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I'm a "weight-weenie" and optimize the bolts I'm using. Replacing steel with aluminium or titanium, depending of the location (to summarize: exerted forces, and dangerosity in case of breakage). Aluminium if possible, otherwise titanium.

For the bottle holders (two M5 bolts for each holder), people (fellow weight-weenies) say these bolts are amongst the less stressed, and aluminium can be used without problem. Some even use nylon bolts.

Though, I don't "feel it". Actually, I'm already using aluminium bolts here for months, and it seems to be okay. But these aluminium bolts are really lightweight, and I still fear they might break. Thus, I'm considering using titanium bolts here.

Do you think I am overfearing about the aluminium bolts and they are really sufficient, or not?

(FYI, I put a 500ml bottle on each holder, and I do city/road cycling, of course with some bumps here and there.)

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    I wouldn’t be too worried, it’s not a safety-critical part and 500ml bottles are on the light side (I’m using 1.5l bottles while traveling ;) ). Just tighten to the specified torque and use thread locker to prevent contact corrosion and the screw coming loose.
    – Michael
    Apr 29 '20 at 5:35
  • I'm mainly worried about a close-cut bolt, where the remaining of the bolt would be difficult to remove from the frame. Also, a bottle falling on the road isn't very kind to the guy behind ;) And indeed, I confirm the thread locker helps a lot here. Apr 29 '20 at 6:09
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    If your worried, use nylon (as if they break, its easy to remove) or titanium. Alternately, save the weight of the bolts, the cage, and half the bottles put a 350ml plastic bag style bottles in your back pocket.
    – mattnz
    Apr 29 '20 at 6:33
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    A full bottle in a cage rattling over cobbles will put quite a high stress on the bolts due to the distance from the tube. I'd go for Ti bolts. If the roads is always smooth, Al is probably sufficient.
    – Carel
    Apr 29 '20 at 15:00
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    I think it's silly to use anything other than steel or SS bolts here. Apr 30 '20 at 18:18
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In general, for weight weenie information, questions, and discussion, I'd recommend joining the Weight Weenies forum.

The bottle cage bolts don't need to withstand impacts. They just need to hold the cage in place against the force you exert when pulling a bottle out. They don't really bear much of a load. I am not sure what torque specs there are aside from just tightening until snug. Aluminum bolts are almost certainly sufficient. Perhaps your steerer expander bolt is another candidate for aluminum, as that component needs minimal torque and it doesn't bear a load when in operation (the load is borne by the stem clamp and its bolts).

In comparison, the stem face plate needs to withstand shocks while riding, not to mention holding the stem together at a significant torque (probably at least 5 Newton meters per bolt). That type of bolt is more a candidate for steel, although high-quality titanium bolts have been used successfully. As another point of comparison, seatpost binder bolts typically need to take at least 5 Nm of torque as well, and I've heard of titanium but not aluminum being used here also.

Probably the highest-stress location where aluminum is frequently used are the chainring bolts and spoke nipples. Chainring bolts probably take in the region of 6-8 Nm of torque. However, they are large bolts. Nonetheless, I've cracked a couple in my career, and probably other users have as well. Aluminum spoke nipples can crack as well, especially if exposed to a lot of road salt. Current generation nipples from the higher-quality manufacturers like DT Swiss and Sapim may have mostly resolved this issue.

Logic would suggest that if you do want to go this route, aluminum bottle cage bolts are safe. You may already be aware that you have to save a massive amount of weight to make a noticeable performance gain, whereas comparable aerodynamic savings are a lot more significant.

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    “Perhaps your steerer expander bolt is another candidate for aluminum” Or you can completely remove the expander and cap after setting the bearing play and tightening the stem. I can confirm bad experiences with high quality DT Swiss aluminum spoke nipples and road salt.
    – Michael
    Apr 30 '20 at 15:35
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i always avoid aluminum fasteners wherever possible due to a lot of bad experiences with them disintegrating over time (especially nipples on fancy wheels), but i'm not a weight-weenie, just weight-conscious.

i would say if you can afford ti bolts that'd be what i would go for, even though it's overkill and you'd be shaving maybe 1/10th of a gram. of course, if you were truly a weight-weenie, you'd leave off bottle cages entirely, right? ;)

if you're using this bike on a trainer, definitely avoid aluminum fasteners, as your bike is bound to be covered in sweat that'll accelerate the corrosion on the bolts. the things i've seen on trainer bikes.... disgusting. weight wouldn't be much of an issue on a trainer though so i imagine you'll be riding it in drier conditions.

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  • If you know a dash of chemistry, look up the galvanic potential of the frame material and the materials of the different bolts you are considering, and select the bolt that is closer to the frame. This will minimize your corrosion issues.
    – EvilSnack
    May 6 '20 at 17:46

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