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    Rohloff Limits

    Hello All,

    I'm looking to build a new commuter bike after having an Ariel Rider M-Class fail to last on the hills in Atlanta. First to break was the Nexus 7 hub. After a few months of riding hills hard, I started to hear the gears clinking around and it only got worse with time (there is a motor cut-out switch in place that prevents me from shifting under load, but that wasn't enough). After replacing the hub, after a few more months the motor (TSDZ3 Towgsheng 48VDC, 5200 RPM, A5 Middle Motor) just seized up and now the bike is out of commission completely. I'm back to tackling the hills on an old Schwinn that I rebuilt a few years ago.

    Now I'm looking at what to do for a more robust way of navigating HotLanta with a motor so I don't always arrive in a pool of sweat. To that end, I want to put a Bafang 750 on my Surly World Troller frame that once served as a touring bike (until I stripped the hub on that using a 1x11 on the hills in Atlanta, the cassette just kept skipping around the hub). I want to pair this with a Rohloff hub hoping that I won't strip more gears and run into the same problems I have been.

    Can the Rohloff hub handle the 120-130 torque output of the Bafang 750W? How can I calculate how much power I will be putting in additionally with the motor (something Rohloff has requested I do if I want to ensure I stay within their warranty requirements)?

    Any help would be great!
    Gratefully,
    CBL

    #2
    Nexus 7 isn't one of the known to be tough hubs so I guess its not that strange to have one fail when used with a mid drive. The Rohloffs do have a rep for being tough but there doesn't seem to be a ton of people using them with mid drives or if there are they are out there having fun and not talking about em on the forums.

    Do you need the gear range of the Rohloff? Could you get by with a 3 speed? I don't recall the exact model but there is a Sturmey Archer 3 speed that has a rep of being pretty tough. I believe its often used on rental bikes and is twice the size of other 3 speeds.

    Comment


      #3
      The rohloff's are very popular for ebikes as far as rohloff's go - they are very expensive so there's just not that many out there but a large percentage of them are on electric and they are know to be very tough

      I've ridden them a few times and they are silly super sweet... shifting is lusciously smooth throughout the entire range and you can skip to whatever gear you want and with 14gears it's about as close to a CVT as a gear hub gets... they are worth the money with the only downside (aside from cost) I saw was a bit of excess weight, they are pretty heavy... used ones hold their value very well and they are rebuildable/repairable so that should also take away some of the apprehension

      All the ones I rode were on BBSHD build and owners rode the heck out of them with no issues

      You do have to let off when shifting of course, I would stop pedaling completely, enough that the motor would stop even without a gear sensor and I'd also make sure to have a gear sensor... the only thing I'd worry about at all is shifting under load but once you get the feel for them it shouldn't be an issue, just slightly different habits... nice that you can shift at a stop...

      I really can't say enough good about them, they are really nice and if I had the coin wouldn't hesitate to use one on a BBSHD or TSDZ3


      However, as always, no warranties expressed or implied! Click image for larger version  Name:	deal.gif Views:	0 Size:	1.9 KB ID:	142194

      Comment


        #4
        The nexus 7 is an older pre E bike commuter hub. Known to be one of the weakest IGH hubs. There are some Alfine, and Redline nexus 8 versions with roller bearings that are stronger slightly and intended for MTB use. If you want to give it a 2nd chance. Shimano makes a Nexus 5 speed E bike hub with 1:1 first gear. They make some larger rear cogs to get the gearing down. Probably the strongest of the Nexus breed.
        https://www.amazon.com/SHIMANO-Nexus.../dp/B07SYZFG8V

        The Rohloff is used in racing tandem bikes in the mountains. It also has shear pins to protect the gears if you do overload it. I think it's kind of like the BBSHD. Usually nobody has to ever open one up for repair. We'll all be seriously impressed if you break one. Limits are pretty much unknown.

        The third solution would be a Sturmey Archer 3 speed which is known to be tough, with a few derailer gears added. There are some tough Surly casette cogs available.
        https://duckduckgo.com/?q=CS-RK3&t=brave&ia=web
        And a few of these.
        https://surlybikes.com/parts/cassette_cog

        Since these all have various overdrive ratios Sheldon Browns gear Calculator will probably be useful. Especially with the Nexus 5 ( which I had them add to the list).
        https://sheldonbrown.com/gear-calc.html
        Last edited by Retrorockit; 09-15-2021, 07:53 AM.

        Comment


          #5
          Thank you all for the thoughtful responses. I've decided that I've spent enough money repairing broken gears already I'm going to invest in the Rohloff. I have one at my LBS getting laced to my velocity cliffhanger 27" rim from my Surly World Troller (my previous touring ride). And, I have a BBSO2 en route as well (I didn't think I needed the 1000W - though I'm sure there are a lot of opinions out there), I will update when able.

          Rohloff is being a bit of a stick in the mud when I asked about ensuring I was within their warranty requirements. I'll have to figure out how to calculate the load that I and the motor together will place on the hub, Rohloff says I may need those calculations in the event of drive loss or shifting issues.

          Thanks again for the clarity on strength of the hub. I also spoke with the service department at Optibike and Jim was super helpful, I felt like I was talking with the mechanic at my LBS. He said that they have used up to 1800W motors and have only had 3 issues with Rohloff since 2008. The issues had nothing to do with excessive load and they were able to get the hubs replaced. More evidence that I should be okay with Rohloff, 750W, and the hills in Atlanta -- I will learn a more mindful shifting method as well.

          Thanks!
          CBL

          Comment


          • CT1274
            CT1274 commented
            Editing a comment
            Hey CBL. I've been thinking about putting a Rohloff on my Troll as well when I do the ebike conversion. Until recently, I didn't know that people were putting bigger (than 26") wheels on Trolls. I'd prefer a 27.5" wheel but I'm hesitant to have one built since I've never ridden with them on the Troll. How was your experience with the 27.5 Cliffhangers? Anything special considerations when changing wheel sizes on the Troll?

          • Retrorockit
            Retrorockit commented
            Editing a comment
            With disc brakes swapping wheel size is easy. The thing to be aware of is tire overall diameter. It changes steering geometry. Larger diameter slows steering response down.This also happens with the same size rims and wider tires. A simple way to measure this is to put a mounted tire against a wall or post and with a square mark the height on a piece of tape for comparison.I used to put 700c wheels on my XC bike for road work, 26x2 slicks for city, and 26x2.5 for dirt. The best handling is with the 2" slicks which are still on there.

          • CT1274
            CT1274 commented
            Editing a comment
            Sounds like something I should experiment with first before making any financial commitments. As long as I can still find adequate 26" tires, I should probably just stick with what I know. I'm really not unhappy with my 26ers, just chasing greener grass, I guess.

          #6
          Originally posted by cbl1988 View Post
          Thank you all for the thoughtful responses. I've decided that I've spent enough money repairing broken gears already I'm going to invest in the Rohloff. I have one at my LBS getting laced to my velocity cliffhanger 27" rim from my Surly World Troller (my previous touring ride). And, I have a BBSO2 en route as well (I didn't think I needed the 1000W - though I'm sure there are a lot of opinions out there), I will update when able.

          Rohloff is being a bit of a stick in the mud when I asked about ensuring I was within their warranty requirements. I'll have to figure out how to calculate the load that I and the motor together will place on the hub, Rohloff says I may need those calculations in the event of drive loss or shifting issues.

          Thanks again for the clarity on strength of the hub. I also spoke with the service department at Optibike and Jim was super helpful, I felt like I was talking with the mechanic at my LBS. He said that they have used up to 1800W motors and have only had 3 issues with Rohloff since 2008. The issues had nothing to do with excessive load and they were able to get the hubs replaced. More evidence that I should be okay with Rohloff, 750W, and the hills in Atlanta -- I will learn a more mindful shifting method as well.

          Thanks!
          CBL
          They are a great investment and should be looked at that way... they are very hard to find on the used market and when they do show up they fetch not a lot less than the new price

          BBS02 is a decent fit for the world troller - a bit lighter than the HD and often just as configurable (depending a bit on where you get it)... You don't want to run them as hard of course, the output transistors (MOSFET's) get hotter more quickly but if you keep the continuos power reasonable you should be just fine...

          I probably wouldn't have mentioned anything to the rohloff guys but you are where you are... I understand they have to cover their own rears...


          If you have you can measure power and pedal cadence it's pretty simple math to figure out the torque being applied to the hub from the motor... unless you buy those pedals that can measure your power you'll just have to do your best guesswork

          Crank torque (N·m) = efficiency (scalar) × power (watts) / [2 × π × crank speed (RPM) / 60]

          If you leave out efficiency (use 1 - motor coupling all the power going in to the out) then you will be conservative

          E.g. if I'm using 500W @ 60RPM and we'll be conservative with efficiency (η) and use 1

          Crank torque = 1 × 500W / [2 × π × 60RPM / 60] = ~80N·m

          Hub torque = crank torque × rear cog teeth / front cog teeth


          Of course the real torque will be less by the efficiency factor but in normal pedaling speeds this is close enough for a conservative estimate - efficiency goes way down at very low crank speeds however so this won't really work there

          To figure out how much you add well that's going to depend on how good a shape you are in! The tour de france guys might be able to get somewhere around 400W but a typical joe might be able to do half that and not likely continuously... I might run with 200 as a guesstimate maximum unless you stand and jump on the pedals (don't do that)... I've measured what I can do and 200W is more.... then again I'm old and disabled...

          Comment


            #7
            You can model your bike here and get speed/power curves. Mid drives are in the advanced menu. Output for mid drives is crank RPM, hub motors are wheel RPM.
            https://ebikes.ca/tools/simulator.ht...setheSimulator
            Unfortunately they don't display speed and RPM together (yet). You have to ask twice. Do your top speed curve, and then play with the rpm output to check your gearing.
            This thing matched my bike exactly when I put in 200W rider input like AZ said.
            They developed this with a dynamometer and a wind tunnel. Since they sell just hubmotors, I think it was very nice of them to develop this data.
            I've never heard anyone complain about a Rohloff hub. Torque from an electric motor is constant and not as hard on parts as intermittent power from pedaling.
            Last edited by Retrorockit; 09-15-2021, 11:51 AM.

            Comment


              #8
              I am puzzled why nobody has mentioned the hubs made by Enviolo. They don't have the gear range of the Rohloff hubs but are used by some very large expensive eBay manufacturers with midrives.

              You can read more about them at their site: https://enviolo.com/
              2021 Himiway All Terrain Cruiser

              Comment


                #9
                Nuvinci's come up from time-to-time for CVT's in the electric bike crowd

                Comment


                #10
                Turns out Nuvinci changed their name to Enviolo so same thing

                hoggdoc if you search for Nuvinci and electric bikes you'll likely find stuff - they have a following

                Comment


                  #11
                  Dost Bikes recently announced their dual battery capable Kope and Drop CVT bikes that couple the BBS02 motor with the enviolo 380% range SP Heavy Duty hub, via a Gates CDX belt.

                  This new hub is available in 135mm and 148mm widths (solid axle).

                  I am surprised that Dost chose the BBS02 and the expense of a customized BB frame motor case (as opposed to one of the "M" series motors like the M600). Perhaps there's a pricing / availability hint here.

                  P.S. several European bike manufactures (such as Riese & Müller) have incorporated Nuvinci / enviolo hubs with Bosch motors for several years.
                  Last edited by ncmired; 09-30-2021, 12:52 PM. Reason: Updated hub link

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