Bottle holder - aluminium or titanium bolts?

Question

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.)

Answer 1

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.

Answer 2

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.