29 September 2017

Batteries, motors and range

Electric bike battery

How far can you ride an electric bike before recharging?

This is one of the most frequently asked questions about e-bikes and there’s no single answer. The battery stores energy which can do a certain amount of work, and how quickly the energy gets used up depends on how hard the motor is working. The main factors affecting the work done and energy expended are, in no particular order, hills, headwind, rider weight, rider effort, level of assist from the bike, speed (produces more headwind), tyre pressure and road surface. Also temperature affects range (cold weather reduces battery output). So it’s not surprising if when you ask, you get an answer starting “It depends…”

Motor type

Mid-motors will generally be more efficient than hub motors as they use the gearing of the bike allowing the motor to operate within it’s efficient rpm range more of the time. But they are more expensive and it could be more cost effective to just buy a higher capacity battery with a hub motor.

For example QWIC make two models that are identical except for the motor: the front motor T FN7.2 is £1,799 and the mid-motor T MN7.2, which is £200 more at £1,999. The real world figures below indicate the mid-motor will increase the range by 20-25%. However for the same £200 you get a battery with 33% more capacity. (The range calculation is definitely not precise, but does illustrate the point.)

Also the mid-motor advantage is greatest with hilly terrain and stop start riding, where a hub motor will be working at lower rpm. So if you spend your time cruising for long stretches without stopping on relatively flat roads there won’t be such a big difference between the two types of motor in terms of range with the same battery.

Real world data

Headwind – photo: capovelo

With so many variables maybe the best way to answer the question of how far you can go with a given bike and battery is to give some real world examples.

I tested a couple of bikes on a full battery and got these results:

On an Ave with a Bosch mid-motor, a 300Wh battery and assistance kept at 75% I got 35 miles riding in London – so plenty of stop/start and a few slight hills. Rider weight is 66 kg.

On an EBCO UCL-10 with a front hub 250W motor, a 320Wh battery with assistance on 75-100% (mostly 100%) I got 29 miles with the same mixed London riding.

To test the difference hills made I rode the same 250W hub motor e-bike up and down a big hill (to Hampstead) and got 23.5 miles.

Test results from others

QWIC P-RD9 with a 250W rear hub motor: 100km (62m) range with 625Wh battery on assistance level 7 (out of 8). Rider weighs 96kg.

Easy Go with 250W motor: 26 miles with 216Wh battery with maximum assist. Rider 81Kg.

The short Answer

When asked I say about 30 miles with a standard battery riding around London, but do point out that I’m relatively light and used to riding bikes.

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