Just had my first real issue with my CFR505- was on a long ride on Saturday and while on an innocuous section of road (no hard hits or anything) one of the two seat clamp bolts sheared in half, leaving me seatless and off balance. Luckily was able to save myself from a crash, but could have been catastrophic.
To be fair, I'm not necessarily blaming Carbonda as this is the second seat clamp bolt I've sheared in half in two years-- last year it happened on a Giant Defy and ended in a crash that left me super injured and the bike in rough shape (part of the reason I got a Carbonda). While I'm a big rider at 225lb (100kg), I wouldn't think I'm so big I'm outside the realm of standard riders, especially for a 60cm frame (I'm just a tall, solidly-built, fit guy, not obese or something)... Certainly tolerances for bolts must account for people bigger than me!?! And, in case you think it was user error, the seat clamp had been torqued to the specs of my (carbon railed) seat and should be pretty standard I'd think, while last time it was torqued to the exact specs from Giant. While the CFR505 has seen a lot of use in one season-- around 3,000 miles so far, it is young enough that I wouldn't expect things to be giving out. Soooo, is it just that parts aren't built for people my size? Are Giant and Carbonda both sourcing poor quality bolts?
Just putting this out there as a warning and I guess to see if others have ever experienced this, or if there are recommendations on replacement bolts (go titanium for strength or is it too rigid? Aluminum for flexibility instead of shearing in half? Clearly steel is not working well for me...). Appreciate any suggestions or thoughts on this,
It all comes to the material used in these bolts. Steel is not steel and Titan is not Titan. Don't use Aluminum on any bolts which are not bottle holder on a bike with your body weight!!!
Titan might work, but the alloy makes the difference. There is Titan which has the values like 10.9 steel. Take that one. It can withstand 10Nm torque in M5. Saddle clamp screws being M6 is capable of more torque.
But in general, braking steel bolts on two different bikes is not normal. Either it's material manufacturer fault of the screw or it's users fault. Please make a picture of how you setup the clamps and screws. Are they angled? And how do you tighten the screws. Tighten one to full torque and then start to torque the second? That would mean the stress increases in the first screw way more than the initial torque did. Tighten screws is always a small step process when having more than one screw like on stem or saddle clamp.