Are rusting screws a sign of cheap/bad material?

Question

I noticed rusting screws at a ~ 1 year old bike and rusting screws at another bike after a few months, where the screws were part of a replacement (front gear ring package).

Both bikes were usually placed in rain protected places when possible.

Thus the question: Is this normal? Or do I have to change my bike dealer?

I mean, are not stainless screws standard? Or are they too expensive?

crasic · Accepted Answer

Stainless steel is rust-resistant not rust-proof, especially if the bike sees the outdoors a lot, it isn't uncommon for screws to get a fine sprinkling of brown spots. The good thing about screws is that they can be easily replaced.
If you were very enterprising you can probably replace your bolts with titanium ones. They don't rust in the same way as steel does at all. However, they are usually weaker than the equivalent steel bolts, so we would not recommend replacing bolts like the stem or seat clamp bolts without careful research on high-quality titanium bolts. If you do this, be sure to research titanium material grades; commercially pure titanium is likely too weak for structural bolts, whereas grade 5 (aka 6/4 titanium) is probably what you would want for these bolts. For reference, most titanium bicycle frames are made of grade 9, aka 3/2.5 titanium. The numbers for grade 5 and 9 reference the proportion of aluminum and vanadium in the alloy.
Painted components (like your bike frame) are naturally rust resistant because the paint prevents contact with oxygen, which means that the metal can't oxidise and also explains why its not a bad idea to touch up on large paint chips or scratches with touch up laquer.
ADDED a quick wikipedia glance explains that while stainless steel gets covered in rust, unlike regular steel the rust is passive meaning that it will just stay there (looking unsightly). With regular steel, rust has the nasty habit of eating away at the metal (it is an active oxidation site). The rust on stainless steel behaves like a coating that prevents further oxidation.
Additionally, see comments by @cmaster: not all steel bolts are stainless, particularly on lower-cost bicycles.

curtismchale · Answer

This is fairly normal. Many of the screws are are stainless but where you use the hex key on them they still rust. My best guess is that this is because you scuff the metal when you remove and put them back in.

I'll also mention that this happens on whitewater kayaks. Again typically in the places where a screw driver has touched the screw/bolt.

To my understanding stainless steel is a trade off between stainless and strength. The more stainless it is the weaker it is and so on.

DC_CARR · Answer

Is your frame aluminum?

It is worth noting that, due to the differing electrical properties of different materials, oxidation (rust on steel) will occur much more quickly when dissimilar metals are joined.  On an aluminum bike with steel hardware, electron transfer between the aluminum and the steel will encourage more-rapid-than-normal deterioration of the steel.  Aluminum will continue to look great--actually protected somewhat by the transfer of oxidation to the steel.  This isn't an uncommon issue.  The U.S. Navy just got done replacing an entire class of destroyers that were built with steel hulls and aluminum superstructures--it's a problem that we sometimes accept as a tradeoff.  It is, as other respondents have said, easy to just replace a few bolts every now and then.  Steel bolts are much stronger than aluminum bolts!  But the aluminum frame is plenty strong and is SO MUCH lighter than a steel one.

The rusting probably has little to do with the quality of your bike shop.

Shira Odeski · Answer

Rusting of bolts and other selected spots on a bicycle is very common, and it is due to galvanic corrosion as others mentioned. Though in the case of Aluminum frames with steel or stainless-steel screws, it technically can't be the reason for the corrosion you're seeing, because both steel and stainless steel are more noble than aluminum, that is to say - if you touch aluminum and steel together, it's the aluminum that will do all the rusting, not the screw. I do think it's galvanic corrosion, but it's not the frame's fault; there's a third, more noble metal on the bike somewhere that's causing all the corrosion. Either the screws are steel and there's stainless somewhere else on the bike, or the screws are stainless and maybe there's a nickel or chrome plated surface on the bike, like front suspension or the like.
Best thing is to google "galvanic series" and see what are the two furthest metals that might be present on the bike, and try to substitute one of them to bring it closer to the rest. Also, try to have the frame be the least noble metal, since it's massive and therefore suffers less from galvanic corrosion, also it's mostly painted.
Also, magnesium ribbon is cheap and readily available online; you can buy some and wrap it around your spokes as a "sacrificial anode". I tried it, and can't say for sure if it did any good. It oxidizes through very quickly, within a year or so, and the theory is that by doing so it protects other metals on the bike, but I'm clearly very biased so it's hard to judge. It couldn't hurt.

Are rusting screws a sign of cheap/bad material?

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