Cracks and spoke tension

[jim beam]

Chalo wrote:
> jim beam wrote:
>> Chalo wrote:
>>> jim beam wrote:
>>>> and what is /your/ spoke tension???
>>> I'll venture a guess: too high for Mavic's overcooked crappy alloy!
>>> (But probably not too high for a better-made rim.)
>> the only mavic rim i've ever succeeded in cracking is one with spoke
>> tension > 175N [off the end of the scale for my park tensiometer]. it's
>> a single eyelet x517 and i weigh #205+. perversely, i don't consider
>> this the result of "overcooked crappy alloy".
>
> Do you mean 175kgf?

yes!

>
> Most of Mavic's rims use 6106 aluminum-- just about the weakest of the
> 6000 series--

any idea what their "maxtal" alloy is?


> in order to get a sharp looking finish on the
> extrusion.

that bit can't be true - they anodize it and that covers a multitude of
sins.

> For using some of the softest structural alloy money can
> buy, their rims sure don't seem very ductile. I believe they do some
> monkey business with heat treatment in an attempt to buy back the
> hardness sacrificed in using a weak, soft alloy. Thus they get spoke
> holes that crack and sidewalls from which segments break off. I have
> seen these things happen much more often with Adidas-Salomon-Mavic
> rims than with all other rims combined.

and most other rims weigh more. what about d.t. rims - they're
weight/feature/performance competitive. have you tried those?


>
> Paradoxically, they seem to do this aggressive heat treatment _before_
> welding, which means they get the worst of both the soft material in
> the weld and the brittle material elsewhere in the rim.

why not declare this a "bash mavic" weekend and be done with it?

 

[[email protected]]

On Sep 15, 1:15 am, [email protected] wrote:
> On Sep 14, 9:15 am, [email protected] wrote:
> Some background: http://www.bikexprt.com/bicycle/pitcheqn.htm
>
>
> Good that you obtained your own values. I looked at the above linked
> article on spoke tension determination by musical pitch: Why Correct
> Musical Pitch Depends On Spoke Length And Not On Thickness. Although
> I am not an engineer, physicist, mathematician, musician, etc, it is
> clear to me that the author, in his initial exposition, unwittingly
> collapsed the distinction between a spoke's tension and a spoke's
> tension per its unit cross-sectional area. The result is his implied
> counter intuitive and erroneous conclusion that two spokes of the same
> length and pitch have the same tension regardless of their thickness -
> regardless of their gauge.
>
> If the author used say 16 gauge spokes to develop his table of
> pitches, then someone building a wheel using 14 gauge spokes and these
> musical pitches should also be prepared for the percussion of popping
> eyelets. Still, I'm a little confused here; the author's credentials
> seems to indicate that he is not just another "ex-metallurgist".

I think you are, indeed, confused here. John Allen explains exactly
what you're worried about in the paragraph under the equation - the
one that ends "It still vibrates at the same frequency."

You can find the equation he quotes in many physics books. As a
double check, you can review the units of measurement on the equation
to indicate that it is valid as it stands. The spoke gage (or cross
sectional area) does not appear in the equation, indicating it does
not make a difference, even if that seems counterintuitive.

BTW, John Allen is an engineer and a musician. (I am too.) He knows
what he's writing about.

- Frank Krygowski

 

[A Muzi]

>>>> jim beam wrote:
>>>>> and what is /your/ spoke tension???

>>> Chalo wrote:
>>>> I'll venture a guess: too high for Mavic's overcooked crappy alloy!
>>>> (But probably not too high for a better-made rim.)

>> jim beam wrote:
>>> the only mavic rim i've ever succeeded in cracking is one with spoke
>>> tension > 175N [off the end of the scale for my park tensiometer]. it's
>>> a single eyelet x517 and i weigh #205+. perversely, i don't consider
>>> this the result of "overcooked crappy alloy".

> Chalo wrote:
>> Do you mean 175kgf?

jim beam wrote:
> yes!

> Chalo wrote:
>> Most of Mavic's rims use 6106 aluminum-- just about the weakest of the
>> 6000 series--

jim beam wrote:
> any idea what their "maxtal" alloy is?

> Chalo wrote:
>> in order to get a sharp looking finish on the
>> extrusion.

jim beam wrote:
> that bit can't be true - they anodize it and that covers a multitude of
> sins.

> Chalo wrote:
>> For using some of the softest structural alloy money can
>> buy, their rims sure don't seem very ductile. I believe they do some
>> monkey business with heat treatment in an attempt to buy back the
>> hardness sacrificed in using a weak, soft alloy. Thus they get spoke
>> holes that crack and sidewalls from which segments break off. I have
>> seen these things happen much more often with Adidas-Salomon-Mavic
>> rims than with all other rims combined.

jim beam wrote:
> and most other rims weigh more. what about d.t. rims - they're
> weight/feature/performance competitive. have you tried those?

> Chalo wrote:
>> Paradoxically, they seem to do this aggressive heat treatment _before_
>> welding, which means they get the worst of both the soft material in
>> the weld and the brittle material elsewhere in the rim.

jim beam wrote:
> why not declare this a "bash mavic" weekend and be done with it?

Weekend? Ongoing for years! It'll probably span the whole century. Or
maybe just Mavic's lifetime, now that we have better alternate rims.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

 

[Ben C]

On 2007-09-15, A Muzi <[email protected]> wrote:
>>>>> jim beam wrote:
[...]
> jim beam wrote:
>> why not declare this a "bash mavic" weekend and be done with it?
>
> Weekend? Ongoing for years! It'll probably span the whole century. Or
> maybe just Mavic's lifetime, now that we have better alternate rims.

Well my cracked rim was a Rigida. And the Mavic I replaced it with is
holding up fine so far.

 

[[email protected]]

Andrew Muzi writes:

>> why not declare this a "bash mavic" weekend and be done with it?

> Weekend? Ongoing for years! It'll probably span the whole century.
> Or maybe just Mavic's lifetime, now that we have better alternate
> rims.

It's been that ever since Solomon Ski bought the Mavic. All downhill,
and not even a slalom.

Jobst Brandt

 

[Antti Salonen]

jim beam <[email protected]> wrote:

> and most other rims weigh more. what about d.t. rims - they're
> weight/feature/performance competitive. have you tried those?

I tried the DT RR 1.1 and wasn't impressed. I built the rear with
about 100 to 110 kg tension on the drive-side, and it started showing
cracks around the drive-side eyelets. Front wheel lasted fine but I
tensioned the spokes only to about 90 kg. I did put almost 15 thousand
km on the wheels, but they were carefully built and I'm only about 60
kg, so I was definitely expecting more.

Not surprisingly, DT started selling a double-eyelet version of the same
rim, but it's of course significantly heavier and in my view not
competetive either. As far as I can tell, probably the best lightweight
road rim on the market is Velocity Aerohead, but Velocity doesn't seem
able to bring their product to the European market.

Actually I'm starting to feel that given the poor quality of road rims
on the market, if you want to get a pair of reasonably light, aero and
durable wheels, boutique wheels might actually be the way to go. For
about 350 euro you can get a pair of Campagnolo (or Fulcrum) wheels with
Record class hubs and rims that seem to last fine. If you're unlucky
you might bust the rim, but other than that serviceability is not a
problem. Replacement spokes are a bit expensive, but 20 euro for the
spoke kit doesn't really change the equation.

Antti

 

[Chalo]

jim beam wrote:
>
> Chalo wrote:
> >
> > Most of Mavic's rims use 6106 aluminum-- just about the weakest of the
> > 6000 series--
>
> any idea what their "maxtal" alloy is?

"20% stronger!" or some such business. Meaning "about as strong as
the 6061 alloy in Alex rims that cost 1/4 as much". Only a couple of
Mavic rims are made with Maxtal alloy, whatever that is. The rest are
6106, including the A719 which turned out to be the most disappointing
rim I ever wasted money on.

http://www.google.com/search?hl=en&q=mavic+6106

> > in order to get a sharp looking finish on the
> > extrusion.
>
> that bit can't be true - they anodize it and that covers a multitude of
> sins.

Well, that's what 6106 alloy is for, and why folks (including
Velocity) use it despite the fact that it's much weaker than other
aluminum alloys commonly used in bikes. Mavic and Velocity extrusions
do look nicer-- crisper and smoother-- than Alex extrusions with
similar finishes. There's a cost, though. Velocity mitigates the
shortcomings of soft alloy by using structurally optimized shapes.
Mavic seems to deal with it by overhardening their extrusions (which
causes other problems in turn).

> > Thus they get spoke
> > holes that crack and sidewalls from which segments break off. I have
> > seen these things happen much more often with Adidas-Salomon-Mavic
> > rims than with all other rims combined.
>
> and most other rims weigh more. what about d.t. rims - they're
> weight/feature/performance competitive. have you tried those?

DT doesn't make any sturdy rims. They are also very poor value
compared to Alex and Sun.

> > Paradoxically, they seem to do this aggressive heat treatment _before_
> > welding, which means they get the worst of both the soft material in
> > the weld and the brittle material elsewhere in the rim.
>
> why not declare this a "bash mavic" weekend and be done with it?

I just call them like I see them. I wanted to like Mavic-- they made
my favorite rims in the '80s and early '90s when other decent choices
were slim. Not just the MA2 and MA40, but the Open 4, Module 3,
Module 4, and Oxygen M6 were excellent rims in most respects,
beautiful and reliable for their weights. But then the M261 showed up
with its achy breaky sidewalls, and things just deteriorated from
there. The decline of Mavic was correlated with the takeover of the
company by Salomon, but I didn't learn that until years after I'd
noticed the symptoms.

Chalo

 

[John Thompson]

On 2007-09-15, jim beam <[email protected]> wrote:

> John Thompson wrote:
>> On 2007-09-14, jim beam <[email protected]> wrote:
>>
>>> how do you know those are the numbers if you're not using a
>>> tensiometer???

>> How do you jknow your tensiometer is properly calibrated? That was the
>> problem we ran into at Trek when we started building wheels. I was
>> recalibrating tensiometers for the builders several times a day. Hard to
>> get anything else done, sometimes.

> that may be, but personally, i find it hard to believe there was /that/
> much of a problem. what kind of tensiometer were you using? why use
> one so unreliable?

I believe they were from Wheelsmith. Basically, a spring-loaded run-out
gauge to measure deflection in a segment of spoke. When you're building
hundreds of wheels a day, they do go out of calibration more quickly
than in a local shop.

--

John ([email protected])

 

[[email protected]]

On Sep 15, 9:07 pm, [email protected] wrote:

snip
> OK, I stand corrected.
snip

Frank,

Wow. All class -- 100% credibility.

Spike

 

[[email protected]]

John Thompson writes:

>>>> how do you know those are the numbers if you're not using a
>>>> tensiometer???

>>> How do you jknow your tensiometer is properly calibrated? That was
>>> the problem we ran into at Trek when we started building wheels. I
>>> was recalibrating tensiometers for the builders several times a
>>> day. Hard to get anything else done, sometimes.

>> that may be, but personally, i find it hard to believe there was
>> /that/ much of a problem. what kind of tensiometer were you using?
>> why use one so unreliable?

> I believe they were from Wheelsmith. Basically, a spring-loaded
> run-out gauge to measure deflection in a segment of spoke. When
> you're building hundreds of wheels a day, they do go out of
> calibration more quickly than in a local shop.

I've been watching this thread and cannot see what goes out of
calibration on these devices. Their springs are not highly stressed
and there are no wearing parts. What is it with these instruments.
None of the ones I've had in hand has a propensity to lose
calibration.

'splain!

Jobst Brandt

 

[jim beam]

[email protected] wrote:
> John Thompson writes:
>
>>>>> how do you know those are the numbers if you're not using a
>>>>> tensiometer???
>
>>>> How do you jknow your tensiometer is properly calibrated? That was
>>>> the problem we ran into at Trek when we started building wheels. I
>>>> was recalibrating tensiometers for the builders several times a
>>>> day. Hard to get anything else done, sometimes.
>
>>> that may be, but personally, i find it hard to believe there was
>>> /that/ much of a problem. what kind of tensiometer were you using?
>>> why use one so unreliable?
>
>> I believe they were from Wheelsmith. Basically, a spring-loaded
>> run-out gauge to measure deflection in a segment of spoke. When
>> you're building hundreds of wheels a day, they do go out of
>> calibration more quickly than in a local shop.
>
> I've been watching this thread and cannot see what goes out of
> calibration on these devices. Their springs are not highly stressed
> and there are no wearing parts.

well, the mounting points can be subject to wear, but that's more an
issue for used wheels where road grit can be abrasive. not much of a
problem on new builds, i agree.

> What is it with these instruments.
> None of the ones I've had in hand has a propensity to lose
> calibration.
>
> 'splain!
>
> Jobst Brandt

 

[jim beam]

John Thompson wrote:
> On 2007-09-15, jim beam <[email protected]> wrote:
>
>> John Thompson wrote:
>>> On 2007-09-14, jim beam <[email protected]> wrote:
>>>
>>>> how do you know those are the numbers if you're not using a
>>>> tensiometer???
>
>>> How do you jknow your tensiometer is properly calibrated? That was the
>>> problem we ran into at Trek when we started building wheels. I was
>>> recalibrating tensiometers for the builders several times a day. Hard to
>>> get anything else done, sometimes.
>
>> that may be, but personally, i find it hard to believe there was /that/
>> much of a problem. what kind of tensiometer were you using? why use
>> one so unreliable?
>
> I believe they were from Wheelsmith. Basically, a spring-loaded run-out
> gauge to measure deflection in a segment of spoke. When you're building
> hundreds of wheels a day, they do go out of calibration more quickly
> than in a local shop.
>

they might, but hundreds of wheels a day and only one tensiometer?
for only 100 wheels and 8 hours, that's one wheel every 4.8 minutes. i
would have thought a more heavy duty tool appropriate to that application.

 

[A Muzi]

> jim beam <[email protected]> wrote:
>> and most other rims weigh more. what about d.t. rims - they're
>> weight/feature/performance competitive. have you tried those?

Antti Salonen wrote:
> I tried the DT RR 1.1 and wasn't impressed. I built the rear with
> about 100 to 110 kg tension on the drive-side, and it started showing
> cracks around the drive-side eyelets. Front wheel lasted fine but I
> tensioned the spokes only to about 90 kg. I did put almost 15 thousand
> km on the wheels, but they were carefully built and I'm only about 60
> kg, so I was definitely expecting more.
>
> Not surprisingly, DT started selling a double-eyelet version of the same
> rim, but it's of course significantly heavier and in my view not
> competetive either. As far as I can tell, probably the best lightweight
> road rim on the market is Velocity Aerohead, but Velocity doesn't seem
> able to bring their product to the European market.
>
> Actually I'm starting to feel that given the poor quality of road rims
> on the market, if you want to get a pair of reasonably light, aero and
> durable wheels, boutique wheels might actually be the way to go. For
> about 350 euro you can get a pair of Campagnolo (or Fulcrum) wheels with
> Record class hubs and rims that seem to last fine. If you're unlucky
> you might bust the rim, but other than that serviceability is not a
> problem. Replacement spokes are a bit expensive, but 20 euro for the
> spoke kit doesn't really change the equation.

We and others commonly ship to UK and EU, both rims and wheels. What
amazes me is that we ship Velocity product to Australia (!?) where
availability seems spotty compared to their US operations. Go figure.

p.s. When last I checked, Finland had a postal limit of 79 inches which
is smaller than a rim. Shipping via small-packet service (UPS, FedEx,
DHL) is considerably more expensive.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

 

[[email protected]]

I just measured that the spoke tension was on DS very constantly 1400
N and on NDS it varied +-10% around 700 N.

joakim

 

[jim beam]

[email protected] wrote:
> I just measured that the spoke tension was on DS very constantly 1400
> N and on NDS it varied +-10% around 700 N.
>
> joakim
>
well, that's the problem causing the rim cracking - drive side tension
is too high. simply re-build with a new rim and correct spoke tension,
then you'll be fine.

 

[Antti Salonen]

[email protected] wrote:

> I just measured that the spoke tension was on DS very constantly 1400
> N and on NDS it varied +-10% around 700 N.

1400 N sounds high for a rim like Reflex. I wouldn't go beyond about 100
kg, and if it's not enough to keep the wheel true for the rider, some or
all of the parts need to change.

If you rebuild the wheel with a lower tension, do something about the
NDS spokes if you've had problem with them before. Use the thinnest
spoke on the market (DT Revolution or Sapim Laser), because they don't
lose their tension under load as easily. Also, don't lubricate the NDS
spoke threads more than necessary when you build the wheel, or even use
some kind of thread lock.

Antti