rear axle breakage -warning signs?

[Wilfred Kazoks]

From your post it seems you have a hub with a screw on freewheel. these
older hub types had the drive side bearings about where the freewheel
threads are so the axle is supported on bearings quite a long way inside the
drive side dropout. This has the effect of bending the axle over the drive
side bearing.

A modern cassette hub has the bearings much closer to the dropouts thus
making the axle actually unlikely to bend and break. As opposed to
inevitably destined to break even with a lightweight rider for a freewheel
hub.

This is one design inovation you can really thank Shimano for. No fashion or
marketing hype involved.

Wilfred

"patrick mitchel" <[email protected]> wrote in message
news:[email protected]...
> Broke the rear axle (unnoticed by me until a hadda flat- am assuming the
> axle was still "solid" until the last time of levering the skewer) on my
> rans stratus lwb recumbent. The original part I think). I was changinge
> the tube after a second flat and mounted the wheel and noticed a severe
> wobble (loose) in the wheel . Thought it might be a loose cup/cone. When
> taken apart, the axle was broken through at the inner adege of the
> threaded section-drive side (freewheel hub). Looks from the shine that the
> majority of the break had been in place for a while. Over 2/3 of the
> circumferance had the shine. Are there any signs of impending failure
> other than the drunken rider look? TIA Pat
>

 

[Peter Cole]

patrick mitchel wrote:
> Ok, a related question. Would a solid axle be a more reliable component?
> Pat
>
>

No, not really. A hollow axle with QR has about 85-90% of the strength
of a solid axle, but has the great benefit of the QR holding things
together if the axle breaks.

 

[[email protected]]

On Wed, 04 Oct 2006 13:28:39 -0400, Peter Cole
<[email protected]> wrote:

>patrick mitchel wrote:
>> Ok, a related question. Would a solid axle be a more reliable component?
>> Pat
>>
>>
>
>No, not really. A hollow axle with QR has about 85-90% of the strength
>of a solid axle, but has the great benefit of the QR holding things
>together if the axle breaks.

And the dual disadvantage of the stress risers on the inside bore, and
the qr increasing the bending force as soon as the axle is not
perfectly, exactly straight.

 

[Peter Cole]

[email protected] wrote:
> On Wed, 04 Oct 2006 13:28:39 -0400, Peter Cole
> <[email protected]> wrote:
>
>> patrick mitchel wrote:
>>> Ok, a related question. Would a solid axle be a more reliable component?
>>> Pat
>>>
>>>
>> No, not really. A hollow axle with QR has about 85-90% of the strength
>> of a solid axle, but has the great benefit of the QR holding things
>> together if the axle breaks.
>
> And the dual disadvantage of the stress risers on the inside bore,

I don't know what you mean. In any case, if there were stress riders,
they would have little effect as the inner wall sees perhaps 30% of the
stress as the outer (which is covered in stress riders -- threads).


> the qr increasing the bending force as soon as the axle is not
> perfectly, exactly straight.

Actually, to the extent that QR compression has any effect on axle
strength, it increases it by adding a compressive pre-load that
subtracts from the tensile stress of bending which causes the fracture.

I can't think of any reason to use solid axles.

 

[jim beam]

Peter Cole wrote:
> [email protected] wrote:
>> On Wed, 04 Oct 2006 13:28:39 -0400, Peter Cole
>> <[email protected]> wrote:
>>
>>> patrick mitchel wrote:
>>>> Ok, a related question. Would a solid axle be a more reliable
>>>> component? Pat
>>>>
>>> No, not really. A hollow axle with QR has about 85-90% of the
>>> strength of a solid axle, but has the great benefit of the QR holding
>>> things together if the axle breaks.
>>
>> And the dual disadvantage of the stress risers on the inside bore,
>
> I don't know what you mean. In any case, if there were stress riders,
> they would have little effect as the inner wall sees perhaps 30% of the
> stress as the outer (which is covered in stress riders -- threads).
>
>
>> the qr increasing the bending force as soon as the axle is not
>> perfectly, exactly straight.
>
> Actually, to the extent that QR compression has any effect on axle
> strength, it increases it

whoa there - that's a massively over-simplistic statement! please do
/not/ make the jobstian mistake of assuming that increasing load =
increasing strength.

for statics, ok, it superimposes stress, but as above, that does /not/
increase strength. the stress/strain graph for this kind of steel is
equal in both tension and compression. for a bending beam, what you may
"gain" in "lack of tension" on the extension side, you're "losing" on
the "additional compression" side as you're bringing the material closer
and closer to compressive yield. the beam will therefore yield at the
same external load. [you can argue "increased strength" in materials
like pre-stressed concrete where one material has no tensile strength
but can be made to appear to have one by "borrowing" from the
compressive side of the graph with pre-load from the material that
/does/ have tensile strength.]

with a bike axle, the only "gain" is in fatigue where the compressive
pre-load can mitigate tensile [the commonest] fatigue initiation.

"increasing strength" statements need to be very carefully qualified.

> by adding a compressive pre-load that
> subtracts from the tensile stress of bending which causes the fracture.

it's fatigue that causes fracture, not static load.

>
> I can't think of any reason to use solid axles.

 

[[email protected]]

On Thu, 05 Oct 2006 08:53:08 -0400, Peter Cole
<[email protected]> wrote:


>
>I can't think of any reason to use solid axles.

How about: they are stronger than hollow ones.