Central vs Hub motors on an E-Bike for cycle touring
What Electric Bicycle is best for a Cycling holiday?
Over the last few years I've been staggered by the increase in the number of electric bikes touring in France. Last year (2019) I guess that perhaps 50% of the bikes that stayed at our campsite – either touring through, or on the back of camper-vans - were electric and at Breton Bikes we've had more and more demand for them.
In the past I have to confess to being a bit negative about the whole electric bike 'thing' – especially when I saw increasing numbers of young people who aught to be fit enough to do it the proper way! But I've made a complete 180 degree turn on the subject and now rejoice at the increase of people just getting out and cycling! The point is that many of those electric bike users wouldn't have ridden at all if it weren't for the assistance – it's not a case of cyclists getting lazy, more that the E-Bike has brought more, or kept more in the cycling fold and that can only be a good thing.
But there is quite a lot of ignorance and misinformation about electric bikes and I thought it was time for a short article on the subject with particular reference to their use for cycling holidays...
How do they work?
I'm not going to be overly technical here – an electric bike is essentially a conventional pedal-bike where an electric motor is used to supplement the efforts of the rider and so make that effort in cycling much less and the range longer... 'Supplement' is an important word here because legally an E-bike can only provide power if the rider is pedalling. If you stop pedalling the motor MUST switch off – otherwise it is classified as a motorbike and needs you to have a number-plate, helmet and insurance. Likewise (in France) the 'assistance' MUST cut out at 25 kmh otherwise again the bike is classed as a motorbike. Lastly the motor cannot exceed 250 W in power output, about 1/3 hp.
So... You pedal, and the motor switches on, boosting your leg power to make the whole thing easier – that is all an E-bike is.
So why are there hundreds of models varying from a few hundred to many thousands of Euro in cost?
Hub motors vs central motors...
All the myriad models available in the shops break down to two completely different systems so lets look at them both.
This is just what it says on the tin. An electric motor is built up into a larger than normal hub and that hub motor can be in either the front or rear wheel – there are advantages and disadvantages to both but we'll do the common bits first... Generally these motors are controlled by a motion sensor on the pedal crank. Remember that you had to be pedalling for the motor to legally work? Well that's how most hub motors are triggered – the crank sends a signal to the control of the motor and switches it on. You then have assistance;-) Stop pedalling and it stops assisting.
This is pretty basic and you could say 'crude' as there's no control of the power of the motor, it just goes full on. Obviously this would be a bit of a pain if the motor then just accelerated you flat-out to 25 kmh! So even these simple systems have a 'power' control, usually giving at least three levels of assistance. They work on a very simple (again) principle. As well as the movement sensor on the crank there's also a speed sensor (just like any bike speedo) and the three assistance levels cut the motor at different speeds. For example 'Low' might take you to 12 kmh then cut out, 'Medium' to 18 kmh and 'High' to the limit of 25 kmh, but in all three the motor is at full power when on.
The effect when you ride the bike is quite interesting – acceleration is rapid up to the cut off - what you then find is that on 'Low' you will find yourself 'bouncing' on and off the motor. 12 kmh is a gentle touring pace, you'll manage that on the flat without assistance, but the second a slight hill comes and you slow, the motor automatically gives you a boost to that 12 kmh then cuts out. It sounds like it's very 'stop/start' but that's not at all how it feels and you soon adapt to it and the motor is pulling for a small fraction of the time – only when you slow. At the 'Medium' setting you're at a more serious touring pace and on the flat will need to work a little to stay off the motor, but each time you drop back the motor kicks in like a little push on the back to help you keep speed up thus the motor is 'on' more often than on 'Low'... Of course get to any more serious hill and the speed drops and the motor will kick in regardless of what setting you have and will therefore take almost all the effort out of climbing – something a lot of people appreciate! Some hub motors use a torque sensing system as outlined below but it's very much the exception.
Given that E-bikes are heavy and thus slower off-power than an equivalent pedal bike, the 25 kmh 'High' setting is something you'll need to be pushing pretty hard even on the flat to stop the motor kicking in – more likely the motor will be powering away most of the time – but this is faster than most people tour. Where this setting comes into its own is when you find yourself in traffic and want to zap up to road speed as quickly as possible and used like this it is very effective, but it will eat into battery life and as you've probably worked out there's nothing to stop you turning your legs over gently with no actual contribution to forward motion, i.e. the E-bike becomes an electric motorbike. It's also great for the last 10 km of a day when you know you've loads of battery left;-)
The motor itself can be in either front or rear hubs. Logic would say the rear would be the more 'normal' but it does have disadvantages. It's a pain to repair punctures – not only do you have to disconnect the power to the hub and fiddle with the locking washers etc (as with a front hub motor) but you have to do this whilst fighting the derailleur gear system and chain. It's a pain in the neck and I hate doing it – a front hub is relatively 'clear' of all but the motor gubbins and so much easier. Some people dislike the front wheel being driven and fear it slipping on gravel etc but to be honest I've never had a problem with it and personally a front hub motor would be my choice of the two.
Otherwise a hub-powered bike can be exactly like a standard pedal-powered bike except for provision to carry the battery, usually in the form of a special rack. Thus at the bottom of the price range you'll find pretty cheap 'shopping' bikes that have had an electric system slapped on – and to be honest there's nothing wrong with that. What you are unlikely to find is a very high quality touring bike that has the same treatment and that, IMHO, is a shame.
Now we get to 'serious' E-bikes, those with a central motor...
When you look at prices of E-bikes it's immediately apparent that central motor systems are far more expensive than hub systems. In fact there's practically no overlap between the cheapest central-motor and the top-of-the-range hub motor. So why the difference?
Central motors are much more complex than their hub equivalents. The latter is simply a motor in a hub – no gearing, just direct drive. The central-motor on the other hand is geared into the chain drive system, has a built-in freewheel (so the motor cannot be driven backwards by the pedals) and requires a custom frame built around its housing. It also has a far more sophisticated control system. Rather than using a simple motion sensor it has a torque sensor usually built into the crank. So if you pedal very gently the crank senses little torque and the motor stays off. As you press harder the sensor 'senses' the increased torque and powers up the motor at a low level, pedal harder and the motor pulls harder and so-on. In fact the motor is acting as a 'force-multiplier' – the more you use your muscles the more it multiplies your efforts. It's a great feeling – you get the impression you have the legs of a Tour de France rider;-) As with the hub system there are also levels of assistance so that at its lowest you have to pedal quite hard to get the motor to help out, at higher levels the motor is more and more 'helpful' so as with the hub-motor it is possible to ride with little effort up hill (though never the zero effort of the hub motor). Some central motors have a more basic system similar to the hub-motors where the crank senses 'torque' at a certain point and just powers on the motor – much like the motion sensor – though in this case the motor 'power' is controlled rather than a cut-off speed, so you get a little assistance on 'Min' and so on.
Because these motor systems are more expensive than hubs you find that manufacturers fit such bikes with better components than the cheaper hub-powered bikes and this exaggerates the price difference well beyond the costs of the system and in my mind unjustifiably so. There's no reason whatsoever that a very high quality E-bike shouldn't be produced using a hub motor because such a bike would have certain advantages (as we shall see) over the central-motor system – but that's not where the market is sadly. And lastly – remember the law... The limit in Europe is 250w of power no matter what the motor, and almost all E-bikes are already at that limit. Paying 700€ or 7000€ won't get you any more power no matter what the adverts imply...
“How far will it go on a charge” is probably the single most common question I am asked. And the primary answer is “depends on how much effort you put in...”. On maximum assistance and with the rider making little (or no) effort you can run any battery down in 40 kms or so, especially if it's hilly. Even just a little effort helps and it's here that the reputation for central motors giving better range comes from. With the simple motion sensor of a hub motor you can ride with no effort at all the motor and battery supplying everything, and when it's 'on' it's flat out. The central motor requires just a little torque input even on the highest setting, and psychologically I think it probably encourages the rider to make a little more effort as they are more responsive. But in actual fact – given the same rider input there's no reason that a hub motor should give less range for a given battery capacity. In fact as the hub drives directly rather than via a cog/chain and gear system it should be even more efficient.
Which brings us the battery capacity. This has a major bearing on price with a battery upgrade raising the cost by hundreds of Euro – and again the manufacturers tend to put bigger capacity batteries on their more expensive, central-motor models... But if you are planning to put any effort at all into your cycling then even the smallest battery is usually good for 50 km – enough for a gentle touring day. I've seen people do 100 km with such a battery without problems, but undoubtedly a larger battery will give you more flexibility or require less effort if you are looking to do longer distances.
So which system should you choose?
I hope you now see how different the two systems are, but the manufacturers have made the differences far greater than they need to be. It's almost impossible to buy a really high-quality bike running a hub motor, or a cheaply equipped bike running a central motor. I'm a bit baffled as over the years of hiring both systems out I find that some people prefer one system over the other regardless of cost. The simple movement-sensor/hub-motor is undoubtedly more obtrusive – you know when the motor is working and you never forget you are on a powered vehicle. On a bike with a central-motor you can kid yourself that you're doing all the work and have suddenly become a superman/woman – which is quite addictive.
In general I find experienced cyclists, who for reasons of age, injury or just lost fitness have decided to 'electrify' prefer central motors. For those who are not experienced and just want to go cycling I've met many who prefer to feel the bike motor kick-in to help as with a hub-motor, and like the fact that when they are completely knackered the bike will bring them home – the system also being more simple to use, most just setting the assistance at 'Min' and riding like it all day.
So let's list the obvious advantages of each system
- Much cheaper to buy
Can power with no effort at all
Motor maintenance easier (e.g. Motor change is remove wheel, 6 bolts and swap motor)
Less wear on conventional drive chain (motor doesn't drive through the chain)
Accelerates to road speed without any effort
- Generally fitted to higher quality bikes (why?)
Makes you feel like Superman/woman
Uses standard wheels (with no motor in the hub any replacement wheel will fit)
Both front and rear wheels no more difficult than a normal bike to change
As you can imagine here I'm in a bit of a dilemma. If all things were equal then the choice of system for a cycling holiday would be very much down to personal taste. But unfortunately things are far from equal and the fact is that if you want a quality touring E-bike to take you around France (for example) the manufacturers almost force you into the central-motor camp. Of course there's nothing wrong with that and they are nice to ride, but if there was a choice between a high quality hub-powered E-bike and a lower quality (components/frame etc) central-motor E-bike for the same price I know what I' choose...
With that in mind we have both sorts of E-Bike in our fleet, both easily capable of a week's cycling holiday, but generally we send people out on the more expensive central-motor models.