Battery usage mid drive vs hub

[krzychoniusz]

Hi everyone, as in the subject line - I was wondering what's the difference in battery usage between mid drive motor (say BBSHD / BBS02) and a hub motor of the same power. Let's assume 10 mile ride, mostly flat, PAS set to max level and identical riding conditions.

Does anyone have an experience with both and could quantify or at least give rule of thumb, I appreciate riding conditions etc. are key but broadly speaking is it about 20-30% more range with mid drives or closer to 5-10% ?

Thanks

 

[anotherkiwi]

I haven't tried with a battery adapted to a mid-motor, the GSM really beat up my bottle battery when I used it. OK so I was running unrestricted and the gearing wasn't sorted.

In theory the usage should be identical with a bike weighing the same weight and the same rider and identical road and weather conditions. You could eek out extra range by clever gearing choice and best use of available gears with a mid-motor. But basic physics say to go a set distance at the same speed etc. etc. etc....

 

[GLJoe]

In theory the usage should be identical with a bike weighing the same weight and the same rider and identical road and weather conditions.

I would have thought this only applies if both motors are operating in the same efficiency zone.

In reality, you can change gear to keep your cadence (and hence the motor RPM) fairly constant with a mid drive.
With a hub drive, only one narrow speed range will be in the max efficiency zone, go slower than this and you waste battery energy as heat.

So in answer to the OP, a 'rule of thumb' is going to be tricky and there won't be only one - it will depend on the motor design(s), your speed relative to this, what your typical cadence is, and how slow things like hills make you go!

 

[Woosh]

is it about 20-30% more range with mid drives or closer to 5-10% ?

much closer to 0%.
In practice, there is no difference unless you are aware of the condition that your motor is in all the time. Efficiency is the ratio between useful mechanical energy and the used battery energy that flows through the electrics. If it's 0.7, then your battery charge produces 70% useful energy, 30% heat. The maximum efficiency for all types of motors is around 0.83. There is room for improvement but progress is very slow on this front.
Besides the fact that a mid drive motor uses the chainring and rear cogs to suit the rider, at the same output in Watts, the efficiency of a crank drive depends on the cadence in the same way that the efficiency of a geared hub drive depends on speed, because both motors work in similar conditions.
So, if both bikes are optimised for 15mph, the CD bike at 80RPM for example, you may just as easily waste energy with a low 50RPM cadence in the same way that you would if you ride your hub drive at 15mph * 50/80 = 9.3mph.
Efficiency depends very much on the riders. High cadence and selecting the right gear are needed for all crank drives. For hub drives, you'll want to get a motor with noload speed at about 30% higher than your main cruising speed.