2018 Surly ECR Bafang BBS02-B 750W/48V Mid-Drive Build

[Rider]

Decided to build a Surly ECR with all the parts left over from my Electra Lux Alloy Cruiser 29+ custom build; that I eventually returned to original and sold off. Basically all the parts except the frame and fork will be transferred over to the ECR: Bafang BBS02-B 750W/48V mid-drive with color display and 42T Lekkie Bling Ring, Velocity Dually wheelset with Sturmey-Archer (S-A) 5-speed IGH laced up with DT Swiss Alpine III spokes for good 230lb. Clyde rider strength and Shimano Deore front hub, Surly Extraterrestrial 29 X 2.5 tires mounted up tubeless, Tektro HD-E350 hydraulic brakes with play-n-play Bafang power cutoffs, Thudbuster L-T seatpost with ISM Urbaine saddle (NOTE: The L-T wouldn’t fit with my leg length, so I ended up using my S-T Thudbuster), and Fouriers Trailhead handlebars with two pairs of ESI Extra Chunky grips. Also ordered a pair of SQlab 411 Inner bar ends that will go right next to the inner edge of the outer ESI grips. The S-A 5-speed top bar lever shifter is installed on the left side on the underside of the handlebar. This will leave the top of the whole handlebar for unmolested multiple hand positions for long trail ride comfort.

The “Blacktacular” frame arrived today and looks great! This frame has the Surly Gnot-Boost rear dropouts. It will take 135mm to 148mm Boost wide hubs and 10mm QR, 10-12mm straight axles, or 12mm thruaxles. It also has a Rohloff torque arm slot and trailer hitch mounts, in addition to fender and rack mounts. The front 29+ fork is 100mm wide and accepts 9mm QR or straight axles.

Let the fun begin!

[Rider]

The initial assembly went smoothly. I had my LBS I bought the frame from install the headset and fork race, so all I had to do was pound in the stem cap star nut and put it all together. Front QR wheel went right on without a hitch, but the rear S-A straight axle is an odd 13/32” diameter, which is slightly larger than the 10mm Surly “HU0001” 10mm to 12mm adaptor washer sleeves that are included with the frame. I bought a second set of the 10-12mm washers to drill out to 13/32” to fit my unique application, that way if I ever upgrade to a Rohloff 10mm straight axle I already have the washes. After that, the 135mm wide S-A 5-speed IGH slide right on perfectly.

The second unique issue that came up is the S-A torque washers have 13/32” blocks on them to prevent the axle from spinning in the dropout. Because the Sulry ECR Gnot-Boost dropouts are 12mm, the S-A torque washers will not work and anti-rotation blocks slop around in the 12mm slot. I will have to make a custom torque arm for my unique application. I haven’t decided if I will use the Rohloff torque arm slot for that or simply make an axle washer with a 12mm anti-rotation block that fits the Surly axle slot.

Here’s the initial mockup assembly. I didn’t install the seatpost, as I can feel some burrs on the inside near the clamp slit that will have to be reamed smooth.

[calfee20]

Where did you buy that bike stand?

[Rider]

On sale at Big 5 Sporting Goods for a whole $12. Assembled the first one with both wheel slots facing the same way, but the handlebars would hit each other if the same wheel on both bikes was in the rack. When I got my third bike, I bought another $12 special and assembled it and reassembled the first one to have the rack on either side. I hope to insert a piece of PVC in the base tubing to join both racks into a four bike rack with two bikes on each side. This will give a full bike space between each bike so I can put both fronts or both rears in the rack on the same side. In doing this, it makes for a big footprint, but easy to park all my bikes any way I want to. I don’t plan on ever having more than four bikes. Time will tell if I can limit my hobby to only four. Lol...

[Rider]

Cleaned up the garage a bit and put both racks together like I plan to use them. As you can see it does take up quite a footprint.

[Rider]

In mocking up the Bafang BBS02-B with a 42T Lekkie Bling Ring installed to the 2018 Surly ECR frame with 73mm standard Bottom Bracket (BB) a 1/8” (3.175mm) spacer was needed to achieve chain ring clearance on the chainstay; without facing the electro-coat paint on the BB edge. I will face the BB edge and recheck with good torque to see if a slightly thicker spacer is required.

Returning to the S-A rear axle torque arm issue, it appears the best place to attach one to the frame is the threaded mount just above the drop slot indicated by the arrow. These mounts are present on both sides of the frame; unlike the Rohloff torque arm slot that is only on the left side. I plan to run the axle all the way forward in the drop slot, so the current plan is a fixed location torque arm, positioning the axle there and also acting as an axle position place-lock bracket.

First I will mockup a cardboard bracket pattern, then decide what material to use to create it. Those that have read each of my builds may recall that when this rear hub was on the Electra Lux Alloy Cruiser I made torque arms out of a cheap Home Depot Gate Latch that already had a square hole that was easily adapted to a 13/32” S-A lock-slot. I’m not sure if that same Gate Latch will work, because the axle slots will need to be vertical on these horizontal drops. After I make a simple cardboard pattern I will go to Home Depot to see if that same part has enough flat material in the position I need it. Otherwise I may simply fabricate what I need from flat stock steel or aluminum.

[Rider]

I can't stress enough how much mocking up installation of all the parts helps in determining how you want to do things. In mock installing the shifter cable I learned that this frame doesn't have any cable attachments on the chain stay, but it does have cable attachments on the seatstay (which is the norm). In order to use these wonderful attachment points for a clean shifter cable installation, I had to spin the axle a quarter turn (90*) to get the shifter cable stop that comes off the rear hub pointing up in a vertical position towards the seatstay cable mounts. This rotated the flat anti-rotation surfaces on the axle from vertical to horizontal. With them in the horizontal position the standard anti-rotation washers that come with the S-A 5-speed now have the anti-rotation block in the 12mm axle slot. So, the simplist solution for someone that has a welder is to just run a weld bead on both sides of the block to build it up to 12mm thickness and use them as they are intended.

If you don't have a welder or access to one, then my original plan will still work, but the angle of the slot in the torque arm has to match the new axle position. Here's some photos for reference.

[Rider]

The SQlab 411 Inner Barends just arrived. Had to slide them on and grab a feel...

Oh boy, I'm going to like these!

[ncmired]

Hi Rider - for these horizontal dropouts, roughly how far back do you have to secure the hub, so you'll have enough chain to clear off the front chainring to get the wheel out?

Or, are you planning on using a tensioner? Or do you have a chain master link? Or ... am I not getting the gist of this type of dropout?

[Rider]

Very good point! And one I hadn't thought of yet.

I planned to use a chain tensioner, but will still need enough chain to remove it from one of the sprockets or use a standard chain link instead of the two side & post type that slide into each other and expand. Those are a pain to remove unless you have the proper pliers...

I haven't bought the chain yet, but am very happy you chimed in. I could have easily made the chain as short as possible while the axle was all the way forward where I want it for handling reasons to get as much playfulness as I can out of this longer chainstay off-road touring/camping frame when not doing hard duty.

I will post up what I calculate when I reach the chain installation point.

[ncmired]

An open cage two pulley tensioner would probably work pretty well ... if there is such a thing still. Sun Tour (gives you an idea of how long ago) used to make open cage derailleurs.

The Surly Singleator is a possibility too.

I asked, as I've been eyeing the Surley frames (among others) for a build.

[Rider]

The $5 Home Depot Gate Latch worked like a charm again. Two of the square holes were filed into the shape of the S-A 5-speed IGH 13/32” axle with two flat sides and a portion of the metal was used for the rest of the bracket. I will be finding someone to weld a bead on both sides of each standard steel S-A anti-rotation washer (installed under the custom made axle position-lock torque arm plate in the pictures). I want to make both while I’m fabricating so I have them as a backup. You can see how it will all fit together once completed. I haven’t drilled the holes in the top of the arm let. Once that is done, I will round that end of the bracket nicely and paint them up.

The last picture is just to show that one could have made simple “L” brackets by filing the square holes into shape and trimming the portion after the bend to fit the 12mm dropout slot; another option if desired.

NOTE: None of this special custom work is needed if not using the oddball 13/32” straight axle S-A 5-speed IGH.

[Rider]

Completed the dual torque arms, stamped them with “R” and “L” for their corresponding side and painted them up. They are drying now.

Test fitted the brake calipers and chased the threads on all the fender and rack mounts with a 5M X 0.80 tap to clean out the ED coating in them (a must do!).

Now turning my attention to mounting the BBS02-B. Like on my Soma B-Side brand new frame build. I really don’t want to groove the BB edge with the Bafang bracket that goes on the left side of the BB. I think I will make another aluminum bracket torque arm for it similar to the Soma build. I might even try to make an additional mount off the motor halves bolts to the lowest water battle mount to add support and strength (gave up and n that idea). If I do that, maybe I can simply file off the ridges on the Bafang BB mounting bracket so that it will not groove the BB edge and let the under the down tube bracket act as a motor torque support point (NOTE: Electric assist torque from the motor is upward toward the down tube). Just brain storming out load to gather my thoughts...

[Rider]

Got the custom made combination torque arms and axle locks installed. That axle shouldn't be rotating and certainly won't slide backwards at all.

Test fitted a JANDD Mountaineering solid bar alloy rack that takes a Topeak MTS strap (battery) bag nicely that I already had left over from the Electra Cruiser build. Eventually I will have a custom frame bag made up, but that can wait.

This project is moving along nicely. I'm taking my time to get everything done right the first time.

[Rider]

Got a chance to start mocking up a motor torque arm bracket so I don't score grooves into the BB edge with the Bafang metal locking bracket on this nice new frame. Also added a washer to the lowest under down tube water bottle mount to extend it a small amount, then put a rubber cap over the bolt head for the motor to rotate up against preventing any part of the motor from touching the frame. The idea will be to lock the motor in this upward position before tightening the large BB nut and have the custom torque arm hold it in place in a solid fashion. This method has worked very well on the Soma B-Side build for other 3,000 miles now. Haven't decided if I will polish this bracket like I did on the other build, as a solid gloss black bracket will be more stealthy and match this build better.

[calfee20]

That is nice. I just use a thin Aluminum shim that comes with the kit and the bracket dents that.

[Rider]

None of my kits came with a thin aluminum shim. Do you have a picture of what you are referring to?

Also, if the Bafang bracket simply bites into an added aluminum shim that is flat on the other side against the BB, what locks the motor in place?

California Ebikes makes a couple BB motor mount torque arms, but they never seem to line up to the lower rear stay on the left side on my bikes. Luna sells them and I think they are made of SS.

[calfee20]

You have to tighten it enough.

[Rider]

Finished up the bracket and test fit it. All looks good! Now the question is, to polish or paint?

[Rider]

Decided to go with gloss black paint and SS bolts like the rest of the frame. It took two 1/4" spacers where the bracket bolts to the motor and in the end the 1/8" spacer on the crank side of the BB worked just right. Put a single speed Sram PC-1 chain on it and took her for a ride. Yippie! Quick handling and super responsive, and with the axle slammed forward in the horizontal drops I had no trouble whatsoever lifting the front end. The SQlab 411 inner bar ends felt great too while riding and my initial best guess is this will be where my hands are the majority of the time, unless it gets technical or I'm ripping single track. Gearing with the 42T X 25T Sturmey-Archer 5spd is low enough for an electric assist bike and 5th appears fast enough for me.

There was one semi-glitch that popped up. The left crank arm is too close to the lower rear stay for comfort. Luckily it wasn't hitting when I test road it or I may already have had a scratched frame the first ride out of the garage. I RECOMMEND OTHERS CHECK THIS CLEARANCE "BEFORE" TAKING IT FOR A TEST RIDE! I will be ordering up a larger offset left crank arm to gain more clearance. In measuring the inside of each crank arm to the center of the down tube, the right measured ~95mm and the left ~65mm, so a 30mm further offset will even them out, but the much offset isn't needed for clearance only.

[ncmired]

Thank you Rider for all of your detailed build posts - they help a great deal with planning my own build possibilities.

[Rider]

You are welcome.

[Rider]

After spending all morning researching different left side square taper diamond/rhombus/rhombic (identifies the orientation of the square in the arm) it appears an Electra Lux Cruiser (not sure if the Lux and Lux Fat are the same and which one calfee20 used in his comparison in the link below) left crank arm has a large offset that comes close to matching the pedal spacing from the center of the frame in a 73mm BB with 1/8” right side spacer. Unfortunately no one seems to list the offset of their crank arms on eBay and few even post top view pictures.

https://electricbike.com/forum/forum...m-bb-bbshd-kit

As I was getting frustrated in my research because of the lack of specifications, an easy immediate solution popped into my mind. I can simply grind off about an 1/8” of the Bafang left crank arm for now to insure no frame scratches if the arm flexes at all under heavy pedaling. Problem solved for now and I can ride! But I will probably end up running a Shimano right arm that appears to be ~1/2” inward and find a left arm that is a ~1/4” outward to give a centered and narrower Q-factor.

[Rider]

Well that was easy. Grind, file, sand and paint with a little semi-gloss; all is good!

Off for a 15 mile round trip test ride in pedal mode to my LBS to get her weighed in without battery...