davidad

Get a Nitto two bolt and forget about it. https://www.amazon.com/Nitto-Dynamic...g%2C187&sr=1-2

Racing Dan

You are most likely over tightening the bolt to begin with. Try backing off a bit or get a torque wrench. Titanium wont help, - at all. At the same dimensions a titanium bolt is WEAKER than steel.

grizzly59

Bolts can come from whoever in the world can make them the cheapest by the ton. I can snap no-grade chicom or Indian bolts pretty easily. I used to be able to get US made 8.8 or 10.9 metric hex head cap screws at NAPA, but I’m not sure you can even get them there anymore. Your pic looks like a cheap fatigued bolt to me, but I’m not an expert. I would try to replace it with a good quality bolt and washer. And then you might pull the threads out of the Al clamp piece.

njlonghorn

I think I solved the mystery, and DiabloScott wins the prize with his statement "Installation error (over torque or improper saddle position eg): 30%". To put it another way, it was what my brother calls an eye-dee-ten-tee error. And yes, I'm the ID10T in this scenario.


I initially followed (and exceeded) the suggestion by grizzly59 and acquired a pair of 12.9 grade bolts -- made for use in aircraft, heavy machinery, etc. I installed one, and it snapped in half after about 2 months. Clearly, the bolt itself was not the problem.


Next, I began looking into buying a new seat post. That lead to a decision about setback, so I looked at how much of a setback my existing post had. Well, to make a long story short, my seat post was installed backwards. There was a 20 mm "set-front". To compensate, the saddle was installed way back on the clamp/post, undoubtedly outside of tolerances. Plus, the saddle still wasn't far enough back so I tended to shift back for more power during steep climbs. That translated to way more torque on the bolt than it was designed for.


I just turned the post around and reinstalled the saddle. The middle of the saddle now sits squarely on top of the clamp/post, and is held together with the spare 12.9 bolt.



With any luck, this will also translate to a better pedal stroke.

Rogerogeroge

I broken a Thomson Masterpiece a few months ago. I weigh 195 lbs. I had that seatpost over 15 years, spent the first half of its life on my gravel bike and the second half of its life was on my greenway bike. I don't begrudge. Still get a Thomson.

Pop N Wood

thats actually a funny story

njlonghorn

I’m always happy to give someone a laugh, even if it’s at my expense.

Pop N Wood

Naw, I mean it is funny in that I could see myself overthinking a problem then over engineering the solution when all along it was something I put in backwards. The type of thing you put hours into only to have he wife solve with a single look.

The idea of parts breaking without warning gives me the heebie jeebies.

sweeks

Heh... brings back a memory of an event that fortunately didn't become a legend! I was a mile into my two-mile commute to the train when I felt a little extra "softness" in my "ThudBuster" suspension seatpost. I stopped (luckily!) to see what was going on... and the entire saddle fell off. The suspension unit had fractured off at the junction with the seatpost. I was *not* going to miss my train, so I rode the last mile standing. Got several strange looks from passing motorists! Luckily, I had a spare seatpost at home.

Cyclic fatigue seatpost failure



Sitting on the train thinking about what *could* have happened!

adipe

12.9 bolts are more vulnerable to HE - hydrogen embrittlement.

10.9 is plenty and you don't need to over tighten the bolts. just tighten to the point when there are no creaks and maybe... use a torque wrench if you have bad estimation of your hand force over the key. usually you use one of your finger, the ring finger in my case. i do so as i apply lubricant that prevents bolts breaking because of HE etc.

to translate the torque used for dry vs lubricated bolts...

https://www.tribology-abc.com/calculators/e3_6a.htm
do not use regular grease but apply chain lube or something that has wax as an additive. usually the CoF gets lower to 0.2 for wax. in rare cases it gets down to 0.1 but i repeat... the way i use the key over the bolts is by feel and experience as to avoid creaks and not get the bolts tighter than needed.

that calculator above can be used to understand the limit of the material for different parameters like dry vs wet lube etc.
nickel over nickel (like stainless) is usually 0.15 CoF even if dry.

adipe

after you tighten the bolt(s) apply some pressure to the key just to release torsional stress from the bolt. no need to loosen the bolt in doing so. apply about 1/2 of force you used to tighten the bolt like trying to loosen it and if you see it move then you may tighten it back and be more cautious/gentle when applying force as to get torsional stress relieved without getting to the point of the threads moving.