• Powerful, with good torque at low revs. You can ride the bike with minimal pedaling
• Versatile: with a few minor changes (such as modifying the motor plate or changing wheels) it will fit almost any derailleur-geared bike
• Neat; the bike looks good and rides very well particularly with the frame-mounted battery
• Options and Accessories: the electrical design is very simple. Throttles, lights, speed limiter etc. are all available. Mechanical options such as different gear ratios, heavier duty chain & nylon chain tensioner also possible
• More powerful motors are available and can be fitted with just 3 bolts.
• Reliable: Motor failures rate ~2-3% Charger failures 4-5%
• Motor temperature sensor and over-heat shutdown

• Not integrated with the bike. The motor hangs out and looks like an add-on
• Original SLA batteries now out-of-date. Heavy and limited range (14-18 miles)
• Not available for hub geared bikes or non-36-spoke 3-cross wheels
• Not all QR wheels can be accommodated
• Rear carrier battery has poor range (8-10 miles) - because it uses small, SLA batteries
• Thumb throttle control only as standard
• 'Buzziing' noise can be a bit intrusive on quiet roads

• Light (2.3Kg) and small (100mm diameter)
• Fits standard fork drop-outs (100mm front and > 122 mm rear)
• Silent!
• available in 3-speeds (factory set)
• front or rear (screw-on block)
• Reasonable peak output power (360W for 36V model)
• Complete range of control options
• uses Hall-effect contact-free sensors throughout

• Needs a wheebuild for non-standard rims
• Few motor power options
• Narrow forks e.g. 16" wheels need modification
• Lower low-speed torque (hill-climbing capability) than electro-drive
• Rear-wheel motor accepts only screw-on blocks

For those wanting off-road power, large hub motor are available to give 500W-1,000W. The Heinzmann motor, though pricey, is unbeaten in high-power performance and is noted for its resilience and reliability. Matched with a 40A controller, twistgrip or thumb throttle and a 36V battery capable of 25A this motor will deliver 500W continuous and 750W peak output power.

The 'Team' motor is a brushless motor that is a little heavier but significantly cheaper. Both motors have an internl gearbox that allows the motor to run nearer to its optimum speed, beating the un-geared motors on low-speed torque.

• Powerful: a real work horse!
• Reliable: never known one to fail!
• available in 2 speeds (factory set)
• 500W motor has good low-speed torque: pulls from rest even on inclines
• front or rear (screw-on block)

• can be heavy (depending on model)
• over-size: even 'standard 100mm forks may need 'springing' apart
• brushes may need maintenance (Heinzmann)
• Rear-wheel motor accepts only screw-on blocks

The Cyclone aims to do what the better purpose-built electric bikes can do - drive the chain/crank and so let you use the gears. It can tackle the steepest hills, yet take you to the full legal speed - and then some!. Because of the wide variations in frame geometry and chainwheels, it isn't a 'universal fit' kit, but it does have special appeal to recumbents, trikes and some road bikes.

It offers a choice of 3 motor powers, various parts to aid fitting and a half-grip speed control. The MkII system uses an in-line gearbox and motor assembly driving a 12T 3/8" sprocket. Like the electro-drive, the speed controller is integrated with the motor

• Motor speed and torque can be adapted to the road conditions using the gears
• Range of motor powers (180W, 360W & 500W)
• Ideal for bikes with long chain runs, such as recumbents, trikes and small-wheel, long wheelbase folders

• Hard to fit - needs expertise
• 24V less desirable for high power motors
• (freewheel) Chainwheel only available in 44T
• Pedal cranks need to be wide apart - dog-leg cranks supplied and new bottom bracket may be needed
• Small installed base

One of the earliest secondary (rechargeable) cells, the Sealed Lead Acid battery is a real workhorse, delivery large peak currents, yet having very low self-discharge. Although containing acid, its contents are largely non-toxic and easy to recycle.

Although deep-cycle batteries are available, the majority of batteries are simply valve-regulated and they do not perform well when deeply discharged. Leaving batteries discharge also causes plate deposits which reduce life. Typically they will deliver 300 charge cycles. Also their voltage output is not very stable and about 35% of the stored energy is inaccessible as the terminal voltage drops too low.

They are technically very unsuitable for electric bikes, but their wide availability and low cost has made their use widespread

• Relatively cheap (£20-£30 per 12V battery)
• Can deliver very high peak currents
• Wide application and so easily available
• Easy to charge & manage
• Wide temperature
• Low toxicity
• Easily recycled
• Esy to monitor capacity

• Very heavy a 12A/hr 12V battery weighs 4kg
• Poor life
• Easily damaged if left 'flat'
• Low energy density and energy volume
• About 1/3 energy is inaccessible

Nickel Cadmium batteries were the first widely used secondary cell for use in a range of portable equipment. They are capable of delivery quite high currents because of their low internal resistance and they offered a much higher charge density than SLA due to their light weight.

Two major problems prevent the NiCd batteries from being among the best batteries to use for electric bikes: the memory effect and other crystalline problems make their management quite complex. Cadmium and to a lesser extent Nickel are toxic substances, and they have been banned in several countries.

• Good at delivering high currents
• Higher energy density than SLA
• Higher Energy/Volume than SLA
• Stable output voltage: 90% of stored energy is usable
• Good cycle life: 600-800 cycles
• Relatively cheap

• Toxic and expensive to recycle. Likely to be banned
• Careful management required to avoid Memory effect (reversible), build up of large crystals (irreversible) and over-charge resulting in venting and damage
• Restricted temperature range for charging and discharging
• Complex charge state indication

The NiMh battery is a good compromise, as it approaches most of NiCd's benefits without the toxicity problems of cadmium and with more manageable charging and discharging. It is available in a range of cylindrical sizes (though only 'D' and 'F' size are generally applicable to electric bike applications)

NiMh batteries are heavier than NiCd and delivering equivalent output current increases cost. They have a restricted temperature range for operation and charging, but they represent an economical and practical battery for electric bike applications

• Higher energy density than SLA
• Higher Energy/Volume than SLA
• Stable output voltage: 90% of stored energy is usable
• Good cycle life: 600-800 cycles
• relatively light - a 12V 9A/hr battery weighs ~1.7kg
• Relatively cheap (c. £50-80 per 12V battery)

• Restricted temperature range for charging and discharging
• Limited output current capability
• Heavier than NiCd
• High self discharge - around 1%/day at normal temperatures
• Complex charge state indication
• 50% overcharge needed as chemistry is inefficient

Lithium offers a great deal of 'potential' for batteries, but in its metallic form it is a highly unstable material. With the huge demand for lightweight electronics a lot of R&D has gone into taming this material, and two technologies have emerged; Lithium-Ion (Li-Ion) and Lithium-Polymer (Li-Po). Lithium Ion represents the most relevant technology to electric bikes today, though at a high price. Their high (3.6V) cell voltage leads to unusual battery voltages e.g. 25.2V and 37V instead of the familiar multiples of 2V (SLA)and 1.2V (Ni-based)

High capacity batteries are achieved by connecting multiple cells in parallel to built 5A/hr+ batteries. Charging and discharging is extremely sensitive, and batteries incorporate their own monitoring electronics (BMS). This includes a resettable fuse and charge control circuits.

Care is still needed when charging these batteries: they should be charged outside, in a cool place away from flammable material.

• Very light: a 10A/hr 37.2V battery weighs around 2.6kg
• Very low self-disharge
• Good life span: 600-800 cycles
• Chargers are simple (onboard battery electronics)
• High energy density
• Most (>85%) of the stored energy is available as useful power

• Expensive: expect to pay £250+ for a 10A/hr 24V battery
• Concern about stability of High capacity batteries
• Shelf life 'issues': they shold be stored at 40% charge to retain charge-holding capability
• Complex charge state indication
• Possibility of 'venting with flame' when charging