MA2 rim cracking - what might be causing this?
David Green
which was interferring with my bottle dynamo. I expected to find a
broken spoke but there were none.
When I removed the tyre and rim tape, I spotted cracks in the
aluminium beside all of the drive-side sockets. (MA2s have full-depth
steel sockets between the double walls.) None of the non-drive-side
sockets had cracks. Each crack is concentric to the spoke hole and
about 1mm away from the edge of the socket, most pronounced towards
the outside edge of the rim. The cracks only appear in the wall of the
rim in contact with the rim tape. No cracks visible when tyre fitted
or in braking surfaces.
I assume that the wheel is going out of true because of these cracks.
Is this kind of thing common in MA2s? Do you think that I over
tensioned the spokes? I don't think so, because the wheel never taco'd
during stress relieving.
This wheel is 32H, which I built approx 4 years ago, ridden about 40
miles per week on decent roads (no pothole colisions). Spokes were
build according to Jobst's book, stress-relieved etc. Campag sf hubs,
SSDB spokes.
Any suggestions for a replacement rim (same ERD) and for improving my
build technique.
David Green.
Cambridge, UK.
MikeYankee
thousands of miles on them, and haven't seen what you describe.
I did have similar cracking on FiR Nettuno rims on a used bike that I bought
several years ago, but that rim is totally different in design and lacks
eyelets.
The Torelli Master rim has the same ERD as the MA-2, I think.
Mike Yankee
(Address is munged to thwart spammers.
To reply, delete everything after "com".)
daveornee
Very interesting! I would like to see what Jobst Brandt has to say on
this one. I say that it is fatigue due to the inner wall handling the
load and not sharing it with the outer wall. It could be that the inner
wall was thinner than it should have been, combined with the socket
putting most all the load there. Drive side spokes on the rear wheel,
with typical dish, carry a considerable amount of the load. If you want
the same ERD you should look in the Rinard or DT-Swiss charts to make
the comparison. http://www.damonrinard.com/spocalc.xls
http://www.dtswiss.com/index.asp for this one you will need to click the
internal link and agree to their terms. If you can afford new spokes and
want to get some help with evening out the load on the dished rear, you
can go with a rim that has offset spoke holes, like Bontrager Fairlane
Asym or Ritchey Girder Pro OCR, etc.
--
Carl Fogel
Dear David,
If you can email me any pictures of your rim, I'd be glad
to host them. There are some current threads about Mavic
rim failures in which MA2's are often mentioned in contrast
to other Mavic rims, so I expect that people would be
interested in pictures for comparison and better able
to give you helpful advice.
In any case, sorry about your wheel troubles.
Carl Fogel
Alex Rodriguez
david2...@ps.ge.com says...
Making some pictures available would help in analyzing the failure.
-----------
Alex
Mike S.
This one I gotta be in on!
Mike
Tim McNamara
> I recently noticed that my rear wheel had developed a lateral wobble
> which was interferring with my bottle dynamo. I expected to find a
> broken spoke but there were none.
>
> When I removed the tyre and rim tape, I spotted cracks in the
> aluminium beside all of the drive-side sockets. (MA2s have
> full-depth steel sockets between the double walls.) None of the
> non-drive-side sockets had cracks. Each crack is concentric to the
> spoke hole and about 1mm away from the edge of the socket, most
> pronounced towards the outside edge of the rim. The cracks only
> appear in the wall of the rim in contact with the rim tape. No
> cracks visible when tyre fitted or in braking surfaces.
Concentric to and not radiating from the spoke holes? Can you post a
photo of this? I'd like to see it.
> I assume that the wheel is going out of true because of these
> cracks.
Makes sense.
> Is this kind of thing common in MA2s?
No. It was common in MA40s. Question for you- is this an MA2
"argent" silver anodized rim, or a polished aluminum rim. I've never
seen one of the former, but have been assured they existed.
> Do you think that I over tensioned the spokes? I don't think so,
> because the wheel never taco'd during stress relieving.
>
> This wheel is 32H, which I built approx 4 years ago, ridden about 40
> miles per week on decent roads (no pothole colisions). Spokes were
> build according to Jobst's book, stress-relieved etc. Campag sf hubs,
> SSDB spokes.
>
> Any suggestions for a replacement rim (same ERD) and for improving my
> build technique.
If you can find an MA2, I don;t htink you can do better. But avoid
the anodized ones (see the other threads going on about anodizing
and premature rim failures).
Matt Cahill
I had a non-anodized, tubular rim tear out a socket and the side split
away from the rest of the rim at that point. However, the rim had
been on the bike for twenty years and been ridden through all kinds of
muck and abuse and was badly out of true. My theory in that case was
that the rim's sidewall had been worn thin and fatigued at that point
to the extent that it could no longer support the compressive forces
on the rim.
The failure mode was fairly benign. I was going down a hill when I
noticed that the tire started rubbing on the frame. Even with this
amount of damage, the wheel easily supported my weight and allowed me
to come to a safe controlled stop.
jim beam
contributor. wheels need to be well tensioned so spokes don't go slack
in use, but they don't need to be over-tensioned. there is a myth that
the tighter the spoke, the stiffer the wheel - simply not true - so some
folks tend to go overboard on this. over-tension will accelerate
aluminum's natural failure process.
David Green
> Dear David,
>
> If you can email me any pictures of your rim, I'd be glad
> to host them. There are some current threads about Mavic
> rim failures in which MA2's are often mentioned in contrast
> to other Mavic rims, so I expect that people would be
> interested in pictures for comparison and better able
> to give you helpful advice.
>
> In any case, sorry about your wheel troubles.
>
> Carl Fogel
Pictures as requested:
Most of the drive side sockets have these cracks:
http://web.onetel.net.uk/~davidwgreen/rimpics/2.JPG
Cracks seem to be concentric with the spoke hole:
http://web.onetel.net.uk/~davidwgreen/rimpics/3.JPG
When I did look more closely, some of the spoke holes with socket
cracks also have small cracks emerging from the ferrule side of the
rim:
http://web.onetel.net.uk/~davidwgreen/rimpics/4.JPG
Any ideas?
David Green
Tom Nakashima
Very interesting failure.
-tom
"David Green" <david2...@ps.ge.com> wrote in message
news:2e60080f.04030...@posting.google.com...
Phil Brown
>Any ideas?
Haven't seen the pictures but sometimes rims crack. MA2s are starting to get
old, ride a lot, get cracks. It's too bad because they arem't made anymore but
it certainly isn't unusual or something rare. Stuff happens. I had one MA2
crack over the years, certainly better then the MA40 where the only ones that
didn't crack are the spare pair of wheels that almost never get ridden.
Phil Brown
Mike S.
HOLY COW! The world's gonna end!
I hate to break it to you Jobst, but your favorite rims crack exactly the
same as any others.
Is nothing worth riding if MA2s are going to crack too? Geez! the pressure!
Mike
Tim McNamara
> Cracks seem to be concentric with the spoke hole:
> http://web.onetel.net.uk/~davidwgreen/rimpics/3.JPG
>
> When I did look more closely, some of the spoke holes with socket
> cracks also have small cracks emerging from the ferrule side of the
> rim: http://web.onetel.net.uk/~davidwgreen/rimpics/4.JPG
Interesting. No. 4 looks like a typical crack seen on all the rim
failures I have had (but those have literally all been with anodized
rims). Nos. 2 + 3 are quite interesting, though. Is the concentric
crack on the non-drive side?
If you posted it, I can't remember: what type of hub, what type of
spokes, how many spokes, and how many miles on this wheel?
Tim McNamara
> HOLY COW! The world's gonna end!
>
> I hate to break it to you Jobst, but your favorite rims crack
> exactly the same as any others.
You seem to forget that Jobst has also reported a cracked MA2, on his
friend Richard Mylarnik's bike during a tour of the Alps.
> Is nothing worth riding if MA2s are going to crack too? Geez! the
> pressure!
Well, we have collected two reports of MA2s cracking, compared to
hundreds of various other rims. At this point, I think the odds are
best to stick with the MA2s if you can find them.
jim beam
briefly, the interesting features to note are:
1. the very good overall condition of the rim - indicative of low
mileage and good environment.
2. cracking on the outside surface is off-center of the eyelet hole -
center is the point of maximum stress and the usual orientation for any
radial cracking due to any anodizing
3. the outside crack also follows a jagged line indicative of an
intergranular fracture mode
4. there is pull-through top & bottom of the socket with cracking on the
inside edge.
5. cracking on this inside surface appears to have initiated at the tire
bead well shoulder - a stress riser.
assuming this rim does not have any particular extrusion issue, all
these symptoms appear to point to a tension problem. it's not possible
to say which occurred first, the inside or the outside, but they are
both symptoms of the same issue.
were these wheels built using a tensiometer for the spokes? mavic
recommended tension for their later rims is ~1,000N to 1,100N drive side
rear. many builders exceed this under the misconception that the
greater the tension, the stiffer the wheel. excess tension does not
alter the modulus of the spokes or the rim so it cannot make wheels
stiffer - all it does is push the rim [and all other components] closer
to their stress limit.
Terry Morse
> mavic
> recommended tension for their later rims is ~1,000N to 1,100N drive side
> rear. many builders exceed this under the misconception that the
> greater the tension, the stiffer the wheel. excess tension does not
> alter the modulus of the spokes or the rim so it cannot make wheels
> stiffer - all it does is push the rim [and all other components] closer
> to their stress limit.
You would recommend enough spoke tension that would prevent the
spokes from going slack, but no more? I think Jobst has said about
100 kgf is about the maximum, before the MA2 rim begins to warp
during stress relieving. Sounds pretty close to the 1,000N
recommendation.
--
terry morse Palo Alto, CA http://bike.terrymorse.com/
jim beam
> jim beam wrote:
>
>
>> mavic
>>recommended tension for their later rims is ~1,000N to 1,100N drive side
>>rear. many builders exceed this under the misconception that the
>>greater the tension, the stiffer the wheel. excess tension does not
>>alter the modulus of the spokes or the rim so it cannot make wheels
>>stiffer - all it does is push the rim [and all other components] closer
>>to their stress limit.
>
>
> You would recommend enough spoke tension that would prevent the
> spokes from going slack, but no more?
yes, thats right.
> I think Jobst has said about
> 100 kgf is about the maximum, before the MA2 rim begins to warp
> during stress relieving. Sounds pretty close to the 1,000N
> recommendation.
yes, 1000N ~= 100Kgf
Carl Fogel
Dear Tim,
Here's the original post. Looks like campag sf hubs, SSDB
spokes, 32h, and 4 years at 40 miles per week ~ 8k miles.
(Personally, I think ugly questions might be raised about
bottle dynamos, which have had a free ride for far too
long from the forgiving folks at rec.bicycles.tech.)
Carl Fogel
David Green
> Interesting. No. 4 looks like a typical crack seen on all the rim
> failures I have had (but those have literally all been with anodized
> rims). Nos. 2 + 3 are quite interesting, though. Is the concentric
> crack on the non-drive side?
No. All the cracks are drive side. In fact, most of the drive side
spokes exhibit them.
>
> If you posted it, I can't remember: what type of hub, what type of
> spokes, how many spokes, and how many miles on this wheel?
It was me. Campag 'Record' 32H small-flange circa 1983. This wheel was
built approx 4 years ago, ridden about 40 miles per week on decent roads
(no pothole colisions). Built according to technique in Jobst's book,
stress-relieved etc. Stainless DB DT spokes.
--
David Green
Cambridge, UK.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
DON'T MAIL THE REPLY ADDRESS! Before you click 'Send',
replace 'deadspam.com' with 'onetel.net.uk'.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
David Green
> were these wheels built using a tensiometer for the spokes? mavic
> recommended tension for their later rims is ~1,000N to 1,100N drive side
> rear. many builders exceed this under the misconception that the
> greater the tension, the stiffer the wheel. excess tension does not
> alter the modulus of the spokes or the rim so it cannot make wheels
> stiffer - all it does is push the rim [and all other components] closer
> to their stress limit.
I didn't use a tensiometer to build this wheel, so I cannot state the
exact tension. What I did was try to get the tension nice and high
because my understanding is that that makes the wheel as strong as
possible. (By that I mean most resistant to possible collapse by spokes
becoming detensioned, say by hitting a pothole.)
I frequently stress-relieved the wheel during tensioning, keeping alert
for it 'tacoing' - which Jobst says indicates the tension is at the
limit the rim can stand. However, I never took the tension that high: I
was satisfied with the nice high 'ping' emitted by the drive side spokes
when plucked, and called it a day.
I find it interesting that you mention wheel 'stiffness'. That certainly
wasn't in my mind as a reason to achieve a decent tension. I was simply
after a durable (strong) build.
Tim McNamara
> 2. cracking on the outside surface is off-center of the eyelet hole
> - center is the point of maximum stress and the usual orientation
> for any radial cracking due to any anodizing
You keep saying this but reality is otherwise. The cracks can be
tangential to the spoke hole or can describe a chord through the hole
quite readily.
> 3. the outside crack also follows a jagged line indicative of an
> intergranular fracture mode
Isn't that how all cracks propogate through aluminum?
> assuming this rim does not have any particular extrusion issue, all
> these symptoms appear to point to a tension problem.
What is a "tension problem" other than something that is treated by a
massage therapist, a nice single malt Scotch or a trip to the sauna-
or all three?
Tim McNamara
> Here's the original post. Looks like campag sf hubs, SSDB spokes,
> 32h, and 4 years at 40 miles per week ~ 8k miles.
> Tim McNamara <tim...@bitstream.net> wrote in message
> news:<m2smgna...@Stella-Blue.local>...
>
>> david2...@ps.ge.com (David Green) writes:
>>
>> > Cracks seem to be concentric with the spoke hole:
>> > http://web.onetel.net.uk/~davidwgreen/rimpics/3.JPG
>> >
>> > When I did look more closely, some of the spoke holes with socket
>> > cracks also have small cracks emerging from the ferrule side of
>> > the rim: http://web.onetel.net.uk/~davidwgreen/rimpics/4.JPG
>>
>> Interesting. No. 4 looks like a typical crack seen on all the rim
>> failures I have had (but those have literally all been with
>> anodized rims). Nos. 2 + 3 are quite interesting, though. Is the
>> concentric crack on the non-drive side?
>>
>> If you posted it, I can't remember: what type of hub, what type of
>> spokes, how many spokes, and how many miles on this wheel?
Thanks. This is very low mileage for any rim to fail in this manner,
IMHO, and is especially so for an MA2. As a result I'm very
intrigued. The rim appears to be the typical shiny version of the
MA2 and not the silver anodized "argent" version, so that variable
seems not to be present.
With a highly dished wheel, almost all the vertical load is carried by
the drive side spokes- basically making this a 16 spoke wheel; that
said, I have a rear wheel with an MA2 laced to Campy 9sp hubs with DT
14/15 g spokes; I have about 10,000 to 12,000 miles on it thus far
with no failure. I weighed about 195 at "racing weight" and, since I
no longer race, now weigh 205-210 during the summer. Needless to say,
I'm not a climber. So I can't solely blame the cracking on the dish
or I'd expect to have replicated it myself.
Since these failures are not commonly reported in this newsgroup about
MA2 rims, which have been around for a long time, I must conclude
there may be something about this *particular* MA2 that contributed
to the failure. What that is, I don't know. If it were my wheel,
I'd rebuild it with an MA2 again, if I could find one, and reuse the
same spokes by transferring them in position to the new rim.
Tim McNamara
> Tim McNamara wrote:
>> Interesting. No. 4 looks like a typical crack seen on all the rim
>> failures I have had (but those have literally all been with anodized
>> rims). Nos. 2 + 3 are quite interesting, though. Is the concentric
>> crack on the non-drive side?
>
> No. All the cracks are drive side. In fact, most of the drive side
> spokes exhibit them.
I didn't phrase that well. I expected the cracks to be associated
with drive side spokes. My question was on which side of the rim are
the cracks- the drive side or the non-drive side?
G.T.
"David Green" <david...@deadspam.com> wrote in message
news:4049...@212.67.96.135...
> jim beam wrote:
>
> > were these wheels built using a tensiometer for the spokes? mavic
> > recommended tension for their later rims is ~1,000N to 1,100N drive side
> > rear. many builders exceed this under the misconception that the
> > greater the tension, the stiffer the wheel. excess tension does not
> > alter the modulus of the spokes or the rim so it cannot make wheels
> > stiffer - all it does is push the rim [and all other components] closer
> > to their stress limit.
>
> I didn't use a tensiometer to build this wheel, so I cannot state the
> exact tension. What I did was try to get the tension nice and high
> because my understanding is that that makes the wheel as strong as
> possible. (By that I mean most resistant to possible collapse by spokes
> becoming detensioned, say by hitting a pothole.)
>
> I frequently stress-relieved the wheel during tensioning, keeping alert
> for it 'tacoing' - which Jobst says indicates the tension is at the
> limit the rim can stand. However, I never took the tension that high: I
> was satisfied with the nice high 'ping' emitted by the drive side spokes
> when plucked, and called it a day.
>
> I find it interesting that you mention wheel 'stiffness'. That certainly
> wasn't in my mind as a reason to achieve a decent tension. I was simply
> after a durable (strong) build.
Don't mind him, he's obsessed with tensiometers. And he also believes
manufacturers.
Greg
David Green
They are on the drive side of the rim. That is, the side of the rim
furthest from the hub.
jim beam
> jim beam <u...@ftc.gov> writes:
>
>
>>2. cracking on the outside surface is off-center of the eyelet hole
>>- center is the point of maximum stress and the usual orientation
>>for any radial cracking due to any anodizing
>
>
> You keep saying this but reality is otherwise. The cracks can be
> tangential to the spoke hole or can describe a chord through the hole
> quite readily.
>
>
>>3. the outside crack also follows a jagged line indicative of an
>>intergranular fracture mode
>
>
> Isn't that how all cracks propogate through aluminum?
depends on the type of fracture. classic mechanical fatigue has 3
stages: initiation/slow growth, crack propagation & finally, fracture.
this example is typical:
http://technology.open.ac.uk/materials/mem/images/images_cc/ccf11_4.jpg
here you see a relatively flat fatigue crack surface which is darker in
color than the rest, including beach marks [helpfully labeled] growing
up from the bottom left of the piece to just under half of the cross
section. this type of crack growth propagates according to the maximum
resolved stress, and is not too sensitive to local microstructure.
once the fatigue crack has grown to sufficient size for the stress
concentrated at its root to exceed the fracture limit for the material,
it then fails dramatically. just as in this piece, you can usually see
a significant difference between the fatigue crack and the fracture
failure on the surface.
the fracture failure surface is generally either brittle or ductile in
nature. brittle will frequently cleave along grain boundaries leaving a
granular surface. ductile will be dull & fibrous in appearance. the
above example shows ductile, although there are brighter regions caused
by someone pressing the two broken pieces back together and moving them
about.
[please! anyone looking at a fracture on which they suspect fatigue -
if you ever want it properly analyzed, DO NOT place the broken pieces
back together!!! this usually mangles or obliterates vital telltale
surface features the analyst will be looking for under the microscope &
it makes their life much harder. just keep them apart and keep them dry.]
an example of brittle is:
http://www.resnapshot.com/MP1199-7.jpg
the fatigue crack growth can be seen on the right with a relatively
smooth surface and beach marks. the jagged brittle intergranular
cracking - in this case of a cast component - is seen on the left.
then again, you can go straight to brittle failure and leave out
fatigue. it's a huge topic. there are may causes - and frequently more
than one.
jim beam
> jim beam wrote:
>
>> were these wheels built using a tensiometer for the spokes? mavic
>> recommended tension for their later rims is ~1,000N to 1,100N drive
>> side rear. many builders exceed this under the misconception that the
>> greater the tension, the stiffer the wheel. excess tension does not
>> alter the modulus of the spokes or the rim so it cannot make wheels
>> stiffer - all it does is push the rim [and all other components]
>> closer to their stress limit.
>
>
> I didn't use a tensiometer to build this wheel, so I cannot state the
> exact tension. What I did was try to get the tension nice and high
> because my understanding is that that makes the wheel as strong as
> possible. (By that I mean most resistant to possible collapse by spokes
> becoming detensioned, say by hitting a pothole.)
well, in terms of static strength, the determinants are the rim and the
spokes. the spokes determine the elasticity with their gauge & pretty
much the same for the rim. high tension cannot give a wheel more static
strength. or stiffness.
what tension /does/ do is affect the fatigue loading cycle and therefore
the fatigue life of the spokes. but this has to be balanced against the
load limit for the rim. and i think your pics illustrate this quite well.
>
> I frequently stress-relieved the wheel during tensioning, keeping alert
> for it 'tacoing' - which Jobst says indicates the tension is at the
> limit the rim can stand. However, I never took the tension that high: I
> was satisfied with the nice high 'ping' emitted by the drive side spokes
> when plucked, and called it a day.
in my experience, that "taco" measure is at least double the recommended
tension. i think jobst needs to be a little clearer in this part of his
book because "the limit the rim can stand" in static strength does not
equate to durability in use. tension needs to be high enough for the
rim, as stated by the rim manufacturer, but no more.
regarding the "ping" test, it is excellent for making sure tensions are
as even as possible, but unless you go to great lengths to "tune" the
ping musically, [sheldon has a link on how to do this], it's only going
to be a relative measure, not absolute. the cheapest most reliable way
to get the absolute measure is the $50 park tensiometer. it's accurate
enough to keep you in the right ballpark on tension and will prevent
expensive repetition of failures like this.
Carl Fogel
Dear Tim,
I expect that Jim means that the spokes have been
over-tensioned for the strength of the rim. If I
understand what Jobst explained in "The Bicycle Wheel,"
the spokes work by losing and then regaining tension
as they roll under the hub.
Given their poor angle, drive-side spokes usually
need more tension than non-drive-side spokes. From
David's description and pictures, it sounds as if
the cracks in his MA 2 are associated with these
higher-tension spokes.
Rougher riding would lead to more fatigue, given
greater tension loss, but David described his riding
as not being terribly rough. Nor is 8,000 miles in
4 years very far or very long for a rim.
Possibly David just had the bad luck of buying the
only bad apple in a batch of MA 2 rims, but I think
that Jim is suggesting that excess tension is a likely
culprit.
There don't seem to be any signs of obvious corrosion,
the cracks are widespread on the more heavily tensioned
side, they come in two different forms centered around
drive-side spokes (half-moon cracks around the spokes
and cracks radiating from the spokes as if the rim is
splitting).
Apart from excess tension and just bad luck in getting
a rim made of bad metal, are there any other explanations
that you can think of? My impression is that MA 2 rims
didn't normally fail in 8,000 miles if they were reasonably
tensioned and weren't just bad-luck lemons. Those half-moon
cracks may be familiar to everyone else, but I was startled
by them--I expected radiating cracks to be the normal kind
of failure.
Carl Fogel
Gary Young
So now you're saying disregard Mavic's recommended tension and go with
just enough to prevent slackness?
Tim McNamara
> Tim McNamara wrote:
> > David Green <david...@deadspam.com> writes:
> >
> >>Tim McNamara wrote:
> >>
> >>>Interesting. No. 4 looks like a typical crack seen on all the
> >>>rim failures I have had (but those have literally all been with
> >>>anodized rims). Nos. 2 + 3 are quite interesting, though. Is
> >>>the concentric crack on the non-drive side?
> >>
> >>No. All the cracks are drive side. In fact, most of the drive side
> >>spokes exhibit them.
>
> > I didn't phrase that well. I expected the cracks to be associated
> > with drive side spokes. My question was on which side of the rim
> > are the cracks- the drive side or the non-drive side?
>
> They are on the drive side of the rim. That is, the side of the rim
> furthest from the hub.
I am really not making my question clear, I guess. Imagine the wheel
is in your bike and you're standing behind the bike. Looking down at
the rim, are the concentric cracks around the spoke holes on the right
of the nipple sockets (towards the cassette) or on the left (away from
the cassette)? My guess is that they would be on the left side, the
side away from the cassette.
Tim McNamara
> Those half-moon cracks may be familiar to everyone else, but I was
> startled by them--I expected radiating cracks to be the normal kind
> of failure.
I have not seen cracks like them before in a bicycle rim, so I am
quite fascinated. For all I know they are common, I've never examined
any of my cracked rims for them. Never even thought of it. So they're
new to me.
Mike S.
> which was interferring with my bottle dynamo. I expected to find a
> broken spoke but there were none.
>
> When I removed the tyre and rim tape, I spotted cracks in the
> aluminium beside all of the drive-side sockets. (MA2s have full-depth
> steel sockets between the double walls.) None of the non-drive-side
> sockets had cracks. Each crack is concentric to the spoke hole and
> about 1mm away from the edge of the socket, most pronounced towards
> the outside edge of the rim. The cracks only appear in the wall of the
> rim in contact with the rim tape. No cracks visible when tyre fitted
> or in braking surfaces.
>
> I assume that the wheel is going out of true because of these cracks.
>
> Is this kind of thing common in MA2s? Do you think that I over
> tensioned the spokes? I don't think so, because the wheel never taco'd
> during stress relieving.
>
> This wheel is 32H, which I built approx 4 years ago, ridden about 40
> miles per week on decent roads (no pothole colisions). Spokes were
> build according to Jobst's book, stress-relieved etc. Campag sf hubs,
> SSDB spokes.
>
> Any suggestions for a replacement rim (same ERD) and for improving my
> build technique.
>
> David Green.
> Cambridge, UK.
All these posts and not one from Jobst.
Hmmm.
Mike
Carl Fogel
Dear Tim,
I'm glad that someone else is startled. There must
be some simple explanation, but I'm damned if I can
figure out how those half-moon cracks appeared.
It seems obvious that the spoke tension is somehow
responsible, but why on only one side and why didn't
a crack radiate from the spoke hole itself?
Maybe half-flower-pot would be a better description?
It's as if the spoke was a flower stalk and the rim
was a flower-pot and the whole pot of dirt started to
come out when you pulled on the flower stalk.
Assuming that it is the spoke tension, the aluminum
around the spoke hole must somehow be stronger than
the aluminum out at the rim where the crack is.
Maybe there is some strange defect in this particular
rim that weakened things out at the edge of the rim,
a straight crack appeared there because the metal
around the spoke hole was strong enough to transmit
the tension, and then--
Well, I haven't figured out why a crack along
a strangely weak edge would decide to curve inward
at both ends into good metal instead of continuing
along the line of weakness.
Luckily, brighter people with more experience will
probably explain it in the end.
Carl Fogel
jim beam
no. 1000N - 1100N is an example because it's mavic's recommendation for
their open pro type rims. use whatever is recommended for the specific
rim you have.
Tim McNamara
> Tim McNamara <tim...@bitstream.net> wrote in message news:<873c8la...@bitstream.net>...
>> carl...@comcast.net (Carl Fogel) writes:
>>
>> > Those half-moon cracks may be familiar to everyone else, but I
>> > was startled by them--I expected radiating cracks to be the
>> > normal kind of failure.
>>
>> I have not seen cracks like them before in a bicycle rim, so I am
>> quite fascinated. For all I know they are common, I've never
>> examined any of my cracked rims for them. Never even thought of
>> it. So they're new to me.
>
> Dear Tim,
>
> I'm glad that someone else is startled. There must be some simple
> explanation, but I'm damned if I can figure out how those half-moon
> cracks appeared.
>
> It seems obvious that the spoke tension is somehow responsible, but
> why on only one side and why didn't a crack radiate from the spoke
> hole itself?
I suspect because one side of the nipple socket is being pulled more
than the other side- the spoke actually tilting the socket towards
the hub flange.
Carl Fogel
Dear Tim,
I was looking at David's pictures of those half-moon cracks
again and was struck by an embarrassingly ignorant thought.
I know nothing about Mavic MA 2 rims and not much more about
wheelbuilding, but David's pictures show what looks like a
spoke-hole offset well to one side on the inside of the rim,
with the half-moon crack in the wide area between the eyelet
and the side of the rim.
Could it be that the spokes were set in the wrong holes?
That is, could the drive side spokes have been put in the
non-drive-side's holes, and vice-versa?
I have a vague notion that such drilling patterns exist, but
I don't know a) if the MA 2 used such a pattern, b) how to
tell if it does, or c) what the effect would be.
With luck, someone will pat me on the head and dismiss
this notion as even more insane than usual.
Carl Fogel
Carl Fogel
Dear Mike,
Jobst may be tired, busy, bored, or laughing himself
sick at what we're all saying about cracks that are
old hat to him.
Or he may be reading everything with deep interest
and quietly trying to figure those cracks out. If
they're new to him, he's found a foe worthy of his
steel.
Silence may be a vritue. Look how much I post and how
little light it sheds.
Carl Fogel
David Green
On the left.
David Green
I have just rechecked my wheel. The drive side spokes are definitely
laced into the holes offset to that side at the rim. That is, the
correct holes! That is why the 'half-moon' cracks are in the wider area
between socket and side of rim.
MA2s appear to be drilled symmetrically.
David Green
Yes, I'm a bit puzzled too. Obviously, this rim is shot - I just want to
better understand how to improve my wheelbuild technique so it doesn't
happen again. I suspect these cracks must be induced by spoke tension,
But I'm sure that I didn't overdo it. Certainly, no sign of rim
'tacoing' during tensioning, and I was satisfied when I had a nice
uniform ping from the drive side spokes.
I don't expect to find another MA2 here in the UK. So I'm considering
the Torelli Master or the Sun CR-18. Both have same ERD I understand. I
wonder whether a 1mm difference in ERD will be acceptable?
Gary Young
You're missing my point. You've recommended two methods for getting
the tension right: (1) consult the manufacturer and (2) get them tight
enough to prevent them from going slack and no more. If Mavic is
recommending a tension almost high enough to cause a rim to taco,
doesn't that mean a tension much higher than needed to prevent the
spokes from going slack? If so, your two recommendations don't agree.
Which is your preferred recommendation and why?
Tim McNamara
> I don't expect to find another MA2 here in the UK.
Same story in the US.
> So I'm considering the Torelli Master or the Sun CR-18. Both have
> same ERD I understand.
I don't know that this is the case.
> I wonder whether a 1mm difference in ERD will be acceptable?
You can readily find out using one of the many spoke calculators
available on the Internet.
dianne_1234
wrote:
>Apart from excess tension and just bad luck in getting
>a rim made of bad metal, are there any other explanations
>that you can think of?
The double eyelet is an assembly of manufactured parts, and
necessarily has tolerances.
I wonder if the socket is (slightly) too short, then when assembled
into the rim it might pull the tire well towards the spoke face. So
there is stress in both walls simply doe to assembling the socket and
eyelet.
Then when the wheel is assembled, spoke tension may add to this stress
in the tire well (and initially subtract from this stress in the spoke
face).
Just a theory...
jim beam
gary, sorry if i'm not being clear.
as far as the spokes are concerned, the only real objective is to have
them tight enough to not go slack in use. as far as the rim is
concerned, the objective is to not over-stress it so that failures like
those seen in this thread don't ocurr. these two objectives overlap,
and the overlap zone is that recommended by the rim manufacturer with
their tension spec.
over = cracking, pull through, etc.
under = spoke fatigue.
that's only one recommendation - stick to spec.
AndyMorris
>
> I don't expect to find another MA2 here in the UK. So I'm considering
> the Torelli Master or the Sun CR-18. Both have same ERD I understand.
> I wonder whether a 1mm difference in ERD will be acceptable?
Is any one bringing Torelli masters into the UK. As far as i know the
Ambrosio Nexus
http://www.ambrosiospa.com/provajpg/pag27.htm
is the same section and is available in the UK
http://www.hewittcycles.co.uk/price_list/rims/
It anodised, which you may or may not like and its pricy compared to MA3's.
I got a pair of their Excellence rims and they seem far better quality than
the MA3's they replaced after a spoke putting thu situation.
--
Andy Morris
AndyAtJinkasDotFreeserve.Co.UK
Love this:
Put an end to Outlook Express's messy quotes
http://home.in.tum.de/~jain/software/oe-quotefix/
Benjamin Weiner
> All these posts and not one from Jobst.
> Hmmm.
I don't think he's posted anything to rbt for 2-3 days, and the
weather has been spectacular here. Maybe he went for a ride.
Gary Young
Really? As narrow a range as 1000 - 1100 (what you say Mavic
recommends for the Open Pro) really encompasses everything from
tigh-enough-not-to-go-slack to at-the-rim's-limit? Sounds like
bullshit to me, but I could be wrong. In light of what Terry Morse
said, do you still maintain that Jobst's method results in tensions
twice the recommended limit?
Also, it wasn't so long ago that you were saying that the MA3 was a
longer-lasting rim than the Open Pro. But in this (or a related
thread), you've compared the Open Pro favorably to "cheap stuff" like
the MA3, which I believe you said was more prone to cracking. Why the
change in mind?
I believe Jobst has said that fatigue failures are generally
attributable to residual stresses and are not related to spoke tension
(except the extent that a properly tensioned wheel is more likely to
have been stress relieved). Your analysis of fatigue would seem to
differ. Why?
Tim McNamara
> as far as the spokes are concerned, the only real objective is to
> have them tight enough to not go slack in use.
And you do not want any, hmm, "safety zone" for unusually large loads,
like deciding to carry home groceries or hitting a bump? Your method
would require the builder to calculate the amount each spoke is
dentensioned in the load affected zone, and then tighten the wheel
accordingly. Surely it makes far more sense to just tension it to
what the rim can deal with without warping.
> as far as the rim is concerned, the objective is to not over-stress
> it so that failures like those seen in this thread don't ocurr.
> these two objectives overlap, and the overlap zone is that
> recommended by the rim manufacturer with their tension spec.
>
> over = cracking, pull through, etc.
Hmmm. I have two rear wheels which, according to my Wheelsmith
tensiometer, are tensioned to 144 kgf per spoke on the drive side.
That's what it took to keep the non-drive side spokes from going slack
under my 210 lbs and a saddlebag. One has an MA2 rim which has been
in service about 4 years; the other has an Open Pro silver anodized
rim which is used sporadically over about 6 years; the latter is/was
my cyclo-cross wheel and is now my winter/bad whether bike wheel.
Your theory- that cracking rims is due to corrosion and/or
overtensioning- again fails to address the lack of such failures prior
to the almost exclusive availability of anodized rims, and the
dramatic increase in such incidents after.
jobst....@stanfordalumni.org
> Pictures as requested:
> Most of the drive side sockets have these cracks:
http://web.onetel.net.uk/~davidwgreen/rimpics/2.JPG
> Cracks seem to be concentric with the spoke hole:
http://web.onetel.net.uk/~davidwgreen/rimpics/3.JPG
> When I did look more closely, some of the spoke holes with socket
> cracks also have small cracks emerging from the ferrule side of the
> rim:
http://web.onetel.net.uk/~davidwgreen/rimpics/4.JPG
> Any ideas?
It appears to me that these sockets were too short fro the depth of
the rim cross section and that when installed and their eyelets
crimped, the rim was locally close to yield. Addition of high spoke
tension caused the inner bed to fail, since this is an additive load,
and when it cracked, only the outer wall supported most of the load.
The small longitudinal cracks in the outer wall are typical of rims
without sockets that rely on the outer wall to support spoke loads.
The reason I come to this conclusion is that I have spoked many wheels
close to the limit of compressive collapse and used them until they
wore out, never having developed cracks. Therefore, I believe it
takes more than high spoke tension to cause such a failure. The
scenario I offer is the only one that comes to mind at the moment.
This rim, as you say, is not a typical anodizing failure, as has been
previously mentioned.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
> All these posts and not one from Jobst.
> Hmmm.
I've been away for a few days. Without having seen a picture of what
occurred, I hadn't offered any conjecture. Your glee at hearing that
an MA-2 failed by cracking is foaming over. Contain yourself!
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
> You're missing my point. You've recommended two methods for getting
> the tension right: (1) consult the manufacturer and (2) get them
> tight enough to prevent them from going slack and no more. If Mavic
> is recommending a tension almost high enough to cause a rim to taco,
> doesn't that mean a tension much higher than needed to prevent the
> spokes from going slack?
The "tight enough to prevent them from going slack" value is illusive
because there is no such tension. I have on occasion heard my spokes
twang (go slack and come back) when hitting smooth lumps in the road
when going fast down hills. These spokes were as tight as the rim
would permit without buckling when braking. To get the best strength
from a wheel, the spokes need to be as tight as reasonably possible.
That point, before anodizing, was the tension at which the wheel would
not taco under heavy (rim) braking, the only condition under which
spoke tension uniformly increases in about half the wheel.
Jobst Brandt
jobst....@stanfordalumni.org
Mike S.
<jobst....@stanfordalumni.org> wrote in message
news:4fU2c.6936$_3.9...@typhoon.sonic.net...
Heaven forbid I say anything like "I told ya so" or anything like that...
I don't like to hear about people's equipment malfunctioning any more than
the next guy, but when said equipment is hyped up, well...
Oh, and welcome back!
Mike
David Green
Jobst,
is your advice, then, that I complain to my LBS and ask for a
replacement rim? I think you are suggesting that this MA2 was
incorrectly manufactured. After all, it's only 4 years old and ridden
about 8k miles. (How many miles would you expect from an MA2?)
Also, when I rebuild the wheel, am I still correct to go for a high
tension, whilst using stress-relieving to detect excessive tension?
David Green.
jim beam
<snip>
>
> Really? As narrow a range as 1000 - 1100 (what you say Mavic
> recommends for the Open Pro) really encompasses everything from
> tigh-enough-not-to-go-slack to at-the-rim's-limit?
it may not be good enough for /everything/ the wheel will encounter, but
where do you draw the limit?
when you have a stress/strain graph like this:
| x
| / 2
| /
| / 1
| /
|/______ "x" is the onset of plastic deformation.
you want to have the rim last a long time, you want to have it operating
nearer point 1 than point 2 because any additional load at point 2 is
too close to causing plastic deformation. it's also affects the
starting position for the rim on the fatigue graph.
> Sounds like
> bullshit to me, but I could be wrong. In light of what Terry Morse
> said, do you still maintain that Jobst's method results in tensions
> twice the recommended limit?
the exact overstress factor depends on a the builders subjective
judgement of what's "tight enough". in my personal case, i ended up
with spoke tensions about twice the recommended max, yes. this i
learned after i bought a tensiometer.
>
> Also, it wasn't so long ago that you were saying that the MA3 was a
> longer-lasting rim than the Open Pro. But in this (or a related
> thread), you've compared the Open Pro favorably to "cheap stuff" like
> the MA3, which I believe you said was more prone to cracking. Why the
> change in mind?
i don't recall that. was it in the context of wall thickness? i
think the ma3 is a good workhorse training rim. that's what i use mine for.
>
> I believe Jobst has said that fatigue failures are generally
> attributable to residual stresses and are not related to spoke tension
> (except the extent that a properly tensioned wheel is more likely to
> have been stress relieved). Your analysis of fatigue would seem to
> differ. Why?
you can't just gloss over the importance of mechanical design, surface
finish or quality of material on fatigue life, and then just launch into
residual stress as fatigue's sole source. especially not for a material
that is cold worked to within a few percent of u.t.s. in addition,
jobst's stress relief theory seems to depend on being able to deform the
material without work hardening - a theory that requires a stress/strain
graph like this:
http://www.umeciv.maine.edu/cie111/images/tension_steel_lx.jpg
the graph rises, peaks, then moves sideways with a jagged line. in mild
steel, this theory might work because that material exhibits this kind
of plasticity.
stainless steel & aluminum otoh have graphs like this:
http://www.umeciv.maine.edu/cie111/images/tension_alum_ss.jpg
that graph is aluminum, but the forms are similar. they rise up in
elastic deformation, then immediately enter their work hardening zone as
they plastically deform. indeed, in the back of jobst's book, he has
some real life stress/strain graphs for real spokes, and none exhibit
the "strain aging" phenomenon of the mild steel graph on which his
theory seems to have been built.
jim beam
questions. have to scram now - will get back to later.
Carl Fogel
Dear Jobst,
So . . .
Some bad manufacturing step almost squashed the rim to
death locally around each eyelet, weakening the inner wall.
When David built his wheel with this defective rim, the
normal tension of the spokes pulled the weakened eyelet
areas on through, creating those odd half-moon cracks.
Then all the spoke tension fell on the outer wall around
the spoke hole, which began to split under what was normal
tension for a double-wall, but far too much for an unintended
single-wall.
I think that I follow you and that you've explained what's
been puzzling all of us. It was an oddly defective rim, not
corrosion or weirdly high tension or spokes in the wrong holes
or any of our other vague guesses.
Thanks,
Carl Fogel
Gary Young
> Gary Young wrote:
> <snip>
> >
> > Really? As narrow a range as 1000 - 1100 (what you say Mavic
> > recommends for the Open Pro) really encompasses everything from
> > tigh-enough-not-to-go-slack to at-the-rim's-limit?
>
> it may not be good enough for /everything/ the wheel will encounter, but
> where do you draw the limit?
You present a constantly shifting target. Earlier you said that spokes
need to be taut enough to prevent fatigue failure of the spokes, no
more. (I question whether your account of fatigue failure of spokes is
accurate, given what Jobst has written on the subject, but that's
another matter.) That implies that the spokes need only be tight
enough to prevent slackness in ordinary riding. Fatigue is related to
repeated loading or unloading, isn't it?
But now in this message you seem for the first time to be cognizant of
the need to have the spokes tight enough to withstand one-time
encounters that exceed the norm. In the past, you've belittled this
concern by mischaracterizing it as a misguided attempt to increase the
stiffness of the wheel. So, do you now acknowledge that increasing
spoke tension helps preserve the structural integrity of the wheel,
regardless of its effect on spoke fatigue? And that consequently
wanting to get the tension high is not just a misguided attempt to
achieve "stiffness"?
For some reason I can't find the original message on Google. But
here's a subsequent post that quotes you (incorrectly?):
http://groups.google.com/groups?selm=qv3330tmj5ap1r04rl8nfq0b7lmj917re3%404ax.com&output=gplain
> >
> > I believe Jobst has said that fatigue failures are generally
> > attributable to residual stresses and are not related to spoke tension
> > (except the extent that a properly tensioned wheel is more likely to
> > have been stress relieved). Your analysis of fatigue would seem to
> > differ. Why?
>
> you can't just gloss over the importance of mechanical design, surface
> finish or quality of material on fatigue life, and then just launch into
> residual stress as fatigue's sole source. especially not for a material
> that is cold worked to within a few percent of u.t.s. in addition,
> jobst's stress relief theory seems to depend on being able to deform the
> material without work hardening - a theory that requires a stress/strain
> graph like this:
>
I should have been more clear. I meant fatigue failures of spokes.
That's relevent because you have said (or implied) that spoke tension
need be no greater than necessary to prevent fatigue failure. (Though
you seem to back off from that position in this post.)
I believe Jobst has said that fatigue failure in spokes is caused by
residual stresses and is not effected by spoke tension (except to the
extent that competent wheel builders are likely both to take spokes to
high tensions and stress relieve them). I take it then that you
disagree with Jobst on the cause of fatigue failures in spokes. Why?
> http://www.umeciv.maine.edu/cie111/images/tension_steel_lx.jpg
>
> the graph rises, peaks, then moves sideways with a jagged line. in mild
> steel, this theory might work because that material exhibits this kind
> of plasticity.
>
> stainless steel & aluminum otoh have graphs like this:
> http://www.umeciv.maine.edu/cie111/images/tension_alum_ss.jpg
>
> that graph is aluminum, but the forms are similar. they rise up in
> elastic deformation, then immediately enter their work hardening zone as
> they plastically deform. indeed, in the back of jobst's book, he has
> some real life stress/strain graphs for real spokes, and none exhibit
> the "strain aging" phenomenon of the mild steel graph on which his
> theory seems to have been built.
Maybe when you achieve some clarity about basic concepts will I bother
to follow out your links. I've looked at enough of them in the past to
know that you often point to material that is equivocal, beside the
point, or, sometimes, in contradiction of what you say.
They don't clarify what you say, they just pile more jargon on top of
what you've already dished up. I'm sure that engineers have perfectly
good reasons for using that jargon, I just don't have any confidence
that you understand the reasons, particularly in light of the fact
that you have never explained what training or experience you have to
back up your oracular pronouncements.
And on top of that, you're a sock puppet.
Carl Fogel
[snip]
> I don't like to hear about people's equipment malfunctioning any more than
> the next guy . . .
[snip]
Dear Mike,
You have more character than I do.
Honesty compels me to admit (despite the sympathy that
I offered poor David) that I love to read about other
people's equipment problems.
How terrible, I grieved, when I read David's original
post about his rim failure, how absolutely terrible--all
those nice details, but no pictures!
Conincidentally, I saw the first turkey vulture of spring
today. (Robins are passé.)
Carl Fogel
Tim McNamara
> Gary Young wrote:
> <snip>
>
>> Really? As narrow a range as 1000 - 1100 (what you say Mavic
>> recommends for the Open Pro) really encompasses everything from
>> tigh-enough-not-to-go-slack to at-the-rim's-limit?
>
> it may not be good enough for /everything/ the wheel will encounter,
> but where do you draw the limit?
>
> when you have a stress/strain graph like this:
>
> | x
> | / 2
> | /
> | / 1
> | /
> |/______ "x" is the onset of plastic deformation.
>
> you want to have the rim last a long time, you want to have it
> operating nearer point 1 than point 2 because any additional load at
> point 2 is too close to causing plastic deformation.
Umm, loads on a bicycle wheel don't increase tension in the spokes.
Loads on a bicycle wheel *decrease* spoke tension. Your concern would
only be valid if the hub hung from the upper spokes, increasing the
tension on those spokes proportionate to the load on the rim; instead,
the hub stands on the spoke beneath it, reducing the tension on those
spokes. Hence plastic deformation as a result of normal loads (not
side loads caused by crashing or acrobatics (bike-robatics?)) won't
happen.
> the exact overstress factor depends on a the builders subjective
> judgement of what's "tight enough". in my personal case, i ended up
> with spoke tensions about twice the recommended max, yes. this i
> learned after i bought a tensiometer.
I've built a few hundred wheels, and in no case did any of the rims
come with any documentation about limiting spoke tension to 100 kgf or
so. That being the case, it seems unlikely that the manufacturer
thinks this is important. Mavic, with their famous aversion to doing
warranty replacements, might well use this as a dodge when a claim is
made.
>> I believe Jobst has said that fatigue failures are generally
>> attributable to residual stresses and are not related to spoke
>> tension (except the extent that a properly tensioned wheel is more
>> likely to have been stress relieved). Your analysis of fatigue
>> would seem to differ. Why?
>
> you can't just gloss over the importance of mechanical design,
> surface finish or quality of material on fatigue life, and then just
> launch into residual stress as fatigue's sole source.
Let's stop mixing apples and oranges. Stress relief is for spokes,
not rims. We're talking about rims in this thread.
Jose Rizal
> jim beam <u...@ftc.gov> writes:
> > when you have a stress/strain graph like this:
> >
> > | x
> > | / 2
> > | /
> > | / 1
> > | /
> > |/______ "x" is the onset of plastic deformation.
> >
> > you want to have the rim last a long time, you want to have it
> > operating nearer point 1 than point 2 because any additional load at
> > point 2 is too close to causing plastic deformation.
>
> Umm, loads on a bicycle wheel don't increase tension in the spokes.
> Loads on a bicycle wheel *decrease* spoke tension. Your concern would
> only be valid if the hub hung from the upper spokes, increasing the
> tension on those spokes proportionate to the load on the rim; instead,
> the hub stands on the spoke beneath it, reducing the tension on those
> spokes. Hence plastic deformation as a result of normal loads (not
> side loads caused by crashing or acrobatics (bike-robatics?)) won't
> happen.
Tension increase on spokes will happen when braking forces are applied,
for half the spokes in a wheel anyway (the other half decreasing in
tension).
The stress-strain graph shown above, however, is nonsensical since there
are no scales in the "graph" and there is absolutely no indication of
magnitudes. It's a self-serving (and useless) way of illustrating a
point that can't be quantified.
> I've built a few hundred wheels, and in no case did any of the rims
> come with any documentation about limiting spoke tension to 100 kgf or
> so. That being the case, it seems unlikely that the manufacturer
> thinks this is important. Mavic, with their famous aversion to doing
> warranty replacements, might well use this as a dodge when a claim is
> made.
Nor can you see any figures for recommended maximum tension at Mavic's
website.
jim beam
interest in the science. it appears not.
if at some point, you /do/ wish to get tech, then i'm happy to oblige.
in the mean time, thanks and goodbye.
jb
jim beam
i understand all that for planar loads, but i guess we now need to
debate the need for a wheel to take the side loads of a rider honking up
a hill. you have the floor on that one tim.
>
>
>>the exact overstress factor depends on a the builders subjective
>>judgement of what's "tight enough". in my personal case, i ended up
>>with spoke tensions about twice the recommended max, yes. this i
>>learned after i bought a tensiometer.
>
>
> I've built a few hundred wheels, and in no case did any of the rims
> come with any documentation about limiting spoke tension to 100 kgf or
> so. That being the case, it seems unlikely that the manufacturer
> thinks this is important. Mavic, with their famous aversion to doing
> warranty replacements, might well use this as a dodge when a claim is
> made.
they may well have a machieavellian plan, but if they do, not providing
documentation would probably play against them, not for them. ianal.
here's an online mavic wheelbuilding pdf that /does/ specify tensions.
http://www.tech-mavic.com/uk/sources/Produits/VTT/CrossCountry/Jantes/GalJtesVTTXC/SpokeTension.pdf
not sure if they mean this to be specific for their mtb rims or not, but
it is an example.
>
>
>>>I believe Jobst has said that fatigue failures are generally
>>>attributable to residual stresses and are not related to spoke
>>>tension (except the extent that a properly tensioned wheel is more
>>>likely to have been stress relieved). Your analysis of fatigue
>>>would seem to differ. Why?
>>
>>you can't just gloss over the importance of mechanical design,
>>surface finish or quality of material on fatigue life, and then just
>>launch into residual stress as fatigue's sole source.
>
>
> Let's stop mixing apples and oranges. Stress relief is for spokes,
> not rims. We're talking about rims in this thread.
well, they are related. the /process/ of what we refer to as "stress
relief" /does/ benefit the rims and hubs by ensuring there is no further
yielding at their contact points under load. that's why "stress
relieved" wheels stay true over time, and those that haven't been, don't.
Carl Fogel
> jim beam <u...@ftc.gov> wrote in message news:<Iy03c.35735
[snip]
> > > [Gary wrote:]
> > > Also, it wasn't so long ago that you were saying that the MA3 was a
> > > longer-lasting rim than the Open Pro. But in this (or a related
> > > thread), you've compared the Open Pro favorably to "cheap stuff" like
> > > the MA3, which I believe you said was more prone to cracking. Why the
> > > change in mind?
> >
[jim replied:]
> > i don't recall that. was it in the context of wall thickness? i
> > think the ma3 is a good workhorse training rim. that's what i use mine for.
> >
[gary wrote:]
> For some reason I can't find the original message on Google. But
> here's a subsequent post that quotes you (incorrectly?):
>
[snip]
> . . . I just don't have any confidence
> that you understand the reasons, particularly in light of the fact
> that you have never explained what training or experience you have to
> back up your oracular pronouncements.
>
> And on top of that, you're a sock puppet.
Dear Gary,
By your reasoning, should I have any confidence in you?
It took only thirty seconds with Google to find what eluded
you:
Actually, I doubt that spokes and wheels care how well
we google or how much you insult Jim. If you're right,
neither insults nor training nor a perfectly excusable
lapse in simple searching matter.
That's the weakness of the ad hominem arguments here
on rec.bicycles.tech. Feel free to call me a sock
puppet if it cheers you up.
Carl Fogel
Jose Rizal
> Tim McNamara wrote:
> > Umm, loads on a bicycle wheel don't increase tension in the spokes.
> > Loads on a bicycle wheel *decrease* spoke tension. Your concern would
> > only be valid if the hub hung from the upper spokes, increasing the
> > tension on those spokes proportionate to the load on the rim; instead,
> > the hub stands on the spoke beneath it, reducing the tension on those
> > spokes. Hence plastic deformation as a result of normal loads (not
> > side loads caused by crashing or acrobatics (bike-robatics?)) won't
> > happen.
>
> i understand all that for planar loads, but i guess we now need to
> debate the need for a wheel to take the side loads of a rider honking up
> a hill.
I couldn't see where the need arises for that debate, except for the
terrific dodge you just tried to execute.
Besides, tension does increase on half the spokes on a wheel when
braking loads are applied, so just what is it that you do understand,
planar loads or not?
> > I've built a few hundred wheels, and in no case did any of the rims
> > come with any documentation about limiting spoke tension to 100 kgf or
> > so. That being the case, it seems unlikely that the manufacturer
> > thinks this is important. Mavic, with their famous aversion to doing
> > warranty replacements, might well use this as a dodge when a claim is
> > made.
>
> they may well have a machieavellian plan, but if they do, not providing
> documentation would probably play against them, not for them. ianal.
>
> here's an online mavic wheelbuilding pdf that /does/ specify tensions.
>
> http://www.tech-mavic.com/uk/sources/Produits/VTT/CrossCountry/Jantes/GalJtesVTTXC/SpokeTension.pdf
>
> not sure if they mean this to be specific for their mtb rims or not, but
> it is an example.
That doesn't even specify what rim is being used, whereas you gave the
impression that Mavic published tension values for all their rims. How
can that be anything but useless?
> well, they are related. the /process/ of what we refer to as "stress
> relief" /does/ benefit the rims and hubs by ensuring there is no further
> yielding at their contact points under load. that's why "stress
> relieved" wheels stay true over time, and those that haven't been, don't.
These are not related. There is no relationship between
stress-relieving spokes and stress-relieving rims, whatever the latter
means. As far as the rim is concerned, it doesn't know nor care whether
spokes are stress-relieved, all it sees is the tension in each.
Carl Fogel
[snip]
> Umm, loads on a bicycle wheel don't increase tension in the spokes.
> Loads on a bicycle wheel *decrease* spoke tension. Your concern would
> only be valid if the hub hung from the upper spokes, increasing the
> tension on those spokes proportionate to the load on the rim; instead,
> the hub stands on the spoke beneath it, reducing the tension on those
> spokes. Hence plastic deformation as a result of normal loads (not
> side loads caused by crashing or acrobatics (bike-robatics?)) won't
> happen.
[snip]
Dear Tim,
While I think that you're right about weight loads
decreasing tension on a pre-tensioned wheel, it may
be worth pointing out that Jobst just mentioned elsewhere
in this thread how braking loads do in fact increase
tension over about half the spokes:
"The 'tight enough to prevent them from going slack' value is illusive
because there is no such tension. I have on occasion heard my spokes
twang (go slack and come back) when hitting smooth lumps in the road
when going fast down hills. These spokes were as tight as the rim
would permit without buckling when braking. To get the best strength
from a wheel, the spokes need to be as tight as reasonably possible.
That point, before anodizing, was the tension at which the wheel would
not taco under heavy (rim) braking, the only condition under which
spoke tension uniformly increases in about half the wheel."
I dutifully looked it up and found the details opposite
figure 8 in "The Bicycle Wheel," where Jobst indicates that
in a wheel with average tension, front spokes become about
5 kg looser and rear spokes about 5 kg tighter under braking.
(What the average tension might be is not mentioned at that
point in the book, and may well have no effect on the +/-
5 kg figure. Browsing around the book suggests that spoke
tension is closer to 100 kg than 200 kg in most examples.)
Carl Fogel
almost fast
> > when you have a stress/strain graph like this:
> >
> > | x
> > | / 2
> > | /
> > | / 1
> > | /
> > |/______ "x" is the onset of plastic deformation.
> >
> > you want to have the rim last a long time, you want to have it
> > operating nearer point 1 than point 2 because any additional load at
> > point 2 is too close to causing plastic deformation.
>
> Umm, loads on a bicycle wheel don't increase tension in the spokes.
I think Jim's talking about the rim, no? But anyway, if you're talking
increased fatigue life of *anything* you want to be closer to 1 than
to 2.
See
http://www.efunda.com/DesignStandards/springs/calc_comp_fatigue_eqn.cfm
This is a Soderberg diagram for judging the likelihood of fatigue
failure, showing mean stress plotted against alternating stress.
The alternating stress is the difference between the stress in the
spoke at it's tightest (no load on the wheel) and at it's loosest
(most load on the wheel). For the most part, alternating stress is a
given for a known rider and wheel.
The mean stress is a little lower than the stress in the spoke at it's
tightest (by about half the alternating stress). So, decreasing the
wheels' spoke tension decreases the mean stress, which makes the
spokes (and rim) last longer.
Between tighter and looser spokes, theoretically the looser ones last
longer in fatigue.
But this is theoretical; spokes won't break very often if properly
releived of residual stresses.
> > you can't just gloss over the importance of mechanical design,
> > surface finish or quality of material on fatigue life, and then just
> > launch into residual stress as fatigue's sole source.
Unless the residual stress is high enough to leave portions near
yeild. No spoke can last long if that's the case.
But to your point, in practice we don't really ignore those other
factors. Mechanical design is set by the components we choose (number
of spokes, etc.), surface finish and quality of material we select by
trusting the spoke maker.
daveornee
Unless the residual stress is high enough to leave portions near yeild.
No spoke can last long if that's the case.
But to your point, in practice we don't really ignore those other
factors. Mechanical design is set by the components we choose (number of
spokes, etc.), surface finish and quality of material we select by
trusting the spoke maker.
For those of you who use long URLs, please learn how to use
http://tinyurl.com/ Some of us don't have browser ability to do all the
cutting and pasting required to follow your arguments.
--
jobst....@stanfordalumni.org
>> It appears to me that these sockets were too short for the depth of
>> the rim cross section and that when installed and their eyelets
>> crimped, the rim was locally close to yield. Addition of high
>> spoke tension caused the inner bed to fail, since this is an
>> additive load, and when it cracked, only the outer wall supported
>> most of the load. The small longitudinal cracks in the outer wall
>> are typical of rims without sockets that rely on the outer wall to
>> support spoke loads.
>> The reason I come to this conclusion is that I have spoked many
>> wheels close to the limit of compressive collapse and used them
>> until they wore out, never having developed cracks. Therefore, I
>> believe it takes more than high spoke tension to cause such a
>> failure. The scenario I offer is the only one that comes to mind
>> at the moment. This rim, as you say, is not a typical anodizing
>> failure, as has been previously mentioned.
> Is your advice, then, that I complain to my LBS and ask for a
> replacement rim? I think you are suggesting that this MA2 was
> incorrectly manufactured. After all, it's only 4 years old and
> ridden about 8k miles. (How many miles would you expect from an
> MA2?)
Until it wears through from braking if you use it year around. That
would certainly be more than 20,000 miles unless you did a lot of wet
descending on steep slow mountain roads.
> Also, when I rebuild the wheel, am I still correct to go for a high
> tension, whilst using stress-relieving to detect excessive tension?
Within the limits I have mentioned here and elsewhere often. Rims
that cannot hold as much tension as the hoop can carry are poorly
designed because they have too much material in one respect and not
enough to support spoke tension. However, most of that came about
from anodizing. I am fortunate in having a reserve of non-anodized
MA-2 rims and do not have any cracking problems in spite of my weight
and rough road use.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
> I think that I follow you and that you've explained what's
> been puzzling all of us. It was an oddly defective rim, not
> corrosion or weirdly high tension or spokes in the wrong holes
> or any of our other vague guesses.
I hope you noticed that Dianne-1234 came up with the same explanation
before I did, something I discovered only after going through the whole
list of responses.
Jobst Brandt
jobst....@stanfordalumni.org
Carl Fogel
> On 6 Mar 2004 14:37:22 -0800, carl...@comcast.net (Carl Fogel)
> wrote:
>
>
> >Apart from excess tension and just bad luck in getting
> >a rim made of bad metal, are there any other explanations
> >that you can think of?
>
>
> The double eyelet is an assembly of manufactured parts, and
> necessarily has tolerances.
>
> I wonder if the socket is (slightly) too short, then when assembled
> into the rim it might pull the tire well towards the spoke face. So
> there is stress in both walls simply doe to assembling the socket and
> eyelet.
>
> Then when the wheel is assembled, spoke tension may add to this stress
> in the tire well (and initially subtract from this stress in the spoke
> face).
>
> Just a theory...
>
> > My impression is that MA 2 rims
> >didn't normally fail in 8,000 miles if they were reasonably
> >tensioned and weren't just bad-luck lemons. Those half-moon
> >cracks may be familiar to everyone else, but I was startled
> >by them--I expected radiating cracks to be the normal kind
> >of failure.
> >
> >Carl Fogel
Dear Dianne,
I'm ashamed to say that I missed your post (an argument for
one of those new-fangled threaded newsreaders).
I saw Jobst's post first, which struck me as a solid explanation,
and said so. He handsomely replied that he'd seen your post
while going through the whole thread.
So everything that I said about his post should have been said
about yours, too. The defective-eyelet theory squashing things
together seems to explain those odd half-moon cracks, and the
collapse of the inner wall would then lead, as Jobst explains,
to the splitting around the spoke holes on the outer rim.
By heavens, I should raise both your salaries!
Carl Fogel
carlfogel
Dear Jobst,
I'm ashamed to say that I didn't.
It's handsome of you to point it out. I'm sure that Dianne appreciates
the credit.
And I have to add that it's also handsome of you not to rub it in that
the post that I missed from Dianne was a reply to one of my posts.
Let this be a lesson to me.
Thanks again,
Carl Fogel
--
David Damerell
>forgive me for being so retarded gary - i mistakenly thought you had an
>interest in the science. it appears not.
_There's_ a neat evasion. Are you going to bring in a fresh sock puppet
now, "tux lover"?
--
David Damerell <dame...@chiark.greenend.org.uk> Kill the tomato!
jim beam
> David Green writes:
>
>
>>Pictures as requested:
>
>
>>Most of the drive side sockets have these cracks:
>
> http://web.onetel.net.uk/~davidwgreen/rimpics/2.JPG
>
>
>>Cracks seem to be concentric with the spoke hole:
>
> http://web.onetel.net.uk/~davidwgreen/rimpics/3.JPG
>
>
>>When I did look more closely, some of the spoke holes with socket
>>cracks also have small cracks emerging from the ferrule side of the
>>rim:
>
> http://web.onetel.net.uk/~davidwgreen/rimpics/4.JPG
>
>
>>Any ideas?
>
>
> It appears to me that these sockets were too short fro the depth of
> the rim cross section
does that account for drive side only failure - what has been described
in this case? rim sockets are stamped in a fixed die. there is not
sufficient variability in their manufacture to create a batch of "short"
sockets. the only possible way would be for a socket for the "wrong"
rim was used, and that's much more likely to be a significant difference
that would be detected before the rim got out the door rather than what
we see here.
imo, you still need to address the effect on reliability of running a
rim at near yield, which is basically what you're recommending below.
if my local garage torqued the lug nuts on my car wheels at double
manufacturer spec because they thought they knew better than honda did,
and they failed because of subsequent fatigue, and i had an accident,
i'd have a winning law suit. over-tightening spokes because "i think it
works best" is not very scientific. you need to produce something in
support of your argument as to why this /won't/ accelerate rim failure
if you want to make this over-tension recommendation.
Mike S.
<snip>
> Conincidentally, I saw the first turkey vulture of spring
> today. (Robins are passé.)
>
> Carl Fogel
Yeah, when you're laying on the side of the road recovering at the top of a
hill for long enough they start to thing you're road kill.
Mike
Gary Young
tried to follow the thread up from Dianne's reply. Google newsgroups
has its occasional glitches, but it's possible I did the search
incorrectly. In any event, why would I want to hide the message, since
it clearly proves that "jim beam" has been talking out of both sides
of his mouth when it comes to MA3's?
> Actually, I doubt that spokes and wheels care how well
> we google or how much you insult Jim. If you're right,
> neither insults nor training nor a perfectly excusable
> lapse in simple searching matter.
>
> That's the weakness of the ad hominem arguments here
> on rec.bicycles.tech. Feel free to call me a sock
> puppet if it cheers you up.
>
> Carl Fogel
I wouldn't call you a sock puppet because you aren't one.
If someone points to his experiences and training as lending weight to
his views, as "jim beam/tux lover" has on several occasions, then I
think its fair to ask what those experiences and training are.
I find "jim beam" particularly annoying because, as a layman, I don't
like to have to wade through a lot of technical jargon only to find
bullshit at the end. I've established to my own satisfaction that "jim
beam" is more interested in self-serving obfuscation than the truth.
The problem isn't just an isolated error or two that one could gently
correct, but a whole pattern of mystification. Thus the ad hominem
argument, which I think is appropriate in this instance. In any event,
I don't feel any guilt in treating rudely someone who is so frequently
rude himself.
jobst....@stanfordalumni.org
>> It appears to me that these sockets were too short for the depth of
>> the rim cross section and that when installed and their eyelets
>> crimped, the rim was locally close to yield. Addition of high
>> spoke tension caused the inner bed to fail, since this is an
>> additive load, and when it cracked, only the outer wall supported
>> most of the load. The small longitudinal cracks in the outer wall
>> are typical of rims without sockets that rely on the outer wall to
>> support spoke loads.
>> The reason I come to this conclusion is that I have spoked many
>> wheels close to the limit of compressive collapse and used them
>> until they wore out, never having developed cracks. Therefore, I
>> believe it takes more than high spoke tension to cause such a
>> failure. The scenario I offer is the only one that comes to mind
>> at the moment. This rim, as you say, is not a typical anodizing
>> failure, as has been previously mentioned.
> does that account for drive side only failure - what has been
> described in this case? rim sockets are stamped in a fixed die.
> there is not sufficient variability in their manufacture to create a
> batch of "short" sockets. the only possible way would be for a
> socket for the "wrong" rim was used, and that's much more likely to
> be a significant difference that would be detected before the rim
> got out the door rather than what we see here.
I don't get it. Part of the time you pedagogically advise this
newsgroup on all aspects of materials and their failures, and then you
ask about obvious effects as though you had no understanding of it.
As I said, the stresses are additive and the right side spokes are
tighter than the left... and pull to the right at the bottom of the
sockets putting a high load on the left side of the upper end to
rapidly take the cross section to fatigue failure at that area.
> imo, you still need to address the effect on reliability of running
> a rim at near yield, which is basically what you're recommending
> below.
Your mix of top and bottom response confuses the issues even more.
Can you get some help in writing to a newsgroup? Of course you could
glean some of that from reading postings for their format as well.
> if my local garage torqued the lug nuts on my car wheels at double
> manufacturer spec because they thought they knew better than honda
> did, and they failed because of subsequent fatigue, and i had an
> accident, i'd have a winning law suit. over-tightening spokes
> because "i think it works best" is not very scientific. you need to
> produce something in support of your argument as to why this /won't/
> accelerate rim failure if you want to make this over-tension
> recommendation.
The yield in this case is compressive buckling of the hoop, not stress
at spoke attachments. This is a fairly static load that cannot
initiate cracks and probably even makes up for some of the tensile
loads around spoke attachments. So who ever said "i think it works
best"? Besides, you throw in "over-tightening spokes" as though
anyone suggested doing so. Spokes in the wheels I describe are
running less than half of yield stress as I just reiterated in this
thread. I see you read these things selectively. The reason for
tight spoking is that the strength of the wheel is dependent on spoke
tension, its strength being given by that tension. I've written about
this in the book and here hundreds of times. I'm sure you could
Google to some of those postings is you were interested.
Now stop whining! ...and find the shift key on your KBD.
Jobst Brandt
jobst....@stanfordalumni.org
Tim McNamara
> Tim McNamara:
>
>> jim beam <u...@ftc.gov> writes:
>> > when you have a stress/strain graph like this:
>> >
>> > | x
>> > | / 2
>> > | /
>> > | / 1
>> > | /
>> > |/______ "x" is the onset of plastic deformation.
>> >
>> > you want to have the rim last a long time, you want to have it
>> > operating nearer point 1 than point 2 because any additional load
>> > at point 2 is too close to causing plastic deformation.
>>
>> Umm, loads on a bicycle wheel don't increase tension in the spokes.
>> Loads on a bicycle wheel *decrease* spoke tension. Your concern
>> would only be valid if the hub hung from the upper spokes,
>> increasing the tension on those spokes proportionate to the load on
>> the rim; instead, the hub stands on the spoke beneath it, reducing
>> the tension on those spokes. Hence plastic deformation as a result
>> of normal loads (not side loads caused by crashing or acrobatics
>> (bike-robatics?)) won't happen.
>
> Tension increase on spokes will happen when braking forces are
> applied, for half the spokes in a wheel anyway (the other half
> decreasing in tension).
Ah, yes, that is correct.
> The stress-strain graph shown above, however, is nonsensical since
> there are no scales in the "graph" and there is absolutely no
> indication of magnitudes. It's a self-serving (and useless) way of
> illustrating a point that can't be quantified.
He was trying to illustrate a concept, but I agree without assessment
and disagree with the concept.
>> I've built a few hundred wheels, and in no case did any of the rims
>> come with any documentation about limiting spoke tension to 100 kgf
>> or so. That being the case, it seems unlikely that the
>> manufacturer thinks this is important. Mavic, with their famous
>> aversion to doing warranty replacements, might well use this as a
>> dodge when a claim is made.
>
> Nor can you see any figures for recommended maximum tension at
> Mavic's website.
I didn't look and just presumed that's there jim beam got those
figures.
Tim McNamara
Dpends on too many variables- weight of the rider, degree of lean,
etc. All I can say about it is that at 210 lbs I've yet to see this
be a problem. Indeed all those anodized rims I broke were tensioned
to about 100 kgf per my Wheelsmith tensiometer; it's only in the last
4 years that I have determined the spoke tension as per Jobst's book,
which has resulted in higher tension in the spokes. And I haven't
broken any rims since. Of course, all those rims are MA2s, so there
are multiple factors and thus conclusions are difficult to draw.
>> Let's stop mixing apples and oranges. Stress relief is for spokes,
>> not rims. We're talking about rims in this thread.
>
> well, they are related. the /process/ of what we refer to as
> "stress relief" /does/ benefit the rims and hubs by ensuring there
> is no further yielding at their contact points under load. that's
> why "stress relieved" wheels stay true over time, and those that
> haven't been, don't.
Bullshit. Adequate and even tensioning is what results in reliable
and true wheels (as well as wheels that are not underbuilt for their
actual use); stress relieving is not a factor in this. My wheels
stayed true long before I found out about stress relieving.
Tim McNamara
> Tim McNamara <tim...@bitstream.net> wrote in message
> news:<m23c8i2...@Stella-Blue.local>...
>
>> jim beam <u...@ftc.gov> writes:
>> > when you have a stress/strain graph like this:
>> >
>> > | x
>> > | / 2
>> > | /
>> > | / 1
>> > | /
>> > |/______ "x" is the onset of plastic deformation.
>> >
>> > you want to have the rim last a long time, you want to have it
>> > operating nearer point 1 than point 2 because any additional load
>> > at point 2 is too close to causing plastic deformation.
>>
>> Umm, loads on a bicycle wheel don't increase tension in the spokes.
>
> I think Jim's talking about the rim, no?
It's hard to tell what jim's talking about. He keeps dodging.
> Between tighter and looser spokes, theoretically the looser ones
> last longer in fatigue.
I don't ride theoretical wheels. It's against my religion. You
might want to read something less theoretical about wheels.
>> > you can't just gloss over the importance of mechanical design,
>> > surface finish or quality of material on fatigue life, and then
>> > just launch into residual stress as fatigue's sole source.
>
> Unless the residual stress is high enough to leave portions near
> yeild. No spoke can last long if that's the case.
>
> But to your point, in practice we don't really ignore those other
> factors. Mechanical design is set by the components we choose
> (number of spokes, etc.), surface finish and quality of material we
> select by trusting the spoke maker.
You're replying to jim here, not me.
Tim McNamara
> forgive me for being so retarded gary - i mistakenly thought you had
> an interest in the science. it appears not.
>
> if at some point, you /do/ wish to get tech, then i'm happy to
> oblige. in the mean time, thanks and goodbye.
Ah, yet another one of jim's hissy fits.
Tim McNamara
> imo, you still need to address the effect on reliability of running
> a rim at near yield, which is basically what you're recommending
> below.
You still need to show that this is in fact "near yield."
Tim McNamara
> <snip>
>> Conincidentally, I saw the first turkey vulture of spring
>> today. (Robins are passé.)
>
> Yeah, when you're laying on the side of the road recovering at the
> top of a hill for long enough they start to thing you're road kill.
Heh. When I moved from Chicago to SE Minnesota and, for the first
time in my life, had decent sized hills to climb I used to be a trifle
worried about those vultures circling over me. I always wondered if
the knew something I didn't.
Rick Onanian
wrote:
>I'm ashamed to say that I missed your post (an argument for
>one of those new-fangled threaded newsreaders).
Threadless newsreaders are lighter and stiffer.
--
Rick Onanian
Bruce Graham
says...
prey love the few main highways, especially the black kites. The
blacktop provides paradise, thermal lift and food via roadkill. So they
cruise down the road, rarely flapping. When they come to a cyclist, they
invariably do one turn to check you out before sailing down the road
ahead.. They have good eyes, so I figure they check the level in your
water bottle....
Tim McNamara
Rick Onanian
No, that's threaded newsreaders. Threadless are *ass-butt* ugly...
--
Rick Onanian
jim beam
that's nearer the mark! not sure that explains where the "short
sockets" come from though.
thanks for clarifying that you're advocating less than half yield
stress, because, with respect, when you make a statement like "I have
spoked many wheels close to the limit of compressive collapse" [1] one
is inclined to think you're advocating something substantially more.
[1] -
http://groups.google.com/groups?selm=q5U2c.6935%24_3.90841%40typhoon.sonic.net&output=gplain]
Carl Fogel
Dear Mike, Tim, and Bruce,
Here, the turkey vultures seem to commute up and down the
Arkansas River valley between opposing bluffs. About two
dozen roost every year in a fifty-foot blue spruce a few
blocks away, probably because it sticks up above the
rest of the trees in the neighborhood. Every evening in
the summer, dozens of other vultures can be seen flying
west over my house to other roosts. Occasionally they
settle in the trees on my block. They're rather graceful
birds, once they're aloft, and seem to enjoy aerobatics.
Here's one that I knew slightly:
http://www.chieftain.com/display/1023688800/lifestyle/1
I met Hurlly several times on my daily ride and found
him to be a perfect gentleman, willing to move out of
the way. He was eventually re-captured and placed in the
zoo, having proved that he was going to keep pestering
people on the nature trail for treats instead of joining
the other vultures.
The bald eagles do the same thing further west, fishing
during the day at the reservoir and then flying even
further up the river to distant roosts. They have
a rather grim, dogged air as they fly past in a dead
straight line.
Carl Fogel
Carl Fogel
Dear Rick and Tim,
Your comments have convinced me--no threaded newsreader.
Think of it as fixed-gear simplicity.
Carl Fogel