On Fri, 02 Feb 2018 08:01:18 -0800, Joerg
wrote:

On 2018-02-01 17:07, John B. wrote:
On Thu, 01 Feb 2018 15:38:39 -0800, Joerg
wrote:

On 2018-02-01 11:26, jbeattie wrote:
On Thursday, February 1, 2018 at 10:24:16 AM UTC-8, Joerg wrote:
Yesterday on the MTB I had to look downwards between my legs to see
what made a rattling noise on the bike, saw some brush tangled in
the rear and hit both brakes quite hard. That's when I noticed how
much the upper diagonal strut in a Horst link bends when applying a
lot of brake force. The center of it bows down several tenths of an
inch and also outward a little. It's a pretty beefy strut:

http://www.analogconsultants.com/ng/bike/Muddy4.JPG

Similar on other bikes:

https://ep1.pinkbike.org/p5pb9586988/p5pb9586988.jpg

One can see such bowing also on aircraft wings which as built and
tested to high stress standards. They make the spars out of stuff
such as 7178 which I assume bike mfgs don't:

https://www.popularmechanics.com/fli...-stress-tests/



Has anyone else with a Horst link bike taken a look while applying the
rear brake hard? Can this fatigue the strut to the point where it
eventally breaks? Should I shore that up with maybe an L- or
U-profile strapped around it?

I am asking because I use my MTB for transportation a lot and ride
about 2000mi a year on it, hard, not just the occasional weekend
loop. It'll see hundreds of such strut load cycles per ride.

Yes, everything breaks after enough fatigue cycles, particularly
aluminum -- which has no fatigue threshold. Even small amplitude
fatigue cycles will affect aluminum. It will break.


Not necessarily. Next time you fly sit right behind a wing and watch
closely what happens at rotation time (when the pilot pulls up and the
aircraft becomes airborne). The wing will bend so much that its tip is
now several feet higher than it was in its resting state. In turbulent
weather it'll then continue to flex up and down like he

https://www.youtube.com/watch?v=tr5qkjlE77Y

https://www.youtube.com/watch?v=NYsFk4I14N8

Yet these aircraft have a service life of 30 years. And then typically
get sold to the freight dogs or lesser devloped countries for another 30
years or so.

It's aluminum. My question is whether the typical upper Host link strut
on a MTB can take similar dynamic stresses and for how long. If Boeing
made them I'd have no doubt but Boeing does not build MTBs.

[...]

True that all large aircraft wings flex - the outriggers on a B-52
will be some 6 feet above the ground with empty tanks :-)

If you are worried about your bike's rear strut why not just reinforce
it. You have explained how clever it is to use a hose clamp to prevent
a nut from loosening why not use the same technique to hold a
reinforcing brace on your MTB?

https://tinyurl.com/yaklvuy6

Figure 14 shows a bridge using plates attached with clamps as
reinforcement.


I know how to do that but wanted to know how much bending is normal. IOW
whether reinforcement is necessary. Hence my post here. Clamping a
reinforcement to the bar back there ain't as easy as a steerer hose
clamp. That area can't have anything protruding and potentially slicing
open a leg in case of a crash.

If you are seriously worried about injuries resulting from a crash it
would seem logical to simply get rid of the bike before the
anticipated failure.

As for clamps see https://tinyurl.com/y97t6n2b
The 19th shows a clamp that can be installed without protruding parts
and several other examples are shown further down the page.
--
Cheers,

John B.