I don't know of any good guide Allen, the lack of one is partly because e-bike design hasn't settled down and there are many variants on the way they work and their batteries. Here's a brief overview that might help.
The regulations which will be effective within about one year are 250 watts maximum continuous power which will be only available while pedalling (pedelec), motor assist speed limit 15 mph. The present regulations provide that power is permissible without pedalling (e-bike) and the change in law will not be retrospective for existing bikes. The term e-bike is however commonly used for all types.
Although the continuous power limit rating is 250 watts, this is a form of average rating, legal motors can peak at up to 700 watts or more, and this peak power can vary considerably between models. The more powerful, the shorter the range for any given battery size of course.
Types. The great majority of e-bikes have either wheel hub motors or those which drive through the same chain as the cyclist. Dealing with those separately:
Hub motors can be direct drive, that is the motor drives at the same speed as the wheel and is quiet and simple, or have
internal gearing reduction which is better for hill climbing for any given power though not so quiet at times. Most on the UK market are that second internally geared type. However, these are all single geared being effectively in top gear only, no motor "change down" for hills, though the cyclist still has their gears. Hub motors are found in bikes at all price levels.
Chain drive motors can be complete units which integrate the bicycle bottom bracket within them like the
Panasonic unit which has a small sprocket after the chainwheel which pulls the chain through. All bikes with these are in the upper price ranges. Alternatively they can bolt onto existing bikes in various ways like the
Cyclone units. Since these chain drive units use the bicycle's own gearing, they are ideal for very steep hills for which one "changes down" gears for the motor as well, just as with a car.
Which type of motor system is very much to do with personal preference, it's always advisable to try both if both are within your price range.
Batteries are a very important consideration, since they can be very expensive and are by far the largest part of the running costs. They mostly come in 24 volts or 36 volts, and the 36 volt types are generally more powerful though this isn't for any technical reason. Their capacity, i.e, the amount of energy they hold is measured in Ampere Hours (Ah), the more Ah, the longer the range for any given motor power.
There are three main types of battery.
Sealed Lead Acid (SLA) are the cheapest at under £100 replacement and last for around a year to 18 months, but they are very heavy, usually shorter range and mostly only on the cheapest bikes now, so quite rarely used.
Nickel-Metal-Hydride (NiMh) are also quite rarely used now, are a lot lighter and can last for up to four years, though with range greatly reduced by then. They are very roughly about two to three times the price of SLA.
Lithium batteries in various types are now the most common. They are the dearest, mostly last around two years, but are the lightest and most convenient in use, these benefits offsetting the costs. The different types are usually shown as Li-ion, Li-Polymer or LiFePO
4.
Origins. Most e-bikes and motors at all price levels are made in China, but there is a substantial European industry based mostly in Germany and The Netherlands, though there are the odd French and Spanish manufacturers. European e-bikes all fall into the upper price brackets as you might expect.
Variants. Some items dont fall into the above main classifications. One "geared" hub motor design uses rollers instead of cogs so is very quiet. There are a couple of examples of "outboard" motors that drive the rear wheel via chain or belt on the opposite side to the bike's chain. One company oddly uses an SCiB battery which isn't very suitable for e-bikes. It's sometimes best to be wary of variants, seek advice before considering them.
The Market. There are so many makes and models on the market that I cannot give a list, best just shop around and try those that members recommend.
I hope this "quicky" guide is of some use to you.
.
