Mid-drive motors like the popular Bafang BBSHD and BBS02 have many advantages over hub motors including: 1. Low and middle center of gravity for better balance. 2. Use of the drive train by the motor. On a hub drive the motor only has a single gear while a mid-drive motor alomg with the cyclist gets to use all of the gears so the the motor's RPMs stay up in it’s most efficient range where power is maximized and battery use is more efficient. This allows the bike under motor power to 3. Go fast and climb steep hills much better. 4. Retain the quick release hubs on both wheels to make fixing a flat easy or removing the wheels quick - the way we like it. I remember adding a 19mm wrench to my seat bag toolkit so i could change a flat on the road with a rear hub motor - not ideal.
However despite these great benefits most mid-drive motors require a huge sacrifice over hub motors. These motors have a single gear up front requiring us to sacrifice our front derailleur and 2 or 3 chainrings to a single chainring. This means your 27 speed is now a 9 speed. If you want to go fast with a comfortable cadence you get a large chainring. If you want to climb hills you get a small one. Unfortunately, you can't have both. People with steep hills to climb are putting small chainrings on their BBSHD. Because of the architecture of the BBSHD chainrings smaller than 42 teeth tend to mess up their chain line. It also sacrifices their top speed. If you stay with the 46 tooth chainring that comes on the BBSHD or put an even bigger one on it you can bog the motor down on steep hills even in the lowest gear. Hence, we see the single track and San Francisco crowds putting on 42 tooth and smaller chainrings like the Luna Eclipse or Lekkie all the way down to the 30 tooth Luna Mighty Mini. These are great for climbing but at the expense of speed and chain line below 42t.
The 10 or 11 tooth high gear you have on your cassette is as high as it goes so if you want speed and a higher gear the only lever you have to play with is the front chainring. This you do at the expense of your low gears for climbing. But I did say you could have it all in the title above didn't I? Indeed you can if you upgrade to a wide range cassette. If you have an 11-32t or 11-34t like mine you are in for a hill climbing eye-opener when you move up to an 11-42T wide range cassette. You still have your top speed 11 tooth high gear but now you have a 42 tooth low gear in the rear to grind up the hills with. As for the front chainring no need to go below 42T for the steepest hills so you can keep your chain line intact. In fact I had a hard time finding hills the stock 46T couldn't handle. You will still want to upgrade it just on principle though (and to save weight) as it is a plain, heavy piece of stamped steel, whereas the new chainring upgrades from Luna and Lekkie are a lightweight and attractive upgrade.
So what is entailed in the upgrade? It depends on what you are starting with. If you have a 10 speed cassette already you are in luck. Most wide range cassettes are made for 10 or 11 speeds and you can just add a wide range cassette. Sunrace makes a good one that is 11-42T with 10 or 11 cogs. You may need to make some changes to your derailleur like a Wolf Tooth Components Goatlink or a longer B-screw to enable it clear the 42 tooth cog.
If however, you are like me and have an 8 or 9 speed cassette you will need to upgrade to a 10 speed as that is where the new wide range cassettes start. (Edit: the previous sentence is no longer true as Sunrace now makes wide range cassettes 11-40/11-42 for 8-speed and 9-speed drive trains. Available here.) Fortunately, Shimano and SRAM 8 and 9 speeds have the same cassette body type as the 10 speed so without needing to get a new hub and wheel you can upgrade the cassette. In addition to a new cassette you will also need a new shifter and derailleur. This can all be had for less than you might think. I will give a list of the components I used later. This is also an excuse and an opportunity to get some good performance components in your drive train. While I was at it in addition to a nice drive train upgrade, I took the opportunity to fix up my handlebars using Shimano I-Spec B components. Handlebars can get pretty crowded and awkward for DIY e-bikers. More about that upgrade here.
The bike I started with was a Cannondale Lefty with a 9 speed cassette. After doing a BBSHD conversion on it I loved everything about it except for the unfortunate tradeoff between speed and climbing ability the loss of 2 of my chainrings forced on me. It was while researching my options that I discovered that this limitation could be overcome with a wide range cassette but I would need to upgrade my drive train to a 10 speed. The best 11-42t 10 speed cassette at the best price I could find was made by Sunrace. I got the Sunrace CSMS3 steel cassette.
I recommend the Sunrace CSMS3 rather than the lighter and more expensive CSMX3 aluminum cassette. It is cheaper and made of steel but with the high torque of the BBSHD bearing down on it, it will hold together better. Karl Gesslein found out the hard way that the MX3 aluminum version will not hold together under BBSHD loads and he wrote about it here. In an update to the article and a picture of a trashed MX3 he says, "Forget about the aluminum version of this cassette, only buy the steel version CS-MS3 do NOT buy the CSMX3 which will catastrophically fail under any real power. You have been warned."
After researching more into drive train components I went with the Shimano XT M786 Shadow+ 10 Speed Rear Derailleur with a medium cage. The medium cage coupled with a Goatlink allows this mass produced (read that less expensive) high-end derailleur to clear the massive 42T cog on the Sunrace CSMS3 cassette. Here it is installed on the Lefty with the Wolftooth Goatlink and working flawlessly right out of the box.
I chose an I-Spec B compatible shifter so I could get my handlebars the way I wanted them. The shifter is a Shimano XT M780 10 Speed Trigger Shifter. More on getting the handlebars right here.
This upgrade turned a great mid-drive conversion into what for me is the ultimate e-bike. I love it and if you have struggled with the speed vs climbing power mid-drive motor issue, you will too.
What do you think about mid-drive gear ratios on your e-bike?
11/4/2016 10:32:05 pm
Thanks for your article! I'm a bit confused about 10 and 11 speed chains being compatible with the bafang, luna, or lekkie chain-rings. Aren't they too narrow to fit on the wider teeth of the mid-drive, or aren't they too weak to support the torque? I want to upgrade to the One-up 10-50t cassette system and get the 42t Lekkie. With this, I'll climb hills with ease in case the motor/battery dies as well as have a 35+mph top speed. Let me know if you believe this would work based on your setup and experience. And I will of course report back if I go ahead with it. Thanks!
1/21/2022 11:11:32 am
I've a 10 speed bbshd system and just fitted a lekkie type alternate tooth sized sprocket and it fits on fine, even wiggle room for possibly an 11 speed although mine is 10 speed.
2/26/2017 10:18:59 am
Thank you for this great info.
2/27/2017 01:37:55 am
Yes, Wipperman are great. KMC also now makes an ebike chain that will take more abuse. I have just been using regular KMC X10.93 Nickel Plated 116 link chains. They hold up well and I don't mind changing them a little more frequently. Another thing to keep in mind with your drivetrain is you should count the number of teeth you have added to the front chaingring and the large rear cog. That is the number of links you will need to add to your chain. Sometimes it requires 2 chains get it long enough. Save what you don't use and you will only need to buy one chain for your next chain change. :)
3/17/2017 11:28:51 am
I recently completed a BBSHD build on a Ghost Speedline 3. I went with a 46t Lekkie in the front and an 11-36t cassette in the rear using the Ultegra derailleur that came with the bike. This combination gives me a comfortable top assisted peddling speed of about 30mph with a powered top speed higher than that. It also gives me plenty of power to climb the steepest hills I encounter around Seattle. This is really an on-road bike only, so I don't see the need for any lower gear ratios. Perhaps with a mtn bike you'd need that on occasion. Anyway, the gearing really is perfect at this point. Just thought I'd pass that along.
9/15/2017 12:23:41 pm
Jeff, I am considering a Bafang on an Ultra drive train. Some folks have advised against it because of the stress on the components. Have you had any trouble with your setup?
9/15/2017 05:49:11 pm
Paul, I know you asked Jeff but thought I would chime in. The real stress is on the chain and gears. Chain above all. I find I replace chains now about every 800 miles. No big deal considering the benefits. I am running a BBSHD so with a BBS01/02 you would see less wear. Be sure and use a shift sensor or use your brake cutoffs to cut the motor when shifting.
9/15/2017 08:48:41 pm
No problems at all. I have about 1000 miles on the bike since the BBSHD upgrade and so far everything is working real well. I keep the chain well lubricated. I also have the shift sensor installed, but it has proven to be unreliable. I gotten in the habit of pulling in the left brake a bit to disengage the motor before shifting. It seems to work just fine; not unlike using a clutch on a motorcycle. I should also point out that I rarely run the bike at full wattage. Most of the time I leave it in PAS level 2 or 3 and have modified the default programming on the Bafang controller to be easier on the drivetrain.
9/15/2017 05:41:25 pm
Verry interesting tech details. I have an ICE ADVENTURER Trike with bafng bbs02 (500v). I fitted a smaller front chainwheel using an adapter for 104mm BCD CHAIN-WHWWL (38T). I have to use the shorter (152mm) crank arms for use with my proshetic legs. With this I can fit a 22t grant-gear' as a get-me-home emergency.
6/17/2017 12:15:39 am
I purchased the setups you called for and my only issue I am having is the derailleur is not switching over to the largest cog. Any advice?
6/18/2017 12:14:16 am
6/19/2017 12:04:13 pm
9/15/2017 06:01:37 pm
After running this setup for a few years now I have a couple obversations: 1. I love it. 2. With the derailleur extended out for the 42T COG the chain starts to slip on the smaller/higher cogs when the chain starts to wear out. It does not show wear on the cheap gauges or 1 foot chain measurement but it does read 50% wear with a Park Tool chain checker which is the recommended point to change a 10/11/12 speed chain. 3. With a shadow plus derailler with the clutch engaged the standard steel 46T chainring works fine. If your derailleur does not have a clutch you may need a narrow/wide chainring to keep the chain from coming off. 4. Did the new 52T Lekkie for a friend and has a great cadence at 35MPH. Wouldn't recommend it on a mountain bike though. 5. The 46T with an 11-42T or 11/40T climbs great in the mountains with a BBSHD. With a BBS02 I recommend a 42T chainring max if you have any really steap hills where it is hard to keep the front wheel on the ground.
12/6/2017 06:32:57 pm
I was wondering if this would work with a 11-46t Cassette? instead of the 11-42t Cassette that you used. With this setup you have will the derailleur be able to clear the large 46t cog on the 11-46t cassette?
1/11/2018 11:49:01 pm
Good question! You may need the Goat Link (or one of the new chinese knockoffs) as well as a longer B screw. I would try it! However, that said I have seen some weird shifting issues creep in on some setups when going beyond manufacturers design intent. But chances are it will work. The one I did that I wrote this article about is still awesome and shifts smooth.
1/11/2018 10:07:21 pm
1/12/2018 12:07:14 am
Mine is a 68mm BB. The wider the BB the worse the chainline potentially is on a 135mm rear dropout. Wider fat dropouts 170/190/192mm can tolerate a wider bb and in fact require it to keep the chainline from getting out of whack in the other direction. If the Chainstays spread out too far too soon for the size chainring you want to use you will need to add spacers between the bb and gear reduction motor casing. This can also make chainline worse. But hey, cool, you are making you own frame so you have control over all of that. You are way more ambitious than I am. :)
2/11/2018 07:51:17 pm
7/27/2018 09:02:46 am
This is a bad idea.. a maximum 36T derailleur shouldn't be hacked into a max 42T.. by doing it you're pushing the upper pulley away from the smaller cogs making the shifting way slower & less precise.
12/31/2018 11:06:50 am
for some wide range gearing would a sramdd3 24 not be the best
3/15/2019 04:22:56 pm
I am considering a mid drive and have been doing research. Used to be a consideration for the lightest bike, but with the electric motors able to lift real weight, then who cares. The amount of stress on the drive line,would to me require all steel components. The cheapest.
9/26/2020 09:21:10 am
Hi Mark! Just installed all of your recommended components
All this talk of woe at the loss of two chainrings. Compensated for by increasing the cassette range ,10-51 even. This philosophy harks back to the good old days of pure person power and is unnecessary after the introduction of an electric motor. I run a , TSDZ2, (250w) - 1/8 chain - 5speed X-RD5(w) and a Truckrun, (500w) TM-05 - 1/8 chain - 3speed X-RD3. Both climb Snowdonia like Welsh mountain goats. The former needs a little help from me on the steepest slopes but the latter is rather under geared , as such there’s nothing yes nothing it won’t climb and then tops out at 30 km/h plus. Throw your derailleurs, cassette and skinny chain in the bottom drawer and replace with an IGH. Electric motors are torquey beasts and need not a multitude of gears , l’d be glad to change my three for five but that’s enough for sure. There’s an excellent chain alignment at all times, introduce a Surley, chain tensioner and it’s virtually maintenance free. My Nuvinci , has all the same pros with the added benefit of continually variable gears. Then there are eight and fourteen geared options available too. I’ve given it considerable consideration and conclude an IGH,to be ,
8/14/2022 07:45:21 pm
I want to try a Bafang on my Schwinn AXUM 1x8 29". It seems made for mid motor conversion with large rims and 2.6 tires that will take the speed. Any recommendations?
2/16/2023 08:06:52 am
This has a lot of good info. This is really well written. Many of the links are out of date?
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