In this article we’ll examine the process of choosing a bike and motor system for road and trail use, and assembling a quality DIY ebike that will exceed many commercial products. Most anyone with a little mechanical ability can do this project, or can find someone who can assist or do the entire job. Then we’ll review how this upgraded bike has performed and talk about some possible future updates. There is a brief conclusion at the end for those who want to skip all the juicy details and experience we have collected along the way.
I’ve built a few ebikes for commuting and riding mostly on paved roads, but for this build I wanted something a bit different. The goal was to make a bike that would be at home on pavement and confident on (occasionally quite steep) dirt roads and trails, as well as lightweight and very bicycle-like. Something I could take camping, on group ebike rides, and have fun exploring the area’s accessible trails with.
My previous builds have tended to get heavy somewhere between the hubmotors and the large battery packs. They did an excellent job of commuting, where the goal is to get to work reliably on time, in spite of a rough and hazard-littered pavement. For that use, a few extra pounds doesn’t matter, reliability is key. When the trail gets too steep or rough and the bike needs to be pushed or carried, those heavy commuter ebikes are not the tool for the job.
A steep unpaved fire road trip in Marin with my first hub motored ebike overheated and nearly melted the motor. This bike needs to be better at climbing the steep rough stuff without getting hot (I revisited that site as part of the testing). A higher torque hub motor could do it, but the weight becomes prohibitive and the resulting machine decidedly less bicycle-like. A mid drive solves this problem by using the bike’s gearing system, taking maximal advantage of a smaller and lighter motor.
The emergence of ebikes into the biking scene is not without considerable trepidation from others, and so to help reduce these fears, this bike should be fairly stealthy and not shout “ebike” nor disturb other bike riders and trail users. It should be quiet, friendly, and promote the integration of ebikes into the bicycling and trail culture.
Good range requires high efficiency, a good sized battery, and the ability to pedal in a useful way to add energy to the system. If the battery becomes exhausted the gearing should allow pedaling without motor power as well (and keeping the system light is important in both cases). For extended trips it is important to be able to fix flat tires in the field. With hubmotors this can be a major chore due to torque arms, heavy wheels and wrenches required, but with a mid drive the easy removal and repair of quick release (QR) hub equipped standard wheels is the same as other bikes.
The new ebike laws in California also provide some requirements for this build. The Class I and II bikes are limited to 20 mph but the new Class III bikes can go to 28 mph but must have Pedal sensing. A mid drive that can be programmed to meet the requirements of these classes is desirable.
Hybrid bikes (with thin and low rolling-resistance tires) were recommended by the local bike shops, but they didn’t appear to have adequate rough road or trail capability. I was reluctant to share my full plans for motorization with the salespersons as this discussion often goes poorly. But their well intentioned concern that the mountain bike is too inefficient for pavement use is tempered by the the motor, so I thanked them for their suggestions and gently steered back into the mountain bike aisles and catalog pages.
I selected a new mountain bike for this project, and in that process found out how much things have changed since I bought a similar bike fifteen years earlier. Tire sizes, shifters, gearing, frame materials and designs have all evolved a great deal. I didn’t want a cheap steel bike, nor did I want to expend the budget for a titanium offroad wonder (though that would be a fun project in itself). I wanted a good basic mid quality mountain bike. I visited local bike shops (LBSs) like Mike’s Bikes, chain stores like REI, and searched online at places like BikesDirect.
The two primary elements of an electric bike are the bike and the electric motor system. They must integrate together in many ways, so choosing a bike without also choosing a motor can produce incompatible or difficult combinations. I was initially very drawn to the excellent Lightning Rods mid drive but decided that it might not be stealthy enough for this build. I also reviewed others including the Cyclone but finally decided that the recently introduced Bafang BBSHD would be a good choice for my objectives.
The Bafang is nicely integrated and fairly stealthy both visually and acoustically. My timeline for the project was also short, and the availability and ease of install weighed on the side of the highly integrated BBSHD system. This Heavy Duty model is the culmination of Bafang’s considerable experience making mid drives, so it should have all the bugs worked out. The BBSHD has pedal sensing and external throttle so you can control it either way, and they have several display options to provide information about speed, distance travelled, etc. It can be programmed to meet the requirements of the new California ebike law if necessary.
Now that the mid drive was chosen I could look at the specific bikes and see how they would work with this drive. The timing was difficult as right after Christmas the store inventories were thin and new models had not started to arrive. But the bikes that were there often had features not well suited to mid drive conversion. Mounting the BBSHD requires having a standard bottom bracket tube, and it replaces the crankset, so all the trick features there are going to get tossed.
More gears on the rear cassette aren’t very beneficial either, and we really would prefer to have steel cassette cogs over alloy, since they will wear better. Cogs smaller than about 12 teeth are marginal for the high torque and resulting tooth loading and wear from a mid drive, but we do want the larger cogs for good climbing ability. Higher priced bikes were often less suitable for the ebike upgrade – strange frame shapes, small triangles, fancy crankset features, etc. That actually helped to keep the price of the bike down.
Rear Suspension (or not) was also a major question. Choosing between a hardtail with front suspension and a full suspension mountain bike can be difficult. Clearly the dual suspension would be nice, but the cost, number of moving parts, weight and the size of the spaces for battery mounting make full suspension bikes a very mixed and often difficult choice for electrification. In the end I decided to keep it simple and stick with a hardtail with a nice triangle for battery mounting, and the ability to have a good solid rack on the back for occasionally carrying stuff. (Note that this bike is a hardtail, but in spite of that it lacks easy mounting arrangements for a rear rack).
I did prefer the bike have hydraulic disc brakes so the guides would be set up for hoses rather than cables, even though they will likely get swapped for ebike type hydraulic brakes during the upgrade.
The bike selected for this project has the “new” 650B / 27.5 inch tire size that is currently popular for mid-size mountain bikes. The 2016 Diamondback Overdrive Sport 27.5 (frame-size medium) is available from a number of sources including Recreational Equipment, Inc (REI), Sports Authority and Amazon. The stores I checked didn’t have the new model in stock yet, so I had to order it from Amazon to make my schedule. This worked out fine, but there is some assembly required, and it could be a problem if the bike had been damaged in shipment, so I would have preferred to get it locally.
I ordered the BBSHD from the Lunacycle.com website before the bike selection process was completed. DON’T repeat this mistake, first get the bike and make certain you know the width of the bottom bracket. I thought the bike I was selecting had a 68mm wide bottom bracket tube (this is the tube the crankset mounts into), but it turned out this was wrong, and it caused some delays getting the right size BBSHD. As it turned out the bottom bracket of this bike is 73mm wide, and the BBSHD comes in several widths including 73mm. Know what you need! So get the bike first and ensure things are going to fit, and order the right BBSHD size the first time!!
So what special tools are required to install the Bafang BBSHD mid-drive? Bikes require some unusual tools, especially for things like the bottom bracket spindle and cranks. So I ordered a modest bike tool kit, figuring that it was time I had more of those tools myself. Removing the cranks and bottom bracket requires tools, knowledge, strength and perseverance. These parts can be very tight, and some have reverse threads, so reviewing the online resources like Sheldon Brown’s excellent website are important to make sure you are turning it the proper direction. Of course the local bike shop can be employed as well and that might be the best technique if you have little bicycle mechanical experience.
If you can locate a local “electric friendly” bike shop or ebike consultant / small business that can be extremely helpful for this project. These folks combine knowledge of bike mechanics with knowledge of motors, batteries and electrical bike systems together which is necessary to work on electric bikes, especially with DIY setups.
Once I got the bottom bracket out of the bike it was quick and easy to slide the BBSHD drive into the bottom bracket shell (tube) for a test fit. The drive unit fit nicely, though the large diameter downtube prevented it from rotating upward as far as I would like. The clearance under the motor is still almost six inches, about the same as the largest chainring. The drive should be rotated until it contacts the downtube as the reaction torque will tend to turn it that way and loosen the locking nuts if it moves at all. Keeping the drive tight is important, special tools are required to snug it down, the ones I used are shown above.
Before I tightened the drive into place I decided to make a conforming “spacer” to spread out the force that the drive would be pushing against the downtube with. With a normal install his force gets concentrated on a very small area due to the shape of the surfaces and can damage the downtube. Using a rubber bumper is not advisable as it will allow the drive to move slightly and promote loosening. A rigid spacer that takes on exactly the shapes of the drive and the downtube is best. This is not something that I have seen others do, but I decided to test it on this build.
I used a one inch ball of Loctite general purpose “Repair Putty” in between the motor and the downtube after first spraying both surfaces with silicone lubricant to reduce the chances the putty would stick. This ball was placed in between and the motor rotated fully into place, indenting the putty, then tightened firmly up against the downtube. The putty forms a hard, form fitting spacer between the motor and downtube to spread the torque reaction force over a larger area.
Bafang BBSHD rotated fully upward against the downtube with spacer of light gray epoxy putty.
The BBSHD provides a single chainring, and the standard one that comes with the unit seems to be universally disliked. It is heavy steel, and not very handsome. It also has more teeth than is optimal for steep climbing. I opted to get the new Lunacycle Eclipse 42 tooth alloy chainring. This is a good compromise in number of teeth, and is designed to hold the chain well and improve the chain line by being offset in toward the bike and the middle of the cassette.
In the case of this particular frame, the chainring teeth contact the chainstay, so a 3mm spacer (also from Lunacycle) was required to provide adequate clearance. Their new 30 tooth chainring was also investigated, but it moved the chain line further out and didn’t provide enough top speed (with reasonable pedaling cadence) for our pavement use. I’ll keep that for a future project, it is well suited for off-road situations and it would probably enable climbing trees, at least up to the traction limit.
Setting up the handlebars is always a challenge and a compromise. Some things are difficult to move, such as the trigger shifters, gear indicators and brake levers. So we work from these anchors and fit everything else around them. In this case the left shifter was removed since the motor precluded multiple front chainrings. The rear cassette trigger shifter remains on the right and doesn’t allow room for a throttle. So the throttle and ON / OFF / PAS selector were installed on the left. The C965 display fit right in the middle. A Fenix BC30R headlight is installed on the left side, and the high beam pushbutton for it is velcroed on the left grip. A Levin Universal Smartphone holder with ball mount from Amazon is on the right. The Mirrycle Incredibell fit best on the far right side. On the far left is the Mirrycle MTB bar end mirror.
The arrival of the Batt-man necessitated a change in handlebar layout, so the light was removed. Further shuffling will be required to arrive at a final configuration that accommodates everything.
The initial plan was to use HobbyKing RC lipo batteries as done on previous builds, but the new 18650 cell based lithium battery packs are lighter and the price and availability were excellent. They have a built in battery management system (BMS) and various safety features that make them an optimal choice. So the decision was made to go with a 52V 20AH Triangle pack using Samsung 26f cells from Lunacycle.com.
When selecting a pack make sure the available current is adequate, the BBSHD can draw up to 30 amps. The choice between 48V and 52V was made toward the slightly higher stored energy of the higher voltage. This does have a downside in that the standard Bafang instrumentation is calibrated for 48V and does not display battery status properly, it shows full until you are essentially out of juice. A secondary battery status gauge will be needed with 52V systems if you want to know what’s left.
The 20-Ah triangle pack is a good fit in this medium size frame, with little room to spare. This pack’s plastic cable tie attachment system is secure and has much less visual impact on the frame tubes compared to the usual wide velcro attachment systems. I did add some floor foam to the right side of the pack to maintain space and protect the display on the lower right section of the pack.
Charging is handled with an existing Ebikes.ca Satiator charger which is programmable for the required voltage and current. It is set to charge to 58.8V. The charger starts out at 8 amps and tapers to 6 amps at the full voltage (due to the 360 watt limit), and then drops from there as the charging cycle completes. This charger indicates the amp hours (integrated charge current) which is very useful to see how empty the pack was.
A protective hard carrying case for the battery was setup using a Harbor Freight tool case with pluck-foam. The battery is generally removed from the bike for charging, transportation and storage. The bike is easier to handle without the additional weight of the battery, and the battery represents a considerable value that can be removed from the bike and kept secure separately. Supervised charging is easier without having the bike attached.
The initial weight of the Diamondback bike as assembled from the factory box was 31 pounds. Removing the crank took off about 3 pounds, and the 13 pound BBSHD installation brought the bike back up to 41 pounds. Installing the 13 pound battery brought it up to 54 pounds, ready to ride. Not bad for an ebike with over 1 kilowatt hour of battery!
I was surprised to discover that the Diamondback’s rear axle area did not contain threaded holes to support a standard rack. So I installed a cantilevered Topeak rack to accept the trunk I often use on my ebikes. This rack is easily removable so also contributes to a lighter bike when not needed. It is handy to carry some tools and snacks, and the charger or secondary battery for a longer trip. This trunk expands upwards and has fold out panniers which are useful to carry some groceries or extra clothes, and it has a water bottle holder and rear light attachment. The trunk and rack interconnect with a slide in rail with a pushbutton lock.
The original seat on the Diamondback was a little hard, so I selected a memory foam seat. So far it has worked out well, though the lettering is wearing off.
Adding a conventional kickstand to an ebike doesn’t always work out since the battery and trunk cause a higher than normal center of gravity. I opted instead for a folding trekking pole combined with a latex free band to hold the brake. This is quite stable and will work with most any bike. The handle fits up under the seat, or can be attached to the seat rails with a carabiner. When nothing else is available the trekking pole makes a stable leg to lean on. It folds and packs on top of the trunk bag.
The Diamondback came with adequate Tektro Auriga brakes and 180/160mm discs, but an ebike puts a heavy load on the brakes, and it is best to have brake levers with motor cutout switches. Adding switches to hydraulic levers can be problematic, and you can’t just swap the levers with the supplied cable ebrake levers, so I opted for the upgraded Tektro Dorado ebrakes from EMPowered Cycles. These come with the Bafang compatible switches and connectors in place for a plug and play installation, and the larger diameter and thicker 203mm discs. It is an easy upgrade that looks great and works well!
Using a 52 volt battery pack has one downside, the displays that come with the BBSHD are not calibrated for this battery voltage, so they won’t give a good indication of battery state. Since the battery voltage is one cell higher than normal the display indicates full until it nearly runs out, so it does not help you know when to turn back or pedal more. Normally I would use a Cycle Analyst from Ebikes.ca for this, but for this project a smaller display is being evaluated.
The Batt-man from Lunacycle.com was added late in the project to provide an accurate remaining battery “fuel” indication, voltage and power readouts as well as improved accuracy for speed and distance displays. A program is available to configure it with a Windows PC to set the wheel diameter, units, and amp-hour battery capacity to match your setup. You will need to supply a mini-USB cable, cable ties and appropriate connectors to mate the current sensor and voltage pickup to the battery and controller.
In my case the sensor needs a custom spacer to get close enough to the spoke magnet. After charging the Batt-man can be reset to “fuel tank full” with a 2 second push of the display selection button, allowing it to display the remaining amp-hours with a bar graph “fuel gauge”. Clicking the button rotates the display between three presentations that each contain several useful values including remaining battery, speed, power, amp-hours consumed, battery voltage, and more. This is the essential information needed to manage range anxiety for those comfortable interpreting it.
For my testing I took the Diamondback to Quartzsite in the desert, exercised it on paved routes such as the Three Bears loop in the East Bay, did a commute run to the ex-workplace and took it on a number of combined rides with both paved roads and rough, occasionally slimy and steep dirt roads and trails. I pushed it, not always flat out, but fairly hard. At the same time I wasn’t interested in taking a fall, so I didn’t push it beyond my comfort level (which is growing as I gain confidence and experience with it).
On one of the trips my riding companion did fall, and there were several moments where I wasn’t sure I was going to keep the rubber side down. I did confirm (as others have reported) that Pedal Assist (PAS) is not a great idea on technical single track, better to turn the assist off and use TWC (throttle with care). When in low gear the BBSHD has a significant hole shot and can surprise you. It generally won’t quite lose traction when you are on the bike, but it’s close, and it can certainly lift the front wheel. The throttle is set for “torque” mode and it does act like a torque throttle. It is very controllable. But don’t bump the throttle when you are not on the bike, it can leap right out of your grasp.
So far I’ve used only the supplied configuration, it is possible with a cable and software to make adjustments and further customize the settings inside the Bafang controller. The way mine arrived from Lunacycle it has 5 PAS levels numbered 1-5 (plus zero where PAS is off). Combined with 9 rear derailleur gear choices, pedaling speed and throttle position this presents quite a lot of possible control combinations. The pedal sensor on the Bafang BBS series of drives is essentially a binary sensor, it detects if you are pedaling forward, or not. If you are pedaling forward it enables the motor with the speed and power settings programmed for that PAS level. So as you start to pedal the motor comes on and accelerates, and as you pedal up to the set cadence the motor power is reduced since the desired motor speed has been reached. Depending on which gear you are in, this occurs at different road speeds.
Selecting higher PAS levels (depending on the programming) generally results in higher cadence and power levels. Using the throttle overrides the pedal sensor, and depending on the throttle setting can result in either less or more power than pedaling. Maximum throttle is generally more power than PAS supplies (again subject to programming). Applying the brakes (if equipped with ebrake sensors) causes the motor power to cease, returning about a second after releasing the brakes.
This all works quite well, so far I haven’t felt the need to make adjustments to the parameters, but I’ll look into that at some point. For relaxed riding I use PAS level 1 with occasional throttle, and for more aggressive riding I use PAS 5 or full throttle. On a group ride to match speeds with others I either change gears or PAS levels, or use some throttle to get finer control. On dirt tracks I use PAS level 0 and TWC (throttle with care).
One thing to keep in mind when riding mid drives is to stay in a low gear and keep cadence high, allowing the motor to spin fast. This is where it is most efficient – making power at lower torque values, which leads to less heat production. If you or the motor are torquing hard, downshift! I do try to reduce power when shifting, however modern bicycle transmissions are made to shift under power. Tapping the brake, reducing the throttle, reversing or stopping pedaling momentarily will reduce motor power for the shift.
Chain wear is a major concern with mid drives. From what I’ve read we can expect 500 to 1000 miles from a chain if we treat it well (and keep it clean and lubricated). Learn to wash that chain, it will last longer. Don’t use spray lube if you want your disc brakes to keep working their best – use a few drops of quality chain lube applied directly to the chain and avoid getting any on the brakes. Use a chain wear measuring tool to check regularly for wear, and replace the chain before the cassette and chainring are ruined. For everyday work commuting and racking up lots of miles the mid drives do require more maintenance than hub motors. Each tool has strengths. But mid drives sure can climb.
One advantage of having an ebike capable of severe climbing is improved access to some very beautiful places, even just a few miles from the house. Places not heavily visited, and very green (and slippery) right now, due to recent heavy rains. The trail to this ridge is a 20%+ grade, most hub motor ebikes would be unable to climb it, but the BBSHD torqued right up without getting more than barely warm, even though I was having difficulty keeping the front wheel on the ground and staying on the bike while keeping it within the remains of what the map calls a fire trail. Part of the way I gave up and walked, using the throttle so the bike was self propelled and I didn’t have to push it as well. It is steep. But most of the way I rode, keeping the speed low and pedaling, the BBSHD did the hard work, and didn’t require much pedal input.
Another result of all this climbing is major descending, and for that I’m glad of the improved disc brakes. The instant cutout of motor power with these ebrake switch equipped hydraulic levers is also important especially when Pedal Assist is employed as merely moving the pedals can generate a jolt of torque with this motor that can upset balance or otherwise cause a spill. Pedal assist is great for churning along a nice safe roadway, but it can be hard to control on a steep, rocky trail. (Note that there are different types of pedal assist systems and some with true pedal torque sensing are more suitable for trail use than others that just detect crank motion).
The Bafang BBSHD drive system is quiet. It is hard to hear, even when sitting on the bike and riding slowly. There’s a slight whirring buried deep inside the motor case that gets covered by tire noise, chain rattle, and other everyday sounds. The sound doesn’t give it away. Many hub motors make more noise than this as they buzz with resonances and high torque loads.
Range is always a major concern on any battery powered transportation. The published ebike range figures in particular are often inflated and impractical. If you pedal enough your range is not limited by the battery at all, but that’s not interesting. So how far can we go without pedaling significantly with this 52V 20AH battery pack? The tires make a difference, and so far we’re using the stock Kenda Honey Badgers at their minimum pressure, 30 psi. Rider and gear weight is about 200 pounds. I’ve collected data from six charge cycles thus far, 98 miles indicated by the BBSHD odometer. It is not calibrated quite right for the 27.5 inch tires, so adjusting for that makes it 104 miles.
Total amp hours replaced in charging is 58.9 amp hours. The net efficiency for this mix of riding is 59/104 = 0.57 amp hours per mile or 29 watt hours per mile. This makes the average range 35 miles on a full charge with minimal input from pedaling. These trips have involved a lot of climbing and some hard runs on pavement at 25 plus mph. The worst range I experienced was 26 miles – on pavement, in a rush, climbing a lot of hills as fast as it would easily go. The BMS tripped off in the driveway on the return trip. On an easy going ride with moderate input from pedaling 50 miles should not be difficult to achieve.
I am also considering setting up another battery for this bike, a smaller 11 amp hour shark pack. One reason is to allow a lighter ride when the distances are short. This would shave about 6 pounds off the bike’s total weight and result in a range of 15 to 25 miles. In combination this pack would provide additional range. Having a total of 31 amp hours available would provide a range of 40 to 75 miles which would be useful for a long day. A shark pack may fit under the downtube. The front tire clearance under maximum suspension compression would have to be maintained.
The Batt-man display was added late in the project to provide better battery charge state information. I tested the Batt-man’s amp-hour discharge reading against the amp-hour charging reading from the Satiator charger. A 20 mile predominantly full throttle trip using just over 50% of the battery capacity was used to gather data. The charge vs discharge amp hours agree within 2% which is excellent.
The voltage readings agree between Batt-man, the meter on the battery and the charger’s display within 2% as well. This is not just adequate but excellent. My only complaint is the things I want to look at aren’t together on one screen. Speed and the fuel bargraph are on one screen, and instantaneous power is on another. That’s one problem with a small screen. Another minor complaint is the minimum voltage reads a very low value, it is probably triggered during the precharge, so it does not provide useful info. If the power was switched separately to the Batt-man this would likely work properly. Overall the Batt-man is a useful addition to the setup. It gives much better information on voltage, amp hours and correct mileage calibrated for the actual tire size.
One upgrade to consider for this project is an internally geared hub (IGH). Quite a few bike shop offerings were so equipped, with various Alfine, Sturmey-Archer, or Nuvinci hubs. Then there is the best of breed Rohloff hub with 526% shifting range in 14 evenly spaced gear combinations! There are a lot of advantages with hub gearing protected from the elements, shifting when not moving, better chain line and in some cases wider gearing than we have with the cassette and single chainring combination of the BBSHD. The downsides are weight, cost and the slight efficiency loss which is more than compensated for by the electric motor’s power. This bike already climbs well and reaches good speed on pavement. But it might be interesting to try an IGH at some point.
In summary, the Bafang “heavy duty” BBSHD kit is a straightforward and clean install that converts most any bicycle to a strong ebike with a wide range of capabilities from steep climbing to cruising at road speeds. It is programmable to meet most local legal requirements and reliable from several generations of experience and improvements by Bafang. It is quiet in operation and minimally impacts the aesthetics of your bike. It certainly has enhanced the capability of my new mountain bike, and I’m considering other platforms where I could use another BBSHD — perhaps a Fat Tire Trike. If you are looking for something a little lighter check out the BBS02 which is the previous slightly smaller model and still a very popular unit.
Till next time and Always Ride Safe!!
San Pablo Reservoir overlook.
Written by Alan Biocca, February 2016
About the Author
Alan Biocca started on a technical track very young. At the age of 12 he passed his ham radio license exam. Later he earned degrees in Electrical Engineering and Computer Science. He worked at Lawrence Berkeley National Laboratory for 37 years in Data Acquisition and Control Software, Electronics Engineering, Computer Networking and Security, Accelerator Controls, Project Management and Electrical Safety. He commuted with bicycles, motorcycles and ebikes for many years. Alan’s hobbies include writing, tennis, electronics, ham radio, hi-tech flashlights, photography and electric bicycles. He can be reached through his website at www.AlansEbikes.com or on the Endless Sphere or ElectricBike forums.