Schlumpf mountain drive

Discussion in 'Mountain Bikes' started by Jim, Aug 18, 2011.

  1. Jim

    Jim Guest

    I know of no-one who uses one of these devices and have seen no
    reports of any usage of them. Does anyone on this group have any
    knowledge of their reliability in practice (as opposed to the
    manufacturer's claims)?

    Rohloff and Mountain Drive can't be combined because the excessively
    low gears are supposedly harmful for the hub gears due to excessive
    torque. I do not understand this. For example, take the hypothetical
    situationof me climbing a steep gradient without mountain drive, at
    say 5 mph, and a cadence of 40 rpm. If I engage mountain drive I could
    have a much more comfortable cadence of 100 rpm to achieve the same 5
    mph. However, the chainring and rear sprocket are still rotating at 40
    rpm.

    So how does the mountain drive cause more strain on the Rohloff when
    there is no apparent difference to the forces going into the rear
    hub?
     
    Jim, Aug 18, 2011
    #1
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  2. Jim

    Tim Downie Guest

    If you're going up the same hill with the same load and at the same speed,
    indeed there will be no extra strain on the Rohloff.

    What I think the makers of the Mountain Drive are concerned about is that
    with even lower gearing, you could put more load through the Rohloff by
    going steeper, faster or more heavily loaded than you were before and
    consequently exceed the Rohloff design parameters.

    Tim
     
    Tim Downie, Aug 18, 2011
    #2
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  3. Jim

    Rob Morley Guest

    In your example the average force is the same but as you don't exert
    constant pressure on the pedals throughout the stroke the peak forces
    are potentially increased. And are you really going to pedal more
    gently when accelerating to compensate for the increased torque at the
    back wheel? Rohloff has a higher gearing limit for heavy riders for
    the same reason - bigger impulses/greater accelerated mass place the
    same increased load on the hub internals.
    You could change the arithmetic by using a smaller wheel to get the
    low gearing with reduced torque at the rear wheel, and an overdrive
    at the front to restore the top end, but that obviously reduces the
    direct drive ratio which may be undesirable. The great thing about
    derailleurs is that they're always direct drive. Actually the great
    thing about an "ordinary" is that it's /really/ direct drive, but
    obviously that has limitations too.
     
    Rob Morley, Aug 18, 2011
    #3
  4. Jim

    Clive George Guest

    There may be no difference in your example at the hub, but the mountain
    drive is multiplying your leg force by 2.5. In your example, you're
    compensating by not pedalling as hard, but in real life there's nothing
    stopping you not compensating and pedalling as hard as you would do
    without the mountain drive. And that's when the forces go up rather
    higher, and things break.
     
    Clive George, Aug 18, 2011
    #4
  5. Jim

    Peter Clinch Guest

    A colleague of mine has had one on his Brom for years with no trouble.
    Sample base of 1 isn't huge, but despite having half an ear to "weird
    shit" when it comes to bikes (I have a 'bent, a unicycle, a Moulton and
    a Brompton...) I've never heard a bad word about their reliability.

    Pete.
     
    Peter Clinch, Aug 19, 2011
    #5
  6. Jim

    Jim Guest

    x-no-archive:On Aug 18, 5:27 pm, Rob Morley <>
    wrote:
    x-no-archive:> On Thu, 18 Aug 2011 12:00:15 +0100
    Will these peak forces be less when spinning a low gear rather than
    mashing a higher one?


    Surely I will be pedalling much more gently when spinning at 100rm
    than mashing at 40?


     Rohloff has a higher gearing limit for heavy riders for
    I'm very heavy. Does the fact that my ride speed is slower due to the
    heavy weight offset these forces to any degree?

    In terms of longevity of the hub gear, I am interested in riding hours
    more than mileage. Will the heavy rider issue only apply to riders
    going at the same speed as lighter ones? I suspect not :(


    Yes, thats a good idea.
     
    Jim, Aug 19, 2011
    #6
  7. Jim

    Jim Guest

    x-no-archive:On Aug 18, 5:27 pm, "Tim Downie"
    Yes, this is what I hope the position to be. I wouldn't go steeper or
    faster, just ride for longer. That would make a Rohloff Schlumpf
    combination very desirable to me.
     
    Jim, Aug 19, 2011
    #7
  8. Jim

    Jim Guest

    x-no-archive:On Aug 19, 12:53 pm, Peter Clinch

    That is helpful because it shows that they can work fine (unlike the
    Alfine apparently).


    but despite having half an ear to "weird
    That also is good, as bad stuff is most likely to be reported.
     
    Jim, Aug 19, 2011
    #8
  9. Jim

    Clive George Guest

    In steady state, yes, but when you do things like come to a steeper bit,
    or even simply setting off, the peak forces could be massively higher
    with the mountain drive in there - the limit is leg strength.
    When accelerating you're not in that state - you start at 0 rpm, and
    have to get the bike up to speed.
    Not really. I've got a pile of broken hub ratchets from our MTB tandem.
    We're heavy and ride slowly, but are quite capable of putting a very
    high force in for a very short time - and it only needs to be a fraction
    of a revolution to break something.
     
    Clive George, Aug 19, 2011
    #9
  10. Jim

    Jim Guest

    x-no-archive:On Aug 19, 6:50 pm, Clive George <cl...@xxxx-
    x.fsnet.co.uk> wrote:
    ?
    This discussion does give me a fair degree of concern about combining
    a hub gear with a 40% reducing gear. However, I'm in a catch 22
    position here. If I don't use this combination, my knees may break!

    It might be best to risk some inanimate metal objects instead.
     
    Jim, Aug 21, 2011
    #10
  11. Jim

    Guest

    Well, maybe. What isn't clear is why you feel you need both the
    40% and a high-ratio hub gear. The point is that, below 3 MPH,
    there is very little point in not getting off and pushing and
    only some cyclists can balance below that, anyway. And very few
    recreational riders go faster than 25 MPH on the flat. That's
    a range of 8.3 which, scaled by 40%, is 3.3. Most riders are
    happy to vary their cadence by at least 1.5, and a relatively
    standard 7-speed would require only 1.1 and even a 5-speed
    would do.

    Note that you DON'T push any harder going slowly for the same
    cadence, as power=cadence*push, and almost everyone is power
    limited. And a factor of 1.5 isn't a lot, starting from the very
    low forces used by almost all riders. Remember that you have to
    all of your weight when walking, but typically push by 10-30%
    when cycling at even fast recreational level.

    If you have serious knee problems, I recommend checking your
    position, posture and riding style - the most common cause is
    too low a saddle.


    Regards,
    Nick Maclaren.
     
    , Aug 21, 2011
    #11
  12. Jim

    Jim Guest

    You are right, I don't need that huge range. There are two reasons I
    focussed on the Rohloff in this thread.

    i) It is specifically not permitted with a Mountain Drive, whereas
    Shimano & SRAM hub gears are promoted. Any discussion of the risk of
    breaking a Rohloff will presumably apply at least equally to the
    cheaper systems.

    ii) Additionally, I wouldn't discount a Rohloff on the grounds of a
    surfeit of gears, if it is otherwise the most suitable product to buy.
    I am thinking along the lines of establishing the lesser of two evils:
    either use a Rohloff alone choosing sprockets that would give me a
    range of 3-15 mph at 90 rpm or use a Rohloff with a sprocket set that
    won't invalidate the warranty but with a Mountain Drive reduction to
    enable me to have similar low gearing.

     The point is that, below 3 MPH,
    I don't agree with some of this. My speed frequently drops below 3
    mph. Below 2 mph and my computer (which doesn't register tenths) shows
    0. This occurred for a stretch of about 50 yards on a narrow lane on a
    local climb yesterday, and I was sufficiently stable to let a car pass
    me. I enjoy cycling up hills, and I enjoy walking up hills, but
    pushing a bike is not fun. I do not have a good sense of balance so I
    can't be unsual in being able to ride easily below 3 mph. (I don't
    know if I could extricate myself from the cleats if forced to stop at
    that speed though!)

    I live in a mountainous area and am very heavy. Most of my cycling
    involves pedalling at speeds below 7 mph, above that and I am coasting
    to recover. Much of the time I am pedalling at 40 to 50 rpm which I
    find uncomfortable and tiring. I am therefore aspiring to a gear
    system which will enable me to ride at very low speeds with my
    preferred cadence of 90. I will then be able to conserve energy to be
    able to pedal more in the undulating stretches between the hills.

    Yes, I agree that fewer gears would be completely fine with a 2.5
    reduction. A 200% ratio hub would be suitable.


    Sorry, I don't follow the above paragraph.
     
    Jim, Aug 21, 2011
    #12
  13. Jim

    Guest

    I am sorry, but you DO have good balance. The vast majority of
    cyclists will wobble dangerously (on a road) if they have to
    BOTH exert themselves AND ride at that speed. You are not unusual
    among posters to this group, but are in a small minority among
    UK cyclists. The very facts that you use cleats and prefer a
    cadence of 90 both indicate that (in other ways)!
    Then what would suit you best is a tandem-rated 5-speed together
    with the mountain drive. On paper. I should be EXTREMELY
    interested to know how you get on with such a thing, as I am
    thinking of configuring a bicycle with that myself :)
    It's basic physics. The distance travelled is constant per pedal
    revolution so, for a fixed power input and cadence, the pressure
    on the pedals is constant. End of story.


    Regards,
    Nick Maclaren.
     
    , Aug 21, 2011
    #13
  14. Jim twisted the electrons to say:
    Assuming you're using 622-28 tyres then 26x18 on a Rohloff would give you
    2.9-15.2mph at 90rpm, according to Sheldon's gear calculator anyway
    (which I have no reason to doubt).
     
    Alistair Gunn, Aug 21, 2011
    #14
  15. Jim

    kimble Guest

    I'll second that. I have very low gearing (19") on my recumbent tourer,
    and will frequently ride below 3mph on loaded climbs. It's infinitely
    preferable to trying to push a heavy USS recumbent up a steep hill in
    cycling shoes (indeed, I consider low gearing to be a much more sensible
    alternative to fitting some sort of brake lever to the rear rack, which
    would make that sort of pushing a lot easier).

    I don't consider my balance to be anything special, but I note that it's
    significantly easier to balance a bike at low speed if you've got spinny
    gears. Pushing hard at lower cadence gives you much more wobble to have
    to counteract with the steering, and that's the tricky bit: Compare
    freewheeling towards traffic lights in the hope they'll change before
    you put a foot down (a skill that recumbent riders tend to develop more
    than most) to climbing steep hills.


    Kim.
    --
     
    kimble, Aug 21, 2011
    #15
  16. Jim

    Jim Guest

    I suspect that is because the majority of cyclists are riding in too a
    high a gear.



     You are not unusual
    It does, though the fact that my average speed is currently 7 mph
    would suggest I have yet to become a fully paid up member of this
    club!

    Yes, I think you are right. There doesn't seem to be much available -
    SRAM p5 cargo, if its still for sale & the Vinci are the only two
    options I'm aware of. I don't know much about either.

    That makes sense, but I'm afraid it sheds no light on the preceeding
    paragraph.
     
    Jim, Aug 21, 2011
    #16
  17. Jim

    Guest

    I doubt it, very much. If they are in too high a gear, the problem
    arises at much higher speeds.
    I don't know what your confusion is, so can't explain.


    Regards,
    Nick Maclaren.
     
    , Aug 21, 2011
    #17
  18. Jim

    Phil W Lee Guest

    considered Sun, 21 Aug 2011 11:37:44 +0100 the perfect
    time to write:
    A large majority of the cyclists I see around Cambridge seem to have
    no difficulty in riding at pedestrian speeds (even if some lack the
    willingness), and a subset of those seem to have considerable
    difficulty going any faster.
    ISTR that a Rohloff has a 350% range, so would be easily adequate even
    without the schlumf.
     
    Phil W Lee, Aug 21, 2011
    #18
  19. Jim

    Adam Lea Guest

    More than that, it is over 500%.
     
    Adam Lea, Aug 22, 2011
    #19
  20. In
    I've heard of a few cases of people setting up bikes thus and even have a
    vague recollection of it being offered as a factory option on Greenspeed
    recumbent trikes. It will void the warranty on the Rohloff, natch, but the
    hub is tandem-rated so *ought* to be meaty enough.

    I am not an engineer...
     
    Dave Larrington, Aug 22, 2011
    #20
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