SmartMotion eMetro Electric Bike

Updated 22 November 2013

Contents

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• SmartMotion eMetro Electric Bike
  
• Introduction
  
• Design, Bike Specification, Geometry, Electrical Specification
  
• Riding and controls, Riding, Seat, Safety, Transporting items, Wheels and Tyres, Weight, Suspension, Gearing, Gearing Range, Brakes
• Electrical Motor and Mounting Electric Motor as a Generator, Level 3 Assist, Level 1 and 2 Assist, Acceleration, Air Resistance Hills, Battery, Wiring
  
• Conclusion
  
  

Introduction

I had the opportunity to take a SmartMotion eMetro electric bike from Wellington Electric Bikes for a test ride around the Mangaroa loop in Upper Hutt, New Zealand. I had been interested in this bike as a reasonable cost means of getting around, especially for people living in hilly areas. We have found that the SmartMotion e20 folding bikes served that role well for us. In addition, light touring was possible.

The SmartMotion eMetro electric bike has an upright style of riding with simple controls. In this short test I was followed by Désirée on her e20 folding bike, initially on a flat section of road. This allowed me to measure the maximum speed, for each assist level, as the eMetro bike did not have a speedometer. At the halfway point we swapped bikes for a while, then I rode the final leg back to the shop.

Along the way I took photos of the bike and its component parts to illustrate this write-up. I also did some speed tests using the three levels of assist. The beginning of the Mangaroa loop ride was a substantial climb from Wallaceville to the Mangaroa Valley Road. This led to the Mangaroa Hill Road and then a descent back onto the relatively flat Fergusson Drive which led back to Upper Hutt. Here I was able to repeat the speed tests.

Some features of interest are shown in the photos. You can enlarge the photos by clicking on them. Use the back control < to return to the web page.

Design

The bike is a step-through type which makes it very easy to ride. It has a comfortable seat and a relaxed riding style. A description can be found on the SmartMotion website. The list below summarises some features of this bike that may be of interest.

Bike Specification

• Model: SmartMotion eMetro Electric Bike
• Price: $1999
• Warranty: 2 years battery, 6 years frame, 1 year other items
• Bicycle weight: 23 kg
• Frame: 6061 T6 Aluminium alloy
• Fork: Rigid chrome-molybdenum steel
• Handlebar and grips: Comfort style with adjustable height, upright riding position, contoured grips
• Stem: Black alloy with adjustable height and reach using allen key
• Brakes front: Tektro 180 mm disc brake
• Brakes rear: Tektro V brake
• Wheels: 36 stainless steel spokes, 2.25 mm diameter, 13 gauge
• Rims: Aluminium alloy
• Tyres: CST 26 X 1.9 inch Commuter Tyres, Kevlar Guard for puncture resistance, reflective sidewalls
• Tubes: Valve - Schrader type
• Front Hub: Electric Motor, 8FUN 36 volt, 250 watt, 225 rpm for 26 inch wheel
• Rear Hub: Shimano Nexus 3 speed internal hub gear, 20 tooth sprocket, Ratios 0.733, 1, 1.364
• Shifter: 3 speed Shimano Nexus Revoshift gear shifter
• Mudguards: Full Length polypropylene with stainless steel stays
• Saddle: Velo Plush Comfort
• Seat-post: 350mm long, 27.2mm diameter suspension seat post
• Pedals: Aluminium platform with rubber grip and reflectors
• Cranks: Lasco 170 mm black alloy
• Bottom bracket: Sealed bearing cassette
• Chain KMC Z51RB rust resistant
• Chain Ring: 40 tooth Lasco
• Chain Guard: Full, P type ABS plastic
• Attachment points: Water bottle, carrier, brakes, reflectors, mudguards, lock, chain-guard
• Lock: Built-in C type, different key from battery
• Carrier: Spring top, elastic hold-down, pannier rails and battery support
• Lighting: Reflectors only
• Cables: Some internal routing
• Kickstand: Centre mounted adjustable black alloy kickstand
• Certification: Bike EN15194 & AS:NZ1998, Battery UN38.3

Geometry

• Bottom bracket height: 292 mm
• Chain-stay length: 443 mm
• Wheelbase: 1100 mm
• Equivalent horizontal top tube length: 585 mm
• Seat-tube angle: 73 degrees
• Head-tube angle: 71 degrees
• Seat height minimum: 850 mm,
• Seat height maximum: 1005 mm
• Wheel circumference: 2020 mm
• Pedal crank length 170 mm
• Overall length: 1792 mm

Electrical Specification

• Motor: 8FUN 36 volt, 250 watt, 225 rpm planetary geared motor for a 26 inch wheel
• Battery: EVE Energy Co., Ltd, Lithium polymer Samsung 18650 cells, weatherproof, 36 volt, 10.4 amp hour, 374 watt hours
• Range: Nominal range at 10 watt hours per km is 37 km
• Battery ports: 42 volt DC into charging port, 5 volt DC out of USB device charging port
• Battery lock: Unlock to remove battery for charging inside, if cold
• Controller: Behind battery on carrier
• Throttle: Grip control
• Pedelec Magnets: 6 magnets on a disc, adjacent to the chainwheel, for pedal assist start
• Cutouts: Brake lever motor cutouts
• Electrical cables: Some internal routing
• Electrical connections: Marine Grade weatherproof
• Display: LED type, 3 pedal assist levels, battery state, 6km/h walking assist button
• Computer: No speed or odometer readings
• Lights: None, reflectors only
• Charger: Modairy 42 volt, 2 amp

Riding and controls

This bike is optimised for a leisurely style of riding. There is no need for a speedometer, which gives time to look around for traffic or to enjoy the countryside. A rear vision mirror should be added.

Riding

It was a pleasure to ride with old style handlebars in an upright position. Very nice contoured hand-grips are provided. The brake levers each have motor cutout switches which stop the motor immediately. The throttle control, next to the left hand-grip, can be used to rapidly accelerate at intersections. If it is not required there is a plug to disconnect it. Next to the right-hand grip is the Shimano Nexus gear change control. This has a clear display. A small bell is part of the left-hand brake lever mount.

The motor control display is basic but sufficient. The LED display shows 3 assist levels, battery state, and has a 6 km/h walking assist button. This allows the bike to be easily moved over difficult surfaces while walking beside it. A bike computer could easily be added. A $30 CatEye Velo 5 bike computer, for example, shows speed, trip distance, total distance, maximum speed and a clock.

Seat

A Velo Plush seat provides good comfort. The seat is mounted on an adjustable suspension seat post. The seat can be adjusted from 850 mm to 1005 mm above the ground.

Safety

The chain guard enables riding in normal street clothes. At the destination the bike can be securely locked with the built-in C lock. Adding a simple cable with a loop at each end allows the bike to be secured to an object. The battery is locked to the carrier, but it may be advisable to remove it from the bike as it is a valuable item.

Transporting items

The carrier is versatile, allowing panniers, bags, boxes, or loose items to be securely held. It also supports and protects the battery. A basket could also be added to the handlebars. Phillips handlebar bags are another option.

Wheels and Tyres

The wheels have aluminium rims fitted with 26 X 1.9 inch CST Commuter Tyres with a Kevlar guard and reflective sidewalls. The tyres are an intermediate size suitable for road and formed trail use. There is a Kevlar fabric band underneath the tyre tread, which helps to prevent punctures. Kevlar is used in bullet-proof vests. The tubes are fitted with Schrader valves, which are the same as on cars. Polypropylene mudguards with stainless steel stays, are fitted.

The 36 stainless steel spokes are 13 gauge or 2.25 mm in diameter. This is thicker and stronger than the usual 14 gauge or 2 mm spokes. On the front wheel the spokes are all laced from the inside of the motor rim, presumably to increase clearance from the disc brake mechanism. The rear wheel has spokes laced alternately, inside and outside the hub rims.

Plated 15 mm wheel nuts, with end caps, are used front and rear on this bike. Patching flat tubes may be slightly easier than changing tubes since cable disconnections need to be made before the wheels can be removed with a 15 mm spanner. In the front, the motor cable-connector can be unplugged. Alternatively, the cable loop allows the wheel to be carefully moved far enough to remove a tube, without unplugging the motor. In the rear a 5 mm allen key is used to remove the Shimano Nexus 3 speed shifter mechanism from the right-hand side, before the wheel is removed. Inside the axle there is a long thin actuating rod which should not be lost. It should be re-inserted so that the undrilled end faces out.

Weight

The bike weighs 23 kg. This weight is evenly distributed, because the motor is in the front wheel and the battery is over the rear wheel, on the carrier. This can make the bike easier to manoeuvre through gates and around obstructions. The extra weight of the bike is nothing when compared with the usual weight range of riders. The bike is solidly constructed and the wheels have thicker than normal 13 gauge spokes.

Suspension

Apart from the suspension seat post, and comfortable seat, there is none. With an upright style of riding there is little pressure on the hands. For this class of bike a front suspension fork is not needed, and it would just add extra weight in the front. With the motor weight in the front wheel the dynamics of any reasonably priced suspension fork would be substantially altered. The tyres can easily be inflated to a pressure which gives a smooth ride.

Gearing

The Shimano Nexus 3 speed gearing is more than sufficient, especially when it is supported by the electric motor. I never needed the lowest gear. It may be a useful gear for starting on hills. With hub gearing the chain always runs true so it should last longer. Secondly, the 20 tooth rear sprocket has more teeth than the the smallest 11 tooth sprocket on an 8 speed derailleur system. Wear of this item is shared and reduced.

Gearing Range

The gearing range for a 40 tooth front sprocket and a 20 tooth rear sprocket is as follows:

• Gear Inches: 37, 51, 69
• Metres Development: 2.96, 4.04, 5.11
• Gain Ratio: 2.77, 3.78, 5.16

These terms are defined here. The gearing range is similar to that found on a typical 7 speed bike.

Brakes

The brakes and brake levers are all Tektro branded. On the front wheel there is a cable-actuated 180 mm disc brake. On the rear wheel there is a cable-actuated V brake. The brake levers have switches to instantly cut off the motor. The brakes worked smoothly on the downhill descent with the stronger 180 mm disc brake correctly fitted to the front wheel.

Electrical

Motor and Mounting

The motor is an 8FUN 36 volt, 250 watt, 225 rpm motor mounted as the hub of the 26 inch front wheel. It is held in place by a substantial chrome-molybdenum steel front fork. The wiring is neatly routed down one leg and enters the motor adjacent to the solid steel axle. The wiring dips down before it enters the motor to discourage water entry. A marine-grade cable-connector allows the motor to be disconnected and the wheel easily removed. The motor can be classed as low-powered so an additional anti-rotation torque-arm is not required.

Electric Motor as a Generator

An electric motor can act as a generator. For a given voltage, the motor will have a maximum speed where the generated voltage is nearly equal to the applied voltage. In this state, little current is drawn and little power is available. The maximum speed of the bike is calculated from the 225 rpm specified for the motor. The wheel diameter is a nominal 26 inches. It has a measured circumference of 2020 mm. The maximum speed is (2020 x 225 x 60)/1000000 km/h = 27 km/h at 36 volts. With a freshly charged battery the maximum speed should be closer to 30 km/h. This bike makes a small trade-off in maximum speed for increased acceleration.

Level 3 Assist

The measured maximum speed in level 3 assist was 30 km/h. By loading the motor down to about 66% of the maximum speed the power output of the motor is maximised. This is at about 20 km/h.

At about 75% of the maximum speed, the efficiency = (motor power output / motor power input) is at a maximum. This is at about 23 km/h which would be the most efficient speed to climb a hill in level 3 assist. At this speed most of the available battery power is used just to move the bike forward. If the bike is run below half the maximum speed in level 3 assist, it is hard on the battery and the motor and controller will heat up.

• At 15 km/h about 40% of the available power is wasted as heat.
• At 12 km/h about 50% is wasted as heat.
• At 7.5 km/h about 70% is wasted as heat.

At these speeds the motor rapidly heats up, and it will be much noisier. It is now time to shift to a lower assist level to protect the motor.

Level 1 and 2 Assist

At lower levels of assist the optimum speeds are lowered in proportion. In levels 1 and 2 the measured maximum speeds were 16 and 22 km/h respectively. The most efficient speeds on hills are therefore 12 and 16 km/h respectively. Riding below these speeds by a few km/h is OK.

Since the eMetro does not have a speedometer, another strategy is needed. An inefficiently run motor is noisier, so speeding up to reduce the noise level increases efficiency and reduces wasted heat. This may require more pedalling effort. Adjusting the assist levels and choosing the appropriate gears will help to set the best speed for any situation.

Acceleration

I noticed when I rode the bike that the acceleration was very good, which is a result of the increased torque (rotating force) at lower speeds. Riding up the steep Wallaceville Road in level 2 assist was quite easy, with little input from me, and I did not need the lowest gear. Désirée found the same when riding up the Mangaroa Hill Road. The hills were not a problem.

Air Resistance

The reduced maximum speed compared with the e20 folding bike means the bike is more efficient at proportionately lower speeds. The power required to overcome the reduced air resistance is lower. But going slower means it takes longer to reach the destination so the reduced demand from the battery occupies more time. It turns out that the power vs speed relationship for a bike is non linear, so there remains an energy advantage with a slower maximum speed. At very slow speeds, where there is little air resistance, this advantage disappears.

Hills

Climbing hills is a different, essentially linear, situation. The power required depends directly on the slope of the hill and the weight of the rider plus bike. Air resistance is usually not so important as speeds are slower. But, because the motor is running slower, it becomes a poorer generator and the power from the battery is split between running the motor and just heating it up. The eMetro motor has a lower maximum speed so it can run at somewhat lower speeds before it becomes grossly inefficient and gets too hot. For this bike, setting to level 1 or 2 and pedalling, using the gears, is the best way to climb hills. Maintaining a speed above 10 km/h will minimise battery use and reduce motor overheating. The intention is that the rider will help to maintain a suitable speed by pedalling.

Battery

The EVE Energy Co., Ltd, lithium polymer battery is rated at 36 volts, 10 amp hours and 360 watt hours. At 10 watt hours per kilometre the nominal range is 36 kilometres. Many riders would exceed that range, especially if some effort is applied.

The battery is charged with a 42 volt power supply rated at 2 amps. This power supply gets warm so it should not be covered. On my bike I use an aluminium sheet underneath to remove some heat. The battery should be topped up as required. Occasionally the charger should be left for a longer time to help individual cells to balance their voltages. This ensures that no particular cell is doing too much work. The battery should be charged at normal room temperatures.

The battery is housed in a metal box. In addition it is protected by and locked to the carrier frame. The key is not needed to run the bike, so it can kept with other keys. The battery has a 42 volt DC port for charging the battery. It also has a 5 volt USB port for charging cell phones and music players. The "ON" button is illuminated.

There is a 12 amp hour battery upgrade available for $175. This has a nominal range of 43 kilometres. For those who might require an even longer range it looks as though the 15 amp hour SmartMotion battery could be readily plugged in. It is a little longer and heavier, but it should fit within the standard carrier.

Wiring

Each electrical item on the bike is connected to the wiring harness by a weatherproof marine grade connector. This allows any item to be easily replaced or even upgraded. The main wiring runs through the frame to the controller. Here another series of connectors allows just the controller to be removed or tested. The controller is part of the carrier, and it sits immediately behind the battery.

Conclusion

This bike was a joy to ride. I had no problems at any point of the ride. It made the hills disappear and it would also make the wind go away as well. It is a sociable way to ride, as riders of different abilities can easily keep pace.

I am attracted to the simplicity of the bike, its neat finish and its ease of riding. There is an attention to detail here.

The bike drive system is usefully redundant. If the chain breaks, the motor can take over. If the battery is flattened the bike is easy to pedal, unpowered, with its wide range gearing. I found that the bike was easy to ride, on the flat, unpowered.

I would personally add a rear view mirror. The only other negative point is that the front wheel is not so conveniently removed for car transport. There are solutions to this, namely a 15 mm spanner or a tow-bar carrier. It is not hard to find a routine that works.

This bike is very good value for money and it is widely supported by many New Zealand bike shops. Because the motor is in the front, routine bike maintenance of most mechanical items on the bike should be relatively easy.

The SmartMotion eMetro has now been renamed the SmartMotion Essence. Some changes include an updated battery and controller design, a five assist-level LED console, an improved carrier which can fit a basket, and a slight price increase to $2099.

I would like to thank Daryl Neal from Wellington Electric Bikes for the opportunity to ride this bike. My main interest in testing this bike was to help retired people, who might now have limited transport options and may want to regain a healthy lifestyle.