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Specialized Demo 8 BBSHD

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    Specialized Demo 8 BBSHD

    Here are a few photos of my Demo8 BBSHD DH bike. In the photos I am running a lekkie 36 with an 11-25 cassette, the chain line is pretty bad on the low ratio gear so I have since swapped to a lekkie 42 which has a better chain line offset, and gone with an 11-36 cassette giving a perfect chain line and better low gearing for uphill climbs.
    The BB on these bikes are a PF30, 83mm width. I used an eccentric bb to get a better clearance between the axle and bb shell, this allowed me to rotate the BBSHD further foreward getting better ground clearance.
    BBSHD is 100mm width.
    I have noticed with the extra width of the bb, the pedals are sitting quite a bit further out from the bike centre and I have found that I am getting pedal strike quite often. Im pretty sure I will get used to this and adjust my riding to account for it. I am running 170mm lekkie cranks, not sure if there are options for shorter cranks that fit the BBSHD.
    I am running a luna 17.5 ah battery in a backpack, which seems to be going well. I have set everything up so I can switch to another bike If this one doesnt work out. So far it seems really good though.
    I will be using it for a combination of riding:
    1, local tracks i can ride to from my house where there is an access road to the top of trail heads (no public driving access) then single track grade 2-5 downhill only trails
    2, general exploring on cross country trails/farm access tracks/coastal tracks
    3, going to my mates place to brew beer where we have one or two beers so dont want to drive the car.
    There is a possibility of getting a trailer to tow the kids around on camping trips etc too.
    Hopefully this info helps anyone else looking into converting a downhill bike into an electric bike using a BBSHD.

    Stew


    #2
    how fast can you get that Demo 8 up to?

    Comment


      #3
      Around 40 kph on the road. Could go faster if the front chainring was bigger but I want to be able to climb hills so need some low ratios.

      Comment


        #4
        Hey Stewinnz, sick ride!

        I am going to be building a 2010 Banshee Legend with BBSHD 100mm here shortly and was curious about your selections. What are your thoughts on the Lekkie 42t with the 11-36 cassette? Is it using a lot of power going uphills?

        In comparison, I have another semi-downhill/freeride bike with a BBS02 motor. I am running a 30t front chainring and 11-34t cassette. Even on the steepest climbs in the 34t I am only using Pedal Assist level 1 (out of 5). As the battery runs low and I become fatigued I might start using Pedal Assist 2 for brief steep parts of a climb. I have a 6ah battery to cut down on weight as much as possible, and can easily get 15-20 miles taking laps up and down a quite steep local mountain. The gearing combo is super efficient with the motor.

        I haven't really looked at the chainline yet on the Banshee, but my other bike had a 68mm bottom bracket, so the chainline isn't really bad in my mind (I will need to take a photo).

        Can you snap a photo of the chainline on your bike with the Lekkie 42t in the 36t cassette gear?

        On your bike, I think if the chainline was still not great, the Luna Eclipse 42t is slightly more offset @ 24.8mm vs 20.4mm from the Lekkie 42t. That's probably like shifting the chainline over by almost 1 full cog/gear on the cassette, right?

        And regarding efficiency, based on your experience so far, do you think it would be worth having a little large granny gear with the 42t chainring, say a 11-40t, 11-42t, or possibly even an 11-46t cassette in the rear? I think 11-40t would be doable on the 9speed Banshee, but I'd have to get a new derailleur with longer cage(?). If I wanted to go to a larger cassette than 40t, I think I'd have to switch to a 10-speed to have access to the 11-42t or 11-46t cassettes. Is any of that worth it, or is the 11-36 ample with the 42t chainring and BBSHD, since the BBSHD supposedly has much more torque?

        I'm including a picture of the gear ration combinations. Options 2 - 4 were what I was thinking about. You'll notice the some annotations for "Remove Gear" or "Disable Gear". Remove Gear would be taking a cassette and physically removing gears, then adjusting the derailleur to limit gear selections to the "first" 6 gears, making the gear ramp up is much greater, but the chainline would be better in the lowest gear (ie 34t), all while having a small front chain ring gear (ie 30t) which doesn't have the offset of the lekkie or luna eclipse. The Disable Gear theory, would be to get a bigger Cassette and again set the limit of the derailleur so the last 1 or 2 gears (say the last 40t and possibly 36t) wouldn't be accessible, so the chainline would be just slightly better in the 36t position (or the 28t position if disabling 2 gears).

        What are your thoughts?

        Thanks!
        Attached Files
        Last edited by TaylorN; 1 week ago.

        Comment


          #5
          I'm running a 36t with a 1600 watt BBSHD from Lunacycle. I live on the front range in Colorado so I built this to climb those hills.

          Total weight: 75 Lbs.
          BBSHD motor: 15 Lbs.
          48v 24AH 1.1 Kilowatt Battery: 11.5 Lbs.
          Range: 50 to 70 miles
          ABS plastic Battery Enclosure: 6 Lbs.
          Console: 1.7 Lbs.
          Bike: 36 Lbs.
          Frame Material: 4130 Chrome Moly
          Frame Make and Model: Mongoose Hilltopper
          Frame Year Made: 1996
          Bottom Bracket: 68mm

          No spacers were used between the motor and the bottom bracket.

          Prior to adding the custom chain guide / bash guard and a return chain guide from Amazon, I had frequent chain drops. The chain dropping always happened around shifting and I finally had enough and built a custom chain guide.

          Click image for larger version  Name:	on top of Dixon Ridge.jpg Views:	0 Size:	142.2 KB ID:	106272
          I'm on top of the very first ridge on the Front Range on the western edge of Fort Collins, CO. Made of limestone, this ridge is home to unique plants species not found anywhere but this single ridge.

          I liked staying with an 8 speed for the heavier duty chain. And I find the steel 8 speed cassettes readily at my local bike coop nearly unused in a bin for $1.25 per cog. Many cog sets you could buy online these days have spiders and or they're not steel, or they're designed to be super light weight. The cog sets at the bike coop are mostly already broken apart so I don't even have to punch a pin out to rearrange and 'retire' (disable) several cogs. You probably don't have to worry so much about the BBSHD, but these considerations might matter with a 3000 watt cyclone.

          Click image for larger version  Name:	36t-sm.jpg Views:	0 Size:	104.8 KB ID:	106274
          36t prior to custom bash guard/chain guide

          Click image for larger version  Name:	chainGuideBashGuardChainLine2.jpg Views:	0 Size:	195.2 KB ID:	106276
          Chain guide / bash guard with lower 'return' chain guide. No more dropped chains ever since.

          Click image for larger version  Name:	attempting to show where the offset naturally leaves the perfect chain line.jpg Views:	0 Size:	108.0 KB ID:	106277
          I've laid a reasonably straight edge to show where the chain line would naturally be with the 36t

          Click image for larger version  Name:	almost no offset with 36t rear view.jpg Views:	0 Size:	83.1 KB ID:	106278
          Sighting down the straight edge from behind the cassette which has a perfect chain line on cog 7


          As you can see, I decided the first cog that had a reasonable chain line was cog 4. Retired cogs were placed in a reverse cascade.


          Click image for larger version  Name:	long limit screw-sm.jpg Views:	0 Size:	83.5 KB ID:	106279
          I needed a longer limit screw to take out the travel to the first three cogs

          Since the 36t has almost zero offset I find that the chain line is no good for the first three cogs.

          Solution? Retire three cogs, use the limit screw on the derailleur to prevent it from accessing the first three cogs.

          I took the cassette apart and placed the first gear (32t) in the cog four position.

          I've opted to go with a larger step up to second gear (cog position five) which is 21t.

          So, the cogs I'm using are: 32-21-16-12-11

          the cogs I retired are: 28-18-14

          I picked up an 8 speed cassette at the bike coop and rearranged it. The cogset numbers are now: 14-18-28-32-21-16-12-11.

          With my battery at 80%, with no wind riding on flat ground, the 32t takes me to 14.5mph. The 21t gets me to 22.5. The 16t takes me to 27.5mph. The 12t I hit 32mph and the 11t maybe 33.5mph. On a 100% charge I hit 36mph with the 12t.

          Attached Files

          Comment


            #6
            Thank you for the details and excellent photos Dee!

            why did you end up going with the 36t chainring instead of the 30t luna might mini chainring? They have the same offset, right?

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