How To Build a Mid Drive Ebike That Doesn’t Break
No wearing-out of the drivetrain early. No broken chains. No motor shifting… No whining. Read this so you don’t become That Guy on the internet.
This article is the follow-up to How To Ride a Mid Drive Ebike Without Breaking It. That article points out how most of the online tantrums about unreliable mid drive ebikes are bad riding, not bad equipment.
This article’s main points are all found in different posts here on this site, and together, here and there, they all cover the ground I am re-covering here. However, this subject comes up so often I decided to try and consolidate things into one place.
I am not trying to list every single thing you need to do to build a bike (I don’t mention tightening all the bolts or putting air in the tires, for example). I’m trying to shine a light on the more common mistakes. Don’t make them and you stand a good chance of having a trouble-free bike. Some of this stuff is pricey, so maybe you’ll want to work it in bit by bit as budget permits.
Remember: a successful DIY mid drive is about both building and riding optimally. Mid drives – particularly the ones made for USA-legal and adventurous, off road DIY builders – up the ante on the required competence of both builder and rider. There is no way around this. If you want idiot-proof and simple do a hub kit. If you want the versatility that comes with a mid drive, though, you need to put in the extra time and effort. There is no way around this.
I’ll FOCUS solely on the mechanical bits this time, and break the process down into key component areas. We’ll start with:
Pick a Frame…
To get a mid drive to work properly, you need to pick a frame that can handle it, and this is not a given. Lots of frames are a bad choice. So what are we looking for?
… That Handles The Torque
I can still remember looking down at my very first mid drive build, a 4kw Cyclone, and saw the motor flex when I hit the throttle. With that flex, the whole bottom bracket flexed with it.
Thats a bad thing. Pick a frame of very sturdy construction. You are going to have an electric motor giving one hell of a pull on a chain that is connected to your back hub. That pull can flex the entire bike frame.
Can your typical mountain bike do it? Yes. Can your road bike with Columbus tubing from the 1980’s do it? Ehhhh lets say no on that one. Whats the problem? Designed for light weight and strength keyed to relatively smooth roads and human power, the stays are too spindly. All that power can pretzel the poor, innocent chainstays and seatstays when the power of ten pro riders yank on the chain.
How do you fix that? A lighter-duty BBS02 with the amp output dialed down is one solution I have seen done successfully several times. The lower amps do not yank on the chain hard. Some effort on the builder’s part to change the settings so pedal assist is kind and gentle is also important (and also preserves an authentic cycling experience).
… That Fits The Motor
Modern downtubes on mountain bikes tend to be curved and swoopy, coming into the bottom bracket at an arc that equates to a roughly 3-o’clock position. That arc means an installed external motor like a BBSxx has no choice but to hang straight down. Kiss goodbye your ground clearance. Here’s a picture of my 2018 Guerrilla Gravity Smash:
Take a look at how the down tube is curved, and how, on the right image where the drivetrain has been removed, its clear the only way to put a BBSxx-style motor on a bike like this will result in that motor hanging straight down.
You can see, sitting on the floor in that right picture, a Cyc X1 Pro motor, which has long arms that mount the motor as far forward as possible to avoid this ‘angle of the dangle’ problem.
How did I do in terms of mounting the motor and preserving ground clearance? Well, look above at the final installation. Look how low the chainring is. Draw an imaginary horizontal line parallel to the ground from that chainring… the motor is above that line.
The higher the better, but bottom line here is the motor is above the drivetrain so we haven’t lost a lot of ground clearance on this frame by using it (with the right mounting kit a Tangent Ascent motor will fit inside the triangle, just under the shock). So, this frame that is totally unsuited to one kind of motor can be pretty well suited to another.
Here’s another example frame. This is the type of frame typically recommended for a BBSHD, BBS02 or similar motor:
The down tube of this frame is straight as an arrow and attaches to the bottom bracket at a high angle. This allows you to rotate a dangly motor like a BBSHD up as far as possible so you lose as little ground clearance as possible. How did this shake out once this bike was built?
It came out pretty good. Bearing in mind this bike used a smaller-than-usual 40T chainring, the motor is roughly at the same height above the ground as the chainring. Maybe just a bit below. This is as good of a fit as you can expect on a bike for this kind of motor.
So… the lesson here is to think through your motor choice if you already have a frame to work with. Or the reverse if you have a motor on the shelf that needs a frame.
… That offers Good Chain / Crankarm Alignment
This is a tough one to nail down in advance. On chain alignment, you can come close during frame selection but you’ll never know for sure until you actually fit a motor into the frame, along with an assembled rear wheel so you can drape the chain and figure out how it lays.
As to crankarm alignment… thats one you will have to work out once you have a bike on a stand during the build. The key is to remember that your desired final result is to align the pedals directly underneath you… not the crankarms. Focusing on the pedals gives you a couple of extra options over and above finding an offset pair of arms to even things up. I have used uneven-width pedal spacers for some big changes, and different washer counts on one side or the other (from zero up to two) to move the pedals an additional 1.5mm to 3mm in either direction.
Buy The Right Drivetrain Parts
So very many builds fall on their face because the builder left cheap parts on the bike rather than replacing with strong ones.
Here is another topic already done to death elsewhere. The options laid out here result in significantly different chain alignments. This is a pretty good general resource on the subject:
Generally speaking for BBSxx style motors with a large secondary housing located where the chainring ordinarily resides, you want a chainring with an inward offset that helps with chain alignment.
You also don’t want to overdo the size of the ring. Generally, “smaller is better” thanks to the rules that go along with riding a mid drive ebike (See below). You don’t want to pick a big ring unless you know exactly what you are doing with regard to gear selection and chainline. 42T is typically considered ideal unless you are riding singletrack. You go as small as you can get away with in that case.
Do a little shopping and you’ll find quality offset chainrings from the usual big name players aren’t cheap. Especially post-COVID. Here’s a new one I found recently on Amazon that offers about 15mm of offset and is well constructed. The offset looks to be more than that simply because the alloy used in construction is so thick.
I bought this ring and it appears a solid alternative – with a great tooth profile – for about half the cost of the other high end rings.
A beefed up chain is often overlooked and just as often results in an Epic Fail. You can’t run a powerful mid drive and expect to use the cheapo chain you already have on your bike. Whatever you do, don’t use a cosmetic (painted) pretty chain, or one of those pricey skeletonized weight-weenie chains. Instead, spring the bucks and buy a proper strong chain.
I run 11-speed systems with a KMC e11 chain – the KMC ‘e’ line is specifically designed to take a mid drive’s punishment. These 11s chains are brutally expensive (today’s price is over US47), but this is part of the cost of admission if you want to run 11s and a high powered motor that doesn’t snap chains (or wear them out really fast). 11-speed is a wonderful thing to have on an ebike – particularly on a bike you pedal instead of throttling – but the cost of durable 11s drivetrain parts is a serious deterrent.
The story gets a lot better if you are using an 8, 9 or 10-speed setup. The SRAM EX1 ebike chain is used for their (hideously expensive) 8-speed EX1 mid drive-stressed drivetrain system. Here’s the thing though: That chain has an MSRP of US28, and is usually sold for about US25. The link above to Amazon has it on sale right now for US18.95.
It gets better still: The EX1 system is 8-speed, but the chain is sized for a 10-speed system. That means you can use this chain on 8-, 9- and 10-speed drivetrains. Since 9s is probably the ideal sweet spot for mid drives, this chain can be considered almost everyone’s inexpensive default. To sweeten the deal, the chain comes with 144 links. So it will fit everything but a longtail without having to buy and section two chains together.
This one is quasi-optional. A quality derailleur is always a good thing. Especially if your alternative is something like a cheapie Tourney or similar.
I use a SRAM GX 2.1 long cage rear derailleur. This is not meant for a 1x drivetrain but if you just use a narrow-wide front chainring, you’re fine. At over US100 a pop this is not a low cost option, and one more reason why you need to know you want more gears and more finely-diced cadence options to bother with 11-speed.
I have found two I consider to be stars:
Box Components Prime 9I have two bikes with these, including my most recent build: The Apostate. My preferred version is the Box Two Prime 9 Extra Wide, coupled to their Box One single shifter, which is tailored for ebike use. The Extra Wide part refers to extra wide range on the rear cluster, which in English means Big. You can go up to I believe a 50T rear cluster with one of these. Combined, shifter-plus-derailleur is about a US185 solution. I like it better as a premium option because… it shifts spot-on, was super easy to initially adjust and runs silky smooth.
Microshift AdventI like the Long Cage version, which runs US60 and is meant for 2x systems but works fine on 1x. The Pro shifter is single-shift like the Box, and costs a whopping US29. This setup is significantly cheaper than the Box. It works just a little less slick, and the fit/finish is more… workmanlike… but its nothing to complain about given the price range its in.
The Storm Bee
This brings me to the Sur-Ron Storm Bee. When I received the message that we were going to test the Sur-Ron Storm Bee my first thought was “who the heck is Sur-Ron?” A quick Google search tells me they have been around since 2014 developing a bike on the quiet.
My next thought was “oh no, not another Chinese bike”. In the past we have tested Chinese bikes which have left us stranded in the bush while we wait for the rescue crew. I told myself I would go into this with an open mind and take the bike for what it is and not judge it too harshly.
Fast Ace Air Absorber rear shock Black and yellow colour scheme suits the name
Looking at the Storm Bee you can see that it is Chinese made but it looked well put together. They have paid attention to things like wire and cable placements and where and how things are mounted. I have noticed in the past Chinese bikes are built to a price not a standard but the Storm Bee appears to have been made with build quality in mind.
E-bikes are generally just a mountain bike with an engine and they feel very foreign but once I threw my leg over the Storm it felt just like a dirt bike. Sur-Ron has done a good job at replicating the feel of a petrol bike. The seat to foot pegs and pegs to bar ratios all seemed correct and comfortable.
I commend Sur-Ron for this is as being a company that has not mass produced dirt bikes in the past this could have been easily overlooked. After a crash course on how to turn the Storm Bee on and how to select the power modes I was off for my first experience on an electric dirt bike.
How Did It Go?
The first ten minutes was me getting used to the electric dirt bike and the power but mostly the brake on the handlebar. While getting used to the Storm Bee I was thinking to myself “how am I ever going to tell people how good this bike is without them thinking I’m full of it?” Honestly, I was riding around wondering whether this was real or the mushrooms in the forest were spawning and I was hallucinating.
The lack of engine noise allows you to hear the chain and tyres as well as the sticks banging on the swingarm and frame. One noise I did find to my advantage was the rear wheel noise. You can hear it biting into the dirt or spinning and breaking traction. This isn’t something you usually hear on a petrol bike and all of a sudden you can use your sense of hearing to control the rear wheel traction rather than feedback through the pegs and seat.
Rear brake is hand operated Suspension is well balanced for trail riding
The rear brake on the handlebar threw me for a while and I did find myself going for the foot brake out of habit. By having the brake on the handlebar you can feather it with your finger while going through tight trails much easier. You don’t have the weight of your foot on the pedal trying to throw off the balance while you‘re trying to steer.
One question thrown at me the most since the test ride was “how was it having no clutch?” I never once felt like I needed a clutch. The torque of the electric motor allows you to pop the front wheel up any time with the smallest blip on the throttle the same as a clutch. The smoothness of the engine allowed me to trail the throttle through turns without needing to pull a clutch in to skid or change direction.
The balance of the chassis works very well. The Fast Ace suspension comes from mountain bikes but they did a good job at developing and tuning a setup for trail riding. The front and rear is balanced and tuned well together.
Minimal clutter on the ‘bars USB charge point
Not having a whole bunch of rotating mass in the engine such as a heavy crankshaft and cam shafts which you fight against to change directions means you can corner and turn the Storm Bee very easily. It is a great bike to stand up on the pegs and tip in and out of the trees. It requires no effort from the rider to steer it whatsoever.
The power modes are a great addition but I found myself riding around in full power and managing it with the throttle. If you don’t have great throttle control the slower modes would be a great addition. The Turbo mode sounds like a cool feature but it wasn’t something I felt I needed to use so I only turned it on a few times. The reverse feature is certainly something different on a dirt bike and while I only used it out of curiosity I could see it being handy if you get stuck in a deep rut or bogged.
The brakes have a nice solid feel to them and while they are not Brembo they did do a good job for trail riding and managed to pull the bike up easy enough.
We rode the Storm Bee for a solid four hours predominately through single trails at slow to moderate speed. We rode it hard for the entire time up many challenging steep hills that required the engine to work hard and we only got the battery down to 50%. I would assume that this run time would cut down if you were riding in sand or on faster tracks and the power would drop at some point but for us the battery did everything we asked.
Black and yellow colour scheme suits the name 240mm rear disc
Handling – The Storm Bee was a very smooth and easy bike to ride. It might be a little on the heavy side but it did not feel that way to ride. Power – This electric dirt bike has plenty for the average trail rider. The bike was smooth but aggressive when you needed it to be. Traction – The throttle feels directly connected to the rear wheel. There is no lag time between the rear wheel and your wrist making the Storm Bee a very easy bike to find traction on.
Racing – While we had loads of fun on the Storm Bee I would want more out of the motor and the suspension if I was going to race it. In saying that we had a petrol bike to back it up against on the day and we all felt faster on the Storm Bee through the tight trails than it. The Name – Come on, Storm Bee? Why not Typhoon Tiger or Monsoon Mamba? There’s nothing tough about a Bee.
I was born and bred a petrol sniffing MX kid but the tech enthusiast in me was always curious about an electric dirt bike. I kept telling myself the technology isn’t there yet to compete with a petrol engine but maybe one day. I feel like I need to toss away a large amount of masculinity to admit this but the technology is there and in some circumstances I would even have to say better.
There is so much rotating mass in a petrol engine that negatively affects the way the bike handles. We try to make parts lighter, move the engine around and alter the way the chassis flexes to make it better but it’s a problem we just can’t eliminate. With an electric engine we solve this problem and the bikes handle and react completely different but in a much better way. I am basing this decision solely on what the Storm Bee was like to ride and if this is the start for electric then I think we are heading in a very exciting direction for the motorcycling industry, as long as we allow it to.
WHERE DO ELECTRIC BIKES FIT INTO THE CURRENT MOTOCROSS LANDSCAPE?
The topic of electrification is a polarizing subject; the off-road motorcycle world is certainly against the idea of electric bikes. Truthfully, there are some valid reasons to be concerned with electric dirt bikes making their entrance into the sport. Politicians have muddied the waters big time with their pie-in-the-sky regulations and bans, with serious implications for the off-road motorcycle industry.
Beyond the gross political agendas, there’s a serious debate about electric bikes in motocross. There are benefits to starting kids out on electric bikes because they are easier to ride and much easier for parents to maintain. Those same e-bike benefits help adults learn how to ride motorcycles more easily as well. We used the KTM Freeride electric bike that we tested in the December 2022 issue of MXA to teach first-time riders the basics with great success. Electric bikes also open opportunities for new riding locations. Noise complaints and dust are the two biggest reasons for tracks closing, and dust can be mitigated.
Where electric bikes present a sticky wicket is in fitting into the traditional class structures of motocross and Supercross. They are not the equivalent of a 250cc four-stroke or 450cc four-stroke and probably never will be. They can be tuned to make abundant power, and that makes catching cheaters a much harder job for race promotors and officials. It is best for the time being to form electric classes, where electric bikes race against other electric bikes, to avoid the AMA travesty that gave four-strokes double the displacement of two strokes, leading to the demise of affordable 125cc and 250cc two-stroke racing. The sport needs to tread lightly down the path of integrating electric bikes into the internal combustion classes.
WAS IT HARD TO RIDE THE CUSTOM ELECTRIC BIKE?
Hard? No. Weird? Yes! Because there’s no gearbox and no clutch, it’s a simple “twist-n-go” operation. That part simplifies the riding, but it certainly feels unusual to be on a dirt bike without the engine noise and without a shift lever or clutch lever. It was especially weird to try to hit turns and make some roost, because we couldn’t rely on the clutch to help light up the rear wheel. Absent a transmission, crank and piston, the SSE electric dirt bike has a lot fewer internal moving parts inside of the motor. On the track, the rotating mass in an engine has a big impact on the bike’s handling. When you get on the gas in a corner, it’s the momentum from all your bike’s rotating parts that stands the bike up on its two wheels. In the same way, it’s the momentum of the wheels that balances your bike out in the air. When you hit the rear brake midair, your front end drops down. Hitting the gas midair (panic rev) causes your front end to come up. And, if you accidentally hit the front brake midair, you’ll become unstable, and the front end will rise slightly. The SSE could do some of these things, but there is a re-education program that needs to be adhered to to get it right.
HOW LONG DOES THE BATTERY LAST?
If the rider is lightweight and mellow on the throttle, the battery lasts for a while, but if he’s heavy on and off the throttle, it won’t last long. With most MXA test riders weighing over 170 pounds and riding the bike hard, we got about 18-20 minutes of full battery power. It rained a bunch in California before Dain arrived, which meant that Glen Helen (and every other public track) was flooded. In search of a place to ride, we went to a one of our fun tracks in the high desert that had some decent little hills, a few fun jumps, a little rhythm whoop section, some loamy sand corners, and some hard-packed spots.
If the track were dry and hard-packed all the way around, the bike would last longer, because you’d have to be smoother on the throttle. But, because traction was at a premium and some of the sections were soft, the MXA test crew was zapping power more quickly on the e-bike. We wanted to make the most of our day of testing this bike, so we never rode a full-length moto from full charge to empty battery, because then we would have had to wait while the battery was recharged. We rode three sessions on the SSE bike, and we had multiple one-hour charging breaks in between. Instead of riding consistent laps, I made sure to only do a few laps at a time, so our camera crew could capture different areas on the track, and we could discuss how the bike was working with Dain.
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