Aluminium's robustness.

[Paul]

I was riding along happily today (around 20mph) and ended up with an insect of some sort in my
eye which then proceeded to squirt something irratant into it, ouch, that'll teach me not to
wear glasses.

Since going 20mph down a main road with both eyes tightly closed didn't seem such a good idea I hit
the brakes. Unsuprisingly the back wheel lifted off the ground and tipped me forward. I didn't go
right over the bars, just slid forward into them (my knee bent the left shifter lever which after
being straightened out was find). The bike hit the ground (losing my mirror) and I ended up standing
over it. Not too bad considering what could have happened.

My main concern is for the bike (I'd be absolutely lost without it). Since I started cycling I've
heard a lot about aluminium frames cracking and I guess that I've become a bit paranoid, I've
checked the bike over and it looks fine, I've also tied thin elastic around the headtube to both
dropouts to check the alignment (which is fine as far as I can tell) and also ridden a further
30miles without problem.

I guess that my question is just how robust are alloy frames (mine is oversized plain guage 7005
T6), is a spill like I've had anything to worry about or do you need to hit something head on to do
damage? I guess that aluminium alloy must be a fairly sound material considering the number of
bikes that are made from it but then again I do seem to hear regularly about how prone to cracking
it can be.

Thanks for any thoughts, Paul.

 

[Billx]

I've owned aluminum frames since 88 and never had a crack in any except the one time I rolled a bike
to dodge a dog in the road that broke the rear derailer dropout. Unless you role a bike I wouldn't
get worried about it cracking.

"Paul" <[email protected]> wrote in message news:[email protected]...
> Thanks, it's pretty new (about a year old) with only around 2500 miles so far. Everything look
> unbent although on the few occassions I have come off
I
> tend to feel the bike pulling a little to the left, probably just being a bit shaken from the
> fall, I usually forget about it after a while. I've wrapped elastic around the headtube to the
> inside of the dropout and
mesured
> the distance from the seattube which seems to be the same so I guess that things are ok. I
> regularly check for cracks when I clean anyway.
>
> The fatigue issue is interesting. My bike is plainguage 7005 T6 and comes with a 3 year warranty,
> whilst I was in the LBS having the gear lever straightened I noticed some Ridgeback cycles, of a
> comparable price to my bike, also of 7005 ally which come with a lifetime guarantee.
>
> Thanks again for taking the time to reply, Kind Regards, Paul.

 

[Tony Raven]

In news:[email protected], Paul <[email protected]> typed:
>
> The fatigue issue is interesting. My bike is plainguage 7005 T6 and comes with a 3 year warranty,
> whilst I was in the LBS having the gear lever straightened I noticed some Ridgeback cycles, of a
> comparable price to my bike, also of 7005 ally which come with a lifetime guarantee.
>

In the German EFBe frame fatigue test, the aluminum bikes lasted far longer than the steel ones.
http://www.sheldonbrown.com/rinard/EFBe/frame_fatigue_test.htm

Tony

--
http://www.raven-family.com

"All truth goes through three steps: First, it is ridiculed. Second, it is violently opposed.
Finally, it is accepted as self-evident." Arthur Schopenhauer

 

[David L. Johnso]

On Sat, 14 Jun 2003 17:38:57 +0000, BillX wrote:

> I've owned aluminum frames since 88 and never had a crack in any except the one time I rolled a
> bike to dodge a dog in the road that broke the rear derailer dropout. Unless you role a bike I
> wouldn't get worried about it cracking.

I would not necessarily be so reassuring. Lots of people have cracked bike frames. I managed to
crack an aluminum frame after about 8000-1000 miles. But this can also happen to steel or titanium.

It is worth checking the bike for problems every so often, but don't lose any sleep over it. Byt the
time it breaks, you will have gotten your money's worth.

--

David L. Johnson

__o | A foolish consistency is the hobgoblin of little minds, adored _`\(,_ | by little statesmen
and philosophers and divines. --Ralph Waldo (_)/ (_) | Emerson

 

[John Carrier]

> One of the main causes of failure in Al frames (besides faulty welding) is fatigue. Aluminum,
> unlike steel has a lower "modulus of elasticity" In other words, it doesn't take as well to being
> flexed very much.

The elastic modulus has nothing to do with the material's longevity, just its stiffness. Other
factors effect fatigue resistance.

Of course, if you exceed the elastic limit, the material will bend and you can't rebend
aluminum safely.

R / John

 

[A Muzi]

"Paul" <[email protected]> wrote in message news:[email protected]...
> I was riding along happily today (around 20mph) and ended up with an
insect
> of some sort in my eye which then proceeded to squirt something irratant into it, ouch, that'll
> teach me not to wear glasses.
>
> Since going 20mph down a main road with both eyes tightly closed didn't
seem
> such a good idea I hit the brakes. Unsuprisingly the back wheel lifted off the ground and tipped
> me forward. I didn't go right over the bars, just
slid
> forward into them (my knee bent the left shifter lever which after being straightened out was
> find). The bike hit the ground (losing my mirror) and
I
> ended up standing over it. Not too bad considering what could have
happened.
>
> My main concern is for the bike (I'd be absolutely lost without it). Since
I
> started cycling I've heard a lot about aluminium frames cracking and I
guess
> that I've become a bit paranoid, I've checked the bike over and it looks fine, I've also tied thin
> elastic around the headtube to both dropouts to check the alignment (which is fine as far as I can
> tell) and also ridden a further 30miles without problem.
>
> I guess that my question is just how robust are alloy frames (mine is oversized plain guage 7005
> T6), is a spill like I've had anything to worry about or do you need to hit something head on to
> do damage? I guess that aluminium alloy must be a fairly sound material considering the number of
> bikes that are made from it but then again I do seem to hear regularly
about
> how prone to cracking it can be.

There's a long and colorful history in the bike business of responding to any inquiry about
something not sold in that shop with "they break".

Have an experienced frame technician look at the frame for alignment problems so you'll be
reasussured. If it rides well and there are no obvious dents or cracks it is most liketly fine.

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

 

[Dave]

[email protected] (Chris Zacho "The Wheelman") writes:

> >"The elastic modulus has nothing to do with the material's longevity, just its stiffness. Other
> >factors effect fatigue resistance.
>
> >Of course, if you exceed the elastic limit, the material will bend and you can't rebend aluminum
> >safely.

This is correct, but ...

>
> >R / John
>
> Actually, it does, for the very reason you stated in your second paragraph. Yes, the modulus of
> elasticity is the amount of flexing a given material can ithstand and still return to it's
> original form.

This is not correct. The modulus of elasticity is a ratio of elastic stress to elastic strain. It is
completely unrelated to the stress level where plastic deformation occurs. Furthermore, the fatigue
strength cannot be reliably predicted from the yield strength, although a higher yield strength
usually goes along with higher fatigue strength.

>
> But a bicycle frame, by it's very nature, is subject to continuous flexing. The more elastic the
> material is, the more flexing it can take without weakening of the molecular structure.

Not even close.

>
> I believe Jobst posted on this subject once, probably knows ore about it than I do, and can also
> explain it better as well.

There are several people who post regularly here who know a lot more about metallurgy then you, and
even Jobst. However, Jobst` usually gets it right when he talks about materials.

Dave Korzekwa

 

[Paul]

Thanks for the thoughts.

This is only the 2nd time I've come off my bike since starting cycling and I think the feeling of
the bike pulling a little is just imagination. I felt the same after the first fall, probably
initially just because I was a bit wobbly and shaken. Although I only ride a cheap bike I'd be lost
without it (I probably do150-200 miles a week recreational riding now the weather is good) so I tend
to worry about it.

There are no obvious cracks, despite bening a gear lever with my me the bars are fine and in
line as is the saddle. I've done the basic tying string around the headtube to each dropout to
check alignment and this looks good too so I think it's just a case of getting back on and
enjoying myself!

Thanks again for the reply, Kind Regards,

Paul.