Conference noted::bicycle

    
    Optimum crank length is one of the outputs of the Fit Kit process.
    If anyone knows about this stuff, it's Paul Randazzo at Category
    One Cyclegoods in Tyngsboro  (617) 649-7599.  Give him a call. 
     - Chris

	It's appears to me that I could buy the correct frame for me
    	and still come out wrong with the wrong length crank arms. Am
    	I missing something, or what?
    
    	Scott

    
    You should be using as SHORT a crank length as is comfortable for
    maximum pedaling efficiency. This allows a more effective tradeoff
    between leverage and spinning ability. The longer crank will give
    you more torque at the expense of spinning effort. The shorter crank
    will spin well at any rpm but you'll have to jump on it on the hills.
    
    It is a fallacy, just like the larger frame size fallacy, that the
    longer the crank length the better, with one exception, time trialing.
    Most TTers use a longer crank for this event because they'll rarely
    spin above 110 rpm, sitting back on the saddle and pushing instead.
    
    My inseam is 32", I use a 170 (Fit-Kit also agrees), except for
    TT where I use 175's.
    
    I'd say you should be using 172.5's for your road bike (34" inseam).
    This is my experience with racers of your size, 99.9% use 172.5.
    Be prepared to pay a pretty penny for new crankarms, though, with
    Campy they're 90% of the cost of a new chainwheel set.
    
    CdH
    

Crank length is one of those black magic things where there's a big difference
of opinions and it's hard to say that any one is more right than any other.
Some generalizations are too general. As with any other opinionated area, you
must weigh the opinions and try it out to see. (For a price, of course, so it 
all depends on what the answer is worth to you.)

Some of the generalizations:

Shorter cranks encourage spinning.  Track cranks are an example of yet smaller
cranks.

Longer cranks are more useful for TT's and hill climbs because of the
better leverage.

If you use longer cranks, you should also use a bigger chainring.

Nonstandard sizes cost more and have to be ordered. (I don't think you'll get
any argument there.)  Most shops will order things for you.

Continually switching cranks on a bike can overly stress the cranks and, 
eventually, cause them to fail.  I think that depends on the torque used to 
install it (18-20 ft-lbs is recommended, gorillas not needed.)

End of generaliztions, begin practical experience.

I put 172.5's on a bike and the first two rides on that bike introduced me
to some new muscle pains (quads) which determined me to reintroduce myself to 
weighttraining this winter.  I think my quads had become highly conditioned to 
only having to move "just so much and no more."  After two rides (about 90 mi)
the novelty was gone and I never had those pains again.  (I'm a 32.)  I do 
think that the 172.5 makes a difference, but for the Wachusett Hill Climb I 
went with the bike on which I had the most experience and 170's.

As for compatibility, the answers are: "probably," and "not precisely."  If 
you read Sutherland's (4th ed), you find the words "vary considerably" and
"most," for example:

"Most axle and cracnk tapers are very close to 2 degrees."  "Most of the 
difficult crank-fit problems are due to taper length differences, not angle 
differences."

With a poor fit, you get either bad chain line or a fit that's loose enough to 
eventually destroy the crank -- or both.

If you'd like to borrow a few pages from the book, I could send you a copy.
(Or if you'd like to stop in ZK some time, come on by -- just check to assure
that the book and I will be here.)

ed

    
    One has to be general when giving this kind of advice. The consequences
    of being too specific are obvious.
    
    DISCLAIMER:
    ***********
    
    Any advice given by myself is just advice. It is recommended that
    the person asking understand this, and make the final judgement
    for themselves.
    
    I have always thought that this was implicit in this file.
    
    The advice I give is based on many years of top catagory racing,
    observing the riders, their styles, techniques and equipment. This
    is EXACTLY what the Fit-Kit is based on. However, Bill Farrell will
    be the first to tell you that it is not gospel, just a GUIDELINE
    to make the proper decision for yourself.

    Some of those "generalizations" are truths. Shorter cranks will
    spin easier than longer ones. Track cranks are shorter for one reason
    only...to clear the banking. Longer cranks have better leverage
    and thus a better torque moment. Using these longer cranks the average
    rider will be able to push a bigger gear if their fitness/health
    level will permit it.
    
    CdH
    

    I just ordered a 175mm New Dura Ace crank from Performance
    with 53/42 chainwheels.  Since I ride TTs as well as other
    events, I figure it'll work for them at the very least.  
    
    I've always been a spinner, so I don't think the extra 
    extension is going to hurt me that much.  My addiction to 
    running seems to keep my cadence up, and to make me crave a 
    wider range of motion.  
     
    I'll report back as soon as I've put some decent miles on.

    Of course, Chuck is right: even if this extra-long crank works
    for me, it doesn't mean that everyone with a 34" inseam should
    go out and spend $100 on a new crank.  I think his advice is
    good for most people.
    
    Thanks to everyone who wrote in.
    
    
    MATT

    It might be useful to point out that a small change in
    crank length is actually a big change in pedaling effort
    and pedal travel.  At first glance, for example, the 
    difference between a 170 and 172.5 mm crank seems miniscule,
    about 1.5%.  However, remember that your foot (attached to 
    the crank) is making a circle with the crank as its radius.
    As a result, the distance your foot has to travel is increased
    by a factor of 2 pi X the difference in radii - a noticable
    difference.

    
    The difference between 170 and 175 is HUGE. I usually warm up an
    hour before a TT when using these cranks, to get used to the
    difference.
    
    Also, be careful on the corners, your Olmo is not known for an
    exceptionally high bottom bracket (rather low in fact) so be aware
    of this. Scratch it if you have the DynaDrive DA crank/pedals.
    
    Enjoy
    CdH
    

    I have often wondered about all the myth and discussion about crank
    length.  So here are some of my thoughts...
    
    - If you consider two bikes with identical setups, but one has
    a longer crank, it is clear that the amount of work you do per crank
    revolution is the same in both case.  On both bikes you will move
    X feet for each turn of the pedals, and this will not change as crank
    lenght changes. (Think about it.)  So, all other things being equal, 
    pedalling at 100 rpms on any length crank is the same energy output.
        
    - You do generate more torque on longer cranks, so it takes less
    pedal travel to move a given distance along the road.  This is 
    offset however by the fact that the pedals must move farther to 
    complete a revolution.  
    
    - For the above two reasons, I always consider discussions of crank
    length not so important.  (I know this is heresy to say.) 

    - The circumference of a circle is directly proportional to
    its radius.  So a 1% change in radius results in a 1% change in
    circumference.  (Try the calculations with two different circles.)
    
    - It is not clear how "spinning" relates either.  If spinning means
    that you like to move your legs over a large distance, then I guess
    long cranks are better.  If spinning means that you like to do less
    work per revolution, then crank lenght makes no difference.
    
    Chuck
    

> Note 181.9 by SUPER::CONNELL

> On both bikes you will move X feet for each turn of the pedals, and this 
> will not change as crank length changes.

> [You get more torque with longer cranks...] so it takes less pedal travel 
> to move a given distance along the road.  

	Sounds like a clear contradiction to me.  You get more torque
	with longer cranks so you can accelerate more easily... but
	you loose cornering clearance and your legs have to flex more.

	I imagine that the legs have an upper limit on the ammount
	of pressure they can apply.  The shorter the cranks, the lower
	the maximum torque available from the legs.

	I also imagine that the legs have an amount of knee flex beyond
	which the leg is too folded to produce pressure (imagine if
	your crankset was moved up a foot!).  The longer the crank, the
	closer the legs will get to this useless position at the top
	of the pedal stroke.

	My guess is that pedal crank length is chosen as a compromise
	between these two limits.  Somewhere between the minimum length
	(0) and the maximum length (leg length / 2) there will be
	one or more optimum lengths.

				-John A. Wasser

RE: .9 and .10

I was thinking about my note (.9) over the last few days and realized I had 
made a mistake [this work stuff really gets in the way of writing quality 
NOTEs].  I then saw that John had already found my error (.10)...

My apologies and (I think) a corrected response...


>    - If you consider two bikes with identical setups, but one has
>    a longer crank, it is clear that the amount of work you do per crank
>    revolution is the same in both case.  On both bikes you will move
>    X feet for each turn of the pedals, and this will not change as crank
>    lenght changes. (Think about it.)  So, all other things being equal, 
>    pedalling at 100 rpms on any length crank is the same energy output.
        
This is still true, I claim.

>    - You do generate more torque on longer cranks, so it takes less
>    pedal travel to move a given distance along the road.  This is 
>    offset however by the fact that the pedals must move farther to 
>    complete a revolution.  
    
You do generate more torque on longer cranks, but the conclusion I reached does 
not follow from that.

You generate more torque because a given lateral displacement (say 1 inch of
pedal travel) move the bike less far as crank length increases.  This allows
you to lift a greater weight since you have more leverage. If you consider
ANGULAR displacement however (say 90 degrees of pedal motion) the bike moves the
same distance regardless of crank length. 

So that is the trade-off.  Each inch of pedal motion is easier (in some sense)
on longer cranks, but you have to move the pedal through more inches to
complete a revolution. 

(I hope I got it right this time.)

All in all, I agree with John's conclusion in .10.  The deciding factor seems 
to be leg comfort; what range of motion is best for your legs.

Chuck

    

    I saw this last night in a sports magazine out of S. Florida.  It's
    a Q&A with Claudio Costa an ex-national coach (Japan, Mexico  and
    others), now a local trainer/coach.  He bases his findings on results
    from testing using the Conconi's AT test.
   
    I just remembered that inseam was mentioned in this note, and I
    with my stubby legs figured I'd never have to worry about longer
    cranks.
     
    Q. Lots of technicians say crank size is determined by the length
    of your legs, short legs-short cranks, long legs-long cranks.
    
    A. If you know any technicians giving this out of date information
    then tell them that they're absolutely wrong.  CRANK ARM LENGTH
    IS ONTLY DETERMINED BY PEDAL REVOLUTIONS AND THE LENGTH OF THE RACE.
    
    
    He adds later that triathletes are usually misfit for cranks, and that
    they should go with cranks "up to" 180mm.  He says that they need
    to conserve energy and tend to pedal below 100 RPM.  (Dave Scott
    recommends 85 RPM).  
    
   
    JD
    
    
    
     

    
    That's just another opinion.
    
    Here's mine:
    Crankarm length is too complex an issue to be determined by *either*
    of the two methods you mentioned, you have to consider ALL the factors,
    like leg length, foot length and pedalling style (often forgotten),
    thigh length, AS WELL AS the type of event.
    
    On the track bike I use 165's, the road bikes 170's, and the time
    trial bike I use a selection depending on the type of TT, for flat
    districts type of events I usually use 175's. For hillclimbs it's
    172.5's.
    
    No one person's opinion should ever be taken as gospel truth.
    
    CdH
    
    

    After several rides on my 175's, I'd have to say that Chuck Connell
    has had the most sensible perspective on crank length so far.  
    In short, it's no big deal, and anyone who spends a lot of money
    (like I did) buying different-sized cranks would most likely
    be better off throwing it away on lottery tickets.
    
    The RPMs are identical, regardless of crank length.  The increased
    bolt circle of my 175s gives them a "roomier" feel, but it's very
    subjective.  Climbing cadence changes a little; so does cornering
    clearence.  Everything else is remarkably the same.
    
    MATT