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Belt drive for a BBSHD

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    Belt drive for a BBSHD

    Is there any interest out there for a modified crank that would fit a Gates or similar carbon fiber belt with an existing BBSHD? I know I would love to jettison the chain and cluster in the back to switch to an all belt drivetrain. Just wondering if others would be interested as well. With Luna's ability to CNC new stuff I was just wondering.....?

    Luna has or has had some belt drive bikes. I never looked close to see if they had a specific chain/belt ring or if they just used a BCD spider.


      Luna's belt drive bikes all use frame-integrated motors, not the BBSHD. The BBSHD-related belt line dimensions won't work for most frame / BBSHD / IGH combinations - as in, you need to get more left at the motor end than is possible. By quite a bit, and as usual with belt drive the belt alignment has to be "right on".

      IGH hubs that can be made to work are the Rohloff 14-speed Speedhub (58mm chain / belt line) and the Sturmey Archer 3-speed CS-RK3 (single sprocket with spacers).

      Derailleur hubs with single sprockets (and spacers) would also work, but a single speed BBSHD doesn't make sense, IMHO.

      This build post (BBS02 and CS-RK3) illustrates some of the the dimension issues. There's also this Spot Acme / BBS02 / Shimano Alfine build, with I suspect a custom spider. The BBS02 is easier to deal with in this case than the BBSHD.

      Another thing to consider is belt tensioning, and having the right frame setup to accomplish it in a repeatable manner - say, after repairing a flat on the side of the road. I suspect sliding/rocking vertical dropouts work best. Finally, the frame has to have a break somewhere to pass the belt AND be stiff enough to maintain consistent belt tension.
      Last edited by ncmired; 10-05-2021, 09:15 AM.


        Trying to build A BBSHD with Shimano N-3 will baby the N-3 until the 3x3Nine is available. As you can see I will have to do a custom front sprocket as I still need 2MM to get a good belt line. Does anyone have a source for a custom belt-ring?

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          "Custom belt-ring" - front or back? Assuming front, which is too bad as the back could move out quite a ways on the Nexus 3 as it's not a rotary shifter hub. But, no I thought, since Gates has patented the system there are no other compatible belt component manufacturers.

          I'm guessing that the chain ring and/or bolts re grinding on the motor's secondary gear housing.


            Can you grind a little off the BBS's gear case where it hits the chain stay and gain that 2mm? There is a decent amount of meat there and because you are usually hitting hitting at an angle so 1 mm of grinding gains you 2 mm of movement. Or if you did that would you teeth then be hitting the chainstay?

            Too bad they don't yet? make rear cogs with more offset like they do for chains. You would think they would just to give more and better alignment options.


              I'm going to take a Luna Eclipse 48T Chain Ring and modify the front gates sprocket to bolt onto the Luna Eclipse. Will have to trim the inside diameter of the gates sprocket and drill new holes. I will use spacers to get a perfect belt line. Does anyone see any flaws in my thinking?


                How much clearance do you have for the outside of the ring vs the chainstay?

                Do the ears on the ring align with the ears on the luna hub? Except for those ears the Luna hub is pretty thin.

                How much 'meat' is there on the rear pulley? Could you maybe mod that to bolt to a standard cog? Those are available with different offsets and diameters so you have some options for a mounting surface assuming it can be modded to mount to something flat. Maybe look at all the possible styles of pulleys to see if one more easily lends itself to custom mounting.


                  I have the CDX 50Tooth sprocket which may not have proper surface mounting to go on the Eclipse. (Eclipse on order) I may have to go to 55/60 tooth front sprocket to have proper mounting surface. I did not know about different rear center track cog offset for Shimano N-3, Will research that. I have plenty of clearance 37MM from outside ring of the gear case to the stay (see pic) Inside of cog before it would be an issue
                  My goal is to find a minimal modification solution for the front so other can do it with hand tools. Since moving to Florida I no longer have my lath/welder and buddies Mill to do parts etc..

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                    Originally posted by wisk9ice View Post
                    Trying to build A BBSHD with Shimano N-3 ...
                    Getting the BBSHD belted to the Shimano hubs has proven very elusive - pretty much impossible with the 5,8 and 11-speed Shimano IGH hubs

                    Shimano N-3, as in Nexus 3 disk? The best, as in farthest out "stock" (XMN-D) Gates pulley belt line available is, gulp, 45.5mm - a very tight number on a BBSHD.

                    The 45.5mm belt line is per the Gates tech manual, and I'm wondering if it's a typo. I say that as I thought the Nexus-3 disc hub chain line was 6mm father out than the Alfine 8, using the same sprocket (and Sheldon Brown's IGH chainline chart seems to agree). What does your current front belt line measure out at?

                    Originally posted by wisk9ice View Post
                    I'm going to take a Luna Eclipse 48T Chain Ring and modify the front gates sprocket to bolt onto the Luna Eclipse. Will have to trim the inside diameter of the gates sprocket and drill new holes. I will use spacers to get a perfect belt line. Does anyone see any flaws in my thinking?​

                    I remember somebody using the Luna Eclipse two-piece face / spider but, it was for a BBSHD / Rohloff build, and the Rohloff belt line is almost 10mm farther out (54.7mm). Then there's this custom spider job (also a Rohloff bike):

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                    Since the Nexus 3 doesn't have the rotary shifter I think I go the route 73Eldo suggests, piggy-backing a Gates rear pulley onto a standard, offset Shimano or Sturmey Archer 3 tab chain sprocket. Or go crazy with the deep dish version, which might give you more (as in lower) front pulley teeth count choices:

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                    Last edited by ncmired; 09-05-2022, 09:41 AM.


                      I found a offset rear sprocket (10MM offset). Thanks 73Eldo​ and ncmired​ for the help. With the shimmed spider and offset rear sprocket attached to my rear belt cog it should work. I will post pictures as I get the parts in and begin the process.​



                        Started with a Momentum UX (Giant) bike. -Already has a frame break for belt.
                        Added 203MM disc up front and Zoom quad piston brakes,Dropper post, C9 seat, Jones H-bar and adjustable bike stem.

                        As 73Eldo suggested piggy-backing a Gates rear pulley onto a 10MM offset Shimano 3 tab chain sprocket.

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                        Had a machinist fit 22 tooth cog onto offset sprocket and a welder weld it on.

                        Front 50 tooth sprocket on a; Luna BBSHD 130bcd Spider Chainring Adapter with 2MM offset. Ground a little off the gear case.

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                        Achieved a near perfect belt line. Could have put rear cog out another 3MM in which eliminate the need for a front shim but I also wonder how the offset will wear on IGH over time.

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                        Tuned the belt via the gates tension app. Uses sound of belt to Tension.

                        Again thanks for the help 73Eldo​ and ncmired​.

                        Got it finished and took it for a 15 mile ride.

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                          Nice bike. With no suspension you might look at some Tannus Tire liners for that one. They do a lot more than prevent flats.
                          I ordered a couple of these for my bike. Kind of like pool noodles made for bike tires. 15mm thick which with Scwalbe Big Ben Plus e bike tires=20mm flat protection.. They claim smoother ride, better grip, and some run flat capability. I didn't watch any Youtube , I just dived right in like an average bicycle enthusiast As


                            There are a few upgrades I plan on doing later. Planning on some tubeless tires due to the fact I find myself riding on rail trails more. Body does not recover like it use to! Florida has a little softer sand but some narley plants.


                            • Retrorockit
                              Retrorockit commented
                              Editing a comment
                              Tubeless vs. Tannus.
                              They both let you run lower pressure. Tubeless would be the way to go if you were still pedal powered. Less weight at the rim is a big factor.
                              But the squish of the Tannus has some damping to it. Not as bouncy. The extra power is already there, and I found control at high speeds is much better. On my HT that won out big time.
                              But I never tried tubeless. I just put the goo in my tubes so.............

                            • stts
                              stts commented
                              Editing a comment
                              waste of time
                              Last edited by stts; 03-24-2023, 04:30 PM.

                            • Retrorockit
                              Retrorockit commented
                              Editing a comment
                              I'm on my first one ,so too soon to tell. I only did the rear because I have a suspension fork, but it made a huge improvement on high speed control. it seems I'm the first one here to try them.

                            Just randomly stumbled upon the Momentum UX. Simple bike but has the IGH and belt drive which is exactly what I wanted. Based on the reading I've done above, it appears you successfully were able to implement the BBSHD, correct? I'm researching the CYC Stealth and Photon motors but knowing the BBSHD can be implemented, that might be a safer bet. Thank you for this post.