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Horst link bending forces
On Fri, 2 Feb 2018 08:21:36 -0800, sms
wrote: On 2/1/2018 8:37 PM, jbeattie wrote: On Thursday, February 1, 2018 at 3:38:32 PM UTC-8, 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. All parts made by a decent company are tested to failure or to the end of a test protocol. Call the company and see how many fatigue cycles it took to fail your linkage. Then count your cycles and go from there. When you get to the magic number, don't ride anywhere near mountain lions. I would put in an optical sensor to count the cycles and then do a replacement after every 10,000 cycles. If you look closely practically every part on a bike bends under a load. Notably, the front forks, the handle bars, the brake arms, the main frame ..... Few of which cause failure and physical injury that the O.P. mentions in a separate post. -- Cheers, John B. |
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