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.

--
Regards, Joerg

http://www.analogconsultants.com/