Crank length: rode with 155mm cranks

Discussion in 'Recumbent bicycles' started by Geob, Apr 1, 2003.

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  1. Geob

    Geob Guest

    I bought a set of 155mm cranks which I installed tonight. I have some tweaking to do, but went for a
    ride. I think this is a major improvement for me. feels lots better. My knees still are very
    slightly at an acute angle I think, but I happy. Had 170mm cranks. I am 5' 8.5", normal proportions.
     
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  2. If the 155mm crank feels better and takes you down the road, then it's a good length. Recumbent
    crank lengths can be more problematic than those on upright bikes. If they're too long, the
    knees of many recumbent riders are more likely to get strained, than if they used the same
    length on an upright.

    There's probably more variation in preferred crank lengths on recumbents, as some people can
    tolerate the tighter knee bending better. But, just because a too-long recumbent crank doesn't
    cause you pain now, doesn't mean it might not lead to trouble later. On my quadraped, I use a
    190mm foot and a 252mm hand crank, but I am tall and have extra long limbs (my wingspan is 7
    inches more than my height). It would be good if every community had a recumbent fitting expert
    to help match us all up with the right crank, before pain comes calling.

    Steve McDonald
     
  3. Don

    Don Guest

    GeoB, What bent are you riding? Where did you get the cranks and what brand are they? I am currently
    trying to decide what to put on a new Lightning that I want. Thanks, Don

    [email protected] (GeoB) wrote in message news:<[email protected]>...
    > I bought a set of 155mm cranks which I installed tonight. I have some tweaking to do, but went for
    > a ride. I think this is a major improvement for me. feels lots better. My knees still are very
    > slightly at an acute angle I think, but I happy. Had 170mm cranks. I am 5' 8.5", normal
    > proportions.
     
  4. Don

    Don Guest

    Anyone with experience: Do you think you lose much power (leverage)with the shorter cranks or do you
    make up for it by being more ergonomically efficient? I am much shorter than GeoB and thought going
    to 165mm would be good on my next bent. Maybe I should go even shorter. My knees definitely come too
    far up on my 170s on my Haluzak. I expect a Lightning to be the same or worse. That is not good for
    the knees over the years and puts my legs too far out of their power at the top of the stroke.
     
  5. On 1 Apr 2003 16:28:03 -0800, [email protected] (Don) wrote:

    >Anyone with experience: Do you think you lose much power (leverage)with the shorter cranks or do
    >you make up for it by being more ergonomically efficient?

    No, you make up for it by being able to use higher cadence. If you shorten the crank by 10%, reduce
    gear ratio by 10% and increase cadence by 10%, the pedal force and power output remain the same as
    before. The difference is that the knee bend is reduced. So if you switch to shorter cranks, you
    really should change to smaller chainrings at the same time.

    Ken Kobayashi [email protected] http://solarwww.mtk.nao.ac.jp/kobayashi/personal/
     
  6. Geob

    Geob Guest

    I ride a Vision R40. It has a 26" City Slicker in back, a 20" Marathon in front. I have a variety of
    gearing I play with. So far I have been happiest with my BMX C'dale Coda 170mm crank set. I think
    the chain rings are 44-32-22 (rear is 11-32). My extra Shimano 170mm crank set has a mish-mash of
    chain rings.. 26-34?-46.

    My new cranks are BMX 155mm Redlines, but is a double, not a triple. I use biopace 46-34? on it.
    After I evaluate these for fitment I will pass them along to someone else for the same purpose, if
    wanted, then buy a triple 155mm set.

    > Anyone with experience: Do you think you lose much power (leverage)with the shorter cranks

    I sure am not a bio-engineer, but I don't let that stop me from expressing opinions! Don't mistake
    'power' with 'leverage'. Different animals. Power is torque (your leverage term I think) times rpm.

    I believe:

    1) if you sat on a stationary bike and pedaled, with no resistance to the rear wheel, you would
    still eventually get tired. If the cranks were long you would get tired more quickly. I think
    this is part of the energy I hope to reclaim by going to shorter cranks.

    2) If I were to climb the piramids and had a choice of steps that were so high I had to bend my
    knees at an acute angle, or steps that were lower so that my knees didn't bend so far, so that my
    leg moved mostly through the arc that most efficiently generated power, I would choose the lower
    steps even though there would have to be more of them.

    3) I may be wrong, but after disecting (and masticating) numerous chicken legs, I have reached the
    conclusion that cartilage is thicker in the area that normally receives most of the wear and
    stress, in the middle area of the knee's travel. I expect my own legs are similarly patterned,
    though my feet look different. I am concerned that with my knees bent too much I am stressing an
    area not intended for so much stress and wear.

    4) Shorter cranks allow you to concentrate leg movement within the knee's range of travel that
    produces the most power. I can down-shift** to get the needed torque to the rear wheel. If I get
    the same or close to the same power without moving my legs as far, I win!

    **If I can't pedal my way up the hill, with my gearing, I just WINCH myself up! (22-front, 32-rear)

    > I am much shorter than GeoB and thought going to 165mm would be good on my next bent. Maybe I
    > should go even shorter.

    I used that crank length calculation which was cited in a similar thread a week or so ago. It says I
    should use 165mm cranks. This may turn out to be true... or not! I guess I will form my opinion on
    this over the next few weeks. This calc was for DF bikes and it wouldn't surprise me to learn that
    it needs tweaked to work for bents.

    > My knees definitely come too far up on my 170s on my Haluzak. I expect a Lightning to be the same
    > or worse. That is not good for the knees over the years and puts my legs too far out of their
    > power at the top of the stroke.

    Sounds like you have made a decision to try shorter cranks!
     
  7. Baronn1

    Baronn1 Guest

    George, any idea what your xseam is? "GeoB" <[email protected]> wrote in message
    news:[email protected]...
    > I bought a set of 155mm cranks which I installed tonight. I have some tweaking to do, but went for
    > a ride. I think this is a major improvement for me. feels lots better. My knees still are very
    > slightly at an acute angle I think, but I happy. Had 170mm cranks. I am 5' 8.5", normal
    > proportions.
     
  8. Gary Mc

    Gary Mc Guest

    Ken Kobayashi <[email protected]> wrote in message
    news:<[email protected]t>...
    > On 1 Apr 2003 16:28:03 -0800, [email protected] (Don) wrote:
    >
    > >Anyone with experience: Do you think you lose much power (leverage)with the shorter cranks or do
    > >you make up for it by being more ergonomically efficient?
    >
    > No, you make up for it by being able to use higher cadence. If you shorten the crank by 10%,
    > reduce gear ratio by 10% and increase cadence by 10%, the pedal force and power output remain the
    > same as before. The difference is that the knee bend is reduced. So if you switch to shorter
    > cranks, you really should change to smaller chainrings at the same time.
    >
    On my GTO I went to lower gearing, 26 tooth granny with a dual drive (about 11 gear inches), coupled
    with 155mm cranks. I ride in the mountains some and wanted to insure that could gear low enough for
    climbs. This combination - trike, low gearing & shorter cranks - opened a lot of new routes to me.

    I have short legs (27" inseam). The shorter cranks seem to make a significant difference in comfort.
    And, it is noticeably easier to spin, especially under the added load of climbing. I am not fast
    uphill but can spin my way up anything that I have come across so far.

    Gary McCarty, Greenspeed GTO, Salt Lake City
     
  9. Geob

    Geob Guest

    > George, any idea what your xseam is?

    Sorry, no.. I measured it once, then discovered that I had measured it wrong and haven't re-done it
    since I had purdy much dialed in my machine. If you will remind me of the correct way to do it I
    will get back to you.

    FLASH! FLASH! JUST IN!

    I rode my R40 to work today, 8 miles, with the 155mm cranks. I had adjusted my shifter but not the
    pedal distance (I have in effect moved it shorter by 15mm).

    I didn't feel particularly strong this morning, and didn't consciously make any special effort to go
    fast, but I handily broke my previous commute record by a good margin. No, I'm not going to say what
    it is! I have been commuting for about a year, and each time I break my record it is by a few
    seconds. This time it was by almost a minute. Generally I feel stronger in the afternoon commute..
    this was morning. This is very subjective since I may skew the numbers by working harder and not
    realizing it, so it is probably premature to announce, but I am hopeful it is indicative of future
    efficiencies.
     
  10. Tom Sherman

    Tom Sherman Guest

    GeoB wrote:
    >
    > > George, any idea what your xseam is?
    >
    > Sorry, no.. I measured it once, then discovered that I had measured it wrong and haven't re-done
    > it since I had purdy much dialed in my machine. If you will remind me of the correct way to do it
    > I will get back to you.

    George,

    To determine your x-seam, measure the distance from the junction of the seat base and seat back to
    the center of one of the pedal axles when it is at is farthest possible point - this works about as
    well as any other method in my experience.

    Tom Sherman - Various HPV's Quad Cities USA (Illinois side)
     
  11. Geob

    Geob Guest

    > I didn't feel particularly strong this morning, and didn't consciously make any special effort to
    > go fast, but I handily broke my previous commute record by a good margin.

    I rode again today, 2nd fastest time in a year. No special effort, kinda kick-back. The shorter
    cranks seem to be making an obvious difference.
     
  12. Mark Stonich

    Mark Stonich Guest

    After my nagging him for a couple of years, a friend finally agreed to try short cranks. Might have
    had something to do with his having made the nosecone of his latest fairing a bit too small to
    swing his 170s in ;-) His comment a few days later was "When I get on my other bikes, the cranks
    sure feel long".

    BTW I just put some AC Mini LE 150s http://www.adventurecomponents.com/bmx_cranks.htm on a Hase
    Lepus. Beautifully made, and available down to 135mm. But the "Q" factor is as wide as the Doteks,
    and there is no area on the arms that can be drilled and tapped for a 74 or 58mm bolt circle.
     
  13. Geob

    Geob Guest

    Third commute with the 155's. Scored another PB!! And I seemed to hit all the lights red. I am down
    almost 3 minutes from my previous long-standing pre-155 Best which I only attained once a few months
    ago. No great exertion this time, bout the same or less. Feel less tired at the end.

    I will measure the X-seam, or rather the pedal to seat-back distance case that helps anyone.

    GeoB

    > > I didn't feel particularly strong this morning, and didn't consciously make any special effort
    > > to go fast, but I handily broke my previous commute record by a good margin.
    >
    > I rode again today, 2nd fastest time in a year. No special effort, kinda kick-back. The shorter
    > cranks seem to be making an obvious difference.
     
  14. <Chas>

    <Chas> Guest

    "GeoB" <[email protected]> wrote in message news:[email protected]...
    > Third commute with the 155's. Scored another PB!! And I seemed to hit all the lights red. I am
    > down almost 3 minutes from my previous long-standing pre-155 Best which I only attained once a few
    > months ago. No great exertion this time, bout the same or less. Feel less tired at the end.
    >
    > I will measure the X-seam, or rather the pedal to seat-back distance case that helps anyone.
    >
    > GeoB

    A few specifics about your bike might help too. Seat-to-pedal distance is useful only in the context
    of other geometry information. What bike is it? LWB/ SWB?

    <Chas> Haluzak Hybrid Race -- the inline wheelchair
     
  15. Geob

    Geob Guest

    > A few specifics about your bike might help too. Seat-to-pedal distance is useful only in the
    > context of other geometry information. What bike is it? LWB/ SWB?

    I ride a 2001 Vision R40, SWB USS. I will supply the seat-to-pedal distance as soon as my aged brain
    remembers to measure it next chance I get.

    I am 5"8.5", and am darn near 200#. Today. Tomorrow it will be less. I use SPD clips. I use Lake
    MX-201 Extreme shoes, 43mm. I moved the plates on my shoes down toward the ball of my foot as far as
    it would go. When I learn what I am doing I may need to adjust this. Seems odd to be at the limit of
    the adjustment, makes me think maybe somebody knows more about where I should put my foot than I do.

    I ride mostly in town, excellent road surface, bike lane most of the 8 miles to work. I have 17-18
    signal lights and a handful of stop signs on my route. I have been 'bent cycling for less than a
    year. My average speed yesterday was 13 mph in town. With my previous 170mm cranks, I averaged 12.2
    mph for 46 miles on the last (and only) organized event I have ridden in. Later in the season the
    same ride would be faster, and I am guessing now that the 155mm pedals may make a difference too.

    I am a fat, sedentary balding middle-aged slow poke. Which is not all of the story. I am also a
    muscular mesomorph who has spent a very active life on ranches, hiking, mountain climbing, hunting,
    etc while growing up on a cattle ranch doing ranch chores. I spent years with the USFS as an
    inter-regional hot-shot fire crew memeber and leader, and used to hump a 85lb saw-pack through the
    woods when fighting fires in the wildernesses of ID.
     
  16. Geob

    Geob Guest

    > Seat-to-pedal distance is useful only in the context of other geometry information. What bike is
    > it? LWB/ SWB?

    I described the bike in my last post.. it is a 2001 Vision R40. I have Shimano 515 clipless pedals
    on it. The front seat mount has two holes, about 2" apart. I moved the seat to the rear hole, and
    tilted the back down as far as it would go. If I had left the front seat mount in the front hole, I
    could tilt the seat down even further. Anyway, my goal was to move some weight rear-ward. I expect
    to fool with this some more. I plan to find out 1st what my weight distribution is now. Should it be
    50/50? What should one shoot for? What are the variables?

    I measure 41" from the joining of the seat bottom and back to the top of the pedal. This joining
    describes a curve, so I measured the pedal distance at the side of the seat to the pedal, and again
    from the center of the seat, to the pedal. It is 1/2" longer at the center of the seat joining.

    For all you guys in Maine and in other cold places, I want you to know that I am already getting a
    good tan-line from commuting in my shorts. But when it is 112 degrees F here, and a hissing,
    crackling sound comes from my skin when I walk out into the sun, at least I will be able to croak,
    "But it is a dry heat".
     
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