Month: August 2021

The Bullitt Build
1. Battery and Battery Box
2. Cargo Box
3. Brakes
4. Front Motor & Wheel
5. Rear Motor & Drivetrain
6. Bits & Pieces (You are Here)

Whats Left?

I’ve hit all the big ticket items. Now for the bits and pieces that may be of interest.

Fahrer Panel Bags and Tools

The Fahrer bags were a late addition. Partly because they cost so damn much. I was not willing to spend the money until I finally realized my idea for a MOLLE panel, trimmed to size, with bags attached was just more effort than I felt like going to get the same result in DIY fashion.

For me, the point of these bags was to move my tools out of the cargo area. I seldom need to mess with/rummage through them so I wanted them in a place that kept them out of the way. At the same time, there is a fair bit of money wrapped up in this toolkit, not the least of which are the battery powered air pump and the ridiculously expensive but wildly useful Knipex pliers/wrench. For a bike that gets left outside of a store a lot, I wanted to be able to easily, routinely remove these bags for carry inside with me.

I settled on putting the tools in a bag that fits inside of the bag. Specifically I used one green and one brown Condor Field Pouch, which have handy top-grab handles for pulling the bags easily and quickly up and out.

Two of these bags, in two contrasting colors – green and brown – so I know which is which on sight.

Ordinarily these Condor bags are used for something like a 1L water bottle, but they are a near-perfect shape for form-fitting directly inside the Fahrer bag. The different colors help me remember straightaway whats in each pouch.

The contents of my tool kit fit along my usual lines: I want to be able to use what I am carrying to do just about any typical field repair. I like to work with full-sized tools, so I am not at a disadvantage on the side of the road where life sucks bad enough already if I’m broken down.

Worth mentioning are those two black disks in the pictures above. Those are not emergency field rations (unless its REALLY an emergency). Those are two regulation hockey pucks. Solid, dense rubber blocks. What the hell for? Set one each under the Bullitt’s 2-leg kickstand. Now either the bike’s front or back wheel is up and off the ground by several inches, depending on which way you tilt the bike. Instant quickee service stand.

Rear Rack

I’ve heard its tough to fit a rear rack on the back of a Bullitt. There are M5 bosses built into the dropouts, but it can be a challenge to utilize them as the brakes get in the way on the drive side.

I found an Axiom Streamliner 29er DLX rack fits perfectly.

UPDATE: Mar 22 2022. I actually used this slightly different Axiom rack that was sold as the Streamliner DLX. Nowadays this same rack is marketed as a 29er rack and now includes the extra-strong center mount (I used a spare from one of my Fatliners) as well as the stay mounts. The current Streamliner is narrower and sold strictly as being compatible with 700C tires (although I have one of them on the front of my Envoy that fits 26×2.8″ tires just fine).

Its lower mounting arms move the rack 4cm out and further back to ensure there will never be any heel clearance issues. Its strong – rated to a whopping 50 kg, although I don’t know about that. I’d say 25 kg is still pushing it, but as racks go its very strong and can stand up to any reasonable level of use. I use it to hold the more delicate items that come from the store. Bread, chips and such. Or if I am just expecting a large or heavy load I may attach the panniers so I can clean out my cargo bay so its one big empty box.

But the rack needs just a bit of surgery to fit. Note in the picture below I did just a bit of filing to give clearance for the brake adapter bolt. Without this small adjustment it won’t clear.

I also used the center mount from an Axiom Fatliner rack (I have several of them). It has about – literally – four or five times the material in it as the Streamliner center support. I did have to drill new engagement holes for it. Maybe I can get away with that 50 kg rating after all.

Kicktail / Reinforcement / reflector

I have done a reflector/kicktail before on many bikes as sort of a signature mod. I usually take a 6″ x 18″ street sign, stand on it, grab an edge and bend up until I have a lazy L shape of roughly 35-40 degrees. I drill some attachment holes and the result is a 1-piece rear rack deck plate. The kicktail ensures no mud comes up at the rider, ever. Coupled to other measures I like this approach better than a traditional fender.

To add utility, I also cover the underside of this kicktail in 3M 3432 Red Micro Prismatic Reflective Tape… Exactly the stuff used in manufacturing municipal street signs in the USA. It so happens that a few years ago I scored a 12″ wide roll of this stuff at a small fraction of its regular retail price, so I can just unroll a bit of it and slap it onto the back side of the kicktail and voila… the world’s largest red bike reflector. I guarantee you I am visible to an overtaking automobile even if I didn’t have my steady and blinkie taillights fired up.

But my usual racks are fat bike racks where a 6″ deck plate works in conjunction with mounting panniers. Not so with the much more narrow ‘normal sized’ tires of the Bullitt. I needed just a narrow strip on the top of the rack with channels on each side to allow the pannier hooks to be engaged.

So I used a narrow 2″ strip of aluminum flat bar in the full length that I needed, and then bent that bar up to the desired angle. Following that, I bolted a second, full-rack-width 4″ x 12″ piece of aluminum flat bar onto the strip to make the kicktail. Line the back side with tape and functionally the job is done. However, since I had discovered a green duct tape that is a near perfect color match for the Larry vs. Harry ‘Lizzard King’ green, I wrapped the upper surfaces of the rack with it for what I think is a nice look.

The ‘Bobtail’

So… the 2-piece kicktail… in the end I decided it wasn’t working for me. The giant red reflector was a big winner as they have always been, but the need to do a 2-piece thanks to the narrower rack caused issues that just grated on my OCD (just kidding I am not diagnosed with this condition). Being 2-piece, it jiggled around some while riding simply because it was heavier than its predecessors. Also, the metal plate rested directly on the rack and rubbed, scraping off the protective powder coating. Trying to pad that with 3M 2228 mastic was only marginally effective as the stuff inevitably wore down and mooshed away under the force of the metal edge bearing down upon it.

To solve this issue I re-thought my approach. I discarded the wide flat plate. Next I cut down the rack deck plate so it was just long enough to intercept all spray coming up off the tire. Then I lined the now-exposed rear with the same prismatic red reflective street sign tape used on the full kicktail. In the front, I affixed a swatch of orange prismatic tape to provide another reflective surface. To finish it off, after filing down the upswept end so there are no sharp edges, I took the added precaution of making a bumper with a layer of that same rubber 3M mastic.

Job done.

With this change, I hit the sweet spot. The bobtail still keeps water off of the rider, it still has a large reflective surface and I quickly grew to appreciate the shorter profile. Godzilla is already about 8 feet long before that tail comes into play, and I don’t miss bumping into the kicktail as I walk around the bike.

Rear Thru Axle

Surprisingly, sourcing a proper rear axle was a major pain in the ass. The rear axle is a 12×166 (12mm in diameter by 166mm in length). The ’12’ part is standard stuff. The ‘166’ is a little unusual but still not a dealbreaker. Mix in the required P1.5 threading and thats where Google and Amazon searches go off the rails.

After a fashion, I ended up finding two of them. I ended up using the cheap one and have kept the fancy one in reserve.

The Cheap One:
Dymoece brand 175mm with 19mm thread length. Its exact specs are written right on it in the picture below. I was surprised at how well this was machined. Its 175mm length is too long, but I had a 3mm thru axle washer in my parts bins. Putting that on sizes the axle so there are 2-3 rows of threads visible coming out the derailleur side. Perfect. Everything lined up on this one from the thread pitch to the slightly longer thread length to allow the use of the washer. I like this axle because it is tool-less. I am already carrying hex keys and they’ll work just fine if I need to remove this axle roadside.

The Fancy One:
DT Swiss model 2160062210. This is a model that has a snap-on lever – that is just a glorified hex key – for removal. It looks nice on the bike, and you can remove it so nobody walks off with the thing. For me, since I am already carrying hex keys, I don’t need another one hanging off the end of the axle. I also like the fact that – on a bike that will sit out alone in public – no lever means no invitation to passersby to remove said axle. Still… its a DT Swiss part so its top quality.

Good luck trying to find details on this thing without looking deep across multiple web sites. The Amazon product listing gets it all wrong, calling it a 142mm length (which is correct for the internal dimension) and saying absolutely nothing about thread length or pitch.

Here’s what it really measures out to: 12x171L, thread pitch is 1.5 (it had better be) and thread length is 13mm.

With the shorter length and shorter thread pitch, it fits the Bullitt frame and dropouts perfectly without a washer, and the thread overhang out the drive side is minimal.

Rear Fender

As usual, I cobbled together something from parts and raw materials. Here’s what the finished product looks like from a few different angles.

This is a pretty non-traditional fender set up that does the same job as full coverage fenders without the full coverage. We’ll first cover the materials, and then we’ll discuss the assembly as a whole.

Gather Your Materials

Every bike builder should own some of this stuff: Flexible black cutting board. Unfortunately the black stuff seems to be off the market for the moment, or I am just not looking in the right places. Here is a link to something made of similar material to give you an idea of what I am talking about. What you want to do is replicate the same base material that is used for flexible MTB mud fenders. Once you have that you can cut that raw material to shape as needed.

Next, I used two of these front fenders, that I interwove together, facing each other, so they made a single longer fender. total cost for the pair – which are the core of the fender project – is US$12.84 delivered.

I created the rack deck plate and bobtail with a 1/8″ thick, 2″ x 24″ piece of 6061 aluminum flat bar stock – sold as a remnant – that cost me $8.00 on Ebay. That is way cheaper than normal. Here is a 48″ long piece that is 1/8″thick x 2″ wide. You can cut down to your needed length. Save the rest for your next project. You can go much wider than this for a rack deck plate, but I decided I wanted to go narrow for reasons that will be clear when you see the next item.

I continued to use the paint-matching duct tape that I found by accident across all parts of the rack. If your Bullitt is not the older, brighter Lizzard King color you will want to go with something different. If black works for you then Gorilla Tape is probably my favorite overall material for this kind of work, and in fact I use it here, as described below.

Put the ‘fender’ together

Its not really a fender, but rather a series of pieces that do the job of a fender.

First of all, there’s the rack deck – the bent-up piece of aluminum flat bar. Its length is determined by how long it needs to be to intercept all water spray coming up off the back wheel. I also want enough of a ‘tail’ so I can add enough reflective tape so it is a sufficiently big rear reflector. I used a relatively narrow piece that is 2″ wide. Why?

I wanted enough free space on each side so I could hook panniers to the rack. I *could* have done a full coverage deck – which would have allowed me to use a wider bobtail, and then used a router or hand files to cut out slots for pannier hooks. Frankly… it was easier to do a narrow piece and then follow up with …

Tape. The color-matching tape is nothing more than a wide series of strips folded over onto themselves to make a 2-sided sheet fully as wide as the entire rack deck. Then I bolted the aluminum flat bar on top of it. To allow for the hooks to be popped onto the top of the rack tubes, I simply took scissors and snipped the tape where there is a crossbar, to allow it to fold down when I clip panniers on. This is a bit cheesy, but it got the job done. If some time down the road I have some time on my hands and about US$30 I will cut a full width bar and slot it so its prettier than what is there now.

The rack and bobtail thus do most of the work keeping water coming up off the wheel. Now we have to deal with water coming forward. That is accomplished with the cheapie, doubled front mud fender. It is attached with small green zip ties to the seatstays, and its length in the back lifts up and contacts the rack deck. So… no water is coming forward past that. The front half of this fender also comes down and butts up against the seat tube fairly low, so there is very little area uncovered. But lets cover that too.

To deal with that last bit, I used the cutting board material and snipped out a rectangular length that is as wide as possible while still staying out of the way of my legs and the crankarms (look for it, installed, in the pics). I poked a couple of holes in the right spots and simply screwed this length of ‘fender’ directly to the frame using the two M5 bosses that are already there for fender mounting, on the back of the seatpost.

Front Fender

On the front, I cheated and found something I could just buy and install.

Godzilla uses a Greenguard-belted Schwalbe Super Moto X tire in 20″x2.40″ size. This is larger than most tires – in fact its a hair under being too large to fit the frame. Most fender solutions will not fit.

The SKS Rowdy 20-24″ fender set provides the solution. I shelved the rear fender and used only the front half of the front fender. The front mount without the fender attached is shown below.

Since the fender slides onto the mount bayonet via a firm interference fit, I keep the fender in my toolbag. If I need it I just slide it on. I like to be able to see the tire when riding, as part of my general need to be over-informed of every aspect of the bike as I go down the road.

In addition to it not fitting the bike, there’s no need to use the rear half of the front fender. The front of the cargo deck shields the rider from any splash coming up off the back of the tire. I did add some waterproof rubber tape to the frame at strategic locations to ensure it is a fully sealed face to splashing water.

Steering Dampener

I am using the generic Larry Vs. Harry steering dampener. I found the bike had a horrific speed wobble prior to adding the side panels, which almost completely eliminated said wobble. It only reoccurred on certain downhill road segments where there were repeated road undulations… that set up just the right harmonics for it to happen again. Installing the dampener and setting it to its lowest level cured the problem forever.

Jones Handlebars

I use Jones bars to alleviate pain from pressure on my wrists that came from getting hit by an inattentive motorist in 2017. Their 45-degree angle works wonders. They also give me a long grip area that lets me change positions, and lots of real estate to attach all manner of gadgets. An AWD ebike with one throttle for each thumb, dual PAS panels and dual displays, headlights, a dashcam, missile launchers etc. benefits from the wealth of mounting points available.

I also use two sets of Wolf Tooth Fat Paw grips. 1 and 1/2 grips per side. The extra diameter works well with my hands and thanks to those wrists, I need the extra padding. I cover the 2-piece-per-side grips with a wrap of silicone plumbers’ tape that keeps them grippy but not sticky. If I tear up the grip tape somehow (this happens rarely) I just wrap on another layer.

Lights

Long ago I gave up on trying to find a light that suited my needs, that I could wire into my main ebike battery. Instead all of my lights have their own internal, rechargeable batteries. Once a week at the office I charge them all on the same day, via a USB hub that is a part of my office garage gear.

I use my lights as daybright, daytime running lights and night use. The need to have the lights day-visible means I am going brighter than most folks’ lighting setups.

My lighting choices are informed by the knowledge that blinkie lights are the best to improve the ‘conspicuity’ (yes thats a word) of a rider, but they inhibit a motorist’s ability to track motion. So I use a combination of steady lights and blinkies, front and rear.

Front lights

Out front I use a pair of Niterider Lumina Micros for my main headlight beams. I split my headlights into two widely separated beams for the same reason cars do it. It makes for a wider beam pattern than you can get even with a dual-bulb single headlamp.

In between the two steady headlights is the front version of the Knog Big Cobber. This is a pricey light, but its also probably the brightest, smartest front blinkie you can get your hands on. It actually has an app that lets you program its modes, and I have mine set to ‘eyesaver’ mode coupled to their econ mode (short but intensely bright) blink. The Cobber lights from Knog shine in a 330-degree arc. So you want the eyesaver mode to keep from having that blink coming back at you.

Rear Lights

Out back, I have another Knog Big Cobber as my blinkie. Again it is set to ‘econ’ mode which is an intense, sharp, short blink. This time I let it ride for its full 330-degree illumination. That blinks light to the ground, to the motorist and up into the red reflector of the bobtail. Hopefully they’ll see me.

To aid said motorist in tracking my motion, I have two Knog Blinder Square lights, set to a steady illumination of the outer half of the light.

Running the light half-strength like this lets it last the full week as I like to charge everything together on Friday.

Clip-In Pedals

After literally decades of riding first toe clips and straps, and later clipless when they were introduced into the market, I have been riding flat pedals and Five Ten Free Rider sticky platform pedal shoes for the last couple of years.

I decided to go back to clipless not too long ago, and I have found the Funn Ripper pedals to be amazing. Their spring loaded cleat mechanism – the cleat sticks up and makes cleating in ridiculously easy – is a wonder. Highly recommended. I’m using Giro Rumble shoes which let me cleat in, or get off the bike and walk into a shop or wherever comfortably without clackclackclacking on the pavement.

As you can imagine, being locked into the pedals again made for an exciting transition period, and I managed to fall over at an intersection within 24 hours of making the switch. But once that little reminder was hammered home, I haven’t done it again.

---

So… Thats That

It seems I’ve come to the end of this somewhat tedious breakdown of all things Godzilla – The Big Green Bullitt. If I come up with any more I’ll amend this post. But, honestly I’m happy this series is done as it lets me get on with other projects I have been looking forward to, but can’t begin because this monstrosity remained unfinished.

The Bullitt Build
1. Battery and Battery Box
2. Cargo Box
3. Brakes
4. Front Motor & Wheel
5. Rear Motor & Drivetrain (You Are Here)
6. Bits & Pieces

The Mid Drive

Godzilla is a 2wd/AWD ebike, with a Bafang geared hub motor in the front, set up as a helper to the Bafang BBSHD mid drive powering the back wheel. This is not the first AWD ebike I have built and we’re now beyond what I call my Gen3 configuration. I don’t call it Gen4 as it is still effectively Gen3, and incorporates all of the lessons I learned (and mistakes I did not repeat). Its different in that the two motors blend together in a kinder, gentler fashion I am calling Drama Free AWD.

Fitment to a late model Bullitt

Lets not sugarcoat this: The BBSHD does not fit a Bullitt. BUT… its pretty easy to rectify that. Thankfully there is very little needed to make it fit.

You will figure out for yourself what the problem is real fast. Just try and slide the motor axle into the bottom bracket. Oof… one of the threaded ‘ears’ that holds the bottom bracket clamp overlaps the frame. There are three ways to fix this. I will warn you right now: If you try Method #3 you will be brought up on charges and imprisoned.

Method 1: File down the ear a little

Thats all there is to it. The ear is quite a substantial piece of alloy sticking out of the motor casing. Just file enough of the corner off so it clears the frame. Do a little at a time with a hand file. File a bit, check to see if it clears. File some more. Check again. Repeat until it fits thru. Do this right and the motor will clear the frame and there will still be plenty of material left so there is no concern of any kind as to the structural soundness of that ear.

Looking at the picture above, its kind of hard to see exactly where I filed it, because I took a black Sharpie to the freshly exposed alloy and just blacked it out. A few months later, its worn off a touch but you still need to know where the work was done to be able to see it at all.

Method 2: Partially disassemble the motor

This method is for the Felix Ungers of the world. If you cannot bear to take a file to the motor casing… take it apart, then position it and reassemble the motor in situ. There are only a few screws involved to make this happen… but Jesus H. Christ this is waaaay more effort than it is worth in my own personal view. If you ever want to pull the motor off you have to take the damn thing apart again to get it off the frame. For me… give me the file and 5 minutes for Method 1 and I’m good.

Even so, if someone goes this route I can understand and respect the insane attention to detail such a course exemplifies. HOWEVER…

Method 3: Take a file to the frame

Yes really. I’ve seen it done. Rather than filing off metal on the motor, some folks decide they want to file down the frame instead. The thing that is in the way on the Bullitt frame is a weld seam, and I suppose that structurally, the stuff in the way is not critical to the frame’s structural integrity. But… as far as I am concerned a bicycle frame is a sacred temple and anyone who violates the sanctity of that temple… well they should be taken out and shot. Don’t do that.

How Well Does It Fit?

Once you get the motor fit into the bottom bracket, Its a great fit for the frame. One of the Lekkie (42-52T) or Luna Eclipse 42 or 48T chainrings will give you great chain line. The motor does hang almost straight down, and this looks a bit disconcerting, but the reality is you have other things on the Bullitt that hang lower. The motor is not in any way a hindrance to ground clearance unless you decide to start rolling up and/or off of curbs and such. I have never hit anything and I have never heard of anyone on a Bullitt having such a problem.

Crankarms

In your typical BBSHD or BBS02 installation, the secondary gear housing – just behind the chainring – is present where, on an ordinary bicycle, nothing exists. Consequently the chainring is pushed perhaps as much as 2cm outboard from where it would be. To counteract this, its common to use special chainrings that offset themselves inward to undo what would otherwise be a disastrous chain line. That fixes the chain line, but it does nothing for the alignment of the pedals underneath the rider.

If you move the chainring mounting 2cm out that means – even if you undo the misaligned chainring – your pedals are also 2cm outboard from where they would be only on the right hand side. Yeah thats right. Your pedals are not centered underneath you.

On many builds, this is dealt with by using crankarms that have a left arm that is offset outward. Typically by 18mm (like I said… “about” 2 cm). That centers your pedals underneath you. Thats the good news. The bad news is you can either use the Bafang stock crankarms – which are cast alloy and not particularly robust – or you buy quality forged crankarms – typically from Lekkie who pretty much owns the aftermarket for strong, high quality Bafang-compatible crankarms. So you get either very cheap kaka crankarms that may or may not survive a proper pedelec rider honking on them, or you spend a bundle (and get top quality stuff).

Figure 2 – Note the secondary gear housing tucked in behind the chainring on the left.

So, Forget Everything I Just Said

The Bullitt is one of the very rare frames that does not need any of this offset crankarm business. You will buy a Bafang BBSHD whose axle is compatible with a 68-73mm bottom bracket. Install that and there is enough axle sticking out the non drive side that there is no need to do anything further. Not only is there no need… you don’t want offset arms since the goal is to center the pedals underneath you. Straight arms with minimal Quack Factor will do that.

I used forged 175mm Shimano FC-E6000 crankarms meant for use with a Shimano Steps drive. They got quite a bit more expensive before the Pandemic ratcheted everything up. I paid less for both arms than you are going to pay for just one of them. In fact they are only sold individually these days it seems. Here is the right 175mm arm and here is the left 175mm arm. If 170mm is more your bag, I know they are made because here is a 170mm left arm. I can’t find a right one. Maybe you can if you want the shorter arms.

Still, the good news is you can use straight crankarms from any vendor… so long as they are square-taper (don’t shoot the messenger on the square taper part).

The Wire Tunnel

I have seen numerous BBSHD’d Bullitts where the wiring from the motor is run forward underneath the main … girder … or whatever that part of the frame is called, and then run up once it splits into the deck support. I don’t like this because it creates visible wiring. Also, wires directly under the bike are potentially subject to ground impacts. A risk I’d prefer to avoid.

I looped the wires up and over the drive side. The secondary housing naturally protects and hides them. The wires then cross over the top of that girder, hidden by the wire tunnel. My original idea was to use a bit of green or black furniture-grade PVC. However, early on in the build process I stumbled across ‘Duck’ Brand neon green duct tape. This is commonly found in hardware stores in the USA. Its a hobby-grade household product and not construction-site worthy, but its fine for this job.

By some miracle the Neon Lime Green color is nearly an identical match to the LarryVsHarry Lizzard King paint. You literally have to be looking at it just right to see any difference between the two. It was perfect to cover the dark green PVC pipe used for the wire tunnel. I did use two very large dark green zip ties to hold it in place. These were the closest color match I could find and, while they are not ideal, I have yet to find a better solution (including taping the thing onto the girder with the matching tape. I tried it and it looked awful).

The inside edges of the plastic PVC pipe are not what I would call ‘sharp’, but they are edged and a little more unforgiving than I would like when rubbing every day on flexible, soft wire casing. I beveled/chamfered the inside and outside edges using a quick pass with a pipe reamer. Problem solved before it becomes a problem.

As it stands, the wire tunnel protects the wires coming out of the motor that have to be run forward and up the steering tube, where they rise to the handlebars. You don’t even see any wires now the Fahrer bags are installed.

Heat Sinks

Godzilla presently lives and works in Fresno California USA. Whats the weather like there, Ollie?

And once it starts getting hot, it stays hot…

When faced with this, you have to take steps on a variety of fronts to at least mitigate the issues that come up. Insofar as the BBSHD is concerned, I have already covered this subject in a fair amount of detail in a separate article that predates the Bullitt build and, yes I pretty much covered the motor in heat sinks just as you see in that article.

Since the crankarms are not offset on this bike, I was not able to use an endcap, but as shown in the linked article above I covered every bit of the motor I could with the things, using both the silver center sinks and the little black squares around the edges.

BBSHD Settings

The settings for the BBSHD are another subject already covered in detail. First in this article that introduces my approach to the subject, and following on with this one that covers some very minor refinements.

To jump specifically to what I am doing on Godzilla, you want to jump straight to Version 2 and look at the right-side image.

Here are the three screens below, but all the explanation for what they mean is in the linked articles above.

Figure 6 – The BBSHD settings used on Godzilla

Drivetrain

If we’re discussing the mid drive, we have to at least touch on the rest of the drivetrain, which is integral to making the bike go places.

SRAM GX 11-speed shifter

I prefer SRAM shifters because the way they mount onto the handlebars, they take up much less real estate than their Shimano or Microshift counterparts.

SRAM GX long cage rear derailleur

SRAM derailleurs in general, once adjusted properly, seem to stay that way. There’s not much to say about this derailleur other than it just works, precisely, smoothly and reliably, does a great job wrapping chain and has no issues with the 42T big cluster I have on the back. I don’t use its clutch feature. It is able to handle a 46T rear cluster just fine, although I don’t have one on Godzilla. I do have one on another bike set up that way with the same drivetrain bits.

KMC e11 chain (mid drive-specific)

When I build a mid drive bike I use a mid-drive specific chain. That is I think part of the reason why, in all of the thousands of miles I have been riding powerful mid drive builds, I have never once broken a chain. Unfortunately the e11 is frightfully expensive. Bide your time, keep your eyes open for deals anywhere in the world (particularly in the EU) and you can find an online deal.

Sunrace CSMS7 cluster: 11-42T

For all mid drive bikes I build, I prefer steel, welded clusters that are 1-piece. Such a thing is not really available in the 11s world, but the Sunrace CSMS7 is as close as it gets. It uses steel spiders and high tensile steel cogs, which is what you want for durability with a mid drive.

NOTE: The CSMS7 has turned into a unicorn these days. I have managed to score two NOS in auctions on Ebay. One for use on this Bullitt build, and a second recently as a backup for the inevitable day when one of mine fail (I have another on my Surly Big Fat Dummy’s street wheelset). But thats it, Nobody in traditional bicycle retail has had them in stock for months.

Given global bike supply issues, there is no telling how long it will take to fix this. I have found that a Sunrace CSMX8 appears to be an excellent performer despite its alloy spiders (one is pictured below). I use this on my mountain wheelset on my Surly Big Fat Dummy and so far it has given me no trouble. Its range is 11-46T which has proven to be no issue for the (lower end) SRAM NX derailleur that is on that bike.

Figure 9 – The Sunrace CSMX8: Lighter weight scaffolding under the hood… but still steel cogs.

Rear Wheel

The core of the rear wheel is a DT Swiss 350 Hybrid rear hub. The Hybrid line of DT’s 350 is, compared to the standard 350, beefed up in just about every way. The flanges are beefier, the cassette body is steel, the internal ratchet mechanism is a solid piece rather than being relieved for light weight, and it is a 24T engagement vs the stock 18T, which gives better response while still maintaining the super strong ratchet mechanism that makes this hub almost indestructible when paired with a powerful mid drive.

The rim is a SunRingle MTX39, which has a 30mm internal width – the ’39’ in ‘MTX39’ comes from its external bead width. The review of this rim over at MTBR described it as “monumentally strong” and “impossible to bend” while noting the penalty for this strength is weight. Since weight is not a factor on a twin-motor cargo bike, I’ll take that strength any day of the week. The rim has proven itself un-dingable both here on Godzilla and on the Mongoose Envoy build I first used them on.

The MTX39 is commonly available in both 32H and 36H configurations. So is the DT350 Hybrid. However, at the time of my builds I was never able to find 36H hubs, so both of my builds are 32H… and they are none the worse for this choice. In particular, a Bullitt’s construction does not put anywhere near as much weight squarely over the back wheel as do for example your garden variety mid- or longtail. That makes it easier to live without 36H. 1100 miles so far in a few months and the rear rim is still perfectly true.

In between the rim and the hub are Sapim Strong spokes with brass nipples. Once again I used the expert services of Stoic Wheels to provide cut spokes to my specs.

Front Chainring

Ordinarily, I advise a builder that you have to keep the motor spinning on a mid drive, and a 52T front chainring is way too big. You’ll bog the motor as its trying to lug itself up from a stop. This is the worst thing you can do to a mid drive, and among other things is a great way to snap your chain.

But Godzilla proved to be an exception. The choice of a 52T chainring (in country that is flat as a pancake) was still not initially obvious. As noted in Musical Chainrings, I have a lot of chainrings available from a variety of builds. With any new bike build, I do not expect to get it right on the first try. Unfortunately I came close here (it would have been nice not to buy another one) but in the end, no cigar.

Plan A

At first, I tried a 46T Lekkie ring pulled from the parts pile. The offset was good and planted the chain in a straight line … about four cogs inboard on the rear cluster. So with that 46T ring I was spinning a little too much with good chain line, and the bike was outrunning me. Time for …

Plan B

I switched to a 130 BCD adapter and a 48T chainring. If the 46T with strong offset was too hot. The 48T with minimal offset was too cold. Now I had a big chainring; good on the flats, but with no offset, good chainline was only on the smallest cogs in the rear. That was great once I hit cruise but bogged the motor when starting from a stop… and thats very bad. Lets try …

Plan C

My third try is a Luna Eclipse body with a 48T (proprietary) ring. So, same chainring size as Plan B but with the most offset possible in any BBSHD aftermarket chainring. This felt pretty good. I was running up in a larger rear cog so my chainline was great. That kept the motor from bogging from a standing start.

But (!) … I was not able to get down into small enough cogs when I was up to cruising speed. The bike was running away from me. The only solution was to let the bike run at slow speeds as it peaked with usable cadence and effort at about 18 mph. I lived with this for awhile – and it was ok (just ok) – until I decided to finally buy a chainring in a bid to have my cake and eat it too.

So now its come to Plan D

A 52T Lekkie chainring that has the same goodly offset as was found with Plan A. I would be biasing my chainline into the upper half of my cluster. But not so much that I would be unable to comfortably use the smallest cog (as was the case with Plan C). I figured the increased tooth count would cause me to run one gear up the cluster from where I was running with Plan C, and slow my cadence enough at that bigger rear cog to still run the bike faster, while at the same time keeping a straight-ish chainline, preserve my ability to gear down to bigger cogs and up to smaller ones.

And this time, finally, I was out of parts and had to buy the thing, using my usual source for Lekkie rings here in the USA. Ouch that one smarted a bit.

But the money was worth it as it completed the bike. Plan D worked perfectly. This is, as far as I can see, the only time a 52T chainring works well on a mid drive build. Worth noting is the fact that this bike lives on table-flat ground, and if there were hills in its way, I would have likely had to go with a 42T front Lekkie ring.

---

Thats it for the rear motor and drivetrain. Lets wrap up discussion of this build with

Bits and Pieces