Physiology of Fixed

[Carl Fogel]

John Dacey <[email protected]> wrote in message news:<[email protected]>...
> "Ille sinistrorsum hic dexrorsum abit, unus utrique error, sed variis illudit partibus." - Horace
> On 12 Dec 2003 10:34:40 -0800, [email protected] (Carl Fogel) wrote:
>
> >John Dacey <[email protected]> wrote:
> >> Sugino is the only manufacturer I've seen to have the moxie to put numbers on the accuracy of
> >> some of their chainrings.
> >>
> >> Documentation that accompanies selected models of their track chainrings contain graphs that
> >> show that to meet the J.I.S. standard, there can be no more than .5 mm runout. They're happy to
> >> go on to point out that the chainring models they designate as the "S3" series have less than
> >> one tenth that amount (no more than .05 mm runout).
>
> >Dear John,
> >
> >Do you have a web address for this? Apart from the numbers, anyone who measures this sort of
> >thing might have all sorts of fascinating stuff about how they make the chainrings and what it
> >all means.
>
> Sugino has a modest web presence, but you won't find this kind of detail listed there. If you're
> determined to look for yourself, the URL is http://www2.odn.ne.jp/suginoltd/. As I mentioned, the
> measurements to which I referred are found on a written sheet included with some of Sugino's premium-
> grade track 'rings. The .5 mm spec refers to _any_ chainring (road, mtn, track) that would aspire
> to meet the JIS standard. Since even Sugino's least expensive track 'rings are quite good, I'd
> expect them to consistently better the .5 mm criterion, but meeting the .05 mm accuracy standard
> is only promised for their more elite S3 models.
>
> To put this in perspective, there is one model of Sugino track chainring (called "Gigas") which
> costs in excess of $300.00 per chainring. Gigas 'rings are ostensibly made to allow G1
> professional keirin racers (who are in a position to afford such things) to minimize the kind of
> chain tension inconsistencies we've been discussing. Other models within their S3 series are
> somewhat more modestly priced (but still not for the faint of heart) from about $100.00.
>
> <snip>
>
> >Whatever Sugino means by runout, that 0.05mm S3 sprocket sounds impressively accurate. But I have
> >to wonder how many laps lasts under a gritty chain. It seems to convert to 0.0019 inches. But
> >perhaps track bikes running indoors on wooden floors escape the polishing effect of outdoor dust?
>
> By comparison to road bikes, most track chainrings, sprockets and chains lead lives that are far
> more sheltered from environmental wear. Only a very small fraction of the worlds' velodromes are
> indoor venues however, and professional keirin racing happens rain or shine.
>
> -------------------------------
> John Dacey

Dear John,

This is what I love about splashing around in rec.bicycles.tech--I'd never heard of keirin and had
no idea that there's a whole world of gambling on weird Japanese bicycle racing, complete with their
own standards for competition equipment.

A quick google of rec.bicycles.tech shows only about 70 mentions of keirin in the last ten years or
so, most of them in passing.

It's interesting that Andrew Muzi measured only about 0.3mm of apparent chain-tooth cog-hop on what
looks like a well-used fixed-gear bike.

Maybe Andrew just got an awfully nice chain ring, as good as an entry-level Japanese 0.5mm tolerance
racing ring?

Or maybe the entry-level Japanese 0.5mm chain rings are, well, overpriced in our eyes? That is, a
$100 price here might be more for the cachet of exotic Japanese racing certification? (Do any other
bicycle racing groups certify chain rings?)

Or maybe cog-hop isn't the same as runout? That is, 0.3mm of rise and fall of gear-teeth might
translate to a much larger lengthwise variation that may be called runout? (David Johnson argues for
such a difference elsewhere in this thread, although I don't think that he or I fussed about what to
call the different dimensions.)

Anyway, thanks for telling me about yet another weird and interesting side of bicycling. I had a
look at the site and see what you mean--it's mostly in Japanese.

Thanks again,

Carl Fogel

 

[Carl Fogel]

"David L. Johnson" <[email protected]> wrote in message news:<[email protected]>...
> On Fri, 12 Dec 2003 10:15:15 +0000, Carl Fogel wrote:
>
> > But this assumption seems to be mistaken.
>
> ??
> >
> > The amount that the tips of the gear teeth (or the crucial curve just below them) varies from an
> > ideal circle is what's being measured.
> >
> > This variation partly reflects any distortion in the sprocket's circularity, but also any
> > distortion in:
> >
> > a) how the sprocket is centered on the pedal arm
>
> I did cover that.
>
> b) how the pedal is
> > centered on the spline
>
> irrelevant
>
> c) how the straight the spline is
>
> Also not releveant.
>
> > d) how circular the cone face of the spline is e) how accurately machined the balls are
>
> Noise
>
> f) how smoothly machined the cups are g) how parallel the
> > two cups are to each other
>
> All these are minor compared with out of roundness of the sprockets, and the sprocket not being
> coaxial with the axle itself.
>
> > If the tips of your sprocket are hopping 0.5mm as you turn it, I suspect that a significant
> > amount of the the hop is not the sprocket, but everything from its attachment point on down to
> > the frame.
>
> Why would you assume that?
> >
> > That is, your sprocket removed from the bike and measured just by itself seems unlikely to show
> > 0.5mm of variation. So while I expect that your calculations make sense, I don't think that they
> > actually apply here.
>
> Even if it is the hub, or the spider, the result is the same, isn't it?
>
> >
> > I think that you're working on how a lumpy sprocket mounted on a perfect shaft
>
> The shaft defines the axis of revolution. Everything else is relative to that.
>
> > I'm assuming that a much less lumpy sprocket that's mounted a little off center on a somewhat
> > eccentric. If that's the case, then X amount of hop may be a better rough-and-ready measurement.
>
> Forgive me, but that is precisely what we measured. Just what you wanted measured, if I recall
> correctly. I suggest that the vast majority of this is in the assymetry or lack of concentricness
> of the sprockets, front or rear. Anything else is for one, better machined, and for another, less
> likely to be off while still being servicable.

Dear David,

Would b) and c) have been relevant if I'd typed "how the pedal arm is centered on the spline"
instead of carelessly omitting "arm"?

(I did remember it in a), but whoops on
b) and c). I'm terrified that if I ever type "crank *rm, I'll be torn to pieces here, so I use the
awkward "pedal arm.")

Do you have any tolerance figures for the various parts and points of connection between the frame
and the front chain-ring?

That is, grade 25 balls are 0.000025 inch tolerance. A perfectly straight spindle (I expect that
they're dreadfully straight, but have no figures) with perfectly tolerant cone surfaces (as good as
the balls?) therefore has its ends potentially encircled by two rings of balls with their variation,
plus some film of grease.

How much does the end of the perfectly straight spindle wobble? Like you, I expect that it's damned
little, but I'd love to have some kind of number.

After all, John Dacey has revealed that Sugino sells what seem like outlandishly true sprockets for
Japanese keirin racers that have 0.05mm (.002 inches) of runout, a term that I'm hoping someone will
reconcile with my crude use of "cog-hop."

How perfectly does a pedal-arm/spider assembly fit onto the bottom-bracket spline? I can't see any
easy way to measure this, but it seems like another source of possible variation.

Maybe I'm misunderstanding the obvious, but aren't we talking about something that can be seen as a
series of concentric rings, like a rifle target? If each ring is imperfectly centered on the
previous ring, doesn't each tiny original variation build up and magnify?

They don't actually increase in size because they're mechanically complicated, but the frame
connects to the two cups, the two cups connect to a film of grease, the film of grease connects
to the ring of balls, the balls connect to the film of grease again, the film of grease connects
to the cone surfaces, the cone surfaces project a square or splined pole (whose straightness must
vary slightly) out to where the pedal-arm squeezes onto it possibly a bit off-center, the pedal
arm/spider has possibly off-center mounting points for the sprocket, and the sprocket itself
ain't perfect, but it's sitting out on the very end of all these potentially slightly out-of-
round linkages.

You're saying that only the sprocket and perhaps its mounting points matter. I kinda-sorta think
that this may be true, but I want some numbers to support it.

My nephews don't always buy it when I dismiss things as "noise" or "irrelevant" or wave my hands--
they ask why and how much, the disrespectful little--

Er, I mean the adorably inquisitive little children.

I realize that these things aren't easily looked up because they're individually probably minute and
because in the end this is a theoretical fuss, so I appreciate your efforts to clear things up. But
like Jobst, who's saying elsewhere that it's obvious with a little deductive logic that the
existence of two headset bearing assemblies means that they can't dimple through impact, you're
saying no and leaving me just as ignorant as before. These things may be obvious to you and Jobst,
but ya gotta spell 'em out for slack-jawed yokels like me.

How much better machined?

Thanks again,

Carl Fogel

 

[David L. Johnso]

On Sat, 13 Dec 2003 11:32:21 +0000, Carl Fogel wrote:

> Would b) and c) have been relevant if I'd typed "how the pedal arm is centered on the spline"
> instead of carelessly omitting "arm"?

Well, maybe, but the only relevant part is whether the spider arms are concentric with the axle.

> Do you have any tolerance figures for the various parts and points of connection between the frame
> and the front chain-ring?

No, but since all but the spider, chainring attrachment, and chainring shape/centeredness are in the
noise, anyway, being dominated by these.

> Maybe I'm misunderstanding the obvious, but aren't we talking about something that can be seen as
> a series of concentric rings, like a rifle target? If each ring is imperfectly centered on the
> previous ring, doesn't each tiny original variation build up and magnify?

Yeah, but if one dominates, as I claim it does, the rest might as well be perfect.

--

David L. Johnson

__o | I don't believe you, you've got the whole damn thing all wrong. _`\(,_ | He's not the kind
you have to wind-up on Sundays. --Ian (_)/ (_) | Anderson

 

[A Muzi]

>>>John Dacey <[email protected]> wrote:
>>>>Sugino-snip-to meet the J.I.S. standard, there can be no more than .5 mm runout. They're happy
>>>>to go on to point out that the chainring models they designate as the "S3" series have less than
>>>>one tenth that amount (no more than .05 mm runout).

(cf)>>>Do you have a web address for this?-snip-

> John Dacey <[email protected]> wrote in message
> news:<[email protected]>...
>>Sugino has a modest web presence, but you won't find this kind of detail listed there. If you're
>>determined to look for yourself, the URL is http://www2.odn.ne.jp/suginoltd/. -snip-

Carl Fogel wrote:> snip-I'd never heard of
> keirin -snip- Maybe Andrew just got an awfully nice chain ring, as good as an entry-level Japanese
> 0.5mm tolerance racing ring?
-snip-I had a look at the site -snip-it's mostly in Japanese.

I measured the outside edge not the critical root. That ring is a not cheap, it's a TA piste
chainring. Measure your own if you want another data point. I said before and I still think you will
find all modern rings under 1mm at the outside of the teeth.

Japanese indeed. It's a Japanese government agency, after all!

The official foreign visitors' Keirin guidebook is (completely - I have one) in French.

--
Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971

 

[John Dacey]

"Nihil est incertius volgo." - Cicero
On 13 Dec 2003 10:20:45 -0800, [email protected] (Carl Fogel)
wrote:

>John Dacey <[email protected]> wrote in message
>news:<[email protected]>...
<snip>
>> Only a very small fraction of the worlds' velodromes are indoor venues however, and professional
>> keirin racing happens rain or shine.

>This is what I love about splashing around in rec.bicycles.tech--I'd never heard of keirin and had
>no idea that there's a whole world of gambling on weird Japanese bicycle racing, complete with
>their own standards for competition equipment.
<snip>

Now that you know, Player, I encourage you to be a responsible bettor.

As for standards, the governing body closely controls the design and materials that may be used in
bikes for the pro keirin circuit and virtually every component fitted must bear a distinguishing
mark denoting its certification. It is commonly believed in the west that these strictures exist to
ensure even competition.

That's true in part, but there's enough money in keirin to put every elite racer on a bike as high-
tech as any olympian's if that's what they wanted. Aside from level racing however, it's every bit
as important to the organizers that the betting public maintains unalloyed confidence that the
results of each race aren't influenced by equipment failures. As a result, the componentry designed
to seek keirin certification generally places a very high premium on reliability.

-------------------------------
John Dacey Business Cycles, Miami, Florida http://www.businesscycles.com Now in our twenty-first
year. Our catalog of track equipment: eighth year online
-------------------------------

 

[Carl Fogel]

A Muzi <[email protected]> wrote in message news:<[email protected]>...

[snip]

> Carl Fogel wrote:> snip-I'd never heard of
> > keirin -snip- Maybe Andrew just got an awfully nice chain ring, as good as an entry-level
> > Japanese 0.5mm tolerance racing ring?
> -snip-I had a look at the site -snip-it's mostly in Japanese.
>
> I measured the outside edge not the critical root. That ring is a not cheap, it's a TA piste
> chainring. Measure your own if you want another data point. I said before and I still think you
> will find all modern rings under 1mm at the outside of the teeth.
>
> Japanese indeed. It's a Japanese government agency, after all!
>
> The official foreign visitors' Keirin guidebook is (completely - I have one) in French.

Dear Andrew,

I've been hoping that someone would ask!

Having no fixed-gear, I peeked at the movement of the outermost jockey-wheel of my derailleur as I
slowly cranked the pedals backward in 53 x 11, 108 rollers.

The derailleur arm hardly moved, suggesting that chain tension wasn't varying much.

"Hardly moved" isn't much of a measurement, so I wound a long wire-and-plastic bag-tie around some
rear spokes and bent it until its end sat just in front of the end of the thin metal derailleur
frame, where its bent sideway behind the furthest jockey wheel.

The whole derailleur arm at the level of the far pulley trembles back and forth less than half the
width of the metal piece. My dial calipers measure the width at 0.090 inches. (Why did Shimano use
this odd thickness instead of 0.010 inches?)

So my best measurement after repeated pedal cycles in hopes of find a tight spot when the worst of
the rear cog coincides with the worst of the front sprocket is that my chain varies about 0.045
inches--1.143mm.

Elsewhere in this thread, Dave Johnson (I think) has suggested that X amount of diameter cog-hop (or
root-hop, if you measure that) provides >X circumference chain-length variation, so my cog-hop
probably is probably <1.143mm.

A twentieth of an inch of lengthwise chain-play still seems awfully small, particularly for an
inexpensive set of sprockets and chain with over 5,000 miles.

And the chain has to wrap around two plastic jockey-wheels at sharp angles, too.

Carl Fogel

 

[Tom Nakashima]

So even if you have this perfect concentric chainring, what if the bolt circle pattern diameter of
the crankarms are not concentric with the center of the taper or center of the crankarm mounting
diameter? -tom

"Carl Fogel" <[email protected]> wrote in message
news:[email protected]...
> A Muzi <[email protected]> wrote in message
news:<[email protected]>...
>
> [snip]
>
> > Carl Fogel wrote:> snip-I'd never heard of
> > > keirin -snip- Maybe Andrew just got an awfully nice chain ring, as good as an entry-level
> > > Japanese 0.5mm tolerance racing ring?
> > -snip-I had a look at the site -snip-it's mostly in Japanese.
> >
> > I measured the outside edge not the critical root. That ring is a not cheap, it's a TA piste
> > chainring. Measure your own if you want another data point. I said before and I still think you
> > will find all modern rings under 1mm at the outside of the teeth.

 

[Scott Hendricks]

[email protected] (Carl Fogel) wrote in message news:<[email protected]>...
> A Muzi <[email protected]> wrote in message news:<[email protected]>...
>
> [snip]
>
> > Carl Fogel wrote:> snip-I'd never heard of
> > > keirin -snip- Maybe Andrew just got an awfully nice chain ring, as good as an entry-level
> > > Japanese 0.5mm tolerance racing ring?
> > -snip-I had a look at the site -snip-it's mostly in Japanese.
> >
> > I measured the outside edge not the critical root. That ring is a not cheap, it's a TA piste
> > chainring. Measure your own if you want another data point. I said before and I still think you
> > will find all modern rings under 1mm at the outside of the teeth.
> >
> > Japanese indeed. It's a Japanese government agency, after all!
> >
> > The official foreign visitors' Keirin guidebook is (completely - I have one) in French.
>
> Dear Andrew,
>
> I've been hoping that someone would ask!
>
> Having no fixed-gear, I peeked at the movement of the outermost jockey-wheel of my derailleur as I
> slowly cranked the pedals backward in 53 x 11, 108 rollers.
>
> The derailleur arm hardly moved, suggesting that chain tension wasn't varying much.
>
> "Hardly moved" isn't much of a measurement, so I wound a long wire-and-plastic bag-tie around some
> rear spokes and bent it until its end sat just in front of the end of the thin metal derailleur
> frame, where its bent sideway behind the furthest jockey wheel.
>
> The whole derailleur arm at the level of the far pulley trembles back and forth less than half the
> width of the metal piece. My dial calipers measure the width at 0.090 inches. (Why did Shimano use
> this odd thickness instead of 0.010 inches?)
>
> So my best measurement after repeated pedal cycles in hopes of find a tight spot when the worst of
> the rear cog coincides with the worst of the front sprocket is that my chain varies about 0.045
> inches--1.143mm.
>
> Elsewhere in this thread, Dave Johnson (I think) has suggested that X amount of diameter cog-hop
> (or root-hop, if you measure that) provides >X circumference chain-length variation, so my cog-hop
> probably is probably <1.143mm.
>
> A twentieth of an inch of lengthwise chain-play still seems awfully small, particularly for an
> inexpensive set of sprockets and chain with over 5,000 miles.
>
> And the chain has to wrap around two plastic jockey-wheels at sharp angles, too.
>
> Carl Fogel

Let me make sure I got this right, you don't own a fixed-gear bike and have up until recently not
even heard of keirin racing, BUT you've been questioning the validity/veracity of statements by many
folks who have incredible experience/expertise with/on fixed-gear bikes, all because no one would
give you specific measurements of the clearly observed phenomenon???

 

[Dvt]

Carl Fogel wrote:
> I'm sorry, but I don't see what's important about the lower slack chain run bouncing in terms of
> chain tension--don't all slack lower chain runs do this?
>
> That is, despite the modest springs of a derailleur, doesn't its comparatively slack lower chain
> run also bounce more than its heavily loaded and taut top run?

I'm simply illustrating that a seemingly small amount of error in cogs and chainwheels translates
into a noticeable bounce in the chain. I think this is a leading cause of the disconnect between
fixie riders and skeptics like you. The chain bounces up and down 0.5" (0.25" one way) and makes the
fixie rider think there is a lot of play in the system. As we've estimated in this thread, a very
small amount of play will lead to that sort of bounce.

Dave dvt at psu dot edu

 

[Dvt]

Carl Fogel wrote:
> (I did remember it in a), but whoops on
> b) and c). I'm terrified that if I ever type "crank *rm, I'll be torn to pieces here, so I use the
> awkward "pedal arm.")

To heck with that. Crankarm. Hallway. Roadway. Frameset. As an English professor knows, the language
is constantly evolving based on common usage. If you don't like it, speak another language. Of
course, that language will also change with time as well, so the naysayers will continue to naysay.
Time rolls on and on....

Dave dvt at psu dot edu

 

[Carl Fogel]

dvt <[email protected]> wrote in message news:<[email protected]>...
> Carl Fogel wrote:
> > (I did remember it in a), but whoops on
> > b) and c). I'm terrified that if I ever type "crank *rm, I'll be torn to pieces here, so I use
> > the awkward "pedal arm.")
>
> To heck with that. Crankarm. Hallway. Roadway. Frameset. As an English professor knows, the
> language is constantly evolving based on common usage. If you don't like it, speak another
> language. Of course, that language will also change with time as well, so the naysayers will
> continue to naysay. Time rolls on and on....
>
> Dave dvt at psu dot edu

Dear Dave,

Ay, madam, it is common.

[email protected]

 

[Carl Fogel]

John Dacey <[email protected]> wrote in message news:<[email protected]>...
> "Nihil est incertius volgo." - Cicero On 13 Dec 2003 10:20:45 -0800, [email protected] (Carl
> Fogel) wrote:
>
> >John Dacey <[email protected]> wrote in message
> >news:<[email protected]>...
> <snip>
> >> Only a very small fraction of the worlds' velodromes are indoor venues however, and
> >> professional keirin racing happens rain or shine.
>
> >This is what I love about splashing around in rec.bicycles.tech--I'd never heard of keirin and
> >had no idea that there's a whole world of gambling on weird Japanese bicycle racing, complete
> >with their own standards for competition equipment.
> <snip>
>
> Now that you know, Player, I encourage you to be a responsible bettor.
>

[snip]

> John Dacey

Dear John,

Alea iacta est.

Nathan Detroit

 

[David Reuteler]

Carl Fogel <[email protected]> wrote:
: Alea iacta est.

you & marge simpson both. but she never quoted caesar.
--
david reuteler [email protected]

 

[Scott Hendricks]

[email protected] (Carl Fogel) wrote in message news:<[email protected]>...
> [email protected] (Scott Hendricks) wrote in message
> news:<[email protected]>...
> > [email protected] (Carl Fogel) wrote in message
> > news:<[email protected]>...
> > > A Muzi <[email protected]> wrote in message news:<[email protected]>...
> > >
> > > [snip]
> > >
> > > > Carl Fogel wrote:> snip-I'd never heard of
> > > > > keirin -snip- Maybe Andrew just got an awfully nice chain ring, as good as an entry-level
> > > > > Japanese 0.5mm tolerance racing ring?
> > > > -snip-I had a look at the site -snip-it's mostly in Japanese.
> > > >
> > > > I measured the outside edge not the critical root. That ring is a not cheap, it's a TA piste
> > > > chainring. Measure your own if you want another data point. I said before and I still think
> > > > you will find all modern rings under 1mm at the outside of the teeth.
> > > >
> > > > Japanese indeed. It's a Japanese government agency, after all!
> > > >
> > > > The official foreign visitors' Keirin guidebook is (completely - I have one) in French.
> > >
> > > Dear Andrew,
> > >
> > > I've been hoping that someone would ask!
> > >
> > > Having no fixed-gear, I peeked at the movement of the outermost jockey-wheel of my derailleur
> > > as I slowly cranked the pedals backward in 53 x 11, 108 rollers.
> > >
> > > The derailleur arm hardly moved, suggesting that chain tension wasn't varying much.
> > >
> > > "Hardly moved" isn't much of a measurement, so I wound a long wire-and-plastic bag-tie around
> > > some rear spokes and bent it until its end sat just in front of the end of the thin metal
> > > derailleur frame, where its bent sideway behind the furthest jockey wheel.
> > >
> > > The whole derailleur arm at the level of the far pulley trembles back and forth less than half
> > > the width of the metal piece. My dial calipers measure the width at 0.090 inches. (Why did
> > > Shimano use this odd thickness instead of 0.010 inches?)
> > >
> > > So my best measurement after repeated pedal cycles in hopes of find a tight spot when the
> > > worst of the rear cog coincides with the worst of the front sprocket is that my chain varies
> > > about 0.045 inches--1.143mm.
> > >
> > > Elsewhere in this thread, Dave Johnson (I think) has suggested that X amount of diameter cog-
> > > hop (or root-hop, if you measure that) provides >X circumference chain-length variation, so my
> > > cog-hop probably is probably <1.143mm.
> > >
> > > A twentieth of an inch of lengthwise chain-play still seems awfully small, particularly for an
> > > inexpensive set of sprockets and chain with over 5,000 miles.
> > >
> > > And the chain has to wrap around two plastic jockey-wheels at sharp angles, too.
> > >
> > > Carl Fogel
> >
> > Let me make sure I got this right, you don't own a fixed-gear bike and have up until recently
> > not even heard of keirin racing, BUT you've been questioning the validity/veracity of statements
> > by many folks who have incredible experience/expertise with/on fixed-gear bikes, all because no
> > one would give you specific measurements of the clearly observed phenomenon???
>
> Dear Scott,
>
> In my ignorance, I asked how much cog-hop anyone could actually observe, having first peeked at my
> own gears and seen next to nothing.
>
> I was curious whether people who own and ride fixed-gear bikes would report impressive cog-hop
> when they measured things.
>
> I was also curious why no one ever mentioned the chain as being a source of this reported
> variation in tension.
>
> So far, no one has measured cog-hop with Andrew Muzi's clever method in excess of .3mm on a front
> chain ring. (With measurements that small, saying about half a millimeter is a bit vague--plus or
> minus a quater of a millimeter?)
>
> Sheldon Brown posted a comment that he had just put together a bike with what he's found to be
> good parts for reducing chain tension problems. Sheldon reported that there was no apparent
> variation.
>
> Real gears and what they mount on must have variation. My question is how much variation actually
> exists on the bicycles in question. Like so many things that seem simple, it turns out to be
> damned tricky.
>
> We're measuring tooth-tips, which are not really the place where the chain engages. But they seem
> likely to be excellent indicators.
>
> Cog-hop doesn't translate directly to what may be called runout--that is, the up-and-down
> variation in the circle described by the gears may be less than how much a chain coming off the
> gear would lengthen or retract.
>
> Assuming a perfect chain, varying chain tension may be easier to measure on a derailleur. When I
> watched my derailleur arm as I cranked the pedals slowly in 53 x 11 a dozen times, the silly thing
> wavered only about 0.045 inches, less than a twentieth of an inch.
>
> How clearly are we "observing" this phenomenon? When we actually start measuring, we're not coming
> up with much, are we? If you have a derailleur, turn your bike upside-down, tie a wire on the
> spokes, and let us know how much the cage wiggles as you slowly crank the pedals. If you have a
> fixed-gear, see Andrew Muzi's post and picture, try to measure how much your gear-teeth hop, and
> let us know what you find.
>
> It's understood that these measurements are tricky and that they may not correspond directly to
> varying chain tension.
>
> But Sheldon Brown reported that:
>
> "The degree of eccentricity varies considerably depending on the quality of the parts at both
> ends. This morning I'm putting together a Phil Wood ******** custom bike using a Rohloff Speedhub
> and a Campagnolo Record track crank, with Phil Wood bottom bracket...and there's no noticeable
> variance in chain tension through the course of the crank rotation."
>
> It's odd how irritable people can become when asked to measure something. I'm not calling people
> liars, any more than Sheldon did.
>
> They may be mistaken. They may be perfectly correct. They may be kinda-sort in-between on a
> tricky point.
>
> I'm just curious about measurements. And it was fascinating that the first seven replies to my
> question about how much slop could be actually measured contained no traces of measurement.
>
> The few measurements since then have not supported the general notion of sloppy components causing
> significant chain variation.
>
> But I'd be just as pleased if someone came up with a method of measuring things that showed what
> so far seems to be missing.
>
> Take a few minutes, wrap a wire on your bike, see how true your gears seem to be running, and let
> us know what you find.
>
> Carl Fogel

Carl,

I can't for the life of me imagine why you're so obsessed with an exact measurement of 'cog hop',
and I don't have an inclination to measure my chainrings to satisfy your concerns.

But, let me say this: I have used chainrings before that were so out of round that you could set
the chain tension such that for most of the rotation of the cranks the chain was visibly 'loose'
and for one small part of the rotation the chain would tighten to the point that, if you were
holding the rear of the bike up and spinning the wheel by hand, it would stop dead-still at the
point of highest tension.

You could still ride the bike like this, but... you wouldn't want to.

My solution was to determine where in the rotation of the cranks the high spot was, then make sure
that whenever I was setting chain tension I did so with the cranks in that spot. As long as it
wasn't too tight at that spot, nor too loose at any other spot in the rotation, then it didn't
really matter to me that the ring wasn't perfectly circular.

For what it's worth, the only rings I've ever owned that didn't exhibit this phenomenon to some
extent were rings made specifically for track racing. All road rings I've used on my various fixed
gear bikes over the years have been out of round to some degree. Shimano rings aren't too bad, many
cheap aftermarket rings are really bad. You can find cheap 'universal' rings designed for BMX bikes
that are worse than biopace rings.

Scott "I don't need to measure to know what I see" Hendricks

 

[Carl Fogel]

[email protected] (Scott Hendricks) wrote in message news:<[email protected]>...
> [email protected] (Carl Fogel) wrote in message
> news:<[email protected]>...
> > A Muzi <[email protected]> wrote in message news:<[email protected]>...
> >
> > [snip]
> >
> > > Carl Fogel wrote:> snip-I'd never heard of
> > > > keirin -snip- Maybe Andrew just got an awfully nice chain ring, as good as an entry-level
> > > > Japanese 0.5mm tolerance racing ring?
> > > -snip-I had a look at the site -snip-it's mostly in Japanese.
> > >
> > > I measured the outside edge not the critical root. That ring is a not cheap, it's a TA piste
> > > chainring. Measure your own if you want another data point. I said before and I still think
> > > you will find all modern rings under 1mm at the outside of the teeth.
> > >
> > > Japanese indeed. It's a Japanese government agency, after all!
> > >
> > > The official foreign visitors' Keirin guidebook is (completely - I have one) in French.
> >
> > Dear Andrew,
> >
> > I've been hoping that someone would ask!
> >
> > Having no fixed-gear, I peeked at the movement of the outermost jockey-wheel of my derailleur as
> > I slowly cranked the pedals backward in 53 x 11, 108 rollers.
> >
> > The derailleur arm hardly moved, suggesting that chain tension wasn't varying much.
> >
> > "Hardly moved" isn't much of a measurement, so I wound a long wire-and-plastic bag-tie around
> > some rear spokes and bent it until its end sat just in front of the end of the thin metal
> > derailleur frame, where its bent sideway behind the furthest jockey wheel.
> >
> > The whole derailleur arm at the level of the far pulley trembles back and forth less than half
> > the width of the metal piece. My dial calipers measure the width at 0.090 inches. (Why did
> > Shimano use this odd thickness instead of 0.010 inches?)
> >
> > So my best measurement after repeated pedal cycles in hopes of find a tight spot when the worst
> > of the rear cog coincides with the worst of the front sprocket is that my chain varies about
> > 0.045 inches--1.143mm.
> >
> > Elsewhere in this thread, Dave Johnson (I think) has suggested that X amount of diameter cog-hop
> > (or root-hop, if you measure that) provides >X circumference chain-length variation, so my cog-
> > hop probably is probably <1.143mm.
> >
> > A twentieth of an inch of lengthwise chain-play still seems awfully small, particularly for an
> > inexpensive set of sprockets and chain with over 5,000 miles.
> >
> > And the chain has to wrap around two plastic jockey-wheels at sharp angles, too.
> >
> > Carl Fogel
>
> Let me make sure I got this right, you don't own a fixed-gear bike and have up until recently not
> even heard of keirin racing, BUT you've been questioning the validity/veracity of statements by
> many folks who have incredible experience/expertise with/on fixed-gear bikes, all because no one
> would give you specific measurements of the clearly observed phenomenon???

Dear Scott,

In my ignorance, I asked how much cog-hop anyone could actually observe, having first peeked at my
own gears and seen next to nothing.

I was curious whether people who own and ride fixed-gear bikes would report impressive cog-hop when
they measured things.

I was also curious why no one ever mentioned the chain as being a source of this reported variation
in tension.

So far, no one has measured cog-hop with Andrew Muzi's clever method in excess of .3mm on a front
chain ring. (With measurements that small, saying about half a millimeter is a bit vague--plus or
minus a quater of a millimeter?)

Sheldon Brown posted a comment that he had just put together a bike with what he's found to be good
parts for reducing chain tension problems. Sheldon reported that there was no apparent variation.

Real gears and what they mount on must have variation. My question is how much variation actually
exists on the bicycles in question. Like so many things that seem simple, it turns out to be
damned tricky.

We're measuring tooth-tips, which are not really the place where the chain engages. But they seem
likely to be excellent indicators.

Cog-hop doesn't translate directly to what may be called runout--that is, the up-and-down variation
in the circle described by the gears may be less than how much a chain coming off the gear would
lengthen or retract.

Assuming a perfect chain, varying chain tension may be easier to measure on a derailleur. When I
watched my derailleur arm as I cranked the pedals slowly in 53 x 11 a dozen times, the silly thing
wavered only about 0.045 inches, less than a twentieth of an inch.

How clearly are we "observing" this phenomenon? When we actually start measuring, we're not coming
up with much, are we? If you have a derailleur, turn your bike upside-down, tie a wire on the
spokes, and let us know how much the cage wiggles as you slowly crank the pedals. If you have a fixed-
gear, see Andrew Muzi's post and picture, try to measure how much your gear-teeth hop, and let us
know what you find.

It's understood that these measurements are tricky and that they may not correspond directly to
varying chain tension.

But Sheldon Brown reported that:

"The degree of eccentricity varies considerably depending on the quality of the parts at both ends.
This morning I'm putting together a Phil Wood ******** custom bike using a Rohloff Speedhub and a
Campagnolo Record track crank, with Phil Wood bottom bracket...and there's no noticeable variance in
chain tension through the course of the crank rotation."

It's odd how irritable people can become when asked to measure something. I'm not calling people
liars, any more than Sheldon did.

They may be mistaken. They may be perfectly correct. They may be kinda-sort in-between on a
tricky point.

I'm just curious about measurements. And it was fascinating that the first seven replies to my
question about how much slop could be actually measured contained no traces of measurement.

The few measurements since then have not supported the general notion of sloppy components causing
significant chain variation.

But I'd be just as pleased if someone came up with a method of measuring things that showed what so
far seems to be missing.

Take a few minutes, wrap a wire on your bike, see how true your gears seem to be running, and let us
know what you find.

Carl Fogel

 

[Carl Fogel]

[email protected] (Scott Hendricks) wrote in message news:<[email protected]>...
> [email protected] (Carl Fogel) wrote in message
> news:<[email protected]>...
> > [email protected] (Scott Hendricks) wrote in message
> > news:<[email protected]>...
> > > [email protected] (Carl Fogel) wrote in message
> > > news:<[email protected]>...
> > > > A Muzi <[email protected]> wrote in message news:<[email protected]>...
> > > >
> > > > [snip]
> > > >
> > > > > Carl Fogel wrote:> snip-I'd never heard of
> > > > > > keirin -snip- Maybe Andrew just got an awfully nice chain ring, as good as an entry-
> > > > > > level Japanese 0.5mm tolerance racing ring?
> > > > > -snip-I had a look at the site -snip-it's mostly in Japanese.
> > > > >
> > > > > I measured the outside edge not the critical root. That ring is a not cheap, it's a TA
> > > > > piste chainring. Measure your own if you want another data point. I said before and I
> > > > > still think you will find all modern rings under 1mm at the outside of the teeth.
> > > > >
> > > > > Japanese indeed. It's a Japanese government agency, after all!
> > > > >
> > > > > The official foreign visitors' Keirin guidebook is (completely - I have one) in French.
> > > >
> > > > Dear Andrew,
> > > >
> > > > I've been hoping that someone would ask!
> > > >
> > > > Having no fixed-gear, I peeked at the movement of the outermost jockey-wheel of my
> > > > derailleur as I slowly cranked the pedals backward in 53 x 11, 108 rollers.
> > > >
> > > > The derailleur arm hardly moved, suggesting that chain tension wasn't varying much.
> > > >
> > > > "Hardly moved" isn't much of a measurement, so I wound a long wire-and-plastic bag-tie
> > > > around some rear spokes and bent it until its end sat just in front of the end of the thin
> > > > metal derailleur frame, where its bent sideway behind the furthest jockey wheel.
> > > >
> > > > The whole derailleur arm at the level of the far pulley trembles back and forth less than
> > > > half the width of the metal piece. My dial calipers measure the width at 0.090 inches. (Why
> > > > did Shimano use this odd thickness instead of 0.010 inches?)
> > > >
> > > > So my best measurement after repeated pedal cycles in hopes of find a tight spot when the
> > > > worst of the rear cog coincides with the worst of the front sprocket is that my chain varies
> > > > about 0.045 inches--1.143mm.
> > > >
> > > > Elsewhere in this thread, Dave Johnson (I think) has suggested that X amount of diameter cog-
> > > > hop (or root-hop, if you measure that) provides >X circumference chain-length variation, so
> > > > my cog-hop probably is probably <1.143mm.
> > > >
> > > > A twentieth of an inch of lengthwise chain-play still seems awfully small, particularly for
> > > > an inexpensive set of sprockets and chain with over 5,000 miles.
> > > >
> > > > And the chain has to wrap around two plastic jockey-wheels at sharp angles, too.
> > > >
> > > > Carl Fogel
> > >
> > > Let me make sure I got this right, you don't own a fixed-gear bike and have up until recently
> > > not even heard of keirin racing, BUT you've been questioning the validity/veracity of
> > > statements by many folks who have incredible experience/expertise with/on fixed-gear bikes,
> > > all because no one would give you specific measurements of the clearly observed phenomenon???
> >
> > Dear Scott,
> >
> > In my ignorance, I asked how much cog-hop anyone could actually observe, having first peeked at
> > my own gears and seen next to nothing.
> >
> > I was curious whether people who own and ride fixed-gear bikes would report impressive cog-hop
> > when they measured things.
> >
> > I was also curious why no one ever mentioned the chain as being a source of this reported
> > variation in tension.
> >
> > So far, no one has measured cog-hop with Andrew Muzi's clever method in excess of .3mm on a
> > front chain ring. (With measurements that small, saying about half a millimeter is a bit vague--
> > plus or minus a quater of a millimeter?)
> >
> > Sheldon Brown posted a comment that he had just put together a bike with what he's found to be
> > good parts for reducing chain tension problems. Sheldon reported that there was no apparent
> > variation.
> >
> > Real gears and what they mount on must have variation. My question is how much variation
> > actually exists on the bicycles in question. Like so many things that seem simple, it turns out
> > to be damned tricky.
> >
> > We're measuring tooth-tips, which are not really the place where the chain engages. But they
> > seem likely to be excellent indicators.
> >
> > Cog-hop doesn't translate directly to what may be called runout--that is, the up-and-down
> > variation in the circle described by the gears may be less than how much a chain coming off the
> > gear would lengthen or retract.
> >
> > Assuming a perfect chain, varying chain tension may be easier to measure on a derailleur. When I
> > watched my derailleur arm as I cranked the pedals slowly in 53 x 11 a dozen times, the silly
> > thing wavered only about 0.045 inches, less than a twentieth of an inch.
> >
> > How clearly are we "observing" this phenomenon? When we actually start measuring, we're not
> > coming up with much, are we? If you have a derailleur, turn your bike upside-down, tie a wire on
> > the spokes, and let us know how much the cage wiggles as you slowly crank the pedals. If you
> > have a fixed-gear, see Andrew Muzi's post and picture, try to measure how much your gear-teeth
> > hop, and let us know what you find.
> >
> > It's understood that these measurements are tricky and that they may not correspond directly to
> > varying chain tension.
> >
> > But Sheldon Brown reported that:
> >
> > "The degree of eccentricity varies considerably depending on the quality of the parts at both
> > ends. This morning I'm putting together a Phil Wood ******** custom bike using a Rohloff
> > Speedhub and a Campagnolo Record track crank, with Phil Wood bottom bracket...and there's no
> > noticeable variance in chain tension through the course of the crank rotation."
> >
> > It's odd how irritable people can become when asked to measure something. I'm not calling people
> > liars, any more than Sheldon did.
> >
> > They may be mistaken. They may be perfectly correct. They may be kinda-sort in-between on a
> > tricky point.
> >
> > I'm just curious about measurements. And it was fascinating that the first seven replies to my
> > question about how much slop could be actually measured contained no traces of measurement.
> >
> > The few measurements since then have not supported the general notion of sloppy components
> > causing significant chain variation.
> >
> > But I'd be just as pleased if someone came up with a method of measuring things that showed what
> > so far seems to be missing.
> >
> > Take a few minutes, wrap a wire on your bike, see how true your gears seem to be running, and
> > let us know what you find.
> >
> > Carl Fogel
>
> Carl,
>
> I can't for the life of me imagine why you're so obsessed with an exact measurement of 'cog hop',
> and I don't have an inclination to measure my chainrings to satisfy your concerns.
>
> But, let me say this: I have used chainrings before that were so out of round that you could set
> the chain tension such that for most of the rotation of the cranks the chain was visibly 'loose'
> and for one small part of the rotation the chain would tighten to the point that, if you were
> holding the rear of the bike up and spinning the wheel by hand, it would stop dead-still at the
> point of highest tension.
>
> You could still ride the bike like this, but... you wouldn't want to.
>
> My solution was to determine where in the rotation of the cranks the high spot was, then make sure
> that whenever I was setting chain tension I did so with the cranks in that spot. As long as it
> wasn't too tight at that spot, nor too loose at any other spot in the rotation, then it didn't
> really matter to me that the ring wasn't perfectly circular.
>
> For what it's worth, the only rings I've ever owned that didn't exhibit this phenomenon to some
> extent were rings made specifically for track racing. All road rings I've used on my various fixed
> gear bikes over the years have been out of round to some degree. Shimano rings aren't too bad,
> many cheap aftermarket rings are really bad. You can find cheap 'universal' rings designed for BMX
> bikes that are worse than biopace rings.
>
> Scott "I don't need to measure to know what I see" Hendricks

Dear Scott,

You could have measured it in less time than it took you to type your reply. I wonder what you would
have found.

Carl Fogel

 

[Scott Hendricks]

[email protected] (Carl Fogel) wrote in message news:<[email protected]>...
> [email protected] (Scott Hendricks) wrote in message
> news:<[email protected]>...
> > [email protected] (Carl Fogel) wrote in message
> > news:<[email protected]>...
> > > [email protected] (Scott Hendricks) wrote in message
> > > news:<[email protected]>...
> > > > [email protected] (Carl Fogel) wrote in message
> > > > news:<[email protected]>...
> > > > > A Muzi <[email protected]> wrote in message news:<[email protected]>...
> > > > >
> > > > > [snip]
> > > > >
> > > > > > Carl Fogel wrote:> snip-I'd never heard of
> > > > > > > keirin -snip- Maybe Andrew just got an awfully nice chain ring, as good as an entry-
> > > > > > > level Japanese 0.5mm tolerance racing ring?
> > > > > > -snip-I had a look at the site -snip-it's mostly in Japanese.
> > > > > >
> > > > > > I measured the outside edge not the critical root. That ring is a not cheap, it's a TA
> > > > > > piste chainring. Measure your own if you want another data point. I said before and I
> > > > > > still think you will find all modern rings under 1mm at the outside of the teeth.
> > > > > >
> > > > > > Japanese indeed. It's a Japanese government agency, after all!
> > > > > >
> > > > > > The official foreign visitors' Keirin guidebook is (completely - I have one) in French.
> > > > >
> > > > > Dear Andrew,
> > > > >
> > > > > I've been hoping that someone would ask!
> > > > >
> > > > > Having no fixed-gear, I peeked at the movement of the outermost jockey-wheel of my
> > > > > derailleur as I slowly cranked the pedals backward in 53 x 11, 108 rollers.
> > > > >
> > > > > The derailleur arm hardly moved, suggesting that chain tension wasn't varying much.
> > > > >
> > > > > "Hardly moved" isn't much of a measurement, so I wound a long wire-and-plastic bag-tie
> > > > > around some rear spokes and bent it until its end sat just in front of the end of the thin
> > > > > metal derailleur frame, where its bent sideway behind the furthest jockey wheel.
> > > > >
> > > > > The whole derailleur arm at the level of the far pulley trembles back and forth less than
> > > > > half the width of the metal piece. My dial calipers measure the width at 0.090 inches.
> > > > > (Why did Shimano use this odd thickness instead of 0.010 inches?)
> > > > >
> > > > > So my best measurement after repeated pedal cycles in hopes of find a tight spot when the
> > > > > worst of the rear cog coincides with the worst of the front sprocket is that my chain
> > > > > varies about 0.045 inches--1.143mm.
> > > > >
> > > > > Elsewhere in this thread, Dave Johnson (I think) has suggested that X amount of diameter
> > > > > cog-hop (or root-hop, if you measure that) provides >X circumference chain-length
> > > > > variation, so my cog-hop probably is probably <1.143mm.
> > > > >
> > > > > A twentieth of an inch of lengthwise chain-play still seems awfully small, particularly
> > > > > for an inexpensive set of sprockets and chain with over 5,000 miles.
> > > > >
> > > > > And the chain has to wrap around two plastic jockey-wheels at sharp angles, too.
> > > > >
> > > > > Carl Fogel
> > > >
> > > > Let me make sure I got this right, you don't own a fixed-gear bike and have up until
> > > > recently not even heard of keirin racing, BUT you've been questioning the validity/veracity
> > > > of statements by many folks who have incredible experience/expertise with/on fixed-gear
> > > > bikes, all because no one would give you specific measurements of the clearly observed
> > > > phenomenon???
> > >
> > > Dear Scott,
> > >
> > > In my ignorance, I asked how much cog-hop anyone could actually observe, having first peeked
> > > at my own gears and seen next to nothing.
> > >
> > > I was curious whether people who own and ride fixed-gear bikes would report impressive cog-hop
> > > when they measured things.
> > >
> > > I was also curious why no one ever mentioned the chain as being a source of this reported
> > > variation in tension.
> > >
> > > So far, no one has measured cog-hop with Andrew Muzi's clever method in excess of .3mm on a
> > > front chain ring. (With measurements that small, saying about half a millimeter is a bit vague--
> > > plus or minus a quater of a millimeter?)
> > >
> > > Sheldon Brown posted a comment that he had just put together a bike with what he's found to be
> > > good parts for reducing chain tension problems. Sheldon reported that there was no apparent
> > > variation.
> > >
> > > Real gears and what they mount on must have variation. My question is how much variation
> > > actually exists on the bicycles in question. Like so many things that seem simple, it turns
> > > out to be damned tricky.
> > >
> > > We're measuring tooth-tips, which are not really the place where the chain engages. But they
> > > seem likely to be excellent indicators.
> > >
> > > Cog-hop doesn't translate directly to what may be called runout--that is, the up-and-down
> > > variation in the circle described by the gears may be less than how much a chain coming off
> > > the gear would lengthen or retract.
> > >
> > > Assuming a perfect chain, varying chain tension may be easier to measure on a derailleur. When
> > > I watched my derailleur arm as I cranked the pedals slowly in 53 x 11 a dozen times, the silly
> > > thing wavered only about 0.045 inches, less than a twentieth of an inch.
> > >
> > > How clearly are we "observing" this phenomenon? When we actually start measuring, we're not
> > > coming up with much, are we? If you have a derailleur, turn your bike upside-down, tie a wire
> > > on the spokes, and let us know how much the cage wiggles as you slowly crank the pedals. If
> > > you have a fixed-gear, see Andrew Muzi's post and picture, try to measure how much your gear-
> > > teeth hop, and let us know what you find.
> > >
> > > It's understood that these measurements are tricky and that they may not correspond directly
> > > to varying chain tension.
> > >
> > > But Sheldon Brown reported that:
> > >
> > > "The degree of eccentricity varies considerably depending on the quality of the parts at both
> > > ends. This morning I'm putting together a Phil Wood ******** custom bike using a Rohloff
> > > Speedhub and a Campagnolo Record track crank, with Phil Wood bottom bracket...and there's no
> > > noticeable variance in chain tension through the course of the crank rotation."
> > >
> > > It's odd how irritable people can become when asked to measure something. I'm not calling
> > > people liars, any more than Sheldon did.
> > >
> > > They may be mistaken. They may be perfectly correct. They may be kinda-sort in-between on a
> > > tricky point.
> > >
> > > I'm just curious about measurements. And it was fascinating that the first seven replies to my
> > > question about how much slop could be actually measured contained no traces of measurement.
> > >
> > > The few measurements since then have not supported the general notion of sloppy components
> > > causing significant chain variation.
> > >
> > > But I'd be just as pleased if someone came up with a method of measuring things that showed
> > > what so far seems to be missing.
> > >
> > > Take a few minutes, wrap a wire on your bike, see how true your gears seem to be running, and
> > > let us know what you find.
> > >
> > > Carl Fogel
> >
> > Carl,
> >
> > I can't for the life of me imagine why you're so obsessed with an exact measurement of 'cog
> > hop', and I don't have an inclination to measure my chainrings to satisfy your concerns.
> >
> > But, let me say this: I have used chainrings before that were so out of round that you could set
> > the chain tension such that for most of the rotation of the cranks the chain was visibly 'loose'
> > and for one small part of the rotation the chain would tighten to the point that, if you were
> > holding the rear of the bike up and spinning the wheel by hand, it would stop dead-still at the
> > point of highest tension.
> >
> > You could still ride the bike like this, but... you wouldn't want to.
> >
> > My solution was to determine where in the rotation of the cranks the high spot was, then make
> > sure that whenever I was setting chain tension I did so with the cranks in that spot. As long as
> > it wasn't too tight at that spot, nor too loose at any other spot in the rotation, then it
> > didn't really matter to me that the ring wasn't perfectly circular.
> >
> > For what it's worth, the only rings I've ever owned that didn't exhibit this phenomenon to some
> > extent were rings made specifically for track racing. All road rings I've used on my various
> > fixed gear bikes over the years have been out of round to some degree. Shimano rings aren't too
> > bad, many cheap aftermarket rings are really bad. You can find cheap 'universal' rings designed
> > for BMX bikes that are worse than biopace rings.
> >
> > Scott "I don't need to measure to know what I see" Hendricks
>
> Dear Scott,
>
> You could have measured it in less time than it took you to type your reply. I wonder what you
> would have found.
>
> Carl Fogel

What I would have found would be a precise measurement that wouldn't serve a purpose, because I
didn't need a confirmation of the phenomenon, nor would knowing the precise measurement allow me to
do anything more about it than I could already do without the measurement.

 

[Carl Fogel]

[snip]

> > > Scott "I don't need to measure to know what I see" Hendricks
> >
> > Dear Scott,
> >
> > You could have measured it in less time than it took you to type your reply. I wonder what you
> > would have found.
> >
> > Carl Fogel
>
>
> What I would have found would be a precise measurement that wouldn't serve a purpose, because I
> didn't need a confirmation of the phenomenon, nor would knowing the precise measurement allow me
> to do anything more about it than I could already do without the measurement.

Dear Scott,

Roughly how much do you think this precise measurement would be?

I'm just interested in figuring out what's going on. Sheldon Brown seems to have arrived at a
situation where the "phenomenon" no longer exists.

The more people who are unwilling to measure something so easy, the more I'm baffled.

How hard is it to wrap a twist tie on the frame or spokes and see how much the tips of the gear-
teeth hop or how much your derailleur cage wavers?

Carl Fogel

 

[Carl Fogel]

"Tom Nakashima" <[email protected]> wrote in message news:<[email protected]>...
> So even if you have this perfect concentric chainring, what if the bolt circle pattern diameter of
> the crankarms are not concentric with the center of the taper or center of the crankarm mounting
> diameter? -tom

Dear Tom,

Sorry for not replying sooner. I just lost track of posts in this tangled thread.

I think that the question is how truly do the gear-surfaces that engage (and presumably tension) the
chain actually run in relation to the frame. The path that they describe incorporates all the slop,
irregularities, and off-centering (some of which might even be self-cancelling).

The tooth-tips are easiest to measure, but are only indicators because it's the slope just below
them that actually pulls on the chain.

Tooth-tips are often machined for derailleur-shifting with slightly different heights, so such
sprockets will look more irregular than they really are.

Looking sideways through the bottom of the tooth-trough would measure the bottom, possibly a better
indicator, but trickier to measure at the small amounts actually reported so far.

Several things may cause the small observed variation in cog-hop.

Most people tend to blame (without any direct measuring) the sprocket, what might be called the lumpy-
sprocket theory.

Others blame a beautifully round but imperfectly centered sprocket, which is the possibility that
you're raising. (No one has said much about the rear cog).

Most people have dismissed any slop or off-centering on the part of the cups, balls, cones, and
spindle as being too minor to matter. (This seems likely to me, but I'd love to have some actual
numbers to give me confidence.)

To a lesser degree, many posts have also dismissed by implication any faulty centering of the pedal
arm on the spindle. I'm less confident about this, but still suspect that it's minor.

Regardless of where the slop lies, it still seems that it could be observed and measured at roughly
the tooth-tips as they go round and round, which is all the chain cares about.

Sheldon Brown found no apparent chain tension variation when he built a bike out of what he's found
to be good parts.

DVT wrote that his chain rings seem to be round and suspects that his problems were due to off-
center mounting because he could remove most of the chain tension variation by using the methods
described on Sheldon Brown's web site.

John Dacey told us about Sugino chain rings with only 0.5mm runout and added that a more expensive
model has only 0.05mm runout.

That's 0.02 or even 0.002 inches of chain length variation from the chain-ring. My dial calipers
only go down to 0.001, so I'm impressed.

(While no one has pinned these terms down, it seems likely that a crude cog-hop measurement of X
indicates a runout or lengthwise chain variation of >X.)

I'm just curious about what the actual measurements are, largely because peeking at my low-grade
derailleur showed no cog-hop that could be measured with anything less than Andrew Muzi's clever
stacked sheets of paper trick and because my derailleur cage barely shivers (0.045 inches) away from
a twist tie on the spokes when I crank the pedals slowly, suggesting no real chain tension
variation.

Given the wide variety of brands of sprockets, spiders, and so forth, plus the vagaries of wear, I
expected to hear from people whose sprockets wobbled and hopped in a lurid and interesting fashion.

But so far, the only actual measurement of a fixed-gear's cog-hop has come from Andrew Muzi, who
reported that his front sprocket's tooth-tips wavered about .3mm and his rear cog about 0.1mm. This
total of 0.4mm is about 0.016 inches, roughly the thickness of four sheets of paper.

It's as disappointing as being promised

wearing coveralls.

Most people have repeated that they've seen fixed-gear chains sag and tighten, so there must be
something going on and it's somehow a mistake to ask for measurements.

I'm not calling them liars, as some of the more excitable posters fear. I'm just wondering
what's going on.

If the gear-teeth are wobbling enough to affect chain-tension, it should be fairly easy to measure
and explain. (Maybe even the tiniest irregularity snaps sagging chains taut? This seems unlikely,
but I'm willing to listen.)

For some reason, a surprising variety of people are reluctant to wrap a twist tie around the frame,
watch their gears go past it, and post some kind of measurements. (Obviously, with the tiny
variations reported so far, it's going to take calipers or something like Andrew Muzi's clever
method to produce useful measurements.)

If it turns out that it ain't the gear teeth describing erratic circles, then perhaps the chains
themselves, never mentioned as suspects, should be looked at more closely. They might be less
uniform than I expect, or they might be binding more than we think.

Or it could be that those minute, almost-impossible-to-measure gear irregularities somehow are
enough to cause chains to sag and tighten noticeably--but then someone should be able to
explain that.

Or it could be that although the tooth-tips are impressively regular, the faces just below them are
somehow wildly erratic? This seems unlikely, but I'll listen to anything.

Or maybe the quality of the components has improved so much that what was once a problem is no
longer visible. That seems to be the case when people actually measure. I can understand wide-spread
doubt about my theories and ability to measure things, but I notice that no one has argued that
Sheldon Brown is crazy when he says that he put together a bike with nice parts and could see no
apparent chain problem.

If you've got a minute or two, wrap a twist tie on your frame and let us know how much your fixed
gear's tooth tips seem to hop or how much your derailleur cage wavers when cranked backwards slowly.

Carl Fogel

 

[David Reuteler]

Carl Fogel <[email protected]> wrote:
: But so far, the only actual measurement of a fixed-gear's cog-hop has come from Andrew Muzi

i did as well, carl.

: but I notice that no one has argued that Sheldon Brown is crazy when he says that he put together
: a bike with nice parts and could see no apparent chain problem.

i wouldn't because my bike is the same way. 1/8" suntour superbe pro track ring, cog and crank.
someone said that tolerances seemed to be better for track equipment. hmm.. i'd wager.

: know how much your fixed gear's tooth tips seem to hop or how much your derailleur cage wavers
: when cranked backwards slowly.

i already did this. go back and look. not much.
--
david reuteler [email protected]