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15" Motobecane Boris FS NX - 100 mm or 120 mm BBSHD? What size ring gear?

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    15" Motobecane Boris FS NX - 100 mm or 120 mm BBSHD? What size ring gear?

    Hi total noob here to ebikes and I have not really touched a bike much since I was 16(43 now). I have a few questions. I just got A Boris FS NX last night in a 15" frame(I have a short legs) and I'm planning on putting a BBSHD in it.

    Cheapest bike on bikes direct right now with a Bluto fork.

    I have read all the threads I can find on the 170 mm rear geometry Boris frames and most have used the 100 mm kit. I only read about one that was able to use the lock nut/beauty ring and it only had 3 mm of spacer to clear the chainstay. Most builds seem to use 6 mm or more for the motor to clear and don't have enough thread to put the ring on. What are the negatives to using the 120 mm BBSHD on this 100mm BB bike?

    Am I going to need an excessive amount of spacers to get the chain line decent? Should I look at offset crank arms? Is the 100 mm a better bet?

    Right now I'm thinking about using either a 36 tooth Luna one or a 40 tooth one piece Luna Eclipse. Both have an 8 mm backspacing but I'm unsure which would be best for the mix of terrain I'm gonna use it in. The bike has a Sram 11-42T-11spd cassette and a 30 tooth front. After riding today there is nothing I would use the last 2 or 3 cogs on locally. Where I live its mostly flat but I do plan to take the bike to do jeep, double, and single track in the mountains in Colorado and Arkansas. I may also use it to pull a trailer with my dog or small game. I am currently leaning towards the 40 tooth is this a mistake?

    Kinda wish I would have got the 17" frame now and just dealt with the potential discomfort. I was hoping to use a 17.1 ah triangle pack from EM3EV but it wont fit. Sadly a Shark wont either.Here is a pic with a template of the Wolf in the triangle. 1/4-3/8" more clearance and it would probably fit.

    I think I'm gonna go with a wolf pack mounted on the bottom of the downtube.
    Last edited by SpookyXJ; 05-29-2018, 05:54 PM.

    After rereading a few build threads I decided to go with the 100mm kit. Also got the 40 tooth one piece eclipse and a wolf pack battery. I've been wanting an ebike for a couple of years and now that I have the bike impatience wins.


      I also have a fat tire bike and started with the 30 tooth then went to the 36 which I like a lot better. It seems to work for everything. Now I have a 42 because it helps make the chain angle better. But it is difficult to climb some hills now. Not sure what I'm going to end up with. I will have to put a few more miles on it.


        If the chain line is good I may pick up a 36 tooth later to see which I like better. What rear cassette do you have?


          Total newbie here too. The ebike bug has bit me and so I am moving forward on a build.

          I am interested to know how your build is going because I purchased the same bike but in a 19 inch version. Came across this forum and your posting so it naturally intrigued me since we purchased the same donor bike.

          I am strongly leaning toward the 100mm BBSHD kit from Luna. As you noted above, this seems to be what most use on this Boris frame. I am curious how easy/not easy it was to remove your bottom bracket and how did 100mm BBSHD fit for you.

          Also, and more importantly, how is your chainring working out, particularly as relates to the chain line? Though I have read a bunch of stuff online, it is all cluttered in my brain now and so I am confused on what would be the best chain ring to the point of having analysis paralysis. I see the stock BBSHD 46T chainring (which I understand to be garbage) has an offset of 19mm. Part of me wonders if it would be best to start with this to see how my chain line will be and then purchase the appropriate better chainring later (with more or less offset).

          Luna suggests the Luna 42T AL chain ring ($40 when added on as part of the kit); however, the offset is only 9 mm if I understand things correctly. Seems the Luna Eclipse is out of stock (only 48T shows on product page but indicates unavailable when clicked). 42T Lekkie Bling Ring looks available and with good offset at 20.4 so maybe that is the best option.

          Finally, i don't see the programming cable as an option (or otherwise available for sale). Does this mean it is out of stock?

          Thanks for any help you can provide.


            I'm waiting on my kit to arrive so I can't really answer your questions yet. Luna says it will be 1-2 more weeks before it ships as they are behind on wolf pack batteries. I did get a bike hand tool kit with a crank puller just in case and I also ordered the socket set from Luna so I can use a torque wrench on the install. I am enjoying the bike though I just don't have the stamina to ride very far plus its freakin hot here in Texas.

            You got me curious so I just pulled the crank. It came out easy. For the SRAM NX Crank you will need a 10 mm Allen to remove the dust cap/jam nut, an 8 MM Allen to remove the nut holding the crank arm on, A crank arm puller to get the crank arm off (ISIS style), and a bottom bracket wrench or socket

            Here is a link to the programming cable
            In stock for only $20. This allows you to change your factory settings and hot rod program your Bafang BBSHD or BBS02


            • max_volt
              max_volt commented
              Editing a comment
              OOS at luna

            • SpookyXJ
              SpookyXJ commented
              Editing a comment
              My bad. Did not notice the out of stock. I see several on Ebay.

            • max_volt
              max_volt commented
              Editing a comment
              No prob I have done the same thing. They don't make it super obvious.

            SpookyXJ, thanks for your reply and information.

            Impatience may win on me too and I may need to push forward, particularly in view of the shipping times.


            • SpookyXJ
              SpookyXJ commented
              Editing a comment
              Yeah I can't wait to get mine. The bike is fun now for about an hour then I'm ready to quit. It'll be nice to be able to run all day and not be dead tired.

            Hey Rider Ralph I don't know if you have ordered yet. My kit showed up tonight except for the battery which is supposed to show up tomorrow.

            The 100 mm kit is almost perfect for this bike. It did require a spacer. Luna did not provide any 1 mm spacers but sent 2) 4 mm spacers with the kit so I used one. It looks like about 2 mm's worth of spacer would have been plenty. The motor was a tight fit in the bottom bracket. The BB on this bike has 4 of what I assume are jig alignment holes for when they weld the BB onto the bike. I had to file the rough edges on these holes and run some sandpaper through the BB to get the BBSHD to fit. I still had enough thread to get the lock nut/trim ring on the bike.

            The 40 tooth eclipse has a horrible chain line and the chain comes off easily. It only works with the 3 smallest gears in the cassette. The stock chain ring is just about perfect with the middle of the cassette being almost straight. I will probably replace it with a 42 tooth better quality ring at some point. I'm kinda sad I wont be able to run a smaller ring.

            Hope this Helps you out.


              Just caught this but we recently did a 170mm dropout boris and a year ago did a 197mm dropout boris - both 11sp

              The 170mm dropout boris would be fine with the 100mm although we used a 120mm. We have a 100mm on the 197mm boris which just barely fit - the 120mm would be more appropriate. bottom line either 100 or 120 can be used on both but I'd avoid the 100 on the 197mm boris.

              On both bikes we went with the 130bcd adapter. The 170 is running a 39t x 11-42t and the 197 sports a 42t x 11-46t.

              The chain line on the 197mm is much better than the 170mm which really shouldn't be unexpected since the cassette is further out. The 170mm can reach all the gears but it's very angled.

              The potentially good news for you is that you should be able to run the 39t 130bcd chain ring which as long as you run a reasonable wide-range cassette will give you excellent low. I found that you want a low speed rear cog that is slightly larger than the chain ring. Hence the 39t x 42t on the 170 and 42t x 46t on the 197...

              Last edited by AZguy; 06-21-2018, 05:40 AM.


              • SpookyXJ
                SpookyXJ commented
                Editing a comment
                Thanks for the info. This bike is the 170 mm rear dropout and I have a 11-42 cassette. Which 130 bcd adapter are you using?

              • AZguy
                AZguy commented
                Editing a comment
                We used the bafang adapter. Luna sells them with a 40t or 44t ( I haven't tried a 40t but it is likely very close to the perfection I found with 39t against the 11-42t. Regardless, the plain chain rings are very inexpensive. I've heard there may be some 38t in 130bcd too but they seem much more unusual.

                There's just enough room for 1mm thick washers between the chain ring and the adapter and that helps the chain line a tiny bit

                FYI - I've tried various combinations of 39t, 42t, 44t & 46t chain rings, and 11-42t & 11-46t cassettes

              Hey Spooky,

              How did your build turn out? Could you post some finished pics please? I'm particularly interested in what battery you went with and how you fit it on your bike because I bought a 15" Boris for my girlfriend and I'm having a helluva time trying to figure out what battery will fit.



                I've got a 17" boris (197mm dropout) and a dolphin won't fit and shark will - barely so I think any of the water bottle batteries aren't going to fit on the downtube.

                Since I run dolphins and sharks I put a rack and dolphin mount on the back of the bike. People say ohhhh it's terrible to have that weight back there but it doesn't give me any grief whatsoever.


                Click image for larger version

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                  Sorry I have been MIA for some time. Summer got in the way of my posting.

                  I did finally get my order from Luna and have my build 95% done. Still need to optimize some things like moving throttle to left side, add gear shift sensor, add brake cutoff sensors, etc. Also, I have already come to terms with the fact that my build will likely always be at 95% b/c there will always be something more to add, tweak, etc. The further I get in my build the bigger my list of desired add-ons becomes.

                  Anyway, the above posts were super helpful in influencing my order and build. Based on above, I purchased the 100mm BBSHD to fit on the 19 inch version of this frame. As mentioned, Luna provided a couple spacers (I think one was 3 mm and one was 4 mm). I used the 3 mm one but as already mentioned a 1 mm spacer would be perfect. When I get around to it, I will swap out the 3 mm spacer for a 1 mm one. I too had to due some work on the bottom bracket to get the BBSHD to slide in (I used a Dremel, WD-40 and some elbow grease). Also based on above, I went with the 40t 130mm bcd Chainring Adapter and it appears to be a near perfect fit. Since my frame is 19 inch, I had no battery fit concerns and decided to go with the 52V Luna Wolf (Samsung 30q 12ah).

                  Also, I have a new problem impacting my ability to get further on my build: the bike is so much fund to ride that I tend to want to ride it now more than work on it.

                  Thanks so much to all of you that posted above!


                    Hi, Sorry I'm a little late here, but I just found this thread.
                    I recently completed a very similar build.
                    Motobecane 2018 Boris FS SRAM NX 1X11 Bluto.

                    I have a 21 inch black frame.
                    The motor is a Luna 1000W BBSHD (100mm) with 30 tooth chain ring.
                    My battery is a Luna 52V Wolf Pack.

                    I have had it working for about 3 weeks now, and am very pleased with this setup.
                    The kIt went together quite easily, and all the needed parts and spacers were included.
                    I did have to do some filing and grinding inside of the bottom bracket as there was some weld and tool marks protruding inside.
                    I've put almost 300 km on it so far.
                    It's a definite head turner and gets a lot of interest as E-Bikes are really not very popular around here yet.

                    I'm a very large guy (6'4", 290#), [193cm, 134kg] and the performance if this E-bike is outstanding IMO.
                    One thing is... I have a totally screwed up Left knee from an old motorcycle injury, so I replaced the Left crank arm with a short 102mm crank arm.

                    This area is quite hilly but the bike has enough torque to climb anything so far both on and off road. whether I pedal or not.
                    I'm a little disappointed in the range, as I'm getting only 17 to 20 miles on a charge, but again given the conditions noted above, I guess it's not too bad.

                    I'm considering a larger chain ring, but I'll need to get a longer chain as the supplied 112 link KMC X-11 EPT chain is not long enough for anything much larger that 34 tooth

                    Here are a few photos:
                    (sorry for the image quality, but my camera has been acting wonky)


                      More about the gearing on my build:

                      The chainring I'm using is a Luna Mighty Mini 30 tooth.
                      It only has 8mm offset so the chain line is pretty lousy.
                      I does have gobs of torque however.
                      Due to the poor chain line, it seems that when in the 2 lowest gears the chain will pull off the rear sprocket if I apply full throttle while pedaling.
                      Using the provided spacer, the BBSHD is mounted as close to the chain stay as possible, with less than a millimeter of clearance to the gear housing.
                      The provided spacer looked like a remnant from the bottom bracket wrench cutout, but It fit perfectly.

                      So I'm still trying to find the optimum setup for gearing.
                      II tried to install the 46 tooth Bafang sprocket but the original 112 link chain was too short.
                      I have ordered a spare 126 link chain to keep as a spare, so I can use that to tryout the 46 tooth sprocket.
                      That will give me a chance to see if the additional offset helps, and check how the bike will perform with a larger sprocket.
                      Because of the BBSHD gear housing, it seems that 42 tooth is the smallest size chainring available with a decent amount of offset.
                      Last edited by Wozzy; 08-27-2018, 06:42 AM.


                      • AZguy
                        AZguy commented
                        Editing a comment
                        I just bought a spare chain (same type of course) and add several links from it whenever I replace the chain

                      Curious if the chain line using the mighty mini chain ring is any better on the 197?
                      2018 Motobecane Boris Fat Bike BBSHD Build


                      • AZguy
                        AZguy commented
                        Editing a comment
                        I can't speak for mighty mini chainring but I'd bet it's no better than the 130adapter - with my 197 I have a good chain line, not "optimal" but only a little short of it

                        To be fair I shimmed mine with 1mm washers, presently on a 42t. that also works with 39t which is the smallest that's readily available - there are 38t but that may require removing a little material here and there on the adapter so it doesn't interfere with the chain - I dunno