Buyer's guide to electric bikes
By Paul Smith & Cycling Plus | Monday, May 2, 2011 7.00am
Buyer's guide to electric bikes Paul Smith
For some cyclists, the idea of an electric bike – even a so-called ‘pedelec’ that supplements pedal power rather than replacing it – will always be cheating. On the other hand, what if having a little help, like a permanent breeze at your back, could open up a whole new world of cycling possibilities?
That could be carrying a week’s shopping on the bike, making a long or too-hilly commute doable, or riding to work every day of the week rather than just when you’re feeling top of your game. Or maybe an electric bike is what it takes for a family member or friend to catch the cycling bug.
In this guide we explain the different types of electric bike, what to look for when buying one and the current legal situation. For reviews of the latest models, see the 'electric' section of our Bikes & Gear browser, where you can search by price, star rating or brand.
Shopping, in a shop
We'd always recommend buying bikes from a good shop whose staff know their stuff, and this is especially true in the case of e-bikes. Electrical assist systems, although relatively simple, can go wrong no matter how good they are. If they do, then the peace of mind of going back to the shop you bought the bike from and chatting to people you know (and who know you – which is important) about a fault, or simply having a cuppa while they fix it, is worth any amount of money you could have saved by getting a cheap deal online.
Bike shops are rarely run as a business to make someone rich. They're run by people who enjoy bikes and want to make a living enjoying bikes. Having a friendly relationship with a good local bike shop can be, at times, priceless. They'll do all they can to help you, and keep you riding your bike (with or without electrics). Partly because this ensures repeat business so they earn a living, and partly because like all of us, they like bikes, they like riding bikes and they like people who ride bikes. As the e-bike market grows, there'll be more and more shops around that know the ins and outs of electrically assisted cycling.
One of the things that's sometimes overlooked when buying an e-bike is the quality of the bike behind the electric gubbins. You need to remember you're buying a bike which has electrical assistance. If the electrics fail, what are you going to be left with? A decent bike? Or a heavy, odd shaped lump that's nothing but hard work to ride?
There are two key areas you have to pay attention to: what quality of bike you're getting, and what quality of electric assistance system you're getting. Both are equally valid, and will differ hugely depending upon the price. At one extreme, there are rubbish bikes with good electric assist systems. At the other, there are good bikes with rubbish electrics. In the middle ground are some models where both the bike and the electric system are good for the money.
Buying a poor bike with good electrics can be an option if you're good with bikes and like the idea of upgrading a basic machine. A good bike with a poor electric system is more or less useless, though – you might as well just buy a good bike. A good all-rounder will have compromises to both the bike and the electrics if it's cheap, but may be utterly wonderful if it costs a lot.
One of the main drawbacks of electric bikes is weight. Add an electric motor and batteries to even a fairly light base bike, and the result is a pretty hefty piece of machinery. Even lightweight e-bikes tend to weigh over 40lb. For comparison, you can pick up a sub-20lb road bike for less than £1,000. Below 15mph the extra weight is okay because the motor takes the strain. But above that speed, more weight means more effort. Bear this in mind when buying.
Types of e-bike
Pedelec or twist-n-go?
There are two mains types of electric bike. The most common is what has come to be termed a ‘pedelec’. This type of system monitors the rider pedalling and automatically adds a certain amount of motor assistance – usually depending upon pedalling rate, pedalling force and bike speed (so it knows if you’re struggling and helps as much as possible for instance).
The other kind is a ‘twist-n-go’. This is where a switch is used by the rider to trigger the assistance from the motor. They can either be simple on/off affairs or a variable twist grip setup. Current regulations only permit the twist-n-go assistance to be delivered if the system detects the rider is pedalling.
Hub or crank motor?
Motor choice falls into two main types. Either it's mounted in one of the wheels (hub motor assist) or it's mounted at the crank and pedal area (crank motor assist) at the bottom of the frame. Typically, crank assist bikes have a reputation for dealing well with steep hills, but can be a little on the noisy side depending upon the brand and type. Hub motors tend to be very quiet, but often don't handle hills as well as crank assist systems.
The difference between the two is now much narrower than it was even just a year ago. As technology moves on, and the bicycle industry's application of existing technology from other markets evolves, we're seeing hub motor systems which cope well with hills, and crank assist systems which are almost silent (apart from the normal noises of a bike).
Batteries are made up of cells, and they don’t all last forever. In a good battery pack the cells will be matched as well as possible at the manufacturing stage. This should mean that in the long run all of the cells in the battery pack ‘wear’ at the same rate, giving roughly the same capacity to store energy throughout the life of the battery. In a not so good battery there might be one or two cells that are less well matched, and this will simply mean that the other cells in the battery will be worked harder every time it is used – thus shortening the life of the battery pack. Good batteries made of quality matched cells are important, but sadly there’s as yet very little comparison data available to base a buying decision on.
Batteries only have a certain number of times that they can be fully discharged and recharged. Eventually their ability to store and deliver electrical energy is degraded to a point where they become more or less useless. Note that this means one complete charge cycle, so if you use half your battery’s capacity, then charge it up, then use half again and charge it up again, that counts as one complete charge cycle despite having charged it two times. Most manufacturers state the upper limit when they give charge cycle figures, so bargain on getting less than what they claim and factor this in to your buying choice by finding out the cost of a replacement battery before you buy.
Batteries don't like cold weather. As the temperature drops the chemical reaction that gives us the electrons used to power the motor happens more slowly. This means that the battery essentially can't keep up quick enough with demand when it’s cold. What we mostly notice as a rider, though, is the drop in voltage the battery can supply when cold. This voltage drop reduces the power the motor can give, and we feel less assistance, as volts x amps = watts, and basically watts is the motor power. It reaches a state where the motor seems to be doing nothing. Hence the feeling of the battery being flat – though technically, it’s not flat, it just can’t supply the demand upon it. Charging your battery indoors where it is warm, and fitting it only when you need to ride out in the cold can reduce the effect considerably.
There are quite a few different battery types out there, but the main two are nickel based or lithium based. Both have their good points and bad points (all batteries have bad points). Nickel Metal Hydride (NiMH) is a well proven and established battery type, and although it doesn’t have the same energy storage capacity per kilogram as most lithium batteries, it is very easy to predict its service life, and it is cheaper. Lithium based batteries come in quite a few types, such as Lithium Ion (Li Ion), Lithium iron phosphate (LiFePO4), Lithium Polymer (LiPo), Lithium Titanate (Li2TiO3) and so on. What they all have in common is a high energy storage capacity per kilogram than more conventional battery types – this helps make e-bikes either lighter, or the same weight with more range when compared to other battery types.
Battery size is important, and we don't mean its physical size, although that could be a concern if it's huge. We're talking about its capacity to store the energy which can be used to do the work of giving you 250 watts of assistance. A battery with a larger capacity will be heavier and physically larger than a battery of a smaller capacity (comparing the same battery materials of course).
Although the difference between a large and a small battery might not sound like much when you measure them and weigh them, there's a difference in the amount of time it takes to charge them. Some of the better charging systems measure the voltage of each individual cell in the battery, and then discharge the higher ones to match the lowest one. A larger capacity battery will generally have more cells, so it'll take longer to balance the cells before charging can even begin.
If you want quick charge times and/or only need assistance for a handful of miles each day then a small battery has benefits. If a longer range is what you're after then you'll need a larger capacity battery, and you'll need to learn to manage your energy usage when riding by lowering the assistance level when you really don't need the full 250 watts helping you along.
There are systems coming along which allow batteries to be "stacked". So if you only need a single battery for short journeys you can save weight and charging time by only using one. But should you need to go further, you can add another battery to the system to effectively double or triple the energy capacity.
What's the difference between Ah and Wh?
Some manufacturers will quote battery capacity in Ah, and some will quote it in Wh. Ah means Amp hours, and Wh means Watt hours. The two are not the same, and typically neither of them accurately reflects the amount of energy a battery stores that can be put to use powering an e-bike. To convert between the two is simple enough though, as there's a relationship between voltage, current, and wattage. To go from Wh to Ah you simply take the battery capacity in AH and times it by the battery rated voltage. To convert the other way, you simply divide the battery's Wh by its rated voltage. No matter what the unit of capacity a battery has written on the side of its casing though, one thing is for sure – you'll rarely, if ever, get what it says or is claimed.
Batteries won't last forever, and it’s worth remembering that a replacement is a maintenance cost that you'll need to prepare for to keep your bike in running order. Realistically, this will set you back £300 or more, but will vary between bikes so check with the supplier before you make your purchase. The battery should last well for around three years, but always make sure you check the warranty so that you don’t incur more frequent costs if your battery isn’t up to standard.
Gears: Gears need to be simple and easy to use, and if they're from a reputable brand like Shimano or SRAM it'll make servicing and parts replacement in the future a whole lot easier. Unless you’re only interested in riding in your local town centre – which also happens to be pancake flat – somewhere near the top of your list of wants should be gearing range.
Asking for more gears on an electric bike might confuse some people – isn’t the whole point that they're supposed to do the work for you? If they were motorbikes then yes. But they’re not, and UK law dictates that you can’t be given any more than 200 watts of extra power. So you’re still going to have to pedal, and you're generally going to have to put in a bit of effort doing it too.
Wheels: Wheels need to be well built and straight, preferably with stainless steel spokes and good quality aluminium alloy rims. Small wheels can be an advantage on electric bikes; as they take less effort to get rolling from a standstill, this battery- and clutch-bothering task can be left to leg power, and then the battery assistance can be saved for taking you from, say, 2mph to the legal limit of 15mph.
Forks: Suspension forks at the front, which are supposed to take the sting out of hitting bumps (much like the suspension on a car) can be very appealing, but on cheaper e-bikes they're just a lump of extra weight that you don't need when riding on roads and cyclepaths. Decent suspension forks cost upwards of £500. Now add that to the price of the electrics and the rest of the bike, and you can see why the forks found on £1,000 e-bikes aren't really worth having.
Accessories: Full mudguards, puncture-proof tyres, integral lights, a rack, luggage straps, side-stands, chainguards and so on all add up to a bike being easier to just jump on, regardless of the weather.
Whether you're an experienced cyclist or not, one thing you should do before committing a large lump of money to an e-bike purchase is go and test ride it. There are, of course, all of the standard issues involved with buying a bicycle, such as getting one that's the correct size, making sure it fits your needs and so on, but there's one important thing you should do when you test ride an e-bike – turn it off!
We can't stress enough the importance of knowing how easy it is to ride an e-bike should the electrics fail or should you run out of energy when out riding. Spending a little extra, or sometimes a little less, to get a bike which is simply a better bike when the electric assist system is taken out of the equation is important. If you get stuck miles from home with a trailer full of shopping and a flat battery, you're not going to be happy when you find out your e-bike is a complete beast to ride without the assistance from the motor.
The UK is about to adopt the EU standard BS EN 15194. This states: ‘The motor must only give 250 watts continuous assistance and a maximum speed (under electrical power or assistance) of 25kph (15.53mph). The bike has to weigh less then 40kg, and have pedals.’ Standard bike regulations also apply, along with a whole bunch of potential loopholes in ‘the law’. The current UK law though, is 15mph max assistance speed, and 200 watts continuous motor power.
The debate about e-bikes being "green" or not will always be around, and it's quite easy to sum up. Compared to a standard bicycle, an e-bike is less ecologically friendly. Compared to a small car or motorcycle, it's more ecologically friendly. There are a few things you can do once you own an e-bike to cut down the environmental impact it'll have due to its need for electricity to charge the battery. The easiest step is to find out where your electricity comes from. There are providers out there who get energy from sustainable sources. You can also look into your own small solar or wind powered setup for e-bike charging and take your bike off the grid completely.
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