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I need to get some bolts to attach bottle cages and a pannier rack to a steel frame. I've had some trouble with cheap alloy ones and steel ones with corrosion and general getting stuck/stripping heads etc. so was thinking going for titanium.
Size wise i think i'm correct in going for M5x15mm?
Is it okay to use copper slip on the bolts for lube and corrosion resistance? No known dodgy chemical reactions between a steel/copper/titanium mix?
And finally, any recommendations on where to purchase said bolts, there is a couple of retailers selling on E bay, prices at around £4-5 for two. Cycle specific retailers reach up to £25 for a pack of 4. I need 8 and £20 is a lot more attractive than £50!
Thanks.
Just get stainless steel ones.
About 4quid will get you loads.
I tend to go longer and cut them to size for whatever I need them for. Some panier racks have spacery bits.
I decided I needed stainless torx bolts for no real reason other than it was different to hexheads. I got them from Westfield fasteners
So stainless steel seems to be the bolt of choice. At that price it seems silly not to try them out.
Thanks.
Does stainless have tensile strength for a rack? (I don't know, was always told to use hi tensile steel).
Yes stainless is strong enough. Its stronger than mild steel IIRC. Never had a bolt sheer despite stupid loads on the bike. Rack mounts are not under sheer forces anyway - remember all the bolt does is clamp the bits together - the friction this creates is what stops parts moving
always use copaslip
So it is stronger so it's ok, but also its strength doesn't actually matter?
Science links please...
You need enough strength to provide the clamping force. we have done this all before a week or two ago. What stops the parts moving is the friction between the surfaces not the tensile strength of the bolt
think about it for a moment. when the bolt is only finger tight the two parts can move. Once its tight they cannot. thats the clamping force creating friction.
I did not say strength does not matter.
I understand the argument but I don't accept it's that simple if a high force is encountered (otherwise strength wouldn't matter, which you accept), and I didn't see the thread 2 weeks ago - happy to read it if it has data/science to justify.
TJ is right. (I know he's never wrong, but this time he's definitely right). The bold is under tensile strength, not shear. It clamps the parts together and the friction keeps everything in place. If the parts can slide around, you have a problem.
Ok so strength matters only up to a point, and as long as the friction holds, all is ok, I understand that. Would be nice to see some number around that and the loads.
I guess the same holds for disc brake bolts but the loads are significantly higher and so tensile strength does come into play?
Braking force from a rotor is transferred to the hub by friction between the rotor and hub. The bolts clamp the rotor hard enough that it doesn't move. The bolts need enough tensile strength to do that. The tensile strength is directly proportional to the diameter. However, if you're screwing into aluminium, you'll generally strip the aluminium threads long before the bolt itself breaks. Most people round off the head of the bolt before the bolt breaks.
From observation of others problems with rack bolts breaking this seems to happen when bolts are allowed to come loose and then can lead to the movement of the rack leg breaking the head of the bolt off, or worse the bold breaking at the point it is flush with the frame.
tj and thols are correct but there can come a point where the load applied will overcome the friction forces, at this point the bolts will be subject to sheering forces. This is where specified safe working loads come in to it.
there can come a point where the load applied will overcome the friction forces, at this point the bolts will be subject to sheering forces.
If your brakes reach this point, you are in serious trouble.
thols
there can come a point where the load applied will overcome the friction forces, at this point the bolts will be subject to sheering forces.
If your brakes reach this point, you are in serious trouble.
You would think so, and it's not something I would like to put to the test over a long period but I have experienced a particular rotor/hub combination where I could see the rotor moving relative to the hub/bolts. This was despite everything being assembled cleanly/correctly and with the bolts to the specified torque and loctited. I rode it like that for some time before fitting a different rotor which solved the problem and I didn't come to grief.
Never had a problem using stainless socket head cap screws in place of the supplied ones, even on brake rotor adaptors. If you're worried about strength, use a A2-70 or A4-70 (or -80).
If you are worried about loosening due to vibrations (racks, etc.) then use a Nord-Lock washer.