Hub or gear drive electric bike?

[scotty94]

Hi, Live in Australia, so don't know if you have any Aussies in this forum. Looking to put together my first e-bike, using an older 21 speed MTB I was thinking of retiring, but still in good condition. I have been looking at different options/kits available, and see that they basically fall into two categories, those that are hub drives, and those that drive through the bicycle's gearing system.

The legislation here may be a bit different here than other parts of the world, but basically we are (legally,) limited to 200 watts. No other restrictions apply. So I guess what I would like to know, are the pros and cons of each type of drive system, bearing in mind differing terrain, expected top speed, and expected range. Any thoughts/suggestions appreciated. For the information of the group, I'm looking for a top speed of 25 - 30 kph, and a range of >30 k's. Cheers,

 

[steve]

It will depend on your priorities and budget as to which is most suitable. Personally, if it's for road use, I'd get rid of the MTB alltogether and buy a purpose made electric bike. This is because MTBs tend to be less suitable for road use than off road and ready made tend to be less Heath Robinson. Originating from New Zealand it's notable how popular MTBs are for commuting use there as well - a triumph of form over functioning. Even here in the UK there's a surplus of MTB style bikes being used on the road. In countries where large numbers of bikes are the norm for personal transport (such as Holland), road bikes are firmly established in the lead.

Just like a car or motorbike, the motors in electric bikes also have peak efficiency at one rotational speed. If you have a hub motor arrangement, under conditions which differ to the ideal 'compromise' speed the bike is geared to, efficiency and therefore range and performance will suffer. Although there are some hub motor bikes which are better than others for flexibility, nothing can beat the flexibility gained by having the motor power going through the gears. Because hub motors only have single gear ratios (if any), as an extreme example it's a bit like designing a car with only one gear - it's fine under one set of conditions and anything else is a compromise.

Hub motor arrangements are often cheaper to implement due to their simplicity and are therefore becoming quite common in off the shelf electric bikes. The very best (and most expensive) electric bikes such as the Swizzbee and Flyer brands still use the good old motor power through the gears design though. If you have no speed limitation on electric bikes there then a derated to 200 Watts Swizzbee is probably going to be the Rolls Royce answer with a cheap Chinese Hub motor powered bike at the other extreme. In terms of add-on kits, I'm not familiar with what products are being flogged down under, perhaps any locals can provide input?

 

[rockvolt]

It appears that the cylone chain drive is offered down under with a 180w motor. should do quite well.

However, considering your speed aspirations, you should use a good power calculator to see just how many watts are needed to move different style bikes at those speeds. makes a faired recumbent rather enticing. cyclone might take you even a little faster, and give good hill climbing.

 

[scotty94]

Yes, having a good look at the Cyclone/E-lation designs. Seem to offer good advantages of spreading you usable power over a much larger range, than the fixed gear/drive type of systems. The only other one I have seen that might be Ok, is the hub design that uses a geared motor. Apparently they work better on hills, but you tend to lose on top end speed. I was a bit concerned with the Cyclone type of design, as I thought that the pedals rotated with the motor, until I found out that the pedals can 'freewheel', when the motor is operating. I just hope, that if I go for this type of design, that the pedal freewheel system, is robust enough for long term use. Thanks for the members that have added their advice! Cheers

 

[steve]

A freewheeling crank is asking for trouble - unless you use one of the expensive ENO freewheels in it....