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Soma B-Side V.2 Belt Drive BBS02 750W/48V Custom Build

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  • Rider
    With the wheels and frame back from the shop I started assembly. Here is the components list and a build photo layout (most parts).

    2016 Soma B-Side Parts List:

    SOMA B-SIDE Frame (Large - 18.5")
    Cane Creek ZS44/28.6 Tall, EC44/40, 52/30 Conversion Race
    RockShox 30 TK Gold Solo Air Fork
    Single 40mm Fork Stem Spacer
    Q2 40* Riser Stem 110mm
    Fouriers Trailhead 58* Sweep Bars
    ESI Chunky Sylicone Grips 32mm
    SRAM X9 Front Hub
    SRAM X9 front 3 Speed Trigger Shifter
    Strumey-Archer 3spd IGH 8-9spd Cassette Disc 135mm (CS-RK3)
    Halo Vapour Rims i21mm
    DT Swiss Stainless Steel Triple-butted Alpine III Spokes Black (14/15/13) Silver Brass Nipples
    Shimano XT M8000 Hydraulic Brakes
    SRAM Centerline 180/160mm Brake Rotors and Adaptors
    Schwalbe Smart Sam Plus Tires with Green Guard (Rated 31mph)
    Schwalbe 27.5 x 2.25 Tubes
    Circus Monkey 27.5 x 18mm Rim Tape
    Cane Creek Thudbuster ST 27.2 x 410mm
    Soma 29.8mm Seat Post Clamp
    WTB Volt Saddle
    Aset Titanium Spindle Alloy Flat Pedals
    Gates Carbon Drive 50T Front Sprocket
    Gates Carbon Drive 28T Rear Cog
    Gates Crabon Drive 118T Belt
    Attached Files
    Last edited by Rider; 06-25-2018, 09:05 AM.

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  • Rider

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  • Rider
    One thing I found by riding the BBS01 350W/36V prior eMTB was that the added power assist allowed me to double shift and even triple shift at times. Most of my riding was done in only three of the 7spd cassette gears and the low gear of those three was only used when climbing hills. Basically for my riding type and style a 2spd with granny low would be fine. Many of the eMTB manufacturers have found that E-bikes can handle a much wider percentage increase between gears than the typical 15-16% of pedal bikes. In addition, the power level button acts like gears on a BBS02 motor. The levels are actually speed levels.

    With this thought in mind, I decided to go with a 3spd IGH for my belt drive build. In reading the electricbike-blog (great real world ride-it-until-it-breaks information there), he found that 3spd IGH rear hubs have a very strong 1:1 2nd gear which is ideal for handling the extra power of electric assist motors that can cause much faster wear on typical bike components.

    There are two main 3spd IGH ratios. The Sturmey-Acher has a 177% range with 33% gear gaps and the Nexus/Alfine have a 186% range and 36% gear gaps. I played with my old eMTB gearing front 42T and 46T chainrings and rear 11-34T cassette and found that the 33% gap seemed to be okay with that smaller motor, so I'm sure it will be fine with this 750W version. I ended up going with the Sturmey-Archer CS-RK3 disc brake 3spd IGH 8-9spd cassette rear hub to get the desired 33% gaps (0.75/1.00/1.33) and full cassette width belt cog alignment abilities.

    Soma gives a 46T X 26T single speed gearing in their FAQ section; a 1.77 ratio. This gives a 1.33-1st (1.77*0.75), 1.77-2nd (1.77*1.00) and a 2.45-3rd (1.77*1.33). It puts the 1:1 2nd gear right at their recommendation (great if I ever want to remove the motor and make it pedal only at some point without having to reinvest in the expensive Gates sprocket, cog and belt). What I call my "granny low" gear ended up about one gear higher than my 42T X 34T low on the 350W eMTB, but I think the incrase in power to 750W will easily make up for that. 3rd gear ends up between my prior 4th and 5th gears, which is penty fast for off-road use and still provides about a 15mph speed at 80 cadence. This stuff can get confusing and whats on paper and how it feels in the real world can be very different. I like real world testing, but have to rely on gear calculators like the one at in addition to my actual testing. It's worth noting that I don't want or need a fast eMTB and the end result is meant to be kept within the California Type-1 classification.

    Another consideration with Gates Crabon Drive and the BBS02 motor is sprocket clearance. The BBS02 requires about 153mm diameter to clear the gear reduction hump on the motor. This was determined by measuring my 42T Lekkie Bling Ring. It turns out that a standard 42T sprocket is about equal to a Gates 50T and the I.D. of the lip that turns out on each side is right at the same diameter. I can't test fit it until I get my motor, but from what I can tell the lip should clear. Now all I have to do is cross my fingers that there is enough belt algnment on the rear cassette.

    With all that said, a 50T Gates Carbon Drive with a 28T Gates Cog (1.78) gives close to the same ratio as the 42T X 25T recommendation, so that's what I used.

    Here is the Gates 50T next to the 42T Lekkie, plus my hubs and blue Halo Vapour rims. That all got laced up DT Swiss triple-butted Alpine III spokes for good strength (I broke a couple spokes on my last ride and didn't what that to be an issue qith this one). Like most things in life, good quality parts last and generally cost a little bit more for that reason.
    Last edited by Rider; 10-30-2016, 10:53 AM.

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  • Soma B-Side V.2 Belt Drive BBS02 750W/48V Custom Build

    A few months ago I embarked on a ground up custom eMTB build after six months of riding a BBS01 350W/36V hardtail eMTB. I made many upgrades to that ride and got my feet wet in the E-bike world. Oh what a feeling they can provide!

    When I sold that E-bike I kept all the upgrades to put on my custom build that I knew I'd be doing at some point. Some of the upgrades included many 7000 series light weight parts such as: riser stem, handlebars, 42T Lekkie Bling Ring and pedals with titanium spindles. The cockpit got upgraded seat and Thudbuster as well as ergonic grips to fit my body and style of riding. I also invested in a set of Schwalbe Smart Sam Plus 27.5 X 2.25 E-bike Rated tires that really changed the way that eMTB performed off-road, but they are a little noisy on the pavement and like to grab everything in site with their traction.

    For the custom build I selected a Soma B-Side V.2 Belt Drive frame in large. I'm 6"2" with a 34" pants inseam and my old eMTB had a 21" XL frame that fit me very well, but what I didn't like about it was the 71* head tube angle. It worked fine for everything except steep declines. I only had one fall on that bike and I attribute part of it to the non-slack head tube angle; went over the bars on Rattle Snake in Crystal Cove State Park (has some steep rutted sections in it) and got bit by the snake. So I knew my next eMTB would have at least a 68*-69* head tube angle on it. The Soma B-Side met that requirement and a life long desire to own a Gates Carbon Drive bike. I went with the 18.5" large because it has a lower top tube so others can ride the bike too. I just make up for my size with a higher seat post and long riser stem with some sweet sweep-back bars for a comfortable position.

    When the frame arrived I was very impressed by the quality of it and the paint job. Note the belt drive frame break circled. That allows the installation of the belt that can't be split like a chain. The frame does require you to face and chase the BB, face and ream the head tube and ream the seat post tube (like most new frames). I took it to one of my well respected LBS shops for that to insure it was done right.

    Last edited by Rider; 06-25-2018, 09:03 AM.