m@Robertson

The BBSHD: Musical Chainrings

It seems inevitable. When I build a bike, I go through front chainrings trying to get the gearing just to my liking. My Mongoose Envoy build has pretty much set the world record for tweaks in this regard. But gearing wasn’t the problem so much as chain alignment. Alignment is one of the most talked about issues with mid drives and up to this point I have not had to work too hard to get it right. This build, not so much but I think I finally got it (like $350 later).

While dealing with this I have fooled around with three different sets of crankarms (160’s, 170’s and 175’s). Not the subject here so if you notice the different crankarms in the pics, I am ignoring them on purpose.

Sidebar: When building the Surly Big Fat Dummy, I found exactly the same thing as I did here insofar as chain alignment is concerned. And used the same solution – the USAMade adapter listed as an Honorable Mention below got pulled out of the parts pile and put to use.

The Right Tool For The Job

The Mongoose build is a first for me in many ways. One thing in particular: the BBSHD fits the frame really well. Its a 68mm bottom bracket with absolutely zero chainstay obstruction for the secondary housing. So I can butt the motor right up against the bottom bracket. Further, its a lonnnng way back there so chain alignment and misalignment – an inevitable concern with an HD build – is a lot more forgiving since the angles are gentler thanks to the longer reach. On this bike, if I want I can even forego the offset non-drive side crankarm and the pedals are still easily centered under me. So the HD is a great fit here.

About That Job…

The Mongoose is a cargo bike. So it hauls heavy stuff (usually groceries). It has a secondary job as an unladen backup commuter, but primarily it needs to be optimized to start from a stop while the entire system – with me – weighs 400-450 lbs (180-204kg). I have really loaded it that heavily so this is not a theoretical exercise. So I want a big-ish chainring for when I am pedaling fast and light, and still need to be able to get to the big cogs in the back for when I am loaded up and chugging along like a two-wheeled freight train.

Plan A: Luna Eclipse (42T)

The Luna Eclipse is one of the best BBSHD chainring setups on the market, with a unique ‘wicked’ tooth profile meant to eliminate the possibility of a chain drop under extreme use. It also has the most extreme internal offset of any chainring option. This will do the most to overcome the grief visited upon the BBSHD builder by that drive’s secondary housing sending the chainring way out to right field.

Its also gorgeous. The gunmetal finish I chose matched beautifully with the dark grey frame. Unfortunately 42T (which is the standard for full-offset chainrings as any smaller and you can’t clear the secondary housing) was not large enough to keep me from clown-pedaling when riding the bike as a commuter. There was another problem: Chain alignment. Running that smaller 42T ring with the smallest rear cog resulted in, after only a few weeks, a whole lot of wear on the inside. This is why mid drive builds demand the most out of the builder in terms of thinking things thru. Time for Plan B.

Its not ruined yet, but its lifespan sure has been shortened. this was only a couple hundred miles of wear.

The Eclipse is a proprietary chainring platform, but fortunately other sizes are available. the largest of which is what I tried next.

Plan B: Luna Eclipse (48T)

So Plan B was to swap in a Luna 48T ring onto the Eclipse center section to fix the clown pedaling, and to stay the hell off the 12T small rear cog to deal with the alignment issue (I am using a welded together steel cluster for durability and the 12T is alloy and not a part of the welded cluster, so its better to stay off it for the sake of longevity anyway). I thought that 48T/14T on this bike was the perfect sweet spot. A small front ring is best when its on cargo duty, and a large one is best when its a commuter. 48T, when used in conjunction with upshifts, gave me pretty much everything I needed.

Pretty much but not everything. First of all, remember the deep offset of the Luna ring? It moves the chain inboard 24.8mm which *usually* eliminates the damage the BBSHD does to chain alignment. Not on the Mongoose, whose narrow bottom bracket effectively papers over all of the sins committed by the motor (at this time I had not yet fully figured this out). So, as I found with the 42T ring, it was inset too far, even when I stayed off the smallest cog.

So Plan B helped, but it didn’t solve the problem. After only a couple weeks (I am now checking carefully and frequently) I saw the beginnings of the same wear on the inside of the chainring. Like the 42T, I had to retire this thing fast so I could use it on some future project.

Not as bad as the 42T, but still bad. Both this one and the 42T looked perfect on the other side.

Sidebar: A mid drive chain powered by a 1500w motor is a chain saw when it comes to components rubbing against it. That is just a reality of a mid drive and you have to deal with it as part of your design/build process. When you get it right, you are golden for thousands of happy miles. Get it wrong and you are sawing thru chainrings and cogs like nobody’s business.

Plan C: Lekkie Bling Ring (46T)

So now what? 42T was too small. 48T was more or less just right. And the chainring offset that lets me use the inner cogs at great alignment still needs to be reduced or I can’t use anything but the lower gears. Lekkie has a Bling Ring available in 46T. It has the same internal offset their 42T ring has and, since I use them on two other bikes I know they are top quality. At 18.3 mm its offset is quite a bit less than the Luna. So I got a 46T. I also added a 2mm spacer underneath it, further reducing the chainring offset to 16.3mm. That is a whopping 8.5mm less than before so I hoped I would be good on the smaller outer cogs and still let me use the big inners.

And, pretty much, it was. Chain alignment didn’t seem to be much of an issue, although it still wore down a bit more on the inside. I was also able to shift up to the biggest cogs in the rear for very low gearing options. Those are important on a full cargo load and if I am dealing with hills.

But… I flat out missed that 48T high gear for commuting. And I was still seeing – very slight but noticeable – wear on the inside of the chainring teeth from the chain, which was still visibly angling outboard a fair distance.

This one was on for a few months and had 8.5mm less offset. But it still shows signs of premature aging. This was undesirable but livable.

I decided to try an extreme option I had not previously considered. But on this bike, where all of the normal chainring offset stuff doesn’t seem necessary, it might actually work.

Plan D: Luna 130 BCD Adapter and Wolf Tooth 48T Ring

BBSHD chainrings are generally all proprietary to the platform. Not so in the cycling world, where chainrings are universal, needing only to match the proper Bolt Circle Diameter for the chainring bolts. Match the BCD between crankset and chainring and you are good to go. There are adapters out there in the world that allow a Bafang motor to use standard 104mm and 130mm BCD chainrings. The problem is they don’t give you anywhere near as much inward offset. But given my experience so far, maybe I can live with that. They should fix my alignment on my ‘commuter’ cogs, but will I still be able to use my ‘cargo’ cogs?

In addition to the LunaCycle 130 BCD adapter, I also chose the Wolf Tooth Drop Stop chainring as those rings are best-in-show for this sort of thing on a mid drive. Attachment to the adapter was a little different than the usual chainring-to-crank operation in that its backwards. The chainring bolts onto the inside. I was able to play some games to good effect: I reversed the chainring so it is logo-side-inward. Not as pretty, but doing that lets me take advantage of the countersunk bolt holes on what is normally the outboard side. The countersinking let me mount a bolt so it is almost flush with the ring, which in turn is butted up almost on top of the secondary motor housing. With the countersinking it now has plenty of clearance.

Plan D Results

FINALLY. Everything is working right. The reduced chainring offset means my 14T cog (still not using the 12T for the reliability issues mentioned above) lines up straight back. This outboard shift did affect my inner cog alignments but I can still get to all of them but the biggest 32T. I’m comfortable with the angles on all but the second-largest 30T for long term use, and in a pinch, that 30T will work fine. I just don’t want to stay on it for a week. So this 9-speed is now a 7-speed and as DIY mid drives go thats still better than a lot of builds can manage.

And worth mentioning, like a lot of what they do, the CNC-machined Luna adapter is freaking gorgeous, and very precisely manufactured. So much so it really stands head and shoulders above another adapter I got my hands on and was able to compare it directly to.

Honorable Mention: USAMade 130 BCD Adapter

I was surprised at how well this worked and how nicely it was made. The part only cost me $29.99 on Amazon. Still, it was Made in USA, well machined and rock solid. The only things I didn’t like about it was the fact it was machined a bit too heavily, which meant it placed the chainring a millimeter or two further outboard than was necessary, and in this game millimeters count. Further, as you can see above I was able to reverse the WolfTooth ring and take advantage of the bolt head countersinks. That didn’t work with this part as USAMade countersunk the outside edge of their part, which made the bolts too long to allow my trying the same trick on the inside, where I needed it. For a different build it might work fine so I am keeping it for my parts pile.

As for the Stone chainring seen on the USAMade adapter (scroll up to the title image at the top of the page), thats a Chinese Special that ran less than the godawfully expensive Wolf Tooth. Its noticeably lighter in construction than the WT and I’m not sure I am sold on the tooth profile. This ring will sit in my parts pile waiting in the wings as an emergency replacement.

Great Big Bags (an important afterword)

Some time ago I made a post about Big And Cheap: DIY Cargo Bike Bags. On that post I noted on the build sheet this last item:

Therm-a-Rest Classic Foam Pad        Amazon   29.95

And then never mentioned another word about it. I still ignored it in the Cheap DIY Cargo Bags: Update follow-on post.

Oops

So, that item is actually sort of a big deal for these bags. Why? Because the padding lines the inside of the otherwise floppy ol’ canvas parachute bag and gives it a soft but firm structure. It also of course pads the interior so your carton of eggs stands a better chance of making it home in the same number of pieces it started out in at the grocery store.

Without further ado: Here’s a look at the end result:

And here’s what it looked like before I took a knife to it:

This is a “Therm-a-Rest RidgeRest Classic Foam Camping Sleeping Pad” in its Large size, which is 77″ long by 25″ wide. The important measurement is the width: 25″. Thats only 1″ wider than the measured 24″ width of the Rothco Parachute Bag we are using for this project. In actual practice, stuffing it into the bag, the width is perfectly sized to the bag.

What about length? Well, I found all you have to do is cut one of these sleeping pads in half, widthwise. This will give you two 25″ wide by 38.5″ long pieces. That 38.5″ is pretty much perfect insofar as lining three sides of the bag (rear, bottom and front face).

Having this sturdy but padded liner inside the bag, you can pile stuff on inside and the bag retains its squared off shape. Further, when using the straps to lift up the bag off the lower rack, the liner allows those straps to carry some of the bag’s weight without flopping down onto the rack in its center. Without the pad as a liner, none of that good stuff happens.

Here are a couple of shots of the bags, empty, and folded up. Here again the pad on the inside gives these monstrous panniers shape so they can fold up and stay neat/tidy.

You can see from the pics above how useless those big straps would be without some sort of internal structure (also notice these are still the early 2″ straps). That internal padding is crucial to making these bags work. Now lets look at the bags loaded:

See that grocery cart in the background? Well, it was mostly full and now its loaded up into the Mongoose. Filling both the 25L (each) front panniers and these almost 77L bags in the rear. Those bags are still well-loaded but as you can see by no means full. They are loaded mostly with 2L juice bottles, a case of 500ml coca cola bottles and a slew of soup cans and such. With all that weight, the straps can still hold the bags up and partially off the lower rack and retain their shape (although I did add a third 2″ strap in the center to supplement the two outer 3″ straps… this load was *heavy*).

So… thats why you need the pads.

Finally, what do these bags look like when truly, fully filled out? Recently I took some old XL sleeping bags out of the house. A city park was midway to the drop off point and I pulled over for a quick set of pics.

Heat Sinks For the BBSHD Ebike Mid-Drive

Not so long ago, someone asked whether heat sinks had ever been applied to the BBSHD with any success. This reminded me to document what I have done for posterity’s sake. I turned a motor whose casing temp was 165 degrees fahrenheit and reduced it to 135. Still pretty warm but a 30-degree reduction nonetheless.

Whats The Problem?

Well, there isn’t one, actually, unless you are really beating on the drive. Even then its only going to be an issue under specific circumstances. The fact is, these motors are pretty well built and they generally don’t suffer from heat issues. Unless…

You are running the motor on the street, say, on long city blocks, and either laying into a high level of continuous pedal assist, or the throttle

AND

You are running the motor on a 52v battery, in its max 30 amp configuration

AND

It is REALLY hot outside. We are talking 100-110 degrees fahrenheit (38-43 Celsius).

So, we’re talking summer commutes or midday shopping runs in Central California on streets like this, where my bike – which I geared for proper pedaling at 28+ mph – is putting out 100% power from the motor, continuously in between stoplights… and its a long way to the next light.

I’m riding in the Class 3 lane on the street, not the Class 1/2 shared use path just to the right

Put all of these things together and now you have a motor that gets hot. How hot? My Stormtrooper – A rescued Motobecane Lurch frame with carbon fiber 90mm deep dish wheels, 52v 30a BBSHD, and a Luna Lander front air fork – was seeing motor casing temps of 165 degrees. Yikes.

The Stormtrooper – Now living the good life in Pacific Grove, CA where it is never hot, unless its on the inside of a freshly baked cheddar bagel.

So…. what can you do? On this bike, I added a whole slew of 8.8mm x 8.8mm x 5mm heat sinks – purchased with thermal adhesive already applied so they are just peel-and-stick. Here is a link to the source I used. You can find them quite a bit cheaper buying direct from China but you will wait a couple of months for them to arrive. When done, the motor casing looked like this (I completely encircled the motor so there are many more of these things on than you can see here):

The small heat sinks are placed in rows, 4-across.

Next, I put on another large round heat sink on the end cap. Since it was sold to me in bare alloy, I used radiator paint (for minimal impact on heat transfer). I also had to apply my own heat transfer adhesive. I chose this style as it had the large center area that could be used for adhesive. Note I also had to fill the very center of the motor where there is a gap thanks to the laser etching for the logo. I did this with 3+ layers of thermal adhesive, cut to fit flush.

You can see the thermal adhesive I applied to the center alloy section of the end cap, just at the top. Hand cutting the adhesive strips to fit was a pain.

Here is a different motor where I used different heat sinks. These are 8mm x 30mm x 8mm in size. So they fit – again almost perfectly – in the smooth channel on the BBSHD motor casing. This time you only need to stack them as they fit the channel 1-across. Much easier. Also they are a bit taller, with more room between the fins. Is that better or worse then the little 5mm units? I haven’t done any testing so I don’t know. On this motor, I did the same end cap as pictured above.

These 30mm-wide sinks were a lot easier to apply as you only have to go 1-wide all around the motor.

Here is a link to the 30mm heat sinks I used. I can’t find a domestic source for these so if you decide to go this route you just have to order them from the source … and wait.

On the Surly Big Fat Dummy I recently built, I used them again. They make a major difference in the intense heat we get here in the California Central Valley

By the way, these identical heat sinks work extremely well on a mini-Cyclone… Those motors overheat if you give them a dirty look. The same combination of 30mm adhesive sinks mounted radially, plus the same end cap. Takes the surface temperature down to the point where the motor can be used with relative confidence once you learn not to overdo the throttle and cook it… The heat sinks cool the motor from the outside literally as much as is possible under the circumstances.

Cheap DIY Cargo Bags: Update

Recently I posted up about how I made some Big And Cheap DIY Cargo Bike Bags. Since I made that post, I have made a couple of improvements worth mentioning (including learning to lock my front wheel… look closely at that pic above… doh!).

The Straps

While I discussed them in my original post, my use of 3″ wide straps hadn’t actually happened at that time. The straps were in transit. They have since arrived and been installed. I do prefer the wider size, and the shorter length of just under 60″ (I’m using two 30″ straps connected together). You can see them in use in the picture above.

It is worth noting the clumsiness I experienced with the longer 2″ x 72″ straps went away with a couple of days’ use. I simply got used to them, so as I mentioned in my original post, there is nothing wrong with 2″ straps. 1-piece, 2″ x 60″ straps should work just fine, will cost a bit less and be a hair less complicated. Although they will give a little less support.

The Hooks

Discussing the improvement to the hooks is a bit more involved.

Lets backtrack a step: Originally when planning this project I ordered some AN970 Large Area Washers from Pegasus Auto Racing Supplies. I intended to use them in conjunction with the M5 mid-frame braze-on bosses on the Mongoose Envoy to permanently anchor the bags to the side of the bike. Later on as the project matured I decided to just use the straps and not bolt the bags to the bike. So I never utilized these washers.

I bought the 1/4″ size which have an outside diameter of 1.125″ (28.6mm). Inside diameter is suitable for an M6 bolt, and usable with an M5. Washer thickness is 1.6mm so these are very beefy. Additionally they are made with Grade 8 heat treated steel. These washers are VERY strong. I have used the 1/2″ size, unsupported except for a nut, to secure end link bushings on a track (race) car and they held firm without bending in that very extreme job. If you toss your bike out of an airplane, these washers will probably be the only thing not bent on impact.

So… I have a bunch of unused washers. So what? Well, as you can see from the original build, the S hooks fit inside of a fairly large 13/16″ hole. The hook has plenty of lip to hang on thru bumps and bonks while going down the road, but it still moves and there is a little rattling. I hate rattling. When I build a bike it doesn’t rattle. I don’t care how big of a cliff you ride off of. No rattles. So… I took steps. Afterwards, the bags remain easy to remove from the bike. You just do it differently.

Fig. 1: Here’s everything we need to get the first part of the job done (stabilize the connection of the hook to the bag)

Step 1: Attach the big washer

These washers are big. 1 1/8″ wide in fact (essentially the same size as a headset stem cap). They are so wide they cannot fit inside of the narrow end of the ‘S’ hook unless we spread it a bit. So lets do that.

Take your pliers and spread the small end of the ‘S’ just barely enough so the washer will fit inside of it. Fit the washer in and then again being very careful not to over-crimp the ‘S’, take it back to being the same shape (parallel) it was originally.

Fig. 2: Original is on the left. You don’t need to do much for the washer to fit.

Fig. 3: This washer has been fitted. The ‘S’ has not yet been carefully crimped back to being parallel in its original position.

When you are done, you can stop here and fit the resulting product onto your bag grommet to see what you have accomplished. You will fix the hook by putting the big end thru from the inside of the bag. It will look like the picture below. At this point the connection is much more solid and when on the bike very unlikely to come undone unless you want it to.

Fig. 4: If you over-crimp the hook it will be too tight and will no longer fit. If you leave it spread out, it will rattle and move around. Just put it back the way it was before you put the washer in and everything will be fine.

So, we could stop here, but if you recall, I said no rattling. So lets take this another step to further solidify the hook into the hole and, as a bonus, make it silent.

Step 2: Add mastic tape to washer

Everyone knows duct tape is a gift from the Gods. A million uses. For bicycles and particularly ebikes, 3M Moisture Sealing Tape, Type 2228, is even more useful. This stuff is available at your local hardware store for about $10 a roll for the 1″ wide stuff. Its magic comes from the fact it is 65 mils thick (five or six times thicker than what you think tape thickness should be) and is a soft, adhesive rubber that can be stretched, bent, squished and molded as you see fit. And when it sticks to itself it literally welds together.

For this job, for each hook I snipped three snips of tape, each about 5mm in length. I didn’t actually measure – no need to be so precise. I just eyeballed it. Two of the snips went to the inside side of the washer, pushed inward to hold the hook in place and more or less fully face the washer with thick, soft rubber tape (3 guesses on how that affects rattling).

Fig. 5: Do a better job than I did here and cut yourself a little more tape so it goes edge to edge on the washer.

Step 3: Add tape to hook

With the above complete, plant the hook in the grommet hole – now you have to do it from the inside of the bag – and use the third snip to wrap around the hook, so the tape is between the hook and the grommet face. Like so, below. This will be a snug fit, but the tape’s tendency to weld to itself makes this job certain despite the fumblefingering that will ensue during job completion. When done, you have this:

Fig. 6: The 3rd strip of tape silences the hook rattling against the grommet.

Repeat the process with all four hooks. Here’s a peek inside the bag. Notice the washers completely cover the grommet hole.

Fig. 7: View from inside. Pretty sturdy connection compared to poking a hole in fabric with a hook.

The hooks worked fine as conceived in the original build. But these are now a more secure, stable mount. For long term use this is a better way to do the job, and the cost to do it is about 80 cents.

FYI its fine if you don’t use these Grade 8 uber steel washers… look for something similar at your hardware store, probably a 1/4″ zinc fender washer. Cheaper, too.

Upgrade The Hooks

This is not such a big deal but it works just a little better. All of the pics above use the black steel hooks that presently retail for $8.99. These hooks are powder coated so the black is on there pretty good, But its not going to be perfect, and rubbing paint (bike frame) on powder coat (hook) means you get some rubbing off on both the frame and the hook. Plus that powder coat isn’t as smooth as polished steel. These hooks come in a polished steel option for an additional $1 for the 30-hook pack. I got a pack of these and they seem to fit more smoothly against my frame (where the hook is exactly the size of the frame rails, so fitment is always rubbing-tight).

There is a slight cosmetic difference as they are slightly visible now whereas the black ones were not. I’ll leave it to you do decide if you care.

These hooks, in the best tradition of Chinese marketing, are described as “premium metal steel” so we’ll have to see whether either behaves differently. I am using polished on one side and powder coated on the other. Time will tell if either will rust.

I Hate Ebike Torque-Sensing (maybe you should too)

Well, I don’t actually hate it, but it is a technology rooted in cycling’s past, whose existence was created to market a product to legacy riders.

As far as I’m concerned, torque-sensing’s existence is primarily owed not to the fact that it is a better system, but instead is a tool to help persuade an existing customer base (recreational, leg-powered cyclists) not to hate the product (ebikes) quite as much as they already do (either that or to sell ebikes while not cannibalizing sales of analog bicycle brethren).

Say what?

What is Torque-Sensing Pedal Assist?

On an ebike, when a torque sensor is used, it applies a strain gauge to the drivetrain (located either inside the bottom bracket, or in the back of the bike near the gear cluster). This measures the amount of force you apply to your pedaling stroke. If you pedal (work) harder, the assist you receive is dialed up. If you pedal more softly – regardless of cadence – the assist level is reduced… or eliminated.

I have heard it said that torque-sensing “rewards pedal effort” and this statement is both correct and indicative of the root problem with its advocacy. Old school cyclists hate the fact ebikes allow someone to make forward progress, without using their muscles in the first place. By restricting/keying the assist to physical exertion levels, the fact that a motor exists at all is less difficult to accept – and more easily sold to the existing cyclist population.

It also allows an ebike to be sold without denigrating the old-school unassisted version. Zillions of which are still manufactured for sale worldwide. If torque sensing just makes it seem “more like a regular bicycle” then that helps preserve the perception that a normal bicycle is still every bit the desirable, viable product that manufacturers still need to sell millions of.

It is unfair to say torque-sensing is ONLY about these things. Its not. You will also hear people say torque-sensing results in the most ‘natural’ bicycle riding experience for them, since you still have to work hard on the pedals. And the assist increases in proportion to your effort, just like a real bicycle. An ebike goes faster of course, but a physical work ethic is still demanded. So to be fair, torque-sensing does indeed give cyclists who want this a familiar and desirable experience. There is nothing wrong with that.

What is Cadence-Based Pedal Assist?

In its simplest form, its nothing more than this: Your assist level goes up or down based on how fast the crankarms are turning. The amount of effort you expend could even be irrelevant if your gearing is low enough. The only thing that matters is the rotational speed of the pedals/crankarms (strictly speaking it is the spindle’s rotational speed that is measured, but thinking ‘pedal rotation’ is easier to visualize).

So if you want more assist, you just turn your legs faster – not harder. Again in simple circumstances this means you can get into a low gear and easily ‘ghost pedal’ your ebike, without expending any effort. So you are breezing right along right up to either the speed limit of the ebike or the road/path you are riding on (please note I am not saying this always happens… only that it is possible with this type of system).

Such a thing is utterly anathema; deeply, personally hated in the cycling community. There, your progress and ability is hard earned through what can only be described as prolonged, personal, stoic suffering whose level outsiders neither understand nor hope to match. Despite the spandex, funny hats and silly shoes, cyclists know they are endurance badasses (they really are).

Except, fate has dictated these solitary warriors suddenly have to share the road with the Griswolds, blowing past them in their two-wheel Trucksters. Ebikes democratize cycling so that now… anyone can do it? WTF!?!

… not a shock the response of cyclists to ebikes has been negative.

Far From Perfect

Finally, lets make the very important point that criticism of cadence-based systems is often entirely justified. Especially on low cost direct-to-consumer ebikes. Unfortunately, rather a lot of these systems have cadence-based pedal assist that is merely an on/off switch. It pays no attention to how fast the crankarms are turning, or how fast the bike is going. It justfires up and produces one of maybe five different power output levels, steady and regular.

Faced with that kind of behavior, its no wonder so many people think torque-sensing is the only way to go.

Its not so simple

I said above the description of cadence-based pedal assist was in “its simplest form”. There are some big exceptions to this that most ridersare unaware of. Criticism of cadence-based assist systems can be entirely justified… but it should be recognized that the concept of cadence-based assist is not the problem, but rather to crappy, cheap-ass implementations of it.

There are some cadence-sensing ebike motors that have settings both complex and rather profound in how they impact the riding experience. Notice I did not say ‘cycling experience’ because a central tenet of my rejection of torque-sensing is that ebikes are bicycle-shaped-objects, but not bicycles. It is a mistake to treat them as if they should behave the same (unless that is something you expressly want).

The Cadence-Sensing Mid-Drive

If there is such a thing as a ubiquitous aftermarket mid drive on the market, its the Bafang BBS02 and its heavy-duty big brother, the BBSHD. There are zillions of them out in the world. If you want to find yourself a drive that has plentiful aftermarket support, countless users in discussion groups with experience to share, and myriad how-to’s out there on Youtube and the internet in general… well the go-to for those things are these DIY kit Bafang mid drives.

From the factory, quite frankly the performance settings on these drives is awful, and this is well-known. Pedal assist is overpowering and easily lets the bike run away from you. That powerful pedal assist also saps the range of the bike. But the bad news gets worse when you factor in the clunky, laggy motor engagement that bashes on the gears, and generally does its best to wear the bike’s drivetrain down sooner, not later.

Fortunately this is all very well known, and there is a rich settings interface hiding under the hood for these drives, with readily-available free software that will let you dig into the motors and completely change (i.e. tame) their character. With that in mind, here are some screen shots showing those settings.

Some cadence assist options are on the left side above. This isn’t even the Pedal Assist screen for this particular motor. These settings determine assist strength and when, based on both speed and motor rpms, the assist gets cut back.

Here you can determine how much the cut-back is when pedal assist is reduced, and more. The graph explains how the various settings on this screen affect output.

This is not at all the simple on/off concept most people think of when they complain about what they think of as cadence-based pedal assist

UPDATE:
Since this article was written in 2019, I have documented a cycling-oriented approach to this motor in BBSHD Programming for the Pedaling Cyclist.

The KT Controller And A Hub Motor

What everyone commonly calls the “KT” controller is in fact a product of the Suzhou Kunteng Electronics Co., Ltd. KT controllers can be found as original equipment inside of manufactured ebikes, and sold individually as aftermarket upgrades and components for builders who are building their own ebike. This is a company that has its products inside of many ebikes, but unless the owner reads the label on the controller, they would have no idea whether its a product made by this company.

I bring them up because KT controllers are very popular in the DIY ebike building community. They provide a quality product that offers features not readily available with other products in their class.

KT controllers use cadence-based sensing, but apply a proprietary algorithm that someone nerd in the basement was allowed to label as ‘imitation torque control‘. I don’t know where that comes from, but as their (poorly translated) web site says,

“Use imitate torque control mode to help achieve a smooth start-up of the vehicle, the power-assist drive will be smooth and natural. Electric power assist is with fast response and always consistent with the rider’s pedal action to achieve the effect of the torque boost.”

Thats fairly typical Chinglish marketingspeak, but they really are onto something.

When you start off from a stop, power ramps on via a recognizable curve. It doesn’t just flick from ‘off’ to ‘full blast’
The startup curve can be adjusted in three separate steps so if that on-curve is too strong, you can set one of three increasing levels of slow-start to give a more shallow slope to that startup curve.
When starting off and crankarm rotation and speed are both slow, power applied is high. This corresponds to what you need when starting from a stop.
As speed increases from ‘stopped’, power is smoothly dialed back, so the bike doesn’t run away from you. When cruising at high cadence, very little power is output.
If during that cruising speed you start going up a hill, the controller senses the combination of reduced speed and cadence and dials in more power to help you get up the hill.

The result is of course not ideal, but it is smooth and easy to adapt to, especially coupled to the other settings options that are available.

So What?

Once again, we see that we are not dealing with a clunky kind of on/off switch that cadence-assist detractors point to. There’s grey area to be had here when it comes to performance.

Torque-Sensing Can Be A Disaster

If you have a physical limitation, torque-sensing doesn’t help you get past it. It does help you go faster while working hard. Studies have shown ebikers in fact can work nearly as hard as, or even harder than bicycle riders… they just don’t realize it. Possibly this is due in part to the exhilaration of being able to go faster, and stay in the saddle for longer periods.

Myself, I am a lifelong cyclist. Or rather, I was. I commuted daily for decades. For many years I eschewed the use of an auto. I commuted and even shopped for groceries by bike (being poor and single had nothing to do with this). But after a couple of heart attacks, my cycling life was over. To stay alive, I gave up the intensely personal activity I most valued. Bummer.

A few years ago, I discovered ebikes, and the one I bought had cadence-based assist. I had no idea there was any other way to do it at the time. I did something many do not: I treated the ebike – which looks like a bicycle but is not one – as a new animal. I threw out much of the knowledge on cycling I had acquired, and started fresh on riding technique.

At the start, pedal effort very quickly led to chest pain and an immediate need to stop doing that. But I could go on if I incremented up the assist and incrementally lowered – but did not erase – pedal effort. This allowed me to keep going (maintain forward progress).

I learned to treat the ebike like an exercise machine. One that went places and was practical transportation. Instead of directly coordinating effort with forward motion, I separated the two. Effort was always maintained, and so was clicking off the needed mileage to my destination. But the two no longer had a 1:1 relationship. This decoupling of effort and speed while maintaining cadence solved everything. The procedure in a nutshell is as follows:

Set a preferred cadence
As heart pain occurs (heart pain is not the same thing as getting tired) click up the assist level so effort is reduced – and keep moving. This relieves the heart pain gradually
On recovery – I’m good after maybe a half block – reduce the assist level back down a click at a time and start working harder again
All the while maintain the same cadence
Rinse and repeat as the miles click off to destination arrival.

You are never just sitting in the saddle doing nothing but exercising your thumb on the throttle, unless you’ve really overdone it and have to enforce a complete break. But that should be very rare and only happen in the earliest stages of getting back on the bike and working out as a daily routine.

Again, to belabor the point: I’m using the bike for utility and transportation. My bike has somewhere to go, so the point of cycling is to reach a destination. If I was a recreational cyclist then maybe its fine to slow to a crawl, or stop and sit on a bench for awhile. But a bike as transportation is a different. The point of riding is to get somewhere . So I must maintain forward progress, while managing a constant – but changing – exertion level.

Only cadence sensing is going to let you do that (and I know this from experience. See Afterword below). Its a different riding experience described most simply as a moving exercise machine. Again… not a bicycle.

Different But Still Good For You

Over time and thru repetition, I scaled back the point where pain occurs to where I was able to manage it with gear changes (upshifts) and not changes to the assist level. Now I’m running at top assist speed while maintaining pedal pressure and exertion at all times during the ride. On my Class 3 daily driver I cruise right at 28-30 mph (legal in my jurisdiction) and I get to those higher speeds above the assist limit by myself. All along doing so by maintaining a set, preferred cadence.

And if I overdo it, since I am now running at full power, I can just downshift (maintaining cadence on the easier gear) to take a break. I’ll go a little slower and dip down to the level where the bike starts providing assist again once its speed gets down into Class 3 territory. This is a different way to use cadence-assist. I am not dialing back power: I’m always running at full blast and I’m working to get the bike up to where I am going fast enough so the motor pulls power back on its own due to its going over the Class 3 limit, or adds some in thanks to a downshift and reduced speed.

Note from The Future:
The above describes my experience using an awd geared hub bike with twin KT controllers and a big battery. This one in particular. That was quite some time ago, and its a platform I moved on from long ago. The kind of variations possible in a geared hub system are different than what they would be if I was, say, doing the same thing with a mid-drive-motor solution like a BBSHD. So, two entirely different cadence-based systems, and two different ways to achieve a good ride… but you have to go into it without thinking you know the answers already..

Broadening The Use-Case

Cadence sensing isn’t just for recovering invalids. For the healthy rider, successful use of cadence-based assist as a hard-exercise tool is easily possible, and rooted in that rider not coming into the experience with pre-conceived ideas. Don’t treat it like a bicycle (yes I am repeating this over and over on purpose).

Using the ebike as an exercise machine as you roll down the road, you’ll be getting fit during time otherwise spent sitting in your car and exercising nothing. A torque-sensing ebike can do this too… but if the ebike is meant to also be practical transportation, your physical condition of the moment will have a direct impact on whether you make it to your destination. Not so with cadence assist.

The Future

It took 34 years for the Tour de France to allow bicycles with derailleurs — because not grinding up a slope in the Alps on a single-speed was cheating.

… Isn’t it better to triumph by the strength of your muscles than by the artifice of a derailleur? We are getting soft.

-Henri DesGrange, world-renowned cyclist and original TDF organizer

If someone tried to make that same case today, their opinion would be regarded as fringe idiocy.

So lets take that same interval: 34 years from now, when ebikes have long-since become the accepted norm (just look at the sales figures) as derailleurs did a century ago… will we be espousing technology or methods rooted to the norms of the past? Will a couple of generations of riders who have known nothing else continue to think of torque-sensing assist as giving a bike a ‘normal’ feel?

My money is on ‘no’. Or more accurately… sorta-kinda-no. I think for higher end bikes a dual system could become commonplace, letting riders choose one or the other as they see fit in the moment. One mode for recreation. One for transportation.

If it has to be a this-or-that binary choice, I think torque-sensing won’t survive the test of time. Why? Sheer weight of numbers, and the growth of the automobile replacement market. Look at global ebike sales. Only a small fraction of ebikes are sold in the European and North American markets, where recreational cycling is a thing. Look at the Far East, where bicycles are simply utilitarian transportation and there is no stigma attached to effortless travel. Whats the norm there?

Cadence-based assist.

UPDATE (February 2021):
Its already happening through a vector I hadn’t considered. Recreational ebike riders are starting to upgrade from their cadence-based budget bikes to what the industry tells them was the ideal product: a better bike with higher end components and… torque sensing. I’m seeing reviews from riders not inculcated in traditional cycling ethos, saying the bikes are no longer fun. They can’t just get on a bike and zip around and enjoy the outdoors for as long as the battery holds out… now their bike is making them work at it. What was once an unconsciously-achieved benefit (exercise) is now an enforced requirement. Riders like this, new to the fold, don’t always appreciate the new rules. With the pandemic rushing literally tens of millions of new riders into the fold, the spread of this effect could manifest itself far more quickly than the slow evolution I originally anticipated.

Afterword

Lest I give the wrong impression… I have an ebike that uses torque sensing, and frankly I love it. But its a recreational bike, not suited for a bike that has a job. Going for a fun ride, where I don’t have a problem stopping and sitting down on a bench or a rock for awhile and enjoying my surroundings… Its almost perfect for that. I wish I had time to ride it more.

But by its nature it can’t be a serious transportation tool.