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CTC Cambridge

Electric bikes: mid drive or hub drive?

Saturday, 14 October 2017 

Mike Stapleton writes: I have recently taken a great interest in the relative merits of the two basic types of electric bike that are available: mid-drive and hub drive, although my experience is limited as I have only ridden three different bikes. There are a range of matters that need to be considered but the question of safety, in general and when riding with our club, has to be a major issue.

What's the difference between the two types of drive?

In a mid drive system the motor is located with the crank system beside the bottom bracket. It drives the crank through a gear and has a free wheel system. When the motor stops there is no drag on the system.

In a hub drive system the motor is located in one of the wheels and seems to have a significant level of drag when it switches off particularly uphill. You don't feel the drag at other times.

There is remarkably little info on these matters available on the internet. Cycle, the magazine of Cycling UK, has published £2000 Pedelecs: Cube Touring Hybrid Pro 400 EE vs Giant Prime E +3W. This reviews two bikes, a Cube and a Giant, and suggests the Raleigh Captus and a Kalkhoff as alternatives. Australian website has published also a good article Mid drive vs hub drive, which compares the two systems.

Neither of these articles address the problems that may occur when riding with a club. To understand these problems you first need to know just how each drive works.

Mid drive systems

Mid drive systems such as my Captus e-bike drive the bike via a normal chain drive system. This means they are closely aligned to the needs of the rider. Furthermore they have three sensors to determine how much power to apply to the system. These sensors detect pedal rotation, pressure on the pedals and speed. They also have an overall setting from the control panel that determines the general level of assistance. The motor has a connection to the system via a freewheel so that when the motor is not running there is no drag on the system. This means that the response of the system is very fast and is proportionate to the rider's need. When starting from stop it cuts in within half a pedal stroke.

Features: As this type of drive senses reduced effort very quickly, mid drive systems do not need to have an independent stop system on the motor, unlike hub systems which have one which is operated by the brake levers. This means that the brake levers can be used to adjust speed while riding without cutting the motor. This means that with a mid drive system it is possible to ride behind others, except when climbing steep hills. Climbing steep hills behind others is impossible as the motor needs to run at a minimum speed and even in the lowest gear it is not possible to ride below about 7mph. I apologise for having to overtake other club riders when going uphill!

Range: Mid drive systems are a little more efficient and so achieve about a 20% greater range than hub drive systems for the same battery capacity. My experience is that my Captus, with a 300 watt hour battery, is capable of 50-60 miles in "eco" mode and about 45 miles in "tourist" mode. Running speeds are about 12-13 mph in eco mode and 13-15 in Tourist mode. Climbing hills in Cambridgeshire (such as Croydon hill) reduces the range by about 2 miles per hill.

Gearing: The Captus had a 9-speed rear mechanism. It has good bar controls which are easy to reach. The Captus has front shocks which are more trouble than they are worth for a road cyclist.

Battery and Recharge: The Captus comes with a 4 amp charger and recharges from empty in less than two and a half hours. An hour of charge gets you an extra 20 miles of range, which means that charging is fast enough to justify taking the charger with me and recharging at a café or garden centre while having coffee. This increases my range to about 65 miles. Larger batteries are available, but I was not offered one when I bought the bike. Prices are very high and the 500 watt hour version is over £600 online and £800 at a dealer. The battery slides into its position under the carrier and locks in place. It is very easy to remove.

Hill climbing: In eco mode my Captus is capable of about 1 in 20 climbs (5%). In tour mode it is about 1 in 10 (10%). In sport mode is is probably able to climb about 1 in 7 (14%). Turbo mode is even more powerful, allowing you to climb 1 in 5 (20%), though in all these cases you still have to work fairly hard.

Computer: The computer is excellent. It is easily the best computer I have ever had on a bike. The display has a remaining charge indicator, a power meter & speed in the main display. It has also a part of the display showing estimated range, trip time, trip distance, odometer, average speed and time controlled by the handlebar switch which enables you to change up, down or off while riding. This controller has a middle button that selects what is on the subsidiary display. There is a button on the side which puts the bike into walking mode. The unit is removable or can be screw locked to the holder. (There are hidden displays for maintenance purposes).

Weight: about 25Kg

Price: £1480 (in 2017). It is expensive but very well made. I've done nearly 6000 miles on mine and have only replaced one tyre and one chain.

Hub Drive systems

I have experience of riding two slightly different e-bikes with hub drive. One I hired on the Isle of Wight and the other I had the use of prior to a sales display for Peter's Pedals at the Melbourn Hub.

The one I hired on the IOW was called a Red Squirrel and was a Chinese build with a fairly standard controller. This controller was also used for the Peter's Pedals bike.

The computer on the Peter's Pedals and the Red Squirrel Bikes

Bosch handlebar controller

The Red Squirrel had a 500 Watt hour battery. It was removable by pulling it out of the carrier in which it was mounted, it had a lock. The bike came with a 7 speed rear dérailleur. It had fairly good bar controls for the gears. There was a 1.8A battery charger that took approx 6 hour for a full recharge so it was not practical to recharge it at a café.

The rider drives the rear wheel while the hub drives the front wheel. On a dry day it managed a 1 in 5 hill... just! It had front shocks which are more trouble than they are worth, and which could not be turned off.

The computer/controller is very basic. There is no subsidiary bar switch. Changing power level while riding is possible but not easy. Changing power level down is not possible without going through the HIGH mode and OFF. There is a power level indicator with three lights which shows low, medium or high. There is a charge level system using four LEDs. There is a button with LED for a good set of cycle lights. There is a USB socket. The unit is not removable. If you ride solo in mid range there is very little need to change the power setting.

The way the system powers the drive is to provide a set level of drive to the wheel irrespective of the effort you are putting into the bike. If you are following someone it usually catches up with them, particularly up hill. Even reducing effort to a minimum by just turning the pedals, even in LOW mode, is usually too much and you start overtaking the person in front. If you stop pedalling there is a significant delay before the motor cuts. Then you slow down suddenly. If you then need more power you start pedalling and after a couple of revs it cuts in and you find yourself catching up. Uphill it is dramatically worse as the cutout feels like you have thrown an anchor out the back and then you struggle to keep a heavy bike going uphill until the motor cuts in again and the process is repeated. Changing mode in this situation is even more dangerous.

Range: this was excellent and I never got near running out of power in the IOW, despite it being very hilly. I did 40 miles twice. Mark you, one huge hill of over 600 ft took a quarter of the charge in 6 miles at maximum setting.

Price: Not known. I paid £150 for 6 days hire.

The bike I tried out for Peter's Pedals was very similar. It had its battery mounted behind the seat post with a lock. Getting the battery out was a little difficult as you had to remove the Saddle using a quick release on the set post before you could lift it out.

Gearing: 6 speed dérailleur. Could have done with a seventh gear to allow higher top speed without motor assistance. There was a fairly good bar mounted control.

Computer/controller: There are two sensors, Speed and pedal rotation. It is similar to the Red Squirrel but seemed to have a longer delay when starting and stopping. It had a switch on each brake to override the motor.

Drive: The motor was located in the rear wheel.

LOW range: I did several tests on LOW range. I rode it in typical local country areas. In LOW or ECO mode it did 25 miles on less than a quarter charge. I guess 100 miles was possible. There was not much assistance so average speed was about 10 mph on the flat.

MID range: In MID mode it did about 48 miles over fairly hilly county going to Saffron Walden. When ridden gently it was doing about 70 miles. The specification quoted a range of 35 to 45 miles. Assistance is about right.

The battery had a 360 watt hour capacity. Charging was slow at 1.8 amps. An hour of charge gave you a mere 8 miles of range, which meant that it was not practical to recharge on the road.

Performance: The cutout and start up time was about 4 pedal strokes which seemed worse than the Red Squirrel. I tried it up the hill out of Saffron Walden and it was not a nice experience, very similar to Red Squirrel. Riding solo it was a good ride. I was sorry to give it back.

Power: It had three power ranges. LOW, which was too low for easy touring, MID which was about right and HIGH which was far too high for Cambridgeshire.

Weight: about 25Kg

Price: Normally £700 but was reduced to £625 at the Melbourn show (a bargain).

All the bikes I tried had cut-outs set at 15.5mph as required by law. I did not notice any significant increase in drag. There is no increase in drag with mid-drive systems as they have a free wheel on the motor.

Mike Stapleton

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