The Bikesmith, Seattle, shutting down

[Dvt]

Carl Fogel wrote:

> dvt <[email protected]> wrote in message news:<[email protected]>...
>>
>>Since the bottom run is not allowed to straighten completely, there will be a *lot* of force on
>>the tensioner during backpedaling. Enough force to ruin the forementioned tensioner without
>>question. Math can be supplied if necessary.
>>
>>If the bottom chain run *is* allowed to straighten, the top run is probably loose and derailing is
>>a distinct possibility.
>>
>>How about the motorcycle chain tensioner?
>>
>>Dave dvt at psu dot edu
>
>
> Dear Dave,
>
> I think (but may be wrong) that the bicycle chain tensioner on that web page attaches like a rear
> derailleur at the axle area, but has only a single idler wheel and instead of trailing points
> forward.
>
> The advantage, I suppose, is easy attachment.
>
> The disadvantage is that the lower run of chain is coming into the end of the arm, so any sideways
> misalignment would indeed let the chain bend the tensioner arm further sideways and tear it off.
>
> That's why trailing arms were used--the lower run of the chain is always heading back toward rear
> sprocket (unless you roll the bike or motorcycle backwards).
>
> I don't see how the force of the lower chain going taut when the force reverses during braking
> will ruin a spring-loaded arm.
If the spring-loaded arm bottoms out before the chain gets completely straight, the arm will be
subjected to a lot of force. From my earlier post:

>>I don't think the bicycle chain tensioners allow the bottom run of the chain to go straight.

> A trailing-arm lower-run chain tensioner pushes a slack lower-run of chain upward. If the lower
> run snaps taut, the chain tensioner is merely pushed down a bit.

That may be true on a motorcycle, but I'm quite sure it's not true on a bicycle chain tensioner.
See above.

> If the upper run is a problem on a fixed-gear bike then an upper-run leading-arm would take
> care of it.

Yes, two chain tensioners that allowed the chain to straighten completely would work on a fixie. One
tensioner on the top, one on the bottom. You'll see this approach taken in the fore (idler?) chain
of a tandem, where people use an extra chainwheel in the middle of the run. See Sheldon's website
for a description of this.

> But no chain forces involved seem to have any way to damage arms trailing from the chain's point
> of view and pressing the chain toward the chain-stay. No math is involved. Possibly we're reading
> diagrams wildly differently?

One more time: If the tensioner reaches the end of its sprung travel before the chain gets straight,
tons of force will be applied to the tensioner.

> As for derailing when the top run goes slack, how is the situation any worse than when no chain
> tensioner is involved? (I don't think that anyone is suggesting that the chain should be slacker
> than normal if a tensioner is added to a fixed-gear bicycle.)

I don't understand that question. Sorry.

Dave dvt at psu dot edu

 

[Dvt]

Carl Fogel wrote:

> dvt <[email protected]> wrote in message news:<[email protected]>...
>
> [snip]
>
> Dear Dave and others,
>
> I finally found some so-so picture of a 1970's trials motorcycle's trailing-arm chain-tensioner.
>
> http://home.connection.com/~dank/montesa.htm
>
> It's the short trailing arm hanging down from the swing-arm, pointing backward. Unfortunately, the
> arm is the same silver color as the rear wheel rim behind it.
>
> You can actually see the chain-tensioner arm better in picture right-3, looking through the
> wheel's spokes from the other side.
>
> A powerful wound spring forces the trailing end of the arm (and the chain slithering over the pad)
> up toward the swing arm.
>
> Such arms survive in deep mud, heavy brush, vicious rocks, and all sorts of other abuse, far worse
> than pavement-oriented fixed-gear bikes ever face.
>
> Again, whether such arms would be of any practical use is quite another question. I'm just puzzled
> to hear that such an arm would be torn off by a fixed-gear bicycle---no forces that I can see will
> trouble it in the slightest.

You are correct. A chain tensioner of that type would not be troubled by a fixie. In the picture
shown, there is not very much chain slack to be removed by the tensioner. That much slack is
probably not cause for concern as it doesn't look like enough to make the chain derail easily.

Bicycle chain tensioners do not operate the same way, though. As I've stated elsewhere, they bottom
out. Try this picture -- it might give you a better idea of my point:

http://www.sheldonbrown.com/singlespeed.html#tensioner

Dave dvt at psu dot edu

 

[Eric M]

In article <[email protected]>, dvt <[email protected]> wrote:
>Eric M wrote:
>
>How does a motorcycle keep the chain from derailing when the chain is slackest (i.e. suspension
>fully compressed?). If one allowed "a couple inches of chain slack" on a bicycle, the chain would
>be derail in a heartbeat.

Dunno, but in 10 years of trials riding I've never had a chain derail or seen another rider's
chain derail.

Maybe it's because the chain's much wider than bicycle chain and does not have the same sort of
sideways flexability needed for sprockets that do not line up.

Eric

 

[Dvt]

Eric M wrote:

> In article <[email protected]>, dvt <[email protected]> wrote:
>>How does a motorcycle keep the chain from derailing when the chain is slackest (i.e. suspension
>>fully compressed?). If one allowed "a couple inches of chain slack" on a bicycle, the chain would
>>be derail in a heartbeat.

> Dunno, but in 10 years of trials riding I've never had a chain derail or seen another rider's
> chain derail.
>
> Maybe it's because the chain's much wider than bicycle chain and does not have the same sort of
> sideways flexability needed for sprockets that do not line up.

I'd dare to bet you're right on. Maybe someone should sell a fixie-only bicycle chain that has very
little lateral flexibility. But I'll bet the market is pretty small unless you can convince the SS
MTB and trackie crowd that the chain is the greatest thing since sliced bread.

Dave dvt at psu dot edu

 

[Carl Fogel]

Howard Kveck <[email protected]> wrote in message news:<[email protected]>...
> In article <[email protected]>, [email protected] (Carl
> Fogel) wrote:
>
> > dvt <[email protected]> wrote in message news:<[email protected]>...
> >
> > [snip]
> >
> > Dear Dave and others,
> >
> > I finally found some so-so picture of a 1970's trials motorcycle's trailing-arm chain-tensioner.
> >
> > http://home.connection.com/~dank/montesa.htm
>
> How far they've come in twenty-five years or so:
>
> http://www.usmontesa.com/html/the_bike.html

Dear Howard,

No! I'm not going to spend six grand on a trials machine that weighs less than I do!

You and Eric should both be ashamed of yourselves for trying to tempt me with pictures like these.

What would my poor old faithful gray Honda think if it woke up one morning and found one these brightly-
painted Spanish machines next to it on the car port, twenty-eight years younger and a third lighter,
with exotic electronic ignition, sassy monoshock suspension, a narrow waist, a tiny gas tank, and
obvious radiator implants?

The next thing I know, you and Eric will be trying to lure me into sin with web pages like this:

http://www.ataq.qc.ca/musee.htm

Er, not that I look at things like that on the internet. No, I just--well, I opened an email that
promised to increase my ground clearance . . .

Carl Fogel

 

[Carla A-G]

"dvt" <[email protected]> wrote in message
news:[email protected]...
> > Maybe it's because the chain's much wider than bicycle chain and does not have the same sort of
> > sideways flexability needed
> > for sprockets that do not line up.
>
> I'd dare to bet you're right on. Maybe someone should sell a fixie-only bicycle chain that has
> very little lateral flexibility. But I'll bet the market is pretty small unless you can convince
> the SS MTB and trackie crowd that the chain is the greatest thing since sliced bread.

I use a heavier duty chain on my track bike and SS, I think they're made by KMC and I've never had a
problem. When I used to ride BMX, I used to use a very heavy duty chain (you could almost use it on
a motorcyle). Altho the chain was more heavy duty, you could punish the heck out of it and it would
keep going on.

- CA-G

Can-Am Girls Kick Ass!

 

[Rick Onanian]

On 30 Jan 2004 10:54:32 -0800, [email protected] (Jonesy)
wrote:
>> >While I cannot be sure that Carl twisted my words with malice aforethought,
>>
>> Be careful; by mincing words like that, you're liable to create, once again, false imagery of an
>> opinion you may not hold.
>
>Are you daft? Let me type it again: I do not know whether or not Carl twisted my words with malice
>aforethought. I do not think it can be known.

"do not know whether or not he did...do not think it can be known" creates a far different image
from "cannot be sure that he did". If you cannot see that, then you are the daft one.

>> >it certainly was effective for his purposes of bashing bike snobs.
>>
>> We could use the occasional bashing to bring us down to earth.
>
>What's this "we" ****? For years, I rode an entry-level mountain bike with no thought of anything
>but riding. I still own the thing, and use it as a beater bike.

And yet, you feel that bike shaped toys are not reasonable transportation.

>I have been recommending used and entry-level bikes. Maybe *your* bike snobbery needs a little
>trimming, but I think mine is about as small as it gets.

...and I have been recommending used salvage bikes requiring minimal work. That's pretty similar.

>I notice that you neglected to address my safety concern. Do I take from that that you concede
>that point?

Did you forget that I had the same safety concern, hence my recommendation?

This is pointless and silly bickering anyway. Who cares?

To move on, let me say this about QR levers facing the wrong way: Looking at my road bike, a 2001
Giant TCR2, I noticed that the rear QR lever was the wrong way! It was leading with the end. I went
to flip it around, and found that the frame PREVENTS IT! The chain stay bulges right at the dropout
such that the QR can lead or face down and very slightly back, but cannot trail. I turned it to it's
down-and-slightly-back position.

I'm not worried, however -- in this whole discussion, when discussing leading QRs as a potential
hazard (separate from using QR closure as a gauge to how the rest of the bike was built), we
completely ignored this: QR levers are on the left side. In the US, where the cheap *Mart bikes are
sold, one rides on the right side of the road. If there's brush sticking out, it would catch the
derailer, not the QR! The QR is on the other side.

The point stands, however, about the shoddy materials and workmanship of such bikes. Somebody
considering one should consider a salvaged / yard sale bike with $20 worth of new tires and tubes,
which would be cheaper than even the cheapest clearance bike at *Mart ($40 or so, sometimes).
Somebody who already bought one should attempt to make the bike safe by properly tightening
fasteners and such, and keep an eye on such things as the brakes for possible breakage.
--
Rick "My cat just stepped on a self-stick label" Onanian

 

[Jonesy]

Rick Onanian <[email protected]> wrote in message news:<[email protected]>...
> On 29 Jan 2004 09:48:54 -0800, [email protected] (Jonesy) wrote:
> >It's a strawman created by quoting out of context. By removing qualifiers and context, you can
> >twist quotes into anything you want.
> >
> >> >Carl has done a very good job at creating this image, but nowhere will you actually find such
> >> >a claim.
> >>
> >> Carl probably did not "create" that image;
> >
> >Sure he did. You certainly bought it. Nowhere did I write what you mistakenly ascribed to me, but
> >that exact image was what Carl has been writing for several posts.
>
> For somebody who in the previous sentence lamented the loss of context, you sure were quick with
> the contextectomey.

Hardly. You state the above, then go about justifying it. Since the justification is based on a
false premise, it is unnecessary and superfluous. In any case, it's a red herring. You misquoted me
(not specifically naming me, but I will take it as given that you were speaking about me) in the
exact (false) image that Carl created. If you had actually *read* what I had written, you might have
not written the misquote.

> You apparently can't accept that, regardless of intent or thought (or, for that matter, logic), an
> image can be created in a reader's mind that was not expressed.

Hogwash. I can accept it just fine, because I have seen it in action. You have just demonstrated
that you got an image that was in no way my intent. The very fact that you ascribed to me a belief
that can in no way be found in my writings points out the truth of your statement. While it was your
intent to paint *me* with that brush, it certainly does have broader application.

> Such an image is worth arguing, precisely because it results in express and specific replies to
> destroy that image.

When one has to repeat multiple times one's intent, then it moves from a mistaken impression to
something more pointed - and it points to purposefulness on the part of the "misunderstander."

> >> He then proceeded to argue what he thought you meant, which, while useless to you, did cause
> >> the whole thing to be cleared up by you saying exactly what you think -- which helps properly
> >> communicate to others who may have read the same image.
> >
> >Except that by explicitly writing down that list, I was forming merely a composite of what *I had
> >already written.* Just a shorter format.
>
> A shorter, more direct, more expressive format that dispels any false imagery.

Indeed it does. But it should not have to be written more than once.

> Having wrote that list, you've solved the problem of the false image -- and again, let me say that
> it exists regardless of intent or fault.

You are attempting to shrug it all off. I do not accept your analysis. Carl continued to infer non-
existent beliefs on my part even after he was corrected. That screams "purpose" to me.

> >While I cannot be sure that Carl twisted my words with malice aforethought,
>
> Be careful; by mincing words like that, you're liable to create, once again, false imagery of an
> opinion you may not hold.

Are you daft? Let me type it again: I do not know whether or not Carl twisted my words with malice
aforethought. I do not think it can be known.

> >it certainly was effective for his purposes of bashing bike snobs.
>
> We could use the occasional bashing to bring us down to earth.

What's this "we" ****? For years, I rode an entry-level mountain bike with no thought of anything
but riding. I still own the thing, and use it as a beater bike.

I have been recommending used and entry-level bikes. Maybe *your* bike snobbery needs a little
trimming, but I think mine is about as small as it gets.

I notice that you neglected to address my safety concern. Do I take from that that you concede
that point?

> >*You* bought it, after all...
>
> What makes you think that?

Shall I quote you back your original misquote? Unless you are just taking up the mantle of basher,
and are continuing Carl's well-started work.

Regards,

R.F. Jones

 

[Dave Lehnen]

dvt wrote:
> Eric M wrote:
>
>>> How about the motorcycle chain tensioner?
>>
>>
>> They allow the bottom run to go straight when throttle is closed and the rear wheel is pulling
>> the engine around.
>>
>> The chain has to run loose enough to allow the suspension to move. Since the countershaft
>> sprocket is not concentric with the swingarm pivot, the chain is tightest when the countershaft,
>> swing arm pivot and rear axle are in line. With the suspension extended or compressed from that
>> position the chain becomes slack.
>>
>> I usually set my modern trials bikes for a couple inches of chain slack. I don't know how much
>> slack a singleator is intended to take up but if it's the same amount that a derailleur would
>> than I could see how it might get damaged by backpedalling..
>
>
> How does a motorcycle keep the chain from derailing when the chain is slackest (i.e. suspension
> fully compressed?). If one allowed "a couple inches of chain slack" on a bicycle, the chain would
> be derail in a heartbeat.
>
> Dave dvt at psu dot edu
>

Are you talking about the same thing? A couple inches of slack on a motorcycle would usually mean
you can move the middle of the lower chain run about 2" difference from pushed all the way up with a
finger to pushed all the way down. The chain is nowhere near 2" longer than it needs to be.

Dave Lehnen

 

[David Kerber]

In article <0ZySb.36666$6O4.1027167@bgtnsc04- news.ops.worldnet.att.net>,
[email protected] says...

...

> > How does a motorcycle keep the chain from derailing when the chain is slackest (i.e. suspension
> > fully compressed?). If one allowed "a couple inches of chain slack" on a bicycle, the chain
> > would be derail in a heartbeat.
> >
> > Dave dvt at psu dot edu
> >
>
> Are you talking about the same thing? A couple inches of slack on a motorcycle would usually
> mean you can move the middle of the lower chain run about 2" difference from pushed all the way
> up with a

On a bike, that's a *LOT* of slack, and as he said, it would likely derail in a hurry.

> finger to pushed all the way down. The chain is nowhere near 2" longer than it needs to be.

--
Dave Kerber Fight spam: remove the ns_ from the return address before replying!

REAL programmers write self-modifying code.

 

[Chris Phillipo]

In article <[email protected]>, [email protected] says...
> Carl Fogel wrote:
> > I'm still puzzling over the fixed-gear bicycle folk and their flat warning that a fixed-gear
> > bicycle will rip any chain-tensioner right off the frame when the load reverses direction.
>
> I don't know what a motorcycle chain tensioner looks like, but perhaps we're talking about
> different beasts. I don't think the bicycle chain tensioners (see
> http://www.surlybikes.com/hotmetal/parts_Singlelator.html for an example on an awful web page)
> allow the bottom run of the chain to go straight. Since the bottom run is not allowed to
> straighten completely, there will be a *lot* of force on the tensioner during backpedaling. Enough
> force to ruin the forementioned tensioner without question. Math can be supplied if necessary.
>
> If the bottom chain run *is* allowed to straighten, the top run is probably loose and derailing is
> a distinct possibility.
>
> How about the motorcycle chain tensioner?
>
> Dave dvt at psu dot edu
>
>

On a MC, becauses the fact that the wheel is adjustable to tightent he chain, the chain also rubs
against a nylon wear plate. Not terribly efficient, but it's not like you have to pedal this thing.
--
_________________________
Chris Phillipo - Cape Breton, Nova Scotia http://www.ramsays-online.com

 

[Smmb]

Are you drinking too much coffee ?

"Jonesy" <[email protected]> a écrit dans le message de :
news:[email protected]...
> Rick Onanian <[email protected]> wrote in message
news:<[email protected]>...
> > On 29 Jan 2004 09:48:54 -0800, [email protected] (Jonesy) wrote:
> > >It's a strawman created by quoting out of context. By removing qualifiers and context, you can
> > >twist quotes into anything you want.
> > >
> > >> >Carl has done a very good job at creating this image, but nowhere
will
> > >> >you actually find such a claim.
> > >>
> > >> Carl probably did not "create" that image;
> > >
> > >Sure he did. You certainly bought it. Nowhere did I write what you mistakenly ascribed to me,
> > >but that exact image was what Carl has been writing for several posts.
> >
> > For somebody who in the previous sentence lamented the loss of context, you sure were quick with
> > the contextectomey.
>
> Hardly. You state the above, then go about justifying it. Since the justification is based on a
> false premise, it is unnecessary and superfluous. In any case, it's a red herring. You misquoted
> me (not specifically naming me, but I will take it as given that you were speaking about me) in
> the exact (false) image that Carl created. If you had actually *read* what I had written, you
> might have not written the misquote.
>
> > You apparently can't accept that, regardless of intent or thought (or, for that matter, logic),
> > an image can be created in a reader's mind that was not expressed.
>
> Hogwash. I can accept it just fine, because I have seen it in action. You have just demonstrated
> that you got an image that was in no way my intent. The very fact that you ascribed to me a belief
> that can in no way be found in my writings points out the truth of your statement. While it was
> your intent to paint *me* with that brush, it certainly does have broader application.
>
> > Such an image is worth arguing, precisely because it results in express and specific replies to
> > destroy that image.
>
> When one has to repeat multiple times one's intent, then it moves from a mistaken impression to
> something more pointed - and it points to purposefulness on the part of the "misunderstander."
>
> > >> He then proceeded to argue what he thought you meant, which, while useless to you, did cause
> > >> the whole thing to be cleared up by you saying exactly what you think -- which helps properly
> > >> communicate to others who may have read the same image.
> > >
> > >Except that by explicitly writing down that list, I was forming merely a composite of what *I
> > >had already written.* Just a shorter format.
> >
> > A shorter, more direct, more expressive format that dispels any false imagery.
>
> Indeed it does. But it should not have to be written more than once.
>
> > Having wrote that list, you've solved the problem of the false image -- and again, let me say
> > that it exists regardless of intent or fault.
>
> You are attempting to shrug it all off. I do not accept your analysis. Carl continued to infer non-
> existent beliefs on my part even after he was corrected. That screams "purpose" to me.
>
> > >While I cannot be sure that Carl twisted my words with malice aforethought,
> >
> > Be careful; by mincing words like that, you're liable to create, once again, false imagery of an
> > opinion you may not hold.
>
> Are you daft? Let me type it again: I do not know whether or not Carl twisted my words with malice
> aforethought. I do not think it can be known.
>
> > >it certainly was effective for his purposes of bashing bike snobs.
> >
> > We could use the occasional bashing to bring us down to earth.
>
> What's this "we" ****? For years, I rode an entry-level mountain bike with no thought of anything
> but riding. I still own the thing, and use it as a beater bike.
>
> I have been recommending used and entry-level bikes. Maybe *your* bike snobbery needs a little
> trimming, but I think mine is about as small as it gets.
>
> I notice that you neglected to address my safety concern. Do I take from that that you concede
> that point?
>
> > >*You* bought it, after all...
> >
> > What makes you think that?
>
> Shall I quote you back your original misquote? Unless you are just taking up the mantle of basher,
> and are continuing Carl's well-started work.
>
> Regards,
>
> R.F. Jones

 

[G.T.]

dvt wrote:
> Eric M wrote:
>
>>> How about the motorcycle chain tensioner?
>>
>>
>> They allow the bottom run to go straight when throttle is closed and the rear wheel is pulling
>> the engine around.
>>
>> The chain has to run loose enough to allow the suspension to move. Since the countershaft
>> sprocket is not concentric with the swingarm pivot, the chain is tightest when the countershaft,
>> swing arm pivot and rear axle are in line. With the suspension extended or compressed from that
>> position the chain becomes slack.
>>
>> I usually set my modern trials bikes for a couple inches of chain slack. I don't know how much
>> slack a singleator is intended to take up but if it's the same amount that a derailleur would
>> than I could see how it might get damaged by backpedalling..
>
>
> How does a motorcycle keep the chain from derailing when the chain is slackest (i.e. suspension
> fully compressed?). If one allowed "a couple inches of chain slack" on a bicycle, the chain would
> be derail in a heartbeat.
>

I don't know. But I never threw a chain in 20 years of off-roading. Deeper teeth on the sprockets?
Better alignment or lack of flex?

Probably beefier chain guides:

http://yzworks.tripod.com/id106.htm

Middle left picture is probably the best.

Haha, ah, the memories. My last bike of my own was a 1980 YZ400. Borrowed others since then, but
that was the last one I could call my own.

Greg

--
"Destroy your safe and happy lives before it is too late, the battles we fought were long and hard,
just not to be consumed by rock n' roll..." - The Mekons

 

[Jonesy]

Rick Onanian <[email protected]> wrote in message news:<[email protected]>...
> On 30 Jan 2004 10:54:32 -0800, [email protected] (Jonesy) wrote:
> >> >While I cannot be sure that Carl twisted my words with malice aforethought,
> >>
> >> Be careful; by mincing words like that, you're liable to create, once again, false imagery of
> >> an opinion you may not hold.
> >
> >Are you daft? Let me type it again: I do not know whether or not Carl twisted my words with
> >malice aforethought. I do not think it can be known.
>
> "do not know whether or not he did...do not think it can be known" creates a far different image
> from "cannot be sure that he did". If you cannot see that, then you are the daft one.

I'm sure you'd be able to explain the "far different" images. I can't wait.

> >> >it certainly was effective for his purposes of bashing bike snobs.
> >>
> >> We could use the occasional bashing to bring us down to earth.
> >
> >What's this "we" ****? For years, I rode an entry-level mountain bike with no thought of anything
> >but riding. I still own the thing, and use it as a beater bike.
>
> And yet, you feel that bike shaped toys are not reasonable transportation.

Yes. The fact of the matter is that the entry-level MTB that I bought is *exactly* the same type as
I would recommend for someone to purchase now. It was not a MTB-shaped toy. It was purchased at a
bike shop.

I think you are confused - when was an entry-level MTB ever considered to be one of the *Mart bikes?

> >I have been recommending used and entry-level bikes. Maybe *your* bike snobbery needs a little
> >trimming, but I think mine is about as small as it gets.
>
> ...and I have been recommending used salvage bikes requiring minimal work. That's pretty similar.

So what are you going on about?? Bashing equipment snobs in any hobby is fruitless.

> >I notice that you neglected to address my safety concern. Do I take from that that you concede
> >that point?
>
> Did you forget that I had the same safety concern, hence my recommendation?

I was getting at the logic of it. So, if we are in agreement, what is your problem?

> This is pointless and silly bickering anyway. Who cares?

Well, I *do* care about having my writings misrepresented. I also care about beginning bicyclists
getting stuck with a piece of **** and thinking that it represents bikes as a whole. A well-adjusted
entry-level bike (as opposed to the bike-shaped toys sold at *Marts, for those who still can't
distinguish between the two) might cost the same or a little more than some of the junk sold at
*Marts. But the performance differences are worlds apart.

> To move on, let me say this about QR levers facing the wrong way: Looking at my road bike, a 2001
> Giant TCR2, I noticed that the rear QR lever was the wrong way! It was leading with the end. I
> went to flip it around, and found that the frame PREVENTS IT! The chain stay bulges right at the
> dropout such that the QR can lead or face down and very slightly back, but cannot trail. I turned
> it to it's down-and-slightly-back position.

My "good" MTB is the same way, due to boxed-in dropouts. I have to accept that the lever will face
forward. On the plus side, it would be tough to "snag it open", due to how the chainstay is shaped.
Anything that would foul the lever would probably foul the spokes as well.

> I'm not worried, however -- in this whole discussion, when discussing leading QRs as a potential
> hazard (separate from using QR closure as a gauge to how the rest of the bike was built), we
> completely ignored this: QR levers are on the left side.

Not the ones I saw at Costco! They were about evenly split between right and left.

> In the US, where the cheap *Mart bikes are sold, one rides on the right side of the road. If
> there's brush sticking out, it would catch the derailer, not the QR! The QR is on the other side.

This assumes the rider is not one of those brain-dead "ride-against-traffic" folks that give
vehicular cyclists a bad name. [There's a rant best saved for another day...]

> The point stands, however, about the shoddy materials and workmanship of such bikes. Somebody
> considering one should consider a salvaged / yard sale bike with $20 worth of new tires and tubes,
> which would be cheaper than even the cheapest clearance bike at *Mart ($40 or so, sometimes).
> Somebody who already bought one should attempt to make the bike safe by properly tightening
> fasteners and such, and keep an eye on such things as the brakes for possible breakage.

Brakes that break? Heh.

Salvage bike from yard sale, some cheap parts, and a downloaded Barnett's Manual. A small,
portable tool kit (cheap, if not the most effective set of tools) that comes with tire levers and
a chain tool.

Sounds like a heck of a plan.

Sincerely,

R.F. Jones

 

[Carl Fogel]

David Kerber <ns_dkerber@ns_ids.net> wrote in message news:<[email protected]>...
> In article <0ZySb.36666$6O4.1027167@bgtnsc04- news.ops.worldnet.att.net>,
> [email protected] says...
>
> ...
>
> > > How does a motorcycle keep the chain from derailing when the chain is slackest (i.e.
> > > suspension fully compressed?). If one allowed "a couple inches of chain slack" on a bicycle,
> > > the chain would be derail in a heartbeat.
> > >
> > > Dave dvt at psu dot edu
> > >
> >
> > Are you talking about the same thing? A couple inches of slack on a motorcycle would usually
> > mean you can move the middle of the lower chain run about 2" difference from pushed all the way
> > up with a
>
> On a bike, that's a *LOT* of slack, and as he said, it would likely derail in a hurry.
>
>
> > finger to pushed all the way down. The chain is nowhere near 2" longer than it needs to be.

Dear Dave, Dave, and Dave,

On elderly twin-spring trials machines, there was only about 3-4 inches of rear-suspension movement,
with the swing-arm pivot a few inches behind the countershaft sprocket (the equivalent of a bicycle
front sprocket, but only around 14 teeth).

Before trailing-arm chain-tensioners were mounted under the swing-arm, typical chain-tension was
supposed to be one-half to an inch of up-and-down play in roughly the middle of the lower chain run.

Once chain-tensioners became common, riders became rather cavalier and would let chains droop and
sag embarrassingly--without any de-railing problems. The tensioners work awfully well.

(Chain-tension was adjusted by loosening the rear axle nut and turning snail-shaped cam-washers
against small posts, moving the axle back and forth in a completely enclosed horizontal slot.)

With the move to mono-shock suspension, rear travel increased wildly, chains ran looser, and guides
were added to the tensioners. (Guides may have been included on the old Montesa and were certainly
on the Honda, along with huge flat shields between the wheel and the chain, but they were usually
removed and considered no more useful than lawyer lips.

This modern looseness due to huge rear suspension travel is what the "couple of inches of slack" means--
two inches or more of up-and-down play in roughly the middle of the lower chain run. Rear sprockets
also seem noticeably smaller in modern trials bikes, probably to reduce unsprung weight and to raise
the lower parts even higher above the rocks.

You've raised some interesting possibilites about the difference in chains and gear teeth. The
motorcycle chains are heavier and the sprocket teeth are wider. The teeth might be proportionally
taller than bicycle sprocket teeth.

Sideways flexibility may differ, but I suspect that trials motorcycle chains will bend sideways a
fair amount right from the factory. Probably there's a chain page somewhere that will save me from
getting my hands dirty flexing chains on the garage floor.

In case you're looking, the motorcycle chains, at least back then, were 428h and 520. I never saw
either de-rail under remotely normal circumstances, although I've seen one broken when a heavy coat
tangled in the rear sprocket at speed and another de-railed by an awkward stick in a mudhole.

Remember, motorcycle chains and sprockets on even feeble trials machines routinely handle a dozen
horsepower and more. A particularly dim-witted rider whose initials are C.F. once secured a Honda
trials bike in a parking lot with a stout padlock by running the hasp over the top chain run and
through one of the large holes in the rear sprocket. When he forgot what he'd done and rode off, the
chain instantly popped the hasp our of the padlock.

The experiment was repeated unintentionally a few months later with the same results, leading the
absent-minded C.F. to swear off mis-using expensive padlocks. Neither the chain nor the rear
sprocket suffered any apparent damage.

C.F.

 

[Carl Fogel]

dvt <[email protected]> wrote in message news:<[email protected]>...
> Carl Fogel wrote:
>
> > dvt <[email protected]> wrote in message news:<[email protected]>...
> >
> > [snip]
> >
> > Dear Dave and others,
> >
> > I finally found some so-so picture of a 1970's trials motorcycle's trailing-arm chain-tensioner.
> >
> > http://home.connection.com/~dank/montesa.htm
> >
> > It's the short trailing arm hanging down from the swing-arm, pointing backward. Unfortunately,
> > the arm is the same silver color as the rear wheel rim behind it.
> >
> > You can actually see the chain-tensioner arm better in picture right-3, looking through the
> > wheel's spokes from the other side.
> >
> > A powerful wound spring forces the trailing end of the arm (and the chain slithering over the
> > pad) up toward the swing arm.
> >
> > Such arms survive in deep mud, heavy brush, vicious rocks, and all sorts of other abuse, far
> > worse than pavement-oriented fixed-gear bikes ever face.
> >
> > Again, whether such arms would be of any practical use is quite another question. I'm just
> > puzzled to hear that such an arm would be torn off by a fixed-gear bicycle---no forces that I
> > can see will trouble it in the slightest.
>
> You are correct. A chain tensioner of that type would not be troubled by a fixie. In the picture
> shown, there is not very much chain slack to be removed by the tensioner. That much slack is
> probably not cause for concern as it doesn't look like enough to make the chain derail easily.
>

[snip]

> Dave dvt at psu dot edu

Dear Dave,

The picture may be a little deceptive if you're not familiar with trials bikes.

The chain is not going around a hard-to-see front sprocket in the dark tangle directly above
the foot-peg.

It's going much deeper into the silver transmission case around a hidden cog almost directly above
the forward end of the brake-pedal. The top right-hand picture barely shows a long narrow opening in
the top of the transmission case--the tiny blue in-line gas filter is pointing down at it.

So the chain-run may be a good eight inches longer than the picture suggests to the non-
motorcyclist.

Another confusing point is that this is a two-hundred pound motorcycle being posed for the camera
with its side-stand propped up on a block. Typically, the machine is left in first gear with the
front sprocket locked solid against the dead engine and rolls slightly backward--which tightens the
lower run. Even on what seem to be flat surfaces, the chain of a parked trials bike is usually under
load in one direction or the other. (They tend to roll back and around the sidestand.)

From experience, I'd expect that this machine has about an inch and a half of up-and-down play in
roughly the middle of the lower chain-run, even though it looks tighter than that in the picture.
It's sort of like the television effect of the camera adding ten pounds.

Still, it's not much slack for this kind of bike and far less slack than modern monoshock machines
use. Yet chain de-railing is practically unheard of on even the sloppiest motorycle, even though it
has all that suspension travel--I keep wondering what makes bicycle chains and gears so much more
prone to parting ways.

Carl Fogel

 

[A Muzi]

dvt wrote:

> Carl Fogel wrote:
-snip long about motorcycle chain tensioners-

Some engine timing chains have used a pusher plate to keep the chain from rattling, too. Those are
never loose enough to derail anyway. The shape of the links and teeth (and ratio of width to height)
are siginficantly different from bicycle equipment. I am not at all familiar with motorcycles but my
impression is that their chain is more like an engine chain and less like ours.

If a motorcycle which has a 'pad block' were to lose same, would the chain just be noisy or would
it fall off?

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

 

[Carl Fogel]

A Muzi <[email protected]> wrote in message news:<[email protected]>...
> dvt wrote:
>
> > Carl Fogel wrote:
> -snip long about motorcycle chain tensioners-
>
> Some engine timing chains have used a pusher plate to keep the chain from rattling, too. Those are
> never loose enough to derail anyway. The shape of the links and teeth (and ratio of width to
> height) are siginficantly different from bicycle equipment. I am not at all familiar with
> motorcycles but my impression is that their chain is more like an engine chain and less like ours.
>
> If a motorcycle which has a 'pad block' were to lose same, would the chain just be noisy or would
> it fall off?

Dear Andrew,

If the pad or block wears out and comes off, there's a bit of noise, but nothing else tears off. If
anything makes the trailing arm swing to one side or the other, the moving chain rattling through
the cage tends to center it again.

I once lost a block during an event and simply finished the first of three loops, stopped at the
parking area, removed the whole tensioner (a single large circlip) so that the chain wouldn't wear
through the exposed metal frame, conscientiously tightened the chain again, and continued.

I found a 14-tooth 428h countershaft (front) motorcycle sprocket and a 14-tooth rear Shimano cog,
with some small pieces of chain, and put up some pictures.

Here are the two chains:

http://home.comcast.net/~carlfogel/download/chain_a.jpg

The thin piece on the bottom of the motorcycle is the long masterlink circlip. A 428h is small,
sissy chain for little trials bikes. Real men use 520.

Here are the two 14-tooth cogs overlaid slightly apart:

http://home.comcast.net/~carlfogel/download/chain_b.jpg

Both cogs have two teeth resting on the same block of yellow sticky-pad. The bicycle cog is
shifted to the left, and this shows the square top of the bicycle cog tooth, which doesn't stick
up as much as the pointed motorcycle cog tooth. It's as if Shimano took a motorcycle cog and
ground the tips flat.

Does the rest of the gear-tooth seen in profile match? Yes, as far as I can tell:

http://home.comcast.net/~carlfogel/download/chain_c.jpg

Hard to tell, but the picture above is looking down at one cog laid over the other with only a tiny
offset. Look closely and you can see the motorcycle cog's tooth-tips sticking out and a slight
misalignment. The bright lines at the base of the teeth are chain-wear marks on the bicycle cog.

Here's an overhead view of the two cogs. The tips of the motorcycle cog's teeth have a small bevel
on all four sides:

http://home.comcast.net/~carlfogel/download/chain_d.jpg

The bicycle teeth, out of focus and too dark to see well, are ground at subtle side-to-side angles,
presumably to help the chain de-rail and shift to the next cog.

Viewed with links in place, both gears seem to engage at about the same point on the roller--but the
motorcycle roller is obviously far larger.

Something in this design must account for why fairly loose motorcycle chains under far greater loads
in both directions rarely if ever de-rail, even with the rear suspension thrashing up and down,
while fixed gear bicycles derail more easily and more often, if I understand what the fixed-gear
folk are saying.

One other thing that might be involved is the difference in gear sizes. The motorcycle has the 14-
tooth gear on the front and a 50+ tooth on the rear, while a fixed-gear bicycle would have something
like a 40-tooth sprocket in front and an 18-tooth in the rear.

Do fixed-gear bikes lose their chains off the large front or off the small rear?

Carl Fogel

 

[Dvt]

Carl Fogel wrote:
> Something in this design must account for why fairly loose motorcycle chains under far greater
> loads in both directions rarely if ever de-rail, even with the rear suspension thrashing up and
> down, while fixed gear bicycles derail more easily and more often, if I understand what the fixed-
> gear folk are saying.

I'd guess you're right. Most bicycle components were designed to make shifting *easy*. Imagine
putting a bicycle-type front derailer on a motorcycle and attempting to shift chainrings. Just how
long do you suppose that dearailer would last? (rhetorical question, of course). That should give us
an idea about the relative ease of chain derailing.

I don't know what it is about the motorcycle chain design that makes it harder to derail, but I'm
guessing it's the width of the parts. Imagine the extreme case where the cog and chain are 1 m
wide but the pitch and tooth profile remain the same. That chain would be very difficult to
derail, I'd think.

I think the relative size of the cogs is probably not a significant part of the difference between
bikes and motorcycles.

As to this part of your message:

> ...while fixed gear bicycles derail more easily and more often, if I understand what the fixed-
> gear folk are saying.

Fixed gear bicycles, set up properly, are actually quite unlikely to derail. A poorly adjusted fixie
is quite likely to throw a chain.

To learn about this first-hand, I propose the same experiment that I proposed before. You can do
this all in your workshop. Take the chain off your bike, shorten it, and route it to your
favorite gear to make a singlespeed. Adjust the wheel properly for chain tension and then try to
derail the chain using your front derailer. Don't try too hard -- you don't want to lose a
perfectly good derailer!

Now readjust your wheel so the chain has plenty of slack (or insert an extra pair of links). Again
try to derail the chain. See how easy that was?

Dave dvt at psu dot edu

 

[quincywally]

I have hired Val at my shop.
Aaron's Bicycle Repair in West Seattle.

I too often went to Bikesmith for 'therapy' as I called it. Val is my friend and I am proud to work with him.

Come visit us.
www.RideYourBike.com