Gearing question

Discussion in 'Recumbent bicycles' started by Tom Blum, Sep 29, 2003.

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  1. Tom Blum

    Tom Blum Guest

    One more question:

    Is the big ring actually more efficient than the middle. They are 38 and 48 tooth, respectively, on
    my bike. It sure seems to be.

    It just seems that on the big ring, even with nearly the same gear inches, I pick up a mile per hour
    just by being on the larger ring.

    At times, I was over 20 mph for a while when conditions were favorable. On long (for me ) rides, I
    try to use a constant force rule, shifting whenever cadence drops at that force. Speed is the
    dependent variable.

    --
    Miles of Smiles,

    Tom Blum Winter Haven, Florida Homebuilts: SWB Tour Easy Clone Speed Machine Clone High Racer Clone
    www.gate.net/~teblum
     
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  2. Tom Blum <[email protected]> wrote:
    : One more question:

    : Is the big ring actually more efficient than the middle. They are 38 and 48 tooth, respectively,
    : on my bike. It sure seems to be.

    Why would it be? AFAIK large cogs (in the rear...) are preferable on streamliners, maybe they are
    more effective overall. But I doubt it's a huge effect...

    : It just seems that on the big ring, even with nearly the same gear inches, I pick up a mile per
    : hour just by being on the larger ring.

    Might be just psychology :)

    Do you do better in a time trial with the big ring vs the small ring - or can you keep a better pace
    with the same heart rate?

    : At times, I was over 20 mph for a while when conditions were favorable. On long (for me ) rides, I
    : try to use a constant force rule, shifting whenever cadence drops at that force. Speed is the
    : dependent variable.

    If you had a power meter you could be sure.

    --
    Risto Varanka | http://www.helsinki.fi/~rvaranka/hpv/hpv.html varis at no spam please iki fi
     
  3. fblum

    fblum New Member

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    Using different chainrings but having the same overall gear (in inches) implies a different cadence, i.e you will be spinning more in the 38 vs the 48. And certainly you will have a preference for one cadence over the other and,I expect, you will be biomechanically more efficient in one vs the other. Your body is telling you something here- listen carefully. This a Blum to Blum communique.
     
  4. Cletus Lee

    Cletus Lee Guest

    In article <[email protected]>, [email protected] says...
    > Using different chainrings but having the same overall gear (in inches) implies a different
    > cadence, i.e you will be spinning more in the 38 vs the 48. And certainly you will have a
    > preference for one cadence over the other and,I expect, you will be biomechanically more efficient
    > in one vs the other. Your body is telling you something here- listen carefully. This a Blum to
    > Blum communique.

    Mis-communique??? The definition of gear inches is the distance(in inches) that a rear wheel will
    travel in one pedal revolution Cadence is pedal revolutions per minute. So at 100 rpm the rear wheel
    will travel the same distance in one minute no matter which gear combination is used if the gear
    combinations produce the same final G.I.

    Generally, you are more efficient when you spin rather than 'mash'. It is easier to spin with the
    smaller chain ring because it takes more rpm to move the same rear cog to produce the same speed in
    a larger gear at a lower cadence.

    So, Tom, I would expect the opposite result from what you have reported. However, I learned to spin
    in a lower gear to keep my crusing speed up to 20 mph. After I was comfortable spinning, I found
    that I could still spin if I went to the larger Chainring and maintained the same high cadence.

    Also since the gear ratios are what they are it is unlikely that the combinations with the large
    front 48T Chainring will be duplicated anywhere with the 38T. So if you shift to the larger
    chainring, you will also shift to a larger rear cog and that will likely have a bigger
    G.I. than the previous shift position.

    --

    Cletus D. Lee Bacchetta Giro Lightning Voyager http://www.clee.org
    - Bellaire, TX USA -
     
  5. Tom Blum

    Tom Blum Guest

    No no no.

    I said same gear inches. I have a gear chart. There are overlaps where combinations on each ring are
    nearly the same. By this, I mean less than 1/4 inch different.

    It seems that on the big ring, things just get easier.

    On a separate note. I have been training to spin. However, on longer rides, this tires me. It seems
    to take more effort to go the same speed. No doubt this is a acclimatization deal and I'm not there
    yet. (Or maybe all my fast twitches got used up in distance running way back when???)

    --
    Miles of Smiles,

    Tom Blum Winter Haven, Florida Homebuilts: SWB Tour Easy Clone Speed Machine Clone High Racer Clone
    www.gate.net/~teblum
     
  6. Jon Meinecke

    Jon Meinecke Guest

    "Cletus Lee" <[email protected]> wrote in message
    news:[email protected]...

    >The definition of gear inches is the distance(in inches) that a rear wheel will travel in one pedal
    >revolution

    http://www.sheldonbrown.com/gloss_g.html#gearinch says:

    [Gear inches are] the equivalent diameter of the drive wheel on a high-wheel bicycle

    So we need GI*PI to make distance travelled per pedal rev, don't we?

    It's the ratio between chainring and drive gear combined with drive wheel diameter (plus any mid
    drive ratio) that make up gear inches. So it's at least theoretically possible to have the same GI
    with a different chainring size as long as the overall ratio is maintained.

    A simple example: a hypothetical 34 chainring to a 34 drive gear setup would be the same as a 60 to
    60, or a 10 to 10, wouldn't it?

    Whether there are mechanical or drivetrain efficiency advantages to larger chainrings (less chains
    bend around larger gears?), I don't know. Crank length may certainly plays a role in biomechanical
    efficiency...

    If the chainring is big enough, heavy enough, spins quickly enough, it could have a flywheel or
    gyroscopic effect, I guess! %^)

    Jon Meinecke
     
  7. Cletus Lee

    Cletus Lee Guest

    In article <[email protected]>, [email protected] says...
    > No no no.
    >
    > I said same gear inches. I have a gear chart. There are overlaps where combinations on each ring
    > are nearly the same. By this, I mean less than 1/4 inch different.

    Remember, I said " it is unlikely that the combinations with the large front 48T Chainring will be
    duplicated anywhere with the 38T" not impossible. and you wee not specific enough when you said "
    nearly the same gear inches".

    So then it boils down to cadence, then doesn't it? I do not have a clue as to why it would be easier
    to maintain a faster cadence with a larger chainring a essentially the same G.I. If what you say is
    true, then why aren't we all pushing 64T chainrings with a 16T small cog instead of a 48T/12T? It is
    the same gear.

    > It seems that on the big ring, things just get easier.

    I really can't feel much difference on my 52T-42T-26T Chainrings. I actually spend most of my time
    in the 42T.

    > On a separate note. I have been training to spin. However, on longer rides, this tires me. It
    > seems to take more effort to go the same speed. No doubt this is a acclimatization deal and I'm
    > not there yet. (Or maybe all my fast twitches got used up in distance running way back when???)

    I think you are born either 'fast-twitch' of 'slow-twitch' dominant. I found out in high school that
    I was better suited to run cross-country than the 100yd dash. The same is still true. I am still
    'slow-twitch' What I have learned that I can train those slow twitch muscles to move it up a notch
    and maintain that. I'd like to manage 110 rpm but the best that I can do for the long run is about
    95. But this is a great inprovement over the 70-80 that I started with.
    --

    Cletus D. Lee Bacchetta Giro Lightning Voyager http://www.clee.org
    - Bellaire, TX USA -
     
  8. Cletus Lee

    Cletus Lee Guest

    In article <[email protected]>, [email protected] says...
    > >The definition of gear inches is the distance(in inches) that a rear wheel will travel in one
    > >pedal revolution
    >
    > http://www.sheldonbrown.com/gloss_g.html#gearinch says:
    >
    > [Gear inches are] the equivalent diameter of the drive wheel on a high-wheel bicycle
    >
    > So we need GI*PI to make distance travelled per pedal rev, don't we?
    >
    Of course, but pi (like the diameter of the wheel) is a constant and has no bearing on the result
    when different gear ratios are used.

    Sheldon also favors the use of 'gain ratios' which eliminates the units and deals with a pure ratio
    for any given gear combination. As you can see not dealing with a pure ratio requires a lot more
    explanation and clarification.
    --

    Cletus D. Lee Bacchetta Giro Lightning Voyager http://www.clee.org
    - Bellaire, TX USA -
     
  9. Chuck Davis

    Chuck Davis Guest

    For bigger gears, the big chain ring should be more efficient. When using the big chain ring with
    the center cogs in the back, the chain line will be straight. To get near to the same gear inches
    with the smaller front ring, you'd have to use the smaller outside cogs in the back resulting in an
    acute chain angle which causes more friction. How much extra power that takes, I don't have a
    number for - and it would depend on chain lubricant and chain newness. It seems like a newer chain
    would have more friction because it wouldn't have the give to bend sideways that a more worn chain
    would have.

    Chuck Davis

    "Tom Blum" <[email protected]> wrote in message
    news:p[email protected]...
    > One more question:
    >
    > Is the big ring actually more efficient than the middle. They are 38 and
    48
    > tooth, respectively, on my bike. It sure seems to be.
    >
    > It just seems that on the big ring, even with nearly the same gear inches,
    I
    > pick up a mile per hour just by being on the larger ring.
    >
    > At times, I was over 20 mph for a while when conditions were favorable. On long (for me ) rides, I
    > try to use a constant force rule, shifting
    whenever
    > cadence drops at that force. Speed is the dependent variable.
    >
    > --
    > Miles of Smiles,
    >
    > Tom Blum Winter Haven, Florida Homebuilts: SWB Tour Easy Clone Speed Machine Clone High Racer
    > Clone www.gate.net/~teblum
     
  10. Jon Meinecke

    Jon Meinecke Guest

    "Cletus Lee" <[email protected]> wrote
    > > >The definition of gear inches is the distance(in inches) that a rear wheel will travel in one
    > > >pedal revolution
    > [...] [email protected] says...
    > > [...] we need GI*PI to make distance travelled per pedal rev, don't we?
    > >
    > Of course, but pi (like the diameter of the wheel) is a constant and has no bearing on the result
    > when different gear ratios are used.

    When I first read about gear inch numbers, I thought as your initial statement above might be
    interpreted, that 20 GI meant 20 inches of travel per pedal rev. At 20 gear-inch, a bike actually
    travels almost 63 inches for each pedal rev (indeed, regardless of wheel size).

    Obviously, using known GI and cadence, one can compute speed, so we can throw out our cyclometers
    and brush up on our real-time cadence counting and multiplication skills! %^)

    There's a number of GI calculators on line.

    http://www.wisil.recumbents.com/wisil/gearinches.asp

    Jon Meinecke
     
  11. Cletus,

    The actual definition if gear inches is the equivalent wheel diameter. The distance in inches that
    circumference of a wheel travels per one revolution of the pedal is called development, and it is
    usually expressed in meters.

    Example:

    A 52t chainring, a 12t cog on a 27" (or 700c, there is variation because of tires, inflation, etc.)
    wheel is 117 gear inches.

    The distance traveled is approx. 367.5663 inches, or 9.336 meters

    Tim Storey

    --
    This look left intentionally blank

    <snipped>
    > Mis-communique??? The definition of gear inches is the distance(in inches)
    that a rear wheel
    > will travel in one pedal revolution Cadence is pedal revolutions per
    minute. So at 100 rpm the
    > rear wheel will travel the same distance in one minute no matter which
    gear combination is used
    > if the gear combinations produce the same final G.I.
     
  12. Cletus Lee

    Cletus Lee Guest

    In article <[email protected]>, [email protected] says...
    > Cletus,
    >
    > The actual definition if gear inches is the equivalent wheel diameter. The distance in inches that
    > circumference of a wheel travels per one revolution of the pedal is called development, and it is
    > usually expressed in meters.
    >
    > Example:
    >
    > A 52t chainring, a 12t cog on a 27" (or 700c, there is variation because of tires, inflation,
    > etc.) wheel is 117 gear inches.
    >
    > The distance traveled is approx. 367.5663 inches, or 9.336 meters
    >
    > Tim Storey
    >
    >
    Ok In an attempt to be brief, I skewed the definition a little. Yes, I knew all that when I wrote
    the reply. I guess I've learned not to leave anything out when in 'communique' (sic) this group.
    Next you will be turning me into another Tom Sherman!!!!

    --

    Cletus D. Lee Bacchetta Giro Lightning Voyager http://www.clee.org
    - Bellaire, TX USA -
     
  13. Tom Blum

    Tom Blum Guest

    Cletus Lee said: "Also since the gear ratios are what they are it is unlikely that the combinations
    with the large front 48T Chainring will be duplicated anywhere with the 38T. So if you shift to the
    larger chainring, you will also shift to a larger rear cog and that will likely have a bigger
    G.I. than the previous shift position."

    I usually shift up to the large ring and up two rings in the rear to keep the same ratio. The
    resulting ratios are within about 1 inch of each other.(I checked my gear chart) The large ring
    ratio is a bit lower, so maybe that is what causes the effect that I notice. Maybe it's
    psychological, for all I know.

    But I like it. Faster is good!!

    --
    Miles of Smiles,

    Tom Blum Winter Haven, Florida Homebuilts: SWB Tour Easy Clone Speed Machine Clone High Racer Clone
    www.gate.net/~teblum
     
  14. Tom Blum

    Tom Blum Guest

    Next you will be turning me into another Tom Sherman!!!!

    Lord help us all!!

    Tom

    <G> for humor impaired
     
  15. <Chas>

    <Chas> Guest

    "Jon Meinecke" <[email protected]> wrote in message
    news:[email protected]...
    > "Cletus Lee" <[email protected]> wrote
    > > > >The definition of gear inches is the distance(in inches) that a rear wheel will travel in one
    > > > >pedal revolution

    Jon,

    gear inches is NOT the distance the wheel travels per pedal revolution. It is the equivalent
    DIAMETER of the rear wheel

    Inches traveled per pedal revolution is called "development"

    Check out the Sheldon Brown site previously cited. He can explain all this stuff a lot better
    than I can.

    <Chas> Riding bikes for >50 years Adjusting, fixing, and building them for ~40 of that
     
  16. Jeff Wills

    Jeff Wills Guest

    [email protected] wrote in message
    news:<[email protected]>...
    > Tom Blum <[email protected]> wrote:
    > : One more question:
    >
    > : Is the big ring actually more efficient than the middle. They are 38 and 48 tooth, respectively,
    > : on my bike. It sure seems to be.
    >
    > Why would it be? AFAIK large cogs (in the rear...) are preferable on streamliners, maybe they are
    > more effective overall. But I doubt it's a huge effect...

    In general, larger sprockets are *slightly* more efficient than smaller- the chain is bent through a
    slightly smaller angle, incurring less friction. On the other hand, smaller chainrings would have
    *slightly* less aerodynamic drag on an unfaired bike. We're talking effects on the order of 1/10 of
    1 percent- barely enough to be measureable, much less noticeable.

    Quit worrying about it and ride your bike.

    Jeff
     
  17. meb

    meb New Member

    Joined:
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    Bigger chainrings are slightly more effiicient than middle chainrings. However, all things equal, you're generally going to be on a bigger sprocket than with a biogger chainring than the middle chainring. The losses are more pronounced at the sprocket because the chain links are turned more. We had a pretty good thread about 2 weeks ago on this issue.
    see-
    "Chain efficiency: losses in runs?" Starter: Simon Brooke
    forum: rec.bicycles.tech last post: meb
     
  18. Jon Meinecke

    Jon Meinecke Guest

    "<Chas>" <[email protected]> wrote in message
    news:[email protected]...
    >
    > "Jon Meinecke" <[email protected]> wrote
    > > "Cletus Lee" <[email protected]> wrote
    > > > > >The definition of gear inches is the distance(in inches) that a rear wheel will travel in
    > > > > >one pedal revolution
    >
    > Jon,
    >
    > gear inches is NOT the distance the wheel travels per pedal revolution. It is the equivalent
    > DIAMETER of the rear wheel
    >
    > Inches traveled per pedal revolution is called "development"
    >
    > Check out the Sheldon Brown site previously cited. He can explain all this stuff a lot better
    > than I can.

    Chas,

    Check out the attributions... %^) I didn't write that. That was me quoting Cletus' brief description
    of GI. My response in fact included a link to Sheldon's site entry for GI.

    BTW, it wasn't my intent to be anal retentive or inspire TS-ness.

    This begs the question, assuming similar GI, development, cadence, etc, are bigger gears actually
    more efficient?

    I tend to stay in the center chainring probably 90% of the time. From the wear on my cassette, I
    seem to spend most time (miles?) in 6-7-8. If for no other reason than equalizing wear, it would
    seem a good idea to use the large front gear more often.

    Jon
     
  19. On 29 Sep 2003 21:46:12 -0700, [email protected] (Jeff Wills) wrote:

    >In general, larger sprockets are *slightly* more efficient than smaller- the chain is bent through
    >a slightly smaller angle, incurring less friction.

    I believe this has been shown to be false. Last year Rich Pinto wrote:

    > John- I always beleived the same thing because I had heard it so many times.
    >
    > However, in an article in the fall 2000 "Human Power" called "Efficiency of bicycle chain
    > drives: results at constant velocity and supplied power" John and Claire Walton did an analysis
    > comparing chain and sprocket efficiency at a constant supplied power and vehicle speed.
    >
    > Using data from the previous Spicer HP article, they found that at constant power and
    > vehicle speed, the efficiencies were 92% for the 11 tooth,
    > 90.5% for the 15 tooth, and 88.5% for the 21 tooth.

    If you want to search for the thread on Google, the thread title was "The elusive 20 mph target/rear
    sprocket efficiencies."

    Ken Kobayashi [email protected] http://solarwww.mtk.nao.ac.jp/kobayashi/personal/
     
  20. Tom Blum

    Tom Blum Guest

    EUREKA!!

    Thanks, Ken.

    That's just the kind of scientific support I was seeking for my percieved sensations.

    3.5 % (3.8% differential ) is not to be sneezed at on my block.

    I will search and read the thread you refered to, since 20 mph is certainly an elusive goal where I
    am concerned.
    --
    Miles of Smiles,

    Tom Blum Winter Haven, Florida Homebuilts: SWB Tour Easy Clone Speed Machine Clone High Racer Clone
    www.gate.net/~teblum
     
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