The popular Bafang BBS02 and BBSHD mid drives are introducing an entirely new generation to electric bikes. Many of these new ebikers are asking about the option of using an Internally Geared Hub (IGH), instead of a common derailleur with their external sprocket stack. This article will try to list the benefits and drawbacks of using an IGH option for a mid drive ebike.
Drop Outs, vertical or horizontal?
The part of the bicycle frame where the rear axle attaches to it, is called a “drop out”. The common style is a vertical drop-out (or sometimes slightly angled), and it is called that because, if you hold the frame up and loosen the axle-nuts…the wheel will “drop out” of the frame.
Since most common bicycles use a derailleur, a vertical drop-out is a good design. If an axle-nut begins to loosen in the middle of a ride, the weight of the bike and rider will help to hold them together. In this way, the rider can often feel that there’s something wrong before the wheel actually comes completely out, causing a crash.
The style of drop-out shown in the pic below is a horizontal “track” style. In the Olympics, and also college-style bicycle races, they used a “fixed gear”type of bicycle. Since it is a single-speed and there was no derailleur, the frame designers needed a way to mount the chain on the sprockets, and then to tension the chain properly. Chains can have a link added or removed to adjust the length, but the chain-length must be loose enough to be assembled onto the sprockets, and then the wheel axle must be allowed to be moved towards the rear of the frame, far enough to properly tension the chain.
Track style drop-outs are a simple, light, and robust way to accomplish this without needing to add the weight and complexity a chain tensioner. These are being seen more often in some of the new cruiser bicycles.
The pic below is a “chain tensioner”. In this example, it is being used to convert a bike with a multi-geared derailleur into a single-speed. The stock derailleur can be used as a “poor mans” tensioner, but many enthusiasts prefer to shorten the chain as much as possible, and to have the resulting tensioner be as light and simple as possible. A chain tensioner is often the best option when converting your derailleur bicycle to an IGH.
Internally Geared Hubs, IGH’s
Why would anyone want to use an IGH instead of a derailleur? Derailleurs are lighter, and that is the main reason they have become so mass-produced for bicycles. Also, if you are adding an electric motor to the drivetrain, you might damage something, and a 7-speed freewheel can be replaced very cheaply.
The number one reason that some bicyclists switch to an IGH is because they often ride in mud and snow, and a derailleur can get so packed with crud, that it stops working in the middle of the ride.
The second most often cited reason is for riders who log a lot of off-road miles each year. They have to clean the derailleur frequently. Plus, they often need to completely replace their derailleur at the beginning of each riding season, due the the wear that results from the accumulated grit acting as an abrasive during the ride. If you do that, then you can save money by getting an IGH, which typically will last many years with proper maintenance, and…with the “after ride” cleanup being reduced to just two sprockets and the chain…
As to using an IGH on an electric mid drive, there are several glaring omissions in the list below. For the sake of keeping this article compact, I will only list the IGHs that I recommend. SRAM in particular, is difficult to buy in North America, and few riders have written about them, so there is not enough data available (SRAM…email me!). If you want a SRAM product, you “might” be able to buy one from Europe through ebay, since they are produced in Schweinfurt, Germany.
Why no 11, 7, or 5-speeds?
This article will mainly concern itself with the strength of the various IGH’s, since we are trying to find appropriate options for mid drive ebikes.
If you are only pedaling (with no electric motor) in a region with widely varying grades, get the 11-speed. Once you add an electric motor, get the 8-speed. There are two reasons. First, the more power you have, the fewer gears you need, and frequent shifting can become tedious. One Rohloff owner said he ended up shifting two gears at a time, because the Rohloff gears all have a close ratio, essentially making this 14-speed into a 7-speed.
The second reason is that the 8-speeds listed below have a very strong 1:1 ratio fifth gear. I would recommend starting out in 5th gear as a habit during your daily ride routine, when using an 8-speed IGH. Unless, of course, you are at a stop on an uphill. Then, you should start out on a lower gear, but…take it easy on the throttle. Don’t hot rod, unless you are using the second gear of a 3-speed. This is relevant because…for many riders, the only reason they want a mid drive in the first place is because they want help on the hills.
When it comes to 5-speed hubs (and some 7-speeds?), the middle gear is a driver-to-hub locking 1:1 just like the robust 3-speeds listed below, so…the 3rd gear in a 5-speed is often VERY strong. The reason why I do not recommend them (and believe me, I wanted to have a 5-speed and 7-speed on this list), There is just not enough data about them available from riders who have abused them in a rough service profile. Here is a German video that is the clearest one I could find to show the parts of a 7-speed (5 speeds are very similar). The dogs shown here are pretty strong, but the axial clutch and some of the gears are not strong enough for a motor (depending on model).
Once hub designers began using the modern style of axle-dogs, a 7-speed IGH became the minimum amount of gears that the majority of customers would buy (so 5-speeds are rare), as a counter-point to having a common external 7-speed sprocket-set. The 3rd gear in most 5-speeds is as strong as anything available, but if you want the strength of the modern style of axle-dog and gears for the other speeds, the 8-speed hub is the way to go…even if you don’t need all 8 speeds.
I would LOVE for someone to produce a wide-ratio 5-speed using a very strong style of axle-dog, but that just doesn’t exist right now. Here is a short video of the Shimano Alfine-11 showing axle-dogs shifting (which is almost identical to my recommended Alfine 8-speed). Here is a 2-minute video of the sliding dogs and axial-splined clutch operating in a SRAM 7-speed.
The design on the classic Fichtel & Sachs 7-speed (often simply called Sachs or F&S, and was purchased by SRAM), has stronger dogs (two dogs for every gear), but creates a weak gear-set that provides both the 2nd speed and 6th speed (1st and 5th don’t look too healthy either, it’s just that… under high power, 2/6 breaks first, as in this short video).
In the classic style 3-speed, 5-speed, and 7-speed, the middle gear is a locked 1:1 (modern 7-speeds sometimes use a different design). A gear set is added that provides two of the speeds, depending on whether it is driving, or it is driven. The strength of the middle gear is dependant on the strength of the style of clutch it uses. A 5-speed typically has a clutch and two gear-sets, a 7-speed has a clutch and 3 gear sets.
For a 7-speed, they took the classic 5-speed design, but instead of adding a physically larger gear-set to one end, they added a smaller gear-set to the other end. Plus, since Sachs has dogs on both sides of the axle, even more material had to be removed from the smaller gear-sets to create slots at the gear ID for the dogs to grab. Plus, the design of most 5-speed 1:1 ratio axial clutches looks strong enough for human legs, but…not a motor.
The 3-speeds listed below have the sun gear cut from a single piece of steel with the axle. The classic 5 and 7-speeds have spinning sun gears that are locked and unlocked by dogs. In a 3-speed, the second and third gear are selected at the planetary shell or the planetary gear-pins (not near the axle with lifting dogs or sliding dogs, where a higher amount of leverage could be applied, and cause breakage), and it’s done by the 4-arm axial clutch (no pawls), so it’s very strong. I’m stating these design features so readers will understand why I claim the 3-speeds are much stronger in all the gears, compared to a 5 or 7-speed.
The pic below shows a gear that slides onto a “fixed dog” (in the hopes that it would be stronger than a sliding dog). Dogs grab the spinning sun gear near the axle to lock and unlock it. An axle-shaft can have several gear-sets spinning around the axle (with all of them having their gear-teeth permanently enmeshed to the hub-shell), and…the one that has its sun gear locked is the gear that is actuated.
If you are want to switch to an IGH, but you don’t know how many gears to buy, ask yourself this question…How many gears are you happy with on your derailleur-equipped bicycle right now?
Do you have a seven-speed on a BBSHD, but…you really only use two or three of the gears? If you have a mild-assist BBS01 in a very hilly region on a bike with a seven-speed (and you frequently use all of those gears), you certainly would not be happy with a 3-speed, so…an 8-speed IGH might be what you’d be most happy with.
The Rohloff 500/14 “Speedhub” is a very famous 14-speed IGH, designed by very serious Germans. It is heavy and expensive, but…each one of the gears is almost exactly a “close ratio” 13.6% away from the next gear, so…if you are riding through a very hilly region with constantly changing grades of elevation, the Rohloff is your best bet to always be able to find ‘just’ the right gear (it vas designed for ze mountains of central Europe, ja?).
This high number of gears is achieved by packaging a common style of 7-speed mechanism alongside a narrow “wide range” 2-speed (a planetary gear-set that is either actuated in low range, or bypassed in high range). The Rohloff has a very wide 526% gearing range from the lowest gear to the top, and it has Gates Carbon belt pulleys available, if you do not want to use a common chain.
There are many 7-speed IGH’s that are very similar to the mechanism inside the Speedhub (minus the Rohloff in-series 2X drive), but what makes the Rohloff special is two features. First, it has a “shear pin” that is designed to break before any of the gears or shifting dogs could break. That’s a very good thing, because the reason you don’t see very many Rohloffs is because they are so expensive. The internal “2 X 7” mechanism is a little heavy, but…it also allows the rider to eliminate the weight and complexity of the front derailleur and second chainring, so…the extra weight is not as bad as it may seem at first.
However, the safety feature of the shear pin would not be much help if you were breaking the pin once a month, so…the second reason the Rohloff is so great is how strong the gears and dogs are. Most IGH’s use a quality of steel in producing their internal parts that is just “adequate” for the leg-force of the average rider. The Rohloff is intended to be a lifetime purchase, and they make every part inside to the highest standard of strength that is possible. Other IGH’s are designed to be as light as possible, the Rohloff is designed to be bullet-proof.
The place where the Rohloff is most appropriate is on a low-powered mid drive in a very hilly region. This is because my experience has shown me that…the more power your system has, the fewer gears you need. Most “pedal only” bicyclists like to have as many gears as possible, but once you have added electric power to your bicycle, the need to frequently be shifting can become tedious.
This may sound odd, but my research has found that the Shimano 8-speeds are widely considered to be stronger than the 7-speeds. I had always assumed that by packing more gears into the same space, each gear (and its dog) would have to be made thinner (maybe weaker?). However, the relative strength of the various models is often not in the gears, it is in the “dogs” that engage the gears. The available 8-speeds may be slightly more expensive, but they appear to be using much stronger dogs, and gears that are large enough that they do not have thin spots.
Here is a short video of the Nexus Inter-8 internals shifting. Notice how the planet gear-sets are always spinning, and each of the central sun gears are only locked to the stationary axle-shaft when its their turn to operate.
The Nexus-8 and Alfine-8 are both a robust 4-speed, coupled with a narrow wide-range 2-speed. However, they have managed to design 5th gear to be an efficient and strong direct-drive (although, to be clear, these are NOT as strong as the 3-speeds listed below). For an electric mid-drive, it may be advisable to choose an input sprocket that makes 5th gear your normal “take off” gear from a stop. You might end up only needing 3rd gear for hills (with first and second being too low to be useful), but…just be aware that 5th gear is the strongest. The currently available 11-speeds and 7-speeds do not have any gears that are a 1:1 ratio.
Shimano is a Japanese company with a long history of designing and producing bicycle components. They make both the Nexus and Alfine lines of IGH’s, and these two IGH models use many of the same internal components. These shared mechanical components are the parts that are most likely to break if overpowered by an electric motor drive. So…the choice of whether to use the Nexus-8 or the Alfine-8 should be made according to their price and external features, since their physical strength is identical.
Both have a disc brake option, but the Nexus is the more affordable product line. The common Nexus IGH’s use plain bearings to help keep the price more affordable, but…the “red band” Nexus hubs have upgraded needle bearings to reduce friction. I have no experience switching the internal lubrication to using automatic transmission fluid (ATF) from cars, but it is being seen more often. (here’s a tutorial on switching your Nexus or Alfine to ATF)
The Alfine line of Shimano IGH’s (pronounced “all-FEE-nay”) could be described as having the Shimano Nexus guts…with upgrades.
All Alfine hubs have needle bearings to reduce friction, and…they also have a robust set of roller-clutches instead of pawls, so…when coasting unpowered, these hubs are just about as silent as it is physically possible. Another feature that makes the Alfine more expensive is that the “wide range” 2-speed gear-set uses helical teeth, in order to make shifting under load easier. They achieve 8-speeds by coupling a 2-speed along aside a 4-speed.
Both the Nexus and Alfine lines can use the option of a “clean and quiet” Gates carbon belt (instead of the common ‘greasy and noisy’ chain that is used by the uncivilized animals like me), and these hubs have the widest selection of “off the shelf” tooth-counts for the pulleys, so each rider can find the optimum ratio for their terrain.
A tech fact that is worthy of note, is that all the Nexus IGH’s and the stock Alfine-8 uses a special grease for lubrication that is designed so that it does not also make the pawls stick (pawls need to move freely to work properly). The Alfine-11 is “oil lubricated”, and as a result the engineers also improved the dynamic seal on the left side so that the internal oil-bath will not leak onto the disc brake.
A frequently-mentioned mod on the internet for the Nexus IGH’s and Alfine-8 was to use automatic transmission fluid (ATF, used in cars), since high-mileage riders are recommended to drain and refill the oil at the beginning of each annual riding season (and Shimano IGH oil is expensive). Be aware there may be an occasional drip on the floor near where you park your bike if you do this, but…reduced friction and easier shifting is often mentioned as being worth the drips.
At the 2015 Interbike convention, I had the pleasure of trying out the Di2 electric shifter. Instead of the rider moving a rotary knob or lever to actuate a cable, you simply tap a water-proof “up or down” button. I found this system to be very pleasant to use, and it was absolutely delightful.
The fact that the gears are shifted by an electrical button also means that the shift button can be provided in different forms. By that I mean that…if you are a road-biker that likes aerodynamic drop-bars, you have the option of having an integrated paddle-switch embedded into a brake handle. This means that…without moving your hand, you can use your fingers alone to either apply the brakes, or shift the gears.
Why 3-speeds are badass for high power
The more power you have, the fewer gears you need. If you have a LOT of gears in a powered bicycle system, you will end up shifting a lot. So…how many gears are ideal? A 3-speed is the sweet spot for high power because of the way that the common and affordable versions are constructed. I am talking about the Sturmey-Archer fat 3-speed SX-RK3 (SeXy-RocKet 3-speed?), and the “normal width” Shimano Nexus Inter-3.
The 8-speed hubs that I recommended above have several gear-sets that have free-spinning sun-gears that become fixed (locked) to the axle by a “dog” being moved from the hollow axle by various means. Doing this is a clever way to allow a compact hub to have many gears, but…it focuses a tremendous amount of stress on the dogs, and when one of these styles of IGH’s breaks, it is often the dog that breaks…instead of the gears.
The classic and well-regarded Sturmey-Archer 3-speed engages the “second gear ” 1:1 ratio by locking the input chain-driver to the shell of the IGH by two large pawls…and they do that near the RIM of the IGH shell. I cannot emphasize enough how important this is. The second gear of these two models of 3-speed are not only stronger than first and third gears, they are a LOT stronger.
On this style of IGH, the central sun gear is permanently machined as a part of the stationary axle. Since the sun gear is near the axle, it has the most amount of leverage applied to it. By not having a separate sun gear that floats (and has to be locked and unlocked at its center)…this is one of the reasons the old style 3-speeds are badass.
The pic above is from RJ the Bike Guy. Thanks RJ, for taking the time and effort to make the videos. Also, here is an account of the tragic history of Sturmey-Archer, started in 1902, and eventually sold to Sun Race (in Taiwan) in 2000.
When it comes to the strength of the other two gears, Its difficult for me to determine which is stronger. In first gear, the bicycles’ pedals are driving the outer ring gear, and the four planet gears (count them, FOUR…not three like some other planetary groups) will output power from their planet-carrier through their central pin-axles. Third gear reverses that flow, and input drives the planets, and then outputs power from the outer ring gear.
Here is Karls review of him beating up on a Sturmey SX-RK3, and this is the very article that got me to spend hours watching IGH teardown videos on youtube to find out why a 3-speed was surviving when the others died so easily (when abused).
In order to keep this classic 3-speed design as small and as light as possible, it uses small planet gears. That is good from a strength point of view, but it also means that on the Sturmey design, first gear is only a 33% under-drive, and 3rd is only a 33% overdrive. For the Nexus, they squeezed-in a 36% underdrive/overdrive, and can provide a 186% range from 1st gear to 3rd (compared to the Sturmey 177%), not really much of a difference between the two. And…as stated before, both have a second gear using the same strong 1:1 lock between the input driver and the hub shell.
The Nexus uses expired patents to create a modern copy of the Sturmey, but there are minor differences. The Nexus uses four small pawls to lock the driver to the hub shell in second gear, and the classic Sturmey uses two large pawls. The Nexus has a slightly better gearing spread, but the choice as to whether to get the Nexus or Sturmey will likely boil down to this…The Sturmey-Archer SX-RK3 is available in a wide fatbike version, and the Shimano Nexus Inter-3 is not. If you have a fatbike, get the Sturmey, and…if you have a bicycle with a common-width rear axle, you can choose between the Shimano Nexus Inter-3, and any one of the many Sturmey-Archer 3-speed models (the S-A rear hub drum brake is highly respected for cruisers that do not have any frame allowances for a disc or V-brake).
The SRAM T3 might be the same as these two, but I haven’t found enough info on them yet. Also, I thought the Sturmey S3X “fixed gear” (no freewheeling) IGH might be an option (at first), if coupled with a freewheeling chainring at the BB. However, it has a very strong 1:1 locked hub in 3rd gear, plus…1st/2nd gears are actuated by sliding dogs near the axle…this makes it weakest in the gears where an ebike mid-drive needs a little more strength the most. (Thanks to Dan Burkhart for his time and effort making the videos)
Here is a discussion by a bike mechanic that works with both the Nexus-3 and the Sturmey-Archer-3
NuVinci IGH’s are made by Fallbrook Technologies. They use a patented design which incorporates large steel balls as the interface between the input driver and the output driver. This means the NuVinci design is a Constantly Variable Transmission (CVT). There are no “steps” between gears, and the rider can select precisely the exact ratio between the input and output that they desire. The only spec for comparison that is useful is…the max torque it can input, and the ratio-spread from bottom gear to top gear.
The N330, N360, and N380 models all use a name that reflects their percentage of total gearing ratio. for the purposes of using a NuVinci for an electric mid drive, I recommend the N380, which has a 380% range between the lowest possible gearing and its top gear. The N360 and N380 have a similar torque handling capability (for some reason, the N330 cannot take much power). The N360 can sometimes be found for a lower price than the N380. Here is a short video of how the mechanism works.
I normally only recommend components that are readily available and currently in production, however, I must make an exception on this IGH discussion. The N380 uses SIX steel balls, and the amount of torque they can survive (without internal slippage) is related to the amount of their respective contact areas.
Fallbrook no longer makes the “eight ball” version, called the NuVinci N171. However the N171 can often be found as a used part for sale (often due to its weight). By using eight steel balls, it has 33% more torque-handling capability compared to the recommended “six ball” N380. The N171 has a slightly narrower 350% ratio from top to bottom (its name does not match its ratio, like the other models). This gear-ratio spread is roughly halfway between a conventional 8-speed and 11-speed IGH.
As a side note, you could double the NuVinci hubs’ torque-handling ability by doubling its RPM’s in relation to the wheel speed. One way to do that would be for a mid drive to power a NuVinci as a jackshaft, with a second chain (or belt) connecting the NuVinci to the rear wheel using a 1:2 ratio. In fact, any of the IGH’s listed above would benefit in the same way, from a similar arrangement.
Conclusions, and Recommendations
Here are a list of gear ratio spreads. If you like very high speeds on the flat land, and also have very steep hills, you might want a big number. Mild hills can run fine with a smaller spread, and the actual total ratio can be chosen by changing the tooth-count of the very inexpensive input sprocket. A smaller sprocket for higher speeds and less hill-torque, a larger sprocket for a lower top speed and better hill-climbing.
307%__Nexus-8 and Alfine-8
Now that you can compare the gearing ranges, what mid drives can use which IGH’s? You will have no problem finding some one who says “I used the X-hub on the Y-mid drive, and it survived just fine”, but…there are many factors to consider. The worst-case scenario is a sudden application of a high-powered throttle to an IGH that is in the wrong gear, and it is driving a large-diameter wheel. Also bad? starting from a full stop on a steep uphill with a fully-loaded cargobike and a heavy rider.
If you swap to an IGH and then break it, you might still be able to use one if (the next time) you take it a little easier on the throttle on start-up, switch to a smaller driven wheel (while making up the speed with a different sprocket tooth-count), or…simply making sure the next time, you are starting out in the proper gear (like driving a car with a manual transmission). If you do break the dogs on your IGH, you don’t have to re-lace a whole new IGH to the wheel, just pull out the old guts and slide in the new ones.
Another question for consideration is…will there be a steady and smooth application of power on a street ebike? or…will this be for off-road riding with jumps? The jarring and sudden bumps that are common on trails can apply shock-loads to an IGH that a street bike doesn’t see.
I would feel comfortable using any of the hubs listed above with this drive 36V X 20A = 720W. There are also a lot of European “street legal” 250W-500W mid drives to choose from, and I would also be comfortable using any of these hubs with those. In fact, I would even feel safe risking an 11-speed with 720W, while using caution with the throttle and a smooth application of power.
If using the optional 52V and also the full 25A, it would equal 1300W of input. If the throttle is programmed for sudden power, it could definitely break some of these IGH’s. Especially in a 29’r wheel, and with the hub in a high gear. Choose the 3-speed if you are a hot-rodder, or…maybe an 8-speed or the NuVinci N380 if you ride in a normal manner. Here is Karls review of the BBS02 with an N380
You could also hammer the N171 (if you can find one) or the Rohloff (if you are rich).
The stator on this drive is 66% wider than the BBS02 (50mm vs 30mm), and that means that…even if they are both using the same input watts, the HD will provide more output torque. The stock controller can use 48V or 52V, and the controllers’ max amps are 30A (and this drive can easily survive 40A of heat). The only reason to have this much power available (52V X 30A = 1560W) is…to USE this much power. If you are happy with 1000W, the BBS02 costs less and weighs less. I would only recommend a 3-speed IGH, or the N171 (hard to find), or a Rohloff. However, with the Rohloff…the gears are so closely spaced that you would end up shifting a LOT.
The 3-speed hubs I listed can really take a beating, but…if you find a way to break one, they are cheap to swap the guts out ($100 in parts?). If I lived where the hills were very steep (like San Francisco). I might get a BBSHD for its great heat-survivability, rather than using it like a hot rod. In that situation, you could probably get away with using a Nexus/Alfine 8-speed or the N380. But…I would mount it in a smaller wheel, and take it very easy on the throttle.
Lightning Rods “small block”
Uuuuh…NO. Way too much torque, and its real strength is being used as an off-roader with lots of jolts. Its not just that the input power that is common for this kit (typically 1500W to 2800W). It has an exceptional 33:1 reduction, and that means it will take the minimum 1500W, and turn that into a ton of wheel-torque. ES member cheekybloke (Darren Eclair) developed a robust 3-speed derailleur system on a steel cassette for his LR kit, using 1/8th inch chain and sprockets. Common 3/32nds bicycle stuff kept breaking.
LR “big block”, Tangent Ascent, DaVinci Astro-drives
No, No, and No…stick to a chain, a really good one (no belts to the rear wheel), and use a derailleur or a single-speed, and maybe even a fixed gear (since all the drives listed have an integrated freewheel).
If you liked the “teardown” pics of IGH internals, here’s another good site I found, called “Ride your bike”.
Written by Ron/spinningmagnets, June 2016