Schlumpf mountain drive

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

  1. Alistair Gunn twisted the electrons to say:
    However that's not a very useful post I made there, as I'd mis-remembered
    and you can't get 18T sprockets for the Rohloff! They only do 15, 16 &
    17s! In anycase, 26x18 would be outside the permitted range for a
    Rohloff and would invalidate the guarantee.
     
    Alistair Gunn, Aug 22, 2011
    #21
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  2. Jim

    Jim Guest

    The cyclists you appear to be referring to are riding in a higher gear
    than me, therefore it does not surprise me that they are more wobbly
    than me up hills. When I have ridden bikes with higher gears up steep
    hills, I too have been wobbly. I really don't have good balance.
    I don't understand the points you are making. I interpret your
    paragraph as meaning the following:

    (i) that one doesn't push harder when going slower,

    (ii) that reducing my cadence from 90 to 60 isn't very significant

    (iii) Most people aren't infinitely strong

    (iv) You do something unknown with your weight when walking, but only
    use 10-30% of your energy when cycling.

    But I know that you don't mean what my interpretation is, if you see
    what I mean!
     
    Jim, Aug 22, 2011
    #22
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  3. Jim

    Phil W Lee Guest

    It seems strange that they are so fussy about sprocket and chainwheel
    sizes when they also sell it with longer cables suitable for tandem
    use.
     
    Phil W Lee, Aug 22, 2011
    #23
  4. Jim

    nmm1 Guest

    No, I am not. I have observed the phenomenon both up hills and on
    the flat. Only a minority of cyclists can steer (and, note, steer)
    reliably below a moderate to fast walk, even if they are not pedalling
    at all. Many can control their balance, but not when buffetted by
    passing traffic, affected by an uneven road, or when they need to
    turn a reasonably sharp corner. And, if you can't do all of those,
    you are in danger from passing traffic.

    People with genuinely bad balance, like me, don't even try to
    cycle at walking speed, but get off and push, even on the flat or
    downhill.
    I will attempt to explain.

    Most people are limited by their aerobic (i.e. 'breathing') capacity
    to between 100 and 200 watts, for anything more than short bursts.

    The power used in pedalling is force*distance/time so, for a fixed
    set of pedals and cadence, the force on the pedals is constant.
    The speed you are travelling does not come into it, unless you have
    to drop cadence.

    For even 200 watts and a cadence of 90, the force involved is about
    22 Kg weight - which is 25-35% of most adult males' total weight.
    Actually, most cyclists won't exceed 100 watts and, from your
    description of yourself, you probably don't - so it's half that.

    When walking, each knee carries your whole weight each step, which
    is why it is called load-bearing exercise, as distinct from cycling,
    which is not.

    Almost all cyclists can vary their cadence down by about a factor
    of 1.5 without losing significant efficiency, and many can do so
    by a factor of 2. But let's assume 1.5.

    The maximum force that you will exert at a cadence of 60 (1.5 times
    less than 90) is between 16.5 and 33 Kg, depending on your aerobic
    capacity. That is much less than the force you exert when walking,
    so the stress on your knees is that much less (if your position and
    riding style are appropriate).


    Regards,
    Nick Maclaren.
     
    nmm1, Aug 22, 2011
    #24
  5. Jim

    Jim Guest

    Rohloff say that the warranty limit is based on two elite athletes
    riding flat out on a tandem.

    I'm inclined to think 26*18 would be fine in many cases, given the
    bullet proof reputation of the Rohloff.
     
    Jim, Aug 22, 2011
    #25
  6. Jim

    Jim Guest

    I don't dispute your observations, but I disagree with your assertion
    that it is due to the vast majority of cyclists having an inferior
    sense of balance than I have. The reasons I would give for your
    observations are:

    1) They are riding in a higher gear than me. The vast majority of
    cyclists that you observe will not be riding with a 22" gear.

    2) Their cyclecraft is poor.



    Thanks for that. I now understand that you are showing how mashing
    relatively high gears uphill puts considerably less force on my knees,
    as opposed to walking. That is an interesting point, so I appreciate
    your clarification.

    I had no idea that is what you meant before!
     
    Jim, Aug 22, 2011
    #26
  7. If you meant that at a fixed power output and fixed cadence someone
    would exert a constant force, that's tautologicaly true, but I also fail
    to see what the point you were trying to make originally was.

    But someone who is using 200W will travel faster than someone using 100W,
    and if they do so at a fixed cadence on the same cranks, they will have to
    exert twice the force to produce twice the power.
    (They won't go twice as fast as a result, because the drag isn't linear.)
     
    Alan Braggins, Aug 22, 2011
    #27
  8. Jim

    nmm1 Guest

    The mind boggles.

    While all of that was true, the point that I was making was that,
    EVEN in that case, the force is considerably less than you have
    to exert when walking, and is therefore not an issue as far as
    knee problems are concerned to anyone with a reasonable position
    and riding style.


    Regards,
    Nick Maclaren.
     
    nmm1, Aug 22, 2011
    #28
  9. Jim

    Phil W Lee Guest

    Given that they state the maximum input torque as 100Nm (73.756ft/lb),
    it should be fairly simple to work out your own custom primary
    reduction ratio limitation based on rider weight, crank length. and BB
    reduction (if any).
    That would be good for any situation other than standing up and
    pulling up on the bars and/or descending pedal.
    It would comply with the spirit of the warranty although not really
    the letter, so it might be better not to tell Rohloff about it if it
    gives a result lower than their recommendations, and keep a suitably
    worn chainring of the approved size around in case of warranty.
     
    Phil W Lee, Aug 23, 2011
    #29
  10. Jim

    Rob Morley Guest

    On Mon, 22 Aug 2011 23:04:42 +0100
    Except that the position and movement of the knee is quite different
    when cycling than when walking, so the two aren't really comparable.
     
    Rob Morley, Aug 23, 2011
    #30
  11. Jim

    Phil W Lee Guest

    Phil W Lee, Aug 23, 2011
    #31
  12. Jim

    Guest Guest

    But when walking your knees are relatively straight(except for ascending
    /very/ steep inclines) compared with the angle they are at when cycling. The
    force on the cartilage is multiplied somewhat above the straight force.
     
    Guest, Aug 23, 2011
    #32
  13. Jim

    Phil W Lee Guest

    considered Mon, 22 Aug 2011 20:22:12 +0100 the perfect
    time to write:
    Like the ones between one pedal stroke and the next?
    Or maybe the difference between different parts of the stroke?
    Aerobic capacity doesn't come into it for short duration leg strength.
    If you can stand, you can by definition exert at least half your own
    weight through each leg. To walk you have to be able to exert your
    entire weight through each leg.
    You can use a big force for a small part of the stroke, or a small
    force over a longer portion, or anything in between.
    You seem to be assuming that the force is level and continuous through
    the entire rotation of the pedal.
    I've yet to meet the rider that can manage that, but it's safe to
    state that novice or non-enthusiast riders are far less likely to
    achieve a smooth pedal stroke than trained enthusiasts or sporting
    riders.
    All that is about long duration averages though.
    Not all that relevant for calculating the maximum torque you can exert
    on a crank during one part of the pedal stroke.
    But can be, for most riders, by the simple expedient of standing up on
    the pedals.
    A fit rider, with the right kit, can exert more than their own weight
    on the pedal, by pulling up on both the handlebars and the (rising)
    other pedal, but for those who can't or don't do that, the maximum
    torque can be derived from the riders weight and the crank length,
    except in those few cases where the rider cannot put their entire
    weight on a pedal through either leg.
     
    Phil W Lee, Aug 23, 2011
    #33
  14. Jim

    Rob Morley Guest

    But fit a 24" wheel and you're laughing. :)
     
    Rob Morley, Aug 23, 2011
    #34
  15. Jim

    nmm1 Guest

    And those remarks are precisely my point about using an unreasonable
    position and style. Traditional upright ones are almost identical
    to walking up a 1:3 hill, except that you are carrying a fraction
    of your weight. And that isn't a problem for almost all walkers,
    except the amount of 'puff' needed!

    The point is that racing cyclists, at 400+ watts, get a massive
    advantage from a 30% reduction in windage. So they use an extremely
    unnatural position and style to minimise the knee damage caused by
    that.

    It provides some advantage for 200+ watt riders, though less than
    is usually claimed (say, 5% in hilly going), but it provides a very
    small amount of speed benefit for those who cannot maintain as much
    as 100 watts.


    Regards,
    Nick Maclaren.
     
    nmm1, Aug 23, 2011
    #35
  16. Jim

    mrc7--urcm Guest

    In message <>
    http://connect.garmin.com/activity/107492284

    Average moving speed 10.3km/h, but during the climb over the Grosse
    Scheideg itself at between 48-65km where we climbed from around 700m to
    2000m you'll see that my speed was frequently below 6km/h.

    I was riding an Airnimal Black Rhino which has a Rohloff gear.

    Mike
     
    mrc7--urcm, Aug 24, 2011
    #36
  17. Jim

    Clive George Guest

    On our recent tour we were occasionally climbing at 4km/hr - on a loaded
    tandem. Derailleur gears, 9 speed at the back, bottom gear 24F32R on 26"
    wheels.
     
    Clive George, Aug 24, 2011
    #37
  18. Jim

    Jim Guest

    Nice trip.



    How many teeth does your front ring and rear sprocket have?

    Why is your Timing chart (and HRM) so smooth between 5:13 and 22:13?
     
    Jim, Aug 24, 2011
    #38
  19. Jim

    Jim Guest

    *> Scheideg itself at between 48-65km where we climbed from around
    700m to
    N


    was riding an Airnimal Black Rhino which has a Rohloff gear.
     
    Jim, Aug 24, 2011
    #39
  20. Jim

    mrc7--urcm Guest

    In message <>
    Yes this was a change from our usual summer walking and mountaineering
    vacations in the Alps.

    Earlier in the year I twisted my knee quite badly during a ski-traverse
    of the Domes du Miages near Mont Blanc. I was airlifted by helicopter



    On returning to the UK it turned out that I'd badly strained several
    ligaments along with other soft tissue injury which initially ruled out
    my usual activities such as caving and hill-walking, but I quickly
    discovered that cycling was still OK. So this year I've been doing much
    more leisure cycling instead of caving, hill-walking and mountaineering.

    We took our Airnimal Rhinos to Switzerland and ended up doing about 11
    days worth of cycling covering about 460km and with 16,000m of ascent.
    This was from 3 different campsite bases during the trip, the Col De
    Mosses, Lauterbrunnen, and Le Locle.
    http://www.airnimal.eu/Rhino/Black.php

    13T at the rear and 48T at the Chain ring, and of course with 20 inch
    wheels. The gear range is 17-92 gear inches.
    You can change the units plotted for the x axis (or at least if I'm
    logged in to my account I can) and rather than time I usually set it to
    distance and with the units in metric. However the direct answer to your
    question above is fairly straightforward in that this was a two day tour
    and the smooth gap when plotted against time is for the period that I
    was staying overnight in Meringen and wasn't wearing a HRM!

    Mike
     
    mrc7--urcm, Aug 25, 2011
    #40
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