23rd November, 2013 in Buyers Guides
People buy electric bikes for all sorts of reasons: leisure, exercise or simply for getting from A to B. Owners may be commuters, shoppers, fun riders or simply very busy people. For whatever reason you ride, the distance your bike assists you will be crucial to enjoying your purchase.
Range should be one of the main criteria when you come to choose yours.
Manufacturers state various claims about bike range and often for “normal” riders these statements are simply not relevant. Some are clearly outrageous with many caveats and small print to digest.
In theory an electric bike will travel infinitely: If the rider is fit and strong then they may not need any electric assistance at all and can keep pedalling into the sunset – then range is infinite. A manufacturer can make this claim, but end up with many disgruntled customers, with perhaps only a contented Chris Froome or Bradley Wiggins able to confirm the bike did what the manufacturer said it would.
Major differences between bikes that can dramatically affect range are the weight of a bike and size of its wheels. Larger wheels have less rolling resistance and good road tyres can also dramatically improve distance covered. ‘Sit-up and beg’ style bikes can also be much less effective than hybrid or sports frames.
Some manufacturers claim their motors are more efficient than others, consuming less energy for the same power output. These claims are hard to confirm for a prospective purchaser and improvements can vary by only a little between brands. A few manufacturers also make use of regeneration – returning energy back into the battery whilst coasting downhill or operating the brakes. Again it is hard to measure the gain in range from such systems – although the best are said to add 15%.
And there is not much on the horizon showing greater promise over the now standard lithium battery chemistry.
Frame style, weight, wheel size and tyre design aside, there is little between the efficiencies of different bike technology. All supply an amount of energy to get the mass of the rider plus bike from one point to another. Some bikes use hub drives and others chain drives, and arguments abound over which system is more or less efficient. Once these drive system and style choices have been made, comparing two similarly equipped bikes for range is more accurately made by comparing a few key factors.
Comparing power and stored energy should be a good way of judging whether one has a greater range than the other.
More volts (V) provide greater power. Amp hours (Ah) is a measure of battery capacity: the larger the Ah, the greater the range. Typically these two measures are multiplied to produce watt hours (Wh) as a measure of energy store.
The power of the motor is measured in watts and a more powerful motor will consume more of the energy stored by the battery more quickly. So a larger motor (more watts) will reduce the range of an electric bike.
Likewise greater loads, less rider input and more hilly conditions will also consume more energy.
In practice there is a legal limit to the power allowed from the motor: 200 watts in the UK, 250 watts in Europe – so for the mainstream road-legal bikes the wattage of the motor is likely to be similar between manufacturers at 180, 200 or 250 watts. In a hilly district, riders can benefit from a more powerful motor (250 watts) but suffer reduced range as a result. The legality of the power of motors used in the UK is about to change (probably in 2016), but no-one knows yet for sure when and how.
So the key comparison between bikes, ignoring manufacturer claims, is between volts, watts and amp hours. A 36V bike with 250W motor and 10AH battery should travel further than a 24V bike with 250W motor and 8AH battery.
Some manufacturers do offer a choice of batteries for their bikes so you can actually select a range, rather than buy what you don’t need or worse, ending up with a bike that doesn’t do what you want it to.
A rule of thumb to preserve the very expensive battery in your bike is to buy one that offers you a range that is twice your regular journey. This is not wasted money! A battery that is regularly fully depleted by your daily commute, for instance, will need replacing much sooner than one that is kept at least 50% charged. Batteries are one of the most expensive parts of an electric bike and should be chosen carefully – and then looked after – to avoid early replacement.
Balancing all these factors – frame style, wheel size and tyre profile, motor drive method, power and battery size – should help you to choose a bike that exactly matches what you need and to enjoy many years of rewarding electric biking.
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