ELECTRIC BIKE KITS
ROUNDING UP THE RETRO-FIT ELECTRICS
Rather than buy a whole new electric bike, why not add extra power to an existing machine? Richard Peace fi ts and tests products from Tongxin, Alien, Heinzmann, Sunstar and BionX which can add electric assist to your pedalling.
ELECTRIC bike kits, it has to be said, have been the poor cousins of ‘off the shelf’ electric bikes, in the UK at least. Whilst 2008 has seen a wave of new E-bikes, ever lighter and with ever longer ranges, kits have remained relatively hard to get hold of and with a very low media (and real-life) profi le compared to complete bikes. Whilst the sheer variety of cycles means coming up with a ‘one size fi ts all’ retro-fi t solution is never going to be realistic, there are signs that several manufacturers – and just as important, knowledgeable retailers – are recognizing and trying to tap into what could prove to be a keen demand from cyclists. Even so, a number of kits have been out there a while (keeping rather a low profi le) and many are in the pipeline. After all, the advantages of retro-fi t kits over complete E-bikes are many; you might want a bit of extra assistance on a cherished machine that fi ts you like a glove, or maybe the type of bikes you prefer just aren’t available as E-bikes (most folders and recumbents are cases in point) or you may want the option to try the kit out on several different bikes. In essence, you get to ride the bike you want, not one that an E-bike manufacturer wants you to. And for those cycling veterans out there who think they have tried every sort of cycling there is, well, this could be a new challenge… Of course, there are cons. I found the biggest problem was getting hold of kits in the fi rst place! There appears to be much more demand than supply (speaking from a UK perspective) with kits selling out quickly and waiting times for further deliveries stretching to weeks. Some of the kits were easier to fi t than others, with the Sunstar defi nitely being the most involved
VELOVISION ISSUE 32 DECEMBER 2008
(quite understandable as it is the only add-on crank motor I’ve come across). Kits are never going to look as neat as pre-fi nished E-bikes, but again some designs were defi nitely sleeker than others. Both the Sunstar and Heinzmann stood out in this regard, with high quality connectors and cabling giving you the confi dence to do smooth tight cable runs to minimize the kit’s visual impact on the bike’s lines. I also took on the challenge of fi tting kits to folding bikes – none of these kits are specifi cally designed for folders, but with a bit of thought about cable runs and where to sit the controller it proved to be no problem. There are no bespoke retrofi t kits for folders, with the exception of certain Brompton-specifi c developments (not offi cially endorsed by Brompton, it should be stressed). See the ‘Future Stars’ section, later. Regardless of the potential downsides, once the kits had been fi tted and tested, and a few technical niggles aside, I was quite impressed and could see a potential role for them all. Read on to fi nd out how they worked out in practice.
THE CONTENDERS Like many other areas of life, the world of electric bike motors fi nds itself in the middle of the seemingly eternal struggle of competing technologies. In the red corner are hub motors, usually housed in the front wheel but sometimes in the rear, and usually controlled by a handlebar-mounted throttle. They can potentially be very sizeable and power hungry (Heinzmann, for example, offer a 500 W version – effectively making your bike into a moped, requiring tax, insurance etc). In the blue corner are crank motors – the
Sunstar being a rare example which has found its way in small numbers from its home in Japan to Europe. Rather more ingenious than their hubhoused competitors, crank motors drive, as the name suggests, through the crank area rather than supplying power direct to the wheels. This lets them provide power over a greater speed range provided that you keep in the ‘right’ gear for the system, which works by sensing pedal force. The choice seems to boil down to the simple ‘power on demand’ of hub motors against the more effi cient but measured power application of crank motors. All UK road legal kits, both hub and crank drive designs, are limited to 15.5 mph assistance and 250 W continuous output motor rating (200 W according to some – a grey area in law perhaps best ignored!) Another battle – perhaps now drawing to a close – is that of NiMH vs lithium-ion batteries. With several large, prestigious companies, Heinzmann being among the latest, throwing their weight behind lithium-ion it seems this more power-dense technology is coming out on top. On paper, lithium-ion wins hands down. It gives more power per unit weight and has no ‘memory effect’, unlike NiMH. However, there is still a question mark over the reliability of some lithium ion batteries, especially at the cheaper end of the range. A good guide is the battery guarantee offered by the manufacturers and retailers. I would say that one year is the acceptable minimum, two years the ideal – replacement batteries are expensive and a rash of Li-Ion battery failures on some bikes (problem now sorted it seems) has knocked confi dence in this facet of E-bike technology in the past.