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    Ideal gear ratio

    I asked about the best gearing ratio for a BBS02. Maybe in the wrong category.

    Any ideas?



    Hoping for some input in the best gearing for my build. Will be using the SX-RK3 in combination with the BBS02B (running at 36V 25A if that matters) and will

    #2
    Originally posted by ilikebikes View Post
    I asked about the best gearing ratio for a BBS02. Maybe in the wrong category.

    Any ideas?


    You are asking a question for which there is no answer because there are to many variables. I will try to answer you though because I have a CS-RF3 which is similar to your 3spd except I carry around 8 different cogs so I can change my gearing when needed.

    For me with tires of 2130mm and a front sprocket of 42 if I had to choose one rear sprocket to live with it would be a 14 tooth. Now I live where it is mostly flat and use a PAs of 3 out of 9 most of the time. that translates into say 400 to 750 watts. If I had your tires it would be a 15 tooth cog. If I had a 44 tooth chain wheel it would be a 16 tooth cog. I checked with Sheldon Brown's gear calculator.

    If I were you I would start with 3 rear cogs the 16 and one a little larger and one a little smaller by one or two teeth. Now because you said urban hilly areas lean toward a larger size. I ride on pavement if you are on dirt go even bigger but you will suffer on top speed.

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      #3
      What ratios are you aiming for?

      Comment


        #4
        Originally posted by ilikebikes View Post
        What ratios are you aiming for?
        I don't aim for a ratio I have any ratio I desire because I have 24 speeds in my rear hub. 3spd IGH X 8spd cassette. I use this calculator. http://www.sheldonbrown.com/gear-calc.html set to gain ratios.

        This is what I get for my bike.

        Click image for larger version  Name:	ratios.PNG Views:	1 Size:	51.3 KB ID:	50174

        To clarify the post above. If I had your bike I would start with a 16 tooth sprocket. This is based on 3000 miles of riding a BBSHD and what rear sprocket I am usually in. I think you will need more than 3 speeds because of your hilly conditions. 3spds will work but once in a while you will think "I need a little higher gear" or "I wish I had one gear lower"

        The bikes WE have, have larger rear dropouts for the tires so we have poor choices for gearing. I think your IGH will be fine but not perfect...............nothing is perfect.

        Rear cogs are cheap and easy to change.

        BTW those are Gain Ratios in the chart.

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          #5
          I run my BB02 on a mountain bike. Top speed isn't my requirement so running a 11-40 wide range 10 speed cassette coupled with a 42t Lekkie seems perfect.

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            #6
            Originally posted by Freewheelingf View Post
            I run my BB02 on a mountain bike. Top speed isn't my requirement so running a 11-40 wide range 10 speed cassette coupled with a 42t Lekkie seems perfect.
            Here is your bike with that calculator.

            Click image for larger version

Name:	rat.PNG
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ID:	50184

            Your low of 2.1 is lower than my road bike that has a low of 2.7. I think I only used a real low gear once while riding through a rough hay field with nearly a foot of grass. Normally I never start lower than 4.1 which is about your 6th speed.

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              #7
              I am riding a mountain bike up mountains (well mostly hills) that can get very steep. It's probably best exemplified by riding prior to eBike conversion. Going up a steep climb I want to have the ability to spin the cranks at a constant speed without stamping on the pedals so that I keep smooth traction at the back and keep the front planted. I still want to do that with my BBS02 as it runs best when the cranks are spinning but I also don't want to be going too fast up a technically steep climb and/or I don't want to be using too much energy from my battery. Therefore I still want access to high gears that will allow the BBS02 to spin but also not push my bike to pick up too much speed or use too much battery energy.

              Does that make sense? Perhaps I've got my thinking wrong and very happy to be put right :-)

              I was running the same 11-42t rear cassette on my 29er but with a double chain ring (36t and 28t). So my lowest get out of jail gear was 28-42 (1.4), which I occasionally did need to use but I'd be maxing out the watts from my poor legs and struggling to keep a constant spin.

              My new lowest is 42-42 (2.1), which I suppose means that it is 50% harder to turn and 50% faster (2.1 v 1.4). Today I rode up a short steep climb that previously needed my 28-42 ratio and maxed me out struggling to spin. In my new second 42-36 (2.3) I span up the climb at I guess twice the speed in assist level 4 (70% of my 36v 500w controller).

              Riding off-road in the UK where other people bike ride/walk/ horse ride it is good practice to slow down for others and it looks anti-social to ride at speeds others see as fast so I don't ride more than 15mph in general. I don't need the 42t chainring but it is the smallest Lekkie that also provides perfect chain alignment./////

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                #8
                For me I just found the proper chain ring to get me going 20mph (PAS 1-8 limit here) in top gear at a comfortable [for me] pedal cadence - my comfortable cadence is likely a fair bit less than others due to missing left leg. At first it was a 42t but I've found I can increase my cadence a bit from where I was before and now a 39t is very sweet for me. I've never reached the full throttle top speed but have reached 35mph like this... I don't want to go any faster than that on this bike anyway!

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                  #9
                  I live in a very flat area. My riding is suburban traffic, and urban traffic with bike paths and sidewalks whenever possible. My need for climbing is limited to parking garages, overpasses, and bridges.
                  My bike is a converted Gary Fisher 26" comfort bike. The 46T BBSHD gear was crap from the start. I have a pile of 8 speed stuff because I have 4 wheelsets that swap around between 2 bikes and casettes for all of them.
                  After some trial and error I came up with a setup that works for me. I ended up with a Surly Stainless steel 130bcd 50T chainring on a Bafang spider adapter. The chainline favors the top 5 gears.
                  I tried some11-28,and 11-32 casettes and the low gear was a little tall for low speed situations, but 50x28 made a good take off gear in traffic.50x11 is good for 28mph cruise and 32mph sprints. I decided to run a chain guide to be sure the chain stays put. Just a bolt with a washer behind the chainring and a nylon bushing to keep the chain down in the cog.
                  I bought an 11-34 Shimano Acera casette. I didn't like the 26T 2nd gear. The 50x 34 was just right. It wheelies so I'm not leaving anything on the table, and I only use it when I need to go slow so the cross chain isn't a big deal. To get the gearing I want and to beef it up for traffic light sprints I took the 34T low and installed it on the hub with it's spacer, then installed the 4 low gear assy. from an XTR 11-28 casette 18-21-24-28T, Then topped it off with the 11-13-15T top gears from the Acera. If you just want a cheap casette with this gearing SR Suntour makes one. SRAM doesn't go 11-34 in 8 speed, and Shimano puts a 26T 2nd gear. I already had the spare XTR stuff so I decided to use it. The Surly chainring isn't Wide=Narrow but it is steel.
                  This could be done on a budget with a Dekkas 50T Narrow Wide $35, a Bafang Spider adapter $30, and the Suntour casette $17
                  https://www.universalcycles.com/shop...66&category=42
                  Last edited by Retrorockit; 10-05-2018, 06:27 PM.

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