting miles on the bikes. Prototypes have been out and about for a few months now, but our test bike is the first that could accurately be called a preproduction machine. The Nano Brompton will be available in kit form to convert an ordinary Brompton, the package including widened forks, a motorised front wheel, and controller for £250, plus battery of your choice (ours is a typical 266Wh lithium polymer costing another £250. The battery is usually mounted in the front pannier bag, with power passing, cleverly, through the front carrier block to reach the motor. The beauty of this elegant solution is that although the power-assist kit adds more than 6kg to the weight of a typical Brompton, the weight is evenly split between the bag and the bike. Our fairly typical donor L3 weighed 11. 3kg before conversion, and 14. 4kg afterwards, plus about 4. 4kg for the front bag. That’s quite a lot to carry up a flight of stairs, but much, much easier than the alternatives.

And, if you can afford to convert a new S2LX, you might be looking at a bicycle weighing only 12. 8kg, which is lighter than most un-assisted folding bikes. You need a battery, of course, but there’s no need to go for the whole pannier/battery option – we’ll come to this. Other bikes have come close to the Nano Brompton on weight, but never on a bike so compact, that goes so far, and does it all so damn effortlessly. The Nano Brompton has its quirks, but in the dysfunctional world of folding electric bikes, it’s close to miraculous.

Key Components

Kits can be bad news for the uninitiated, and on the Brompton, things like cableruns and the precise alignment of bits and pieces are rather critical to avoid folding tangles. So although the kit is supplied with clearly illustrated instructions, we wouldn’t recommend fitting it unless you have reasonable engineering skills, and a good understanding of how and why the Brompton folds the way it does. It took us about four hours, including two dashes to the computer to ponder the illustrations, particularly concerning the motor cable exit, where a lot happens in a small space. Nevertheless, once fitted, it worked right out of the box, and worked rather well.

The key component is the Nano – a new breed of sensor-less brushless motor. Just to recap very quickly:older DC motors (Powabyke, for example) have mechanical brushes and are only so-so efficiency-wise, newer ‘hall-effect’ motors (almost everything else) replaced the brushes with little sensors in the motor, linked by a fat cable to electronic switches in a separate control box. The sensors tell the switches when to fire, spinning the motor. These devices can be very efficient, but if one of the tiny wires breaks, they’re out of action that’s a big problem on a folding bike, where cables can have a hard time.

On the Nano, the sensing is done by a clever feedback system, so the motor only needs three small power wires. A slight oddity is that the Nano gives three little kicks before the sensing system settles down, producing a brief rattle, but the noise is followed by absolutely silent power. This is possible because of another technological advance – the whining (howling in some cases) sun and planet gears common to most electric bike drives have been replaced by a group of rollers. The old Yamaha PAS used something similar, but it made a few noises:the Nano Brompton is silent. On a very quiet road, pulling hard at low speed, the motor makes a tiny hum, but to put this into perspective, it’s quieter than the soft ‘shshsh’ of the over-run clutch when the motor is turned off. In practice, you can ride with a group and no-one would guess that there was anything unusual about the bike, except for the control box on the handlebars, the larger than usual front hub, and the fact that the rider apparently has bionic legs.

On the road

Brompton Nano graph

So what’s it like to ride? Plonk the bag in place, and if the battery is inside and turned on, a movement of the twistgrip will give instant assistance, so you need to take care. The twistgrip is supposed to be on the right, but we fitted in on the left, allowing throttle-on gear changes, although this does leave the control working backwards, so even greater care is needed when mounting and dismounting. We’d like to see a safety switch in a nice accessible position.

Engage first gear, open the throttle, and with that characteristic tiny rattle, the motor engages and pulls cleanly away. Power seems limited at first, but the motor gets into its stride from around 9mph, pulling with a startling amount of torque just at the point where your acceleration would normally be slackening off. The silent waft of power keeps coming until just over 14mph, when assistance suddenly ceases, the bike reverting back to being a conventional, if slightly heavy, Brompton. Most riders will go faster if conditions allow, but when the next hill approaches, you simply reopen the throttle. At first, nothing seems to happen, but as speed falls below 13mph, the motor begins to pull, silently and without fuss. And that’s all there is to it.

Maximum assisted speed is barely more than 14mph (13mph as the battery approaches empty), but this ability to climb rolling hills at 12 or 13mph results in surprisingly fast journey times. Our ten-mile commute takes 37 minutes, which is about average for an electric bike, and on the fast side for a conventional bike – three minutes faster than the unassisted Brompton S2LX, for example.

Not very exciting? Our commuter route is largely flat, in a Dorsetshire sort of way the Nano Brompton only really comes into its own in hills. Once the gradient has pulled speed down to 10mph, the motor begins to really pull. Oddly, but not uniquely, the Nano averages a higher speed in hilly country than it does on the flat (14. 7mph against 14. 2mph). On these more serious gradients, it just knuckles silently to the task, climbing more or less anything you put in front of it – not particularly fast, but at a good steady pace. On longer gradients, the kindest technique is to put the Brompton in gear two and keep speed down to a steady 10mph or so by adjusting the throttle, which takes some practice. On really steep hills, just open the throttle, select first and power on up. We found a restart on a 1:6 hill very easy, despite a little wheelspin, and the bike is soon romping away at 7 or 8mph. The maximum gradient depends on the number of gears available and the amount of muscle power you can provide. A typical cyclist should find 1:5 fairly straightforward and 1:4 seems possible, provided it isn’t too long. Incidentally, putting all this torque through the front wheel doesn’t cause the slightest instability, even with 16inch wheels.


In the past we’ve tested folding electric bikes that went 16 miles (disappointing), 12 miles (hopeless), five or six miles (waste of space), and so on. They tend to have lightweight batteries, poor gearing so you can’t put any effort in, short cranks, tiny wheels and squidgy tyres. This is the first time we’ve tried one with quality free-running tyres, a decent-sized battery (266Wh lithium-polymer) and efficient motor. It looked as though the Nano Brompton was going to go a long way on a charge, but just how far? After gobbling up our 14-mile hilly course in the morning, we kept going after lunch. . . and ended up going, and going. At 20 miles it passed the maximum endurance of the Giant Lafree and other efficient but under-batteried electric bikes. At 22 miles (still averaging 14. 3mph) it passed the ‘muscle’ bikes, such as the Ezee Torq. At 30 miles it passed the ‘big bike being ridden with economy in mind’ barrier. At 35 miles (and still averaging a healthy 14mph) it passed the big, heavy, crude machines like the Powabyke. At around 40 miles, power began to wilt quite significantly, bringing the average speed down below 14mph, but the Nano Brompton just kept right on going. Not very fast, admittedly, but powering up hills at a steady 8mph when requested. We’d love to have seen 50 miles, but in fact the bike cut out at 47. 9 miles, having averaged 13. 4mph for just over 3 1 / 2 hours. In ten years testing electric bikes of all kinds, we’ve only beaten that once, and then only very marginally. In June 2001, the special longrange version of the Dawes S-Drive did 48. 9 miles at exactly the same 13. 4mph average speed. And that had a battery weighing 8. 2kg. The new Giant Twist (tested in A to B58 ) is supposed to go 40 miles on a charge, but it’s so slow, quite frankly you’d die of boredom before finding the limit.

We should put our figures in perspective because if you don’t pedal the Nano Brompton, you might see less than 20 miles, and if you pedal with limited enthusiasm, you might see only 30 miles. On the other hand, the sky’s the limit for maximum range, because it’s a nice bike to ride unassisted, so on a sunny day in East Anglia it might go 50 miles on a charge, or 100 miles, and so on. We try to ride all power-assisted bikes in the same way:at the sort of gentle pace a reasonably fit person could expect to keep up all day. What this tells us is that if you ride the Nano Brompton in that fashion, with power engaged for about 2/3rds of the time, but the motor only working really hard on hills, you can expect to see in excess of 40 miles.

When the battery is flat, you keep riding, and the bike effectively reverts to being an ordinary Brompton. We found that the over-run clutch in the motor caused a little drag at first, but this disappeared after a few miles. At 14. 7mph, the roll-down speed is excellent for a bike with 16-inch wheels.

Recharging takes about five hours. The charger is fairly compact, and weighs only 540 grams, so it’s easy to carry with you. Overall fuel consumption (including charger losses) works out at 7. 7Wh/mile – a tiny figure, and easily the lowest consumption we’ve seen. Running costs (including the depreciation cost of a donor Brompton) come out at a lowish 7. 8p/mile, boosted by the generous range per change.


Whip the bag off, and the bike folds like an ordinary Brompton. It’s about 3cm wider at 32cm, but the other dimensions – 61cm long and 58cm height are typical. The result is a folded volume of 113 litres, or exactly 4 cubic feet. The only other folding electric bike to even register on the radar is the Dahon Roo EL with a volume of 210 litres or 7. 5 cubic feet. Almost twice the size.

The Nano is seriously practical and compact stuff – when you get to the bus stop, the railway station or the office, you’re left holding one bag weighing 4. 4kg (plus your luggage, of course), and a bike weighing another 14. 4kg. You wouldn’t want to run up stairs carrying it, but you wouldn’t with most ordinary folding bikes either. What most people should be able to do is lift the bike into a car boot, or across a railway bridge and onto a train. It isn’t light, but it’s better by an order of magnitude than anything else. This one works.

If you like to travel really light, use a smaller battery. Tony has been testing a tiny 76Wh battery pack that clips on the front carrier block in place of a bag, so your luggage will have to go in a backpack. This weighs 1. 2kg, and although we haven’t tested it to destruction, we think it should be good for ten miles or so, which might be enough for the sort of journey you do. You could keep one of these at the office and one at home, or. . . well, you get the idea, and the bike and battery then weigh only 15. 6kg. Basically, you choose a battery that suits your lifestyle and biceps.

The ability to fold to nothing and and pop on and off the train is priceless. We found quite quickly that the motor was well up to the task of assisting our SP trailer bike, producing a unique three-wheel-drive machine. For us, this makes all sorts of longer train-assisted journeys practical with an eightyear-old, where traffic or gradients would make solo riding impractical.


Where exactly is the competition supposed to come from? The only other decent electric folder is the Dahon Roo, which weighs 18. 1kg complete with battery. That’s more or less the same weight as the Nano Brompton and front pannier bag, but the Dahon offers only (only!) 20-mile range and rather dismal performance. It also costs £1, 199, which is a lot of money for what it is and – more importantly – what it does. We have some sympathy with the Ezee Quando, which climbs hills with remarkable vigour, but is otherwise rather a lump. The rest can be dismissed.

What we can’t tell you is whether Tony will be able to satisfy demand, or whether the Nano will prove reliable in the long run. We’ve had it for a few weeks and ridden a threefigure mileage. A few advance models have been out and about for a matter of months, but no-one really knows how the innovative motor and control system will survive in the notoriously brutal cut-and-thrust of commuting.

All we can say for sure is that it’s a delightful little beast. It does everything it’s claimed to do, plus a bit more, and it offers great value for money. At £499, the motor/battery kit is in the same sort of price bracket as the utter rubbish, yet it’s a smashing bit of kit, comparable in performance to the Heinzmann and other systems costing £800+. Even with a new Brompton M3L, the total comes to only £1, 000 (although you may have to pay someone to fit it). But enough superlatives. If you’re looking for a folding electric bike, take a closer look at the Nano. We trust you will not be disappointed.

Nano Brompton Specifications

Nano Brompton £499 (kit only) . Weight Bike 14.4kg Battery and Pannier 4.4kg Total 18.8kg (41lbs) Gears typically 3-spd Sturmey Archer hubGear Ratios 49″, 65″, 87″ . Folded Dimensions H58cm L61cm W32cm . Folded Volume 113 litres (4 cu ft) . Battery Li-pol . Nominal Capacity 266Wh Max Range 48 miles . Full Charge 5hrs . Consumption 7. 7Wh/mile inc charger losses . Running Costs 7. 8p/mile Manufacturer EGO www. egopt. co. uk tel 07974 723996 mail tony@egopt. co. uk

A to B 60 – June 2007