Are a Hub and Mid Drive comparable by power?

Blunderbuss

Pedelecer
Mar 11, 2018
158
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Cambridge
I am just about to embark on building my second ebike and whilst it will again be for off road i am going to give a mid drive a go, so does anyone know if i can make a simple comparison for power. My current bike is a 500W 48V bafang geared hub with a 20 amp controller, so if i spec the Mid Drive at the same (a BBS02B 48V 500W) am going to be getting something similar in power?
 
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Deleted member 4366

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It depends what you mean by similar. They have completely different characteristics. What is it that you're trying to achieve/improve?
 

Woosh

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May 19, 2012
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so if i spec the Mid Drive at the same (a BBS02B 48V 500W) am going to be getting something similar in power?
if you compare climbing power on a gradient then yes, but as D8veh said, they feel very differently on the bike. The BBS02 is more suitable for off-road.
 

Blunderbuss

Pedelecer
Mar 11, 2018
158
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Cambridge
Having had a hub motor with a big battery on a rack i want to get back to something that feels more like a bike. Don't get me wrong the current bike is great, but compared to a normal bike it is unbalanced/top heavy. So a mid drive with a down tube battery seems the way forward - also it will give me experience of this type of setup as i love the "building it" part as well.
 

wheeliepete

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Feb 28, 2016
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Go for it.:) Mid drive with downtube battery will certainly be more balanced than what you have at present. If you are going for a Bafang unit, make sure you get the improved B version. Lots of sellers still knocking out the older model slightly cheaper.
 
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Deleted member 4366

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Moving the battery to the downtube will make a massive difference without having to change the motor. I'll bet that you won't like the mid-drive as much as your present motor.
 

Blunderbuss

Pedelecer
Mar 11, 2018
158
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Cambridge
Moving the battery to the downtube will make a massive difference without having to change the motor. I'll bet that you won't like the mid-drive as much as your present motor.
Why do you say that about the mid drive? You are right that i really like the G/H but i can only compare that to the D/D. On my present frame (has dual suspension) there is no room for a down tube so i am looking at a 3 or 4 year old Carrera or something similar on ebay for £150 to be the donor bike.
 

Woosh

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Blunderbuss

Pedelecer
Mar 11, 2018
158
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Cambridge
Unfortunately i don't have even that amount of room - i made a bad choice for the frame type. I thought the dual suspension would be best but it occupies most of the space. I had managed to cable tie a 10AH bottle battery in the gap when i first built it (it did not fit with the holder screwed to the bottle screws) so i could give that a go.
 

Woosh

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one of my customers fit the battery under the downtube. The kit is a GSM, same dimensions as the BBS.

 
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Deleted member 4366

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Why do you say that about the mid drive?
Jerky torque in the lower gears; crunchy gear-changing, especially when going up hills or caught stopped in too high a gear; the need to be always in the right gear; chain-line problems cause chain to come off; noise; reliability issues.

None of these things are bad enough to be a deal-breaker, but they all add up to give a less satisfying riding experience. I can remember when I first fitted a 500w crank-motor. I thought it was great for the first half hour as I powered through each gear like a racing motorbike, but in the depths of winter with cold hands, all that gear shifting started to become very tedious.

For me, the only real advantages of a crank-drive are for off-road cycling, where the lack of mass in the wheels allows the suspension to work properly and the central mass gives better response to changes in direction, plus you can get more torque for very steep climbs that you don't find on the road. On the road, a CD could still be useful if you wanted ultimate speed from low power, because a CD can still give max power at any speed, depending on gearing. That could be what you want with a road bike conversion, but for touring, commuting and generally riding around, the correct choice of hub-motor can give you all the speed and power you want and it'll deliver its power in a much more user-friendly way.
 

Woosh

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I have 5 favourite bikes, only one of them has a crank drive and it's not a BBS.
 

rilot

Pedelecer
Jul 16, 2017
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That bike with the battery mounted underneath the down-tube.... Won't the front wheel hit it when the suspension bottoms out? I can see that being potentially lethal.
 

Blunderbuss

Pedelecer
Mar 11, 2018
158
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Cambridge
From what you folks are saying my plans for the C/D are melting away fast - if i just get a better frame for my existing components then i may get what i need. My "quest" was get the weight down and move the bits you do need into the centre and as low as possible (mounting the battery under the downtube looks an excellent idea if there is room). My current frame is a cheap Argos bike (no problems with it for the money) but i know i can do better for a riding experience.
 

Woosh

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I can see that being potentially lethal.
he's counting on the wheel going in the right direction, the battery will help to push the tyre away.
 

rilot

Pedelecer
Jul 16, 2017
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I suppose he could drop some rubber stoppers in the bottom of the forks to stop them from compressing for their entire travel.
 
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Deleted member 4366

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I'd look for a new donor bike. They don't cost much. You can always take the opportunity to improve it too.
 

Woosh

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May 19, 2012
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I'd look for a new donor bike. They don't cost much. You can always take the opportunity to improve it too.
year after year, I find that customers are willing to spend more on the mechanical bike. This year, we sell a lot more bikes with hydraulic brakes than mechanical brakes. I guess we'd stop selling mechanical brakes in a couple of years.
I am looking at reducing the bike's weight this year. Fit lighter pedals, saddles and seat posts for a start.
I would recommend to go for a very good donor bike, aim for £500 donor bike before looking into fitting a kit to it.
 

anotherkiwi

Esteemed Pedelecer
Jan 26, 2015
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Answer: the power is identical, how it is applied to the rear wheel is different.

When I had the hub motor bike I was always changing gears and assistance levels, I can't see any difference with a mid drive in that respect. I don't have issues changing gears in fact they change so quietly sometimes I check to see if it has changed. Jerky torque goes away with the right controller and a 12 magnet PAS disk. On the hilly bits (most roads around here) the mid motor is more relaxing if you want it to be - just change down and spin in cadence. I think hub motors climb faster but as I only have a legal one that means I have to pedal harder to keep it happy. My terrain probably requires a 500 W hub motor like the Q128 to get the same climbing performance as I get from the GSM. My chainline is so-so because I have two chainrings mounted - the big ring is OK in the 4 top gears and the little ring OK in the 4 bottom gears. That does mean I have a bit of a gap between the two but the assistance helps to smooth that out.

If you want to break the law it is easier with a mid drive - turn of restriction and you will be riding at s-pedelec speeds on the flat. As d8veh notes higher up you get all the Watts available in all of the gears so, as you need about 500W to do 45 km/h, you just turn assistance up to level 4 and get in the right gear. Once you get to those speeds air resistance becomes a major problem, sometimes I dream of a tri-athlete style bike for the GSM just to scare the willies out of me and whoever else is out for a ride :)