How do you size the right Mid Drive?

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geosped   100 W

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How do you size the right Mid Drive?

Post by geosped » Oct 15 2020 10:53am

So I'm not new to e-bikes. I built a really cool off road mountain bike that I used for years. BMC Rear hub on 50v made well over 1000w and had plenty of power. Actually with all the weight including the battery on the rear tire it was very sketchy at times. All I do is just ride for fun and exercise off road on mountain bike trails. So I want a new mid-drive but how do I size the right one?

1) Strictly off road mountain biking trails.
2) 250lbs
3) Trails are I ride have some really steep sections with lots of big thick roots. Not uncommon where I have to get off and walk around it.
4) lots of tight single track with lots of switch backs. Very slow and challenging especially when going up hill.

I'm using a 26" full suspension bike. Now the big question is how much power do I need? There are several great mid drives out there. All of the commercial hard core mountain bikes ($3500) and up seem to use a much lower power system and much smaller batteries that what I'm seeing. Tenshong and Bfang offer 500w 750w 1000w on 48v and 750w 1200w 1500w on 52v batteries respectively. Assuming the controller is setup to take the higher voltage batteries. So how do I make sure I get a system strong enough to carry me up the hill with out burning anything out and at the same time not too powerful where it's dangerous? Do I really need 1500w to get me up a steep hill?

Thoughts and suggestions.

Green bike is what I used to ride. This hub motor easily made 1200w but like I said it was very sketchy the way I had the battery pack mounted. Not ideal at all. In the end I burned out the halls sensors and decided to go in another direction.

Blue bike is the new donor bike. Just need help in deciding to go to the 750w 48v - 1200w 52v BBSH02 option OR should I go with the BBSHD 1000w 48v - 1500w 52v option?
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geosped   100 W

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How do I size the proper mid-drive for off road use?

Post by geosped » Oct 15 2020 10:56am

So I'm not new to e-bikes. I built a really cool off road mountain bike that I used for years. BMC Rear hub on 50v made well over 1000w and had plenty of power. Actually with all the weight including the battery on the rear tire it was very sketchy at times. All I do is just ride for fun and exercise off road on mountain bike trails. So I want a new mid-drive but how do I size the right one?

1) Strictly off road mountain biking trails.
2) 250lbs
3) Trails are I ride have some really steep sections with lots of big thick roots. Not uncommon where I have to get off and walk around it.
4) lots of tight single track with lots of switch backs. Very slow and challenging especially when going up hill.

I'm using a 26" full suspension bike. Now the big question is how much power do I need? There are several great mid drives out there. All of the commercial hard core mountain bikes ($3500) and up seem to use a much lower power system and much smaller batteries that what I'm seeing. Tenshong and Bfang offer 500w 750w 1000w on 48v and 750w 1200w 1500w on 52v batteries respectively. Assuming the controller is setup to take the higher voltage batteries. So how do I make sure I get a system strong enough to carry me up the hill with out burning anything out and at the same time not too powerful where it's dangerous? Do I really need 1500w to get me up a steep hill?

Thoughts and suggestions.

Green bike is what I used to ride. This hub motor easily made 1200w but like I said it was very sketchy the way I had the battery pack mounted. Not ideal at all. In the end I burned out the halls sensors and decided to go in another direction.

Blue bike is the new donor bike. Just need help in deciding to go to the 750w 48v - 1200w 52v BBS02 option OR should I go with the BBSHD 1000w 48v - 1500w 52v option?
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Last edited by geosped on Oct 25 2020 1:23pm, edited 1 time in total.
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Wolfeman   100 W

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Re: How do I size the proper mid-drive for off road use?

Post by Wolfeman » Oct 15 2020 11:31am

geosped wrote:
Oct 15 2020 10:56am

Blue bike is the new donor bike. Just need help in deciding to go to the 750w 48v - 1200w 52v BBSH02 option OR should I go with the BBSHD 1000w 48v - 1500w 52v option?
Good morning. I have 2 bikes with BBS02 drives from Luna Cycle that max out at 1.3kW and I love them both. That being said, my next MTB build will be a BBSHD just for extra durability. I think the HD gives you more room to grow/hotrod later on. Put on a 36T Lekkie chainring with a good battery and you will not be disappointed. Mid-drives are really fun.
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Re: How do I size the proper mid-drive for off road use?

Post by markz » Oct 15 2020 1:07pm

BBSHD is the better choice. How many gears are on the rear (8,9,10,11,12 speed?) of those two bicycles?

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Re: How do I size the proper mid-drive for off road use?

Post by MikeSSS » Oct 15 2020 1:20pm

Battery location: My FS bike is much like the green bike, uses a rear MAC motor with 52v, 20ah, 14s, 8p battery.

Battery in the bag made it hard to handle when stopped or riding uphill, especially in tricky conditions.

I moved the battery to the left side of the mid frame tubes, adjacent to where the battery would be if there was a center triangle to mount it in. Now the bike is much easier to handle when stopped or in slow climbing or tight stuff. I don't notice any problems from the weight offset to one side. I did use a pedal extension on the battery side.

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geosped   100 W

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Re: How do I size the proper mid-drive for off road use?

Post by geosped » Oct 15 2020 1:45pm

markz wrote:
Oct 15 2020 1:07pm
BBSHD is the better choice. How many gears are on the rear (8,9,10,11,12 speed?) of those two bicycles?
Both bikes have a 9sp cassette in the rear.

From what I've read the BBSHD is better than the BBS02 in several ways someone correct me here. 1) steel housing is bigger heavier better cooling 2) internals are beefier 3) motor handles a lot more power. 4) larger controller. 30a vs 25a
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Re: How do I size the proper mid-drive for off road use?

Post by kcuf » Oct 15 2020 7:09pm

bbshd = bbs03

somewhat more rugged

hd about 3lbs heavier than 02

hd motor seemingly less efficient windings


hd likely hold up better off roading


can be found in wider BB spacing too

fat tire bikes hmm
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Re: How do I size the proper mid-drive for off road use?

Post by Balmorhea » Oct 16 2020 1:03am

The less power you have in a mid drive, the lower the gear ratios you'll need to deal with any given situation.

Conversely, the more power you have, the faster you can ride uphill or on difficult surfaces.

So it becomes less a question of how much power you need, and more about how fast do you want to go? (And how often do you want to break your toys?)
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Re: How do I size the proper mid-drive for off road use?

Post by markz » Oct 16 2020 2:00am

Carry a spare chain or 2 just in case, the long walk home is a good time for pondering the ebike life.

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Re: How do you size the right Mid Drive?

Post by Limbs » Oct 16 2020 7:55am

I don't have any experience of different powered mid drives, just a 250w Bosch system, but seeing as no one else has answered so far.

I ride with only one arm, plus other health conditions, which that mean I don't have much energy, but I mange to ride pretty much everywhere I want to in Tenerife, which includes some incredibly steep & very rocky climbs. Due to my health issues, I ride almost exclusively in turbo mode and it's great; the beauty of a mid drive is that the motor gets geared down at the same time as you change down for the benefit of your legs. I ride with a couple of other guys, who ride more for the exercise and only use Eco or Tour modes, they have also fitted larger rear sprockets to help on the steep climbs, but they still get off and walk sometimes, where I ride (I carry a spare battery, they don't).

Whilst the Bosch is rated @ 250W, I have seen peaks of 720W on a meter the same as yours.

So, in summary, 250w is enough, but it does depend on your fitness level, how much effort you want to put in etc, I'm half your weight BTW. If you want to put in less effort, go faster etc, then a more powerful unit would be beneficial.

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Re: How do you size the right Mid Drive?

Post by ZeroEm » Oct 16 2020 8:25am

I'm sure the mid Drive fans will chime in soon!
If he was talking about DD hub then more watts the better. With the mid drive you need to thing about the chain and how fast you want it to replace it all. So I would stay below 1200w.
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Re: How do you size the right Mid Drive?

Post by SlowCo » Oct 16 2020 8:45am

You seem to be a slow (in a positive way) and technical rider. If you don't need speed then it's all in the gearing and a mid drive will help in any gear. Riding such technical climbs weight and CoG are key I think. So you'll probably be happiest with a low weight torque sensor system like the TSDZ2 with the open source firmware. And get the smallest battery pack that will do your longest ride distance.

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Re: How do you size the right Mid Drive?

Post by pwd » Oct 16 2020 8:58am

The beauty of a mid drive is that you can utilize the bike's rear cassette/freewheel which allows you to tackle those steep; rooty, low speed climbs with minimal power.

Here is a quick example in the simulator using a BBS02 Motor set to 20A max battery current @52V. I only picked this motor because it is very common and one of the few mid drives available in the simulator. You can see the performance with two different rear cogs selected (You can adjust the grade etc... as necessary):

https://ebikes.ca/tools/simulator.html? ... mass_b=120

If we dial the max current down to only 10A battery / 30A phase you can see the bike will still make the same climb without overheating:
https://ebikes.ca/tools/simulator.html? ... _30_0.03_V

Here is a comparison of 20A battery 60A Phase vs 10A battery 30A phase with the same gear selection:
https://ebikes.ca/tools/simulator.html? ... _60_0.03_V

With more power; you can climb steeper hills more aggressively depending on the size of the motor. Larger motor's (more copper) will be able to take more power before overheating with all gearing etc... being equal. For what it's worth; I really enjoy my Cyclone 3000 motor on 52V /40A batt (not sure what the phase amps are) on "technical" mtb trails. I have tried dialing both the phase current and battery current down to 50% and was still able to do the same climbs; just at a slower rate.
Commuter/Street Build viewtopic.php?f=6&t=98286:
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geosped   100 W

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Re: How do I size the proper mid-drive for off road use?

Post by geosped » Oct 16 2020 9:49am

markz wrote:
Oct 16 2020 2:00am
Carry a spare chain or 2 just in case, the long walk home is a good time for pondering the ebike life.
I have a couple of chain links I carry in my back pack but wow your saying carry a whole chain? Has anyone waxed there chain? A couple of youtube video's on doing a DIY chain wax increases the durability and reduces a lot of the friction blah blah blah.... Just curious if this is a "thing" in the e-bike community seeing how much more stress we put on the bikes. The guy seemed very convincing. His video series was pretty cool. And was thinking about going through the trouble but I dont have an extra crock pot to spare lol.

Let me know if this is worth doing.

https://www.youtube.com/watch?v=HHr9znwpwmQ
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geosped   100 W

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Re: How do I size the proper mid-drive for off road use?

Post by geosped » Oct 16 2020 9:55am

I just noticed I created two identical topics. Man getting old sucks. lol sorry about the two threads which cover the same topic. If I could merge the two I would.
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Re: How do I size the proper mid-drive for off road use?

Post by kcuf » Oct 16 2020 10:24am

carry chain breaker and spare links + master

if when derailleur craps

or chain breaks

can usually rework chain

for limp mode


chain lube over rated

measure chain wear

replace $10-$15 chain showing minor wear
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Re: How do I size the proper mid-drive for off road use?

Post by 2old » Oct 16 2020 10:51am

My BBS02 has survived five years of socal fairly hilly off road travel without a whimper, but I like to pedal and the BBSHD probably would be overkill. One thing you'll learn if riding tight switchbacks is how to pedal smoothly since you can't stop pedaling "going round the bend" or the power shuts off. Also, I carry a chainbreaker and extra link, but have never broken a chain in probably 500 outings. An eight-speed drivetrain is inexpensive and wears well. AFAIK, chains from eight-speed to at least eleven speed have the same inner width, and only the outer changes. Seems to me the thicker chain would wear less.

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Re: How do I size the proper mid-drive for off road use?

Post by HrKlev » Oct 16 2020 12:34pm

If you're building a bike for exercising and like pedaling, why not build something lightweight with proper torque sensing assistance to keep the bike feel?
DIY lightweight mid drive with torque sensing build thread: viewtopic.php?f=6&t=107622

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Re: How do I size the proper mid-drive for off road use?

Post by markz » Oct 16 2020 1:19pm

Because you all know a bicycles drive train, crank, chain, front der, rear der is designed and engineered for 10+ times human power
:oops:

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Re: How do I size the proper mid-drive for off road use?

Post by Balmorhea » Oct 17 2020 12:37am

HrKlev wrote:
Oct 16 2020 12:34pm
If you're building a bike for exercising and like pedaling, why not build something lightweight with proper torque sensing assistance to keep the bike feel?
Until there's a reliable system for DIY torque sensing power assist, I'm going to recommend against that. It would be nice. What we actually have is either fussy, fragile, expensive, complicated to install torque sensing enhancements for the Cycle Analyst, or TSDZ2 which is a flaming bag of turds.

If you know of something better that's DIY friendly, please let us know.
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Re: How do I size the proper mid-drive for off road use?

Post by HrKlev » Oct 17 2020 2:15am

Balmorhea wrote:
Oct 17 2020 12:37am

Until there's a reliable system for DIY torque sensing power assist, I'm going to recommend against that. It would be nice. What we actually have is either fussy, fragile, expensive, complicated to install torque sensing enhancements for the Cycle Analyst, or TSDZ2 which is a flaming bag of turds.

If you know of something better that's DIY friendly, please let us know.
I will have to agree for the most. There are solutions out there, but they are not in the bolt-on category. So it depends on how much fab work OP would be willing to do. For bolt-on, If I had the patience for it, I would wait and see how the first lightest.bike kits will perform. Having owned a couple tsdz2's myself, they are awesome when they work, but I would not recommend it because of all the flaws.
DIY lightweight mid drive with torque sensing build thread: viewtopic.php?f=6&t=107622

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Re: How do you size the right Mid Drive?

Post by leisesturm » Oct 17 2020 3:50am

geosped wrote:
Oct 15 2020 10:53am
. So how do I make sure I get a system strong enough to carry me up the hill with out burning anything out and at the same time not too powerful where it's dangerous? Do I really need 1500w to get me up a steep hill?
If your choice is between the BBS02 and the BBSHD I would say get the BBSHD. 1500W is not dangerous unless you do something ... unwise. The bigger motor will be built tougher and that will pay off because any kind of off-road puts tons more stress on every part of an ebike drivetrain and motor than any kind of street use.

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Re: How do you size the right Mid Drive?

Post by Skaiwerd » Oct 17 2020 9:12am

I’m with PWD and the cyclone. I have years on mine but don’t run at %50. More is always more. You can always ride under full throttle and have some reserve power for bursts and an out for tricky situations like wiping out or falling over, like something with power can do. More power is less shifting. Find the right gear setup and go single speed if you want, may require 75v to have speed for the flats.

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geosped   100 W

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Re: How do you size the right Mid Drive?

Post by geosped » Oct 17 2020 9:52am

So I went with the BBSHD and 52v 17.5 ah triangle pack. I was torn between the BBSHD and Tenshong. I started looking at the TenShong because I really like the idea of torque sensing and pedal assist. More natural feel more of a real assist. Keeps the bike lighter and more nimble but also let's it feel more like a normal bike. All these positive attributes are really important to me. The big hurdle I couldn't get over was I didn't think it would be strong enough to haul me up. I think with a 52v battery folks have been pushing it to 1000w which would probably be just fine. A bit of fear kicked in since I already burned out my BMC rear hub motor at 1200w. And that's how I made my decision. If Tenshong had a more powerful option I would have probably gone in that direction.

For me getting an ebike is about getting my phat butt up the hill without having to get off and walk BUT more importantly it's about exercise. Unfortunately most of the trails are I ride I half to get off and walk a little. It sounds like I may have to adjust the BBSHD to allow me to work a little harder so I get that good workout and at the same time not having to get off and walk. If it's not so natural that's a consession im willing to make.
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Re: How do I size the proper mid-drive for off road use?

Post by Balmorhea » Oct 17 2020 11:29am

I had not heard of lightest.bike systems. I hope they work out.
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