Advertise on Bikeforums.net



User Tag List

Results 1 to 6 of 6
  1. #1
    Member
    Join Date
    Apr 2006
    Location
    Seattle
    Posts
    28
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    short crank and stem riser for limited hip ROM

    I've been posting and reading other parts of the forum as I was putting together my bike, but recently read old posts here. I see there are quite few about shorter cranks, and more upright riding to relieve back and neck problems. My own issue with a pretty limited range of motion in both hips made me push the limits of bike ergonomics with a really upright riding position, short crank, and electric assist motor on a 20" folding bike.

    I'm not quite done but here is what I've done:
    I'm using a Sinz Isis 115mm crank (I've also used crank shorteners in the past).
    The crank doesn't provide a lot of leverage, and I travel hills to and from work. So I also have a front hub motor (BMC 500W high torque motor that will climb hills), and I put all on an old folding bike with 20" wheels to maximize torque ($40 on Craigslist).
    I sit upright and am putting on a 15" stem riser (remember it is a 20" bike). I will use a 1" threaded to 1.125" threadless adapter, make a simple stem riser from the downtube of an old mountain bike, and use a threadless stem. I think it will be plenty strong.

    What I really want to try is the Streetstepper stepper bike out of Austria, but it currently seems impossible to get one in the USA.

    Robert

  2. #2
    I am the Snail~! Peter_C's Avatar
    Join Date
    Sep 2009
    Location
    Near Akron, Ohio
    My Bikes
    2010 TerraTrike Rover 8
    Posts
    1,583
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Dropping to 152mm cranks allowed me to start riding much sooner after my hip replacement. Getting the angle below 90 degrees was key for me. In my eyes, the increased comfort is well worth the lower torque - I won't be going back either.
    Peter_C
    http://s1103.photobucket.com/albums/g475/Peter_CC/ <-- My Photos

  3. #3
    Senior Member Bill Kapaun's Avatar
    Join Date
    Feb 2007
    Location
    Mid Willamette Valley, Orygun
    My Bikes
    86 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds.
    Posts
    6,487
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    There gets to a point that too short doesn't work well either.
    It's not a loss of torque issue, but long legs just don't spin well in tiny circles.

    I've experimented with cranks from 160 to 175MM because I don't have full range of motion in my right knee.
    Cadence is basically what I can sustain for 15-20 minutes on a "pleasant" day before I start to "taper off" a bit.. (no 100+ temperatures or extreme wind chill etc.)
    Length- Cadence.
    175 - 60 foot/whole leg is "thrown" off the pedal about 62-63 because the knee quits bending
    170 - 80 knee usually had slight pain on a regular basis. No extra miles ridden for "pleasure" because they aren't fun.
    165 - 85 OMG! Did 600 miles that month. Previous high YEARLY total ever was less than that!
    160 - 80 I used these for about 6 months between the 170's and the 165's. No "real" knee pain, but they just didn't feel right (cranks & knee) . I went back to 170's for a short time until I realized I had an old Cottered set of 165's "attached" to an early 70's 10 speed road bike stuffed in the back corner.

    Point being, don't go shorter than absolutely necessary.

    What lengths have you experimented with?

    Also, REALLY experiment with your seat height!
    I thought I had mine right by some of the formulas/opinions found on the web.
    Then, one day I looked down at my size 13's and realized what applies for someone with a size 9 and what applies to me CAN'T be the same.
    I ended up raising my seat nearly 3/4"!
    That cut my normal "miles logging circuit" from 32-38 minutes to 30-36 minutes.
    Last edited by Bill Kapaun; 02-16-12 at 02:07 AM.

  4. #4
    coprolite fietsbob's Avatar
    Join Date
    Jun 2010
    Location
    NW,Oregon Coast
    My Bikes
    7
    Posts
    35,727
    Mentioned
    15 Post(s)
    Tagged
    0 Thread(s)
    Pedal plate height additions have a different effect than short crank arms,
    as they are still offering Leverage at the power stroke, as the lever length does not change,
    but the top and bottom of the pedal stroke are a shorter distance.

    somewhat akin to shoe sole differential thickness ..

    any pedal with screw on cages can be modified.

  5. #5
    I am the Snail~! Peter_C's Avatar
    Join Date
    Sep 2009
    Location
    Near Akron, Ohio
    My Bikes
    2010 TerraTrike Rover 8
    Posts
    1,583
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by fietsbob View Post
    Pedal plate height additions have a different effect than short crank arms,
    as they are still offering Leverage at the power stroke, as the lever length does not change,
    but the top and bottom of the pedal stroke are a shorter distance.

    somewhat akin to shoe sole differential thickness ..

    any pedal with screw on cages can be modified.
    No offense, but adding a 'plate' to the bottom of the pedal will *increase* RoM at the top of the pedal stroke - it may help aqt the bottom, but it's worse at the top.
    Peter_C
    http://s1103.photobucket.com/albums/g475/Peter_CC/ <-- My Photos

  6. #6
    Member
    Join Date
    Mar 2012
    Posts
    36
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    just curious on which shops in the USA sells custom crank sizes?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •