Conference noted::bicycle

>< Note 915.0 by HPSTEK::EKOKERNAK >
>                            -< Triple Chainrings? >-
    
>    I looked in my Performance catalog, and all they have in triple
>    rings are Biopace and Dura ace.  Can I just add one more ring to
>    my set?  How do I know what size I should get (now I have 52 and 40)?  
    
     A biking friend opines that real non-circular chainrings are not
     that efficient for the cadence "real" bikers use - that they were
     initially tested on instruments that could only go up to 50rpm.
     Hence, Biopace and their ilk would be most unsuited to racers, but
     also experienced tourists, I think.  They apparently seem most
     natural to walkers, runners, hikers.  I speak very vulnerably,
     because I've no experience with them.

     After one tour which contained 20% and 25% grades, some of which
     I barely made, some of which I walked, I elected to go back to a
     bigger rear-cluster (32 teeth) rather than switching out for a
     granny in front.  You get a triple in front, you also need a new
     front derailleur for it.

     I know there are plenty of people who like triples, and like
     Biopace, etc., and are obsessive bikers.  Let's here from them...

     -john

    The Challenges with a double chain ring in the front: 
    
    .Low enough gears for hill climbs and early season training
    .High enough gears for high speed (20mph) touring
    .With only 10-12 speeds, getting gear combinations with no gaps
    and no overlaps.
    .Getting a shift pattern that you like. 
    
    With a Triple in the front, many of these challenges become easier.
    I ride a 38-48-52 front for touring; and a standard 14-32 rear.
    This gives me a half step shift pattern on the top 2 chainrings,
    and still some good low gears. Could use lower in the mountains
    fully loaded. I also dont have to worry about a duplicate gear
    'cause with a 15 speed you might not need all 15, with a 10 speed
    there are no gears to waste.
    
    Dick Anson
      

    My wife and I could have been the couple on the tandem but we don't
    pass anyone going up hill. We have a triple and I love the half-step
    gearing 54-49-28 front and 13-34 rear. We always like to save the
    low gear for those walls that always seam to come near the end of
    a century(metric). The biggest prouble I have is chain wrap, 54-34
    can not be used, or 28-13, 28-15, or 28-18, 28-22 can be used but
    it rattles so I don't. I can alway find a the right gear and I like
    that!!
    
    	Sheldon

    Re .0:
    
    If you have a double chainset now, I doubt very much that you can add a
    third ring to it. You'll almost certainly have to scrap it and buy a
    complete new chainset, so it won't be a cheap upgrade! You'll need a
    new bottom bracket too, because the triple chainsets need a longer
    spindle - but this is often included when you buy a new chainset.
    
    You don't HAVE to have Biopace rings when you get a triple. I know that
    that's about all Shimano offers these days, but other manufacturers
    still make round triples; don't ask me for names, though.
    
    
    Re others:
    
    I wouldn't personally go for this half-step approach on the front that
    is mentioned, eg 38-48-52 at the front and 14-34 at the rear. A 14-34
    rear block is heavy and involves massive steps between gear changes. 
    
    Why not try 28-38-48 or similar at the front and 13-28 at the back? The
    smaller rear block has closer ratios making for better changing, and is
    lighter. Combined with a 28 chainring at the front, you've got 1:1
    gearing, which should get you up anything. The chain capacity necessary
    with a set-up like this is 35, which any long-arm derailleur should
    handle. In practice, you'd avoid extreme crossing of the chain (48
    front to 28 rear, or 28 front to 13 rear), so you could actually get
    away with a shorter arm derailleur. 
    
    
    Rod

    
   Dura Ace does not have a triple!!!  Dura Ace is a "racing" group.
    
    You will need to buy a new crankset and bottom bracket. The whole
    thing will cost around $70 or so new.  Maybe you could pick something
    up used????
    
    I recently purchased a Mountain Bike which has Bio-pace, and to
    be perfectly honest I can tell much of a difference from my road
    bike which has circular chainrings....  I'm sure other people will
    disaggree with that but....  Give Bio-pace a try!  It aint so bad.
    
    Stew

    re .0	If tandems are passing you on climbs I'd guess that
    the problem is NOT with your gearing (also see .3) and I'd also
    guess that the tandem riders who suggested you get a triple might
    have as easily suggested you wear faster jerseys :-^)
    
    	If tandems pass you on the flats, thats OK let 'em go, they
    are good at that;  but they (typically) can't climb worth a hill
    o' beans.  Hint, hint, here's a clue, you said you were puffing,
    were they also puffing ?  The cape is flat, right ?
    
    	R
    

    
    	I like the widest gear range possible, for the Colorado hills...
    I have Biopace; 26-38-48 on the front, on my touring bike, and a 
    34-28-23-18-16-14-12 freewheel on the rear.   It is often handy to 
    have a couple of walking speed gears.   
    
    	I like Biopace chainrings, and have no problem spinning them at any
    speed.   They don't help *that* much, though, and if I were using round
    chainrings I could go down to a 24, where the biopace bottoms out
    at 26 teeth.  
    
    	I'll even put a triple chainring on my next racing bike :-)   
    I've grown so used to the advantages.   I'd probably go for round 
    chainrings next time, and whichever brand offers the greatest 
    variety of chainring sizes, and a sealed bottom bracket.
    
    					Alan.

    re: .5
    
    You're correct, the Triple is not Dura Ace.  It's pretty confusing
    reading some of these catalogs.
    
    Re: rest
    
    I didn't get a chance to check the count of the rear 6 this weekend.
    It sounds like I need to see what I have, and then figure out what
    I want.  I guess the worst case will be if I want new chainrings
    which require a new derailleur, and a whole new freewheel and shifter.
    Well, I guess that's what winter's for!
    
    Thanks for enlightening me!
    
    Elaine

Re: .2

> The Challenges with a double chain ring in the front...

There are good answers to all these problems.  Some of the answers get a 
little tougher with a triple.

> . Low enough gears for hill climbs and early season training
> . High enough gears for high speed (20mph) touring

A wide range can be achieved with 12 or 14 speeds.  See below, where I 
lay out a 12-speed Alpine (1-1/2 step) progression that gives 40-110
gearing.  You can drop the entire range if you like - the top of this one
is rather stiff for 20-mph touring, since it'll crank out 29.5 mph at 90
rpm - but it demonstrates the point. 

Range is, if course, even easier to obtain with a triple.

> . With only 10-12 speeds, getting gear combinations with no gaps
>   and no overlaps.

See below.  No overlaps, 12 usable gears.  My 10-speed is geared half-
step, with 10 usable gears.

Getting full utility of all your gears is *far* more difficult with a
triple.  I've never bothered to do it.  The whole raison d'�tre of 
triples is to give wide range without having to be able to hit all the 
combinations.

> . Getting a shift pattern that you like. 

That's a matter of personal preference, obviously.  I'm tremendously 
pleased with the half step I use, and I could be happy with an Alpine 
if I wanted the wider range.

Any real progression making full use of a triple is by definition a
bitch when you have to shift two rings at one jump.  I suggest that a 
well-designed double with a granny is the best alternative.  Use the 
granny for the two big cogs, and align everything else as for a double.


Here is a 12-speed Alpine progression with 12 usable gears.  The two 
extreme gear combinations (big/big and small/small) are tough, but they 
*are* usable unless you have really short chainstays, which is lousy 
practice for a touring bike anyway.

				Chainrings
		  Cogs	|	42	53
		--------+-------------------
		   13	|      87.2   110.1
		   15	|      75.6    95.4
		   17	|      66.7    84.2
		   20	|      56.7    71.5
		   24	|      47.2    59.6
		   28	|      40.5    51.1

This graphs out as in the next screen.



   40        50        60        70        80        90        100       110

53  |         |X        X         | X       |   X     |    X    |         X
    +---------+---------+---------+---------+---------+---------+---------+
42  X      X  |      X  |      X  |     X   |      X  |         |         |

It's not *ideal* - but it works as advertised.  Total chain wrap-up is 
only 26 teeth, which is no problem for any number of sport or touring
derailleurs. 

I developed both this progression and the half step I have on my
10-speed using a mathematical system I worked out about ten years ago. 

- Dick

    Elaine,
    
    It's hard to say why the couple on the tandem went by you easily,
    but one factor may be that it is a more efficient machine (two people's
    pedal power - one person's drag).  I had one pass me on a 1/2 century
    this past September, and I never saw them again after the first
    checkpoint.  I was going at what I considered a good pace - I finished
    the ride in ~3:45.
    
    As for the chain rings.  I have a triple (26,36,46) on my (mountain)
    bike.  I don't use the lowest gears unless I happen across a killer
    hill.  They really are helpful then, because it allows me to keep
    my cadence up (I prefer 85-95).  My chain rings are not bio-pace,
    maybe it's because my bike is 3 years old, and they weren't standard
    then.  I have been considering changing over to a bio-pace set this
    winter (and maybe increasing the range a touch too), but I'm hesitant
    because I'd hate to spend the money and not notice any difference.
    
    Rich

    Re .9:
    
    An interesting reply, but I must argue with it (must I? I must!).
    
    I would agree that a 42-53 front and 13-28 rear is an Alpine set-up -
    but only for a racing bike. It's too highly-geared for touring. Touring
    needs significantly lower gears, not surprising given a heavier bike,
    loaded panniers and wider tyres. 
    
    What I have on my own bike at present is 36-48 front and 13-30 rear.
    This gives gearing from 33 to 99, in contrast to your 40 - 110. Even as
    it is, I use the 33 inch gear (36 front, 30 rear) more than the 99 inch
    gear (48 front, 13 rear), so I could easily use a lower gear still.
    
    I'm reluctant to go to a bigger cog at the back, since gear-changing
    becomes more difficult and the weight increases. Besides, people
    might sneer at me! So I think a triple with a small inner ring would
    be the way to go, as I've indicated in .3 or thereabouts.
    
    Rod 

Maybe there is confussion on the term "alpine gearing".  As I understand it it
means that to go from lowest to highest gears you must switch chain rings, it
does not mean that it is designed to climb the alps.  Someone suggested to me
that the term may have come from alpine skiing where you switch back and forth
between gates.  But than again that may be all BS.



       small   large
       -----   -----
        x

        x
                 x           Any gearing that maps out to something like this
        x                    would be alpine gearing.
                 x
        x
                 x
        x
                 x
        
                 x

    I don't know what Alpine means,but I feel as Rod does in .11, that
    the gearing ratio suggested could be too high for touring, certainly
    loaded touring. I rode for a couple of years using gearing very
    close to the aforementioned "alpine" set_up listed (I had a 52 on
    the front). I could have done with lower gearing on a number of
    occasions when touring loaded, and I invariably didn't use the higher
    gears at all.  I get the feeling that gearing is sometimes influenced
    by what is "macho" rather than what is appropriate.
    
    I also feel that a double in front can almost always be set up to
    suit a touring bike, particularly if the very high gears (95in +)
    are foresaken.
            
    John (who would love to be macho but keeps getting passed out by
    kids !)                                                        

	Rod is probably right - my gearing for touring (light
	camping and B+B) has been 46/52 and 13-26 or 13-28,
	but it's a racing frame.  It gets pretty tough going
	above 13%.  The 20% and 25% grades in parts of Cornwall
	and Scotland are what convinced me maybe a change would
	be in order for the future.  But for the Alps and the
	Rockies, you can get by with the 26 pretty much.
	
	-john

Re: .9, .11

Rod (.11), please remember what I said in .9, which was agreed with by 
the writer of .13:

> You can drop the entire range if you like - the top of this [40-110 
> progression] is rather stiff for 20-mph touring, since it'll crank out
> 29.5 mph at 90 rpm - but it demonstrates the point. 

Just to prove the point (here he goes again, folks), I'll lay out a nice
low 12-speed Alpine.  I'll take your 30-inch bottom as a start. 


				Chainrings
		  Cogs	|	36	48
		--------+-------------------
		   13	|      74.8    99.7
		   16	|      60.8    81.0
		   19	|      51.2    68.2
		   23	|      42.3    56.3
		   27	|      36.0    48.0
		   32	|      30.4    40.5

This progression gives a top speed of 26.7 mph at 90 rpm, and it graphs
out as in the next screen.  It has a 41-tooth wrap-up and so requires a
good touring derailleur.


   30        40        50        60        70        80        90        100

48  |         |X      X |     X   |       X |         |X        |         X
    +---------+---------+---------+---------+---------+---------+---------+
36  X     X   |  X      |X        |X        |    X    |         |         |

Now then.  If it's low gears you're after but you don't want to use a 
big freewheel for fear of being thought a wimp (was it .12 who said
that?), try the higher 40-110 progression I laid out in .9, and add a
26-tooth granny chainring.  That will give you two stump-pulling gears
of 25.1 and 29.2, without the pain of aligning and using an ordinary
triple. 

- Dick

Re: .9, .15

>It has a 41-tooth wrap-up and so requires a good touring derailleur.

Dick, I don't think you need a touring derailleur per se.  This is
exactly why I am trying to set up my dream machine with the
Campy Chorus rear derailleur (See my note 917 "Colnago/Athena Group")

I'm looking for a double chainring machine that will take me up most
of the New Hampshire and Mass. hills that Ed Fisher usually throws
into his long rides and still be comfortable (marginally) at the
end of the tour.  With my size (I'm not looking forward to Turkey Day)
and ability, I think your ratios with the Chorus derailleur is the way
to go.  Now if I could just get up the bucks.  

       						Jerry

>
>				Chainrings
>		  Cogs	|	36	48
>		--------+-------------------
>		   13	|      74.8    99.7
>		   16	|      60.8    81.0
>		   19	|      51.2    68.2
>		   23	|      42.3    56.3
>		   27	|      36.0    48.0
>		   32	|      30.4    40.5
>
>This progression gives a top speed of 26.7 mph at 90 rpm, and it graphs
>out as in the next screen.  It has a 41-tooth wrap-up and so requires a
>good touring derailleur.


Could you define wrap up? How was the 41 arrived at? If you take largest
combination - smallest I get 31.

Also what is the formula for calculating the distance of each combination?

JC

Re: .17, .16

JC (.17):

>				Chainrings
>		  Cogs	|	36	48
>		--------+-------------------
>		   13	|      74.8    99.7
>		   16	|      60.8    81.0
>		   19	|      51.2    68.2
>		   23	|      42.3    56.3
>		   27	|      36.0    48.0
>		   32	|      30.4    40.5

Oops.  It is indeed only 31 teeth of wrap-up.  The definition of wrap-up 
is the amount of chain the derailleur has to be able to put somewhere.  
It is, as you surmised, the difference between big/big and small/small.  
When you're on the big/big combination, yuou have to have enough chain - 
when you go to the small/small, you need a lot less, and the derailleur 
has to be able to take up the slack.

> Also what is the formula for calculating the distance of each
> combination? 

"distance of each combination"?  I don't understand the question.  If 
you mean what is the math I use to generate progressions, I can explain 
it.  I worked it out about 10 years ago.  If anyone expresses interest,
I'll post a note on it.

-----------

Jerry (.16):

You're missing the point a little in re: touring.  The Chorus, with its 
ability to handle a 32-tooth cog in the "B" position, is actually sort 
of a touring derailleur.  Its cage is a little too short for real 
monster ranges, but my 30-100 Alpine will probably give it no trouble.

- Dick

    Re .15:
    
    Yes, I see that you did say it might be worthwhile lowering the entire
    range. Also, I misunderstood your use of the term "Alpine". Was it you
    who defined it as any gearing setup where you must change chainring to
    go from highest to lowest? I find that a little confusing, since I
    can't think of any multiple-chainring setup where that WOULDN'T happen.
    
    As to chain-wrap, as I said, you can get away with a derailleur
    offering less than the amount strictly required, if you never use
    large-large or small-small gears. That's desirable anyway, since using
    those gears maximises chain wear and duplicates other more sensible
    gear combinations.  
    
    
    Rod 

Regarding -.2

What I meant by distance of each combination:

I was under the impression that the numbers in the lower left hand side 
of the tables you generated were the distance the bike would travel (in 
inches) for one revolution of the pedals. I have heard of this 
convention being used before. Is this what those numbers represent? I 
was just curious how one comes up with the numbers.... I can imagine it 
has to do with the gearing ratio related to the circumference of the 
bike wheels.

JC

>I was under the impression that the numbers in the lower left hand side 
>of the tables you generated were the distance the bike would travel (in 

Make that lower right side of the table...

JC

    The distance on the lower right hand side of the table -- the "gear
    inches" number that folks talk about -- is the diameter of the virtual
    or imaginary wheel that you would have if you had pedals connected
    directly to an Ordinary or Penny Farthing or ... -- one of those
    old high wheelers which only had one gear.
    
    The distance that the bicycle will travel forward with one revolution
    of the pedals, assuming no coasting, of course, is the number of
    gear inches times pi (3.14159265... or 3.14 for short).
    
    Gear inches is (front #teeth/rear #teeth) * rear wheel diameter
    Rear wheel diameter is generally assumed to be 27 though it changes
    by a few percentages with either 700C tires, tubulars and bigger
    tires except when it's significantly different as in ...
    
    Oh, enough of this baloney.
    
    As for earlier items in this topic.  Tandems can and do blow by
    folks on uphills if the pair is an experienced and aggressive pair
    of riders who can individually blast up hills.  The reason most
    tandems do not blow up hills is that tandem pairs generally cannot
    do better on a hill than would the lesser of the two riders.  For
    those of you who have seen the TTRA tape, this explains why Haldeman
    and Penseyres did well on hills.
    
    ed, who does admit to having a bike or two with 20 inch lows.

I've started a new note, number 920, to discuss generic gearing 
questions and thoughts.

- Dick

    
    	So it sounds like the gears don't actually go in order according
    	to front ring size?
    
    	I'd have to go through and calculate total "chain length" based on
    	front and rear teeth?
    
    	Not that it's a big deal, mind you ... I think I can do it.
    
    	8^)
    

    
    	Can someone explain the physics behind the sizes of the front
    	and rear rings, and why front/large and rear/small are hardest
    	to pedal, but front/small and rear/large are easiest to pedal?
    
    	Sounds backwards to me.
    

RE: <<< Note 915.25 by BUSY::SLABOUNTY "Holy rusted metal, Batman!" >>>

Concerning the rear cogs, I think of it this way. The amount of chain required
to make the rear wheel complete one revolution is equal to the cog's
circumference. With a large cog, that's a large amount of chain. So when
pedaling -- pulling the chain around -- the mechanical work of revolving the
wheel one time is spread out, making it easier. With a small cog, there is a
small amount of chain required to complete one wheel revolution, and so the
mechanical work is concentrated. In both cases, the forward travel of the bike
is one wheel-circumference's worth. In the large-cog case, to accomplish this
you get to pedal more to cover this distance. In the small-cog case, to
accomplish this you only pedal a little to cover the same distance.

The net amount of work (defined in the physics sense of force times distance)
is the same in both cases: large-cog is small force times big distance,
small-cog is big force times small distance. Just a case of mechanical
advantage, like block and tackles. 
						-- Tom

    
    	Ummm, I knew that ... my question was "Why does it appear that
    	the front/rear rings are exactly opposite in terms of size and
    	work"?
    
    	Front and small = rear and large = easy
    	Front and large = rear and small = hard
    
    	Wouldn't it stand to reason that the big gears on the front and
    	rear would be the lowest gear, and that the small gears on the
    	front and rear would be the highest gear?
    

         Here goes nothing!  In short, think of it as how many times you
    spin the crank for one rotation of the wheel.  If you had the same size
    sprocket on the crank and the wheel, one crank rotation would produce
    one wheel rotation.  If you double the size of the crank sprocket,
    leaving the wheel sprocket alone (2 x number of teeth), one crank
    rotation would produce two wheel rotations.  At this point, intuition
    alone might satisfy you that to turn the wheel twice is more work,
    moving the bike farther, and therefore more difficult.
    
         If you are having any trouble with this remember that the chain
    makes sure that one tooth = one tooth, front to rear.  If the crank
    sprocket has 50 teeth and the wheel sprocket has 25 teeth, one crank
    rotation will move the chain fifty links.  Fifty links on the rear
    sprocket will require two wheel rotations.  
    
         Similarly, if the wheel sprocket is twice the size of the crank
    sprocket, one crank rotation produces half a wheel rotation.  This is
    less work, moving the bike less.  If you want the physics behind this,
    you need to think of the concept of work; the application of a load
    over some distance for a period of time.
    
         There is a balance (ignoring friction losses) between the work 
    done by your feet on the pedals and the tire on the road.  To move
    the bike forward a unit D, using a wheel of radius R, requires some
    amount of energy.  With no gear reduction, the same energy must be
    applied to the pedals.
    
         If you use gear reduction such that one rotation of the pedal
    rotates the wheel less than one full revolution, the bike is not moved
    as far.  Less energy is required and the load on the pedals can be
    less.
    
         In real life, we try to do the opposite.  We try to keep the
    energy input constant against a varying load.  When the bike is on
    level ground, all the energy is used to overcome friction and wind
    resistance.  As we go up hill, the additional load of lifting us up
    against gravity requires more energy to move that distance D.  We
    sacrifice speed by using gear reduction to move less distance per pedal
    revolution, but we can keep the energy input to the pedals constant.
    When we go downhill, gravity does some of the work for us so we can 
    use gear multiplication to gain additional speed. 
    
         I hope this makes sense.  If not.... never mind.
    
    Tom

    re. .27
    
    High and low refer to numerical gear ratio which is drive to driven.
    Large front and small rear is a higher number, ie. 52/13 = 4/1 than
    small front and large rear, ie. 28/32 = .875/1.
    
    A high ratio gives speed.  A low ratio gives power.  

RE: <<< Note 915.27 by BUSY::SLABOUNTY "Holy rusted metal, Batman!" >>>

>    	Ummm, I knew that ... my question was "Why does it appear that
>    	the front/rear rings are exactly opposite in terms of size and
>    	work"?

I can't describe how your intuition process works, Steve, sorry! :-)

Attacking this from a colloquial, non-physics view:

     o	A big chainring in front means you're pulling a lot of chain per pedal
	revolution, which is hard work. A small chainring pulls less chain per
	pedal revolution, which is easier.

     o	At the same time, a big cog in the rear allows a lot of chain to be
	"absorbed" by a small amount of wheel rotation, while a small cog
	forces a small amount of chain to be "used up" by a large amount of
	wheel rotation.

Combine these two (big chainring pulls lots of chain, small cog uses up lots of
wheel rotation) and you've got reality.
						-- Tom