Humidity - Headsets and Bottom Brackets

Since we’re in the topic of corrosion, here’s something that you should know about corrosion that’s very non-intuitive.

There’s many types of corrosion including galvanic, crevice, oxidation without salt, etc. But the most common is your typical corrosion is due to periodic exposure to water and electrolyte (salt) and includes temperature and humidity cycles.

I have experience in salt spray testing for automotive products. The testing involves spraying a salt solution on parts and seeing how bad they rust in comparison to some standard steel pieces (the control to verify you tested correctly). Intuitively you would think that we tightly controlled how much salt solution was sprayed on the parts. Nope. We’re just made sure they got fully wetted. That’s it. If that took 10 seconds or 2 minutes it doesn’t matter!

What matters is the control of the temperature and humidity of the test chamber. It cycles from room temp and low humidity, to hot and humid, to hot and dry. Spray the salt solution for a minute or so on the test part during the room temp portion. Let it dry on there (so now there’s a light salt film on the part). Then make it hot and super humid (foggy) so the salt gets wet again. Then slowly make it really hot and dry. Then repeat. It’s the slow drying of the salty parts that corrodes them. If corrosion wasn’t happening fast enough, slow down the drying process more. That’s it.

So, moral of the story is, there’s a few key ways to reduce corrosion:

  1. Don’t get the salt (or drink mix) on the bike in the first place (not feasible for those living near the coast since it’s in the air mate).
  2. Rinse the salt off before it dries, using non-hard water (but not distilled water either)
  3. Actively dry the bike off so corrosion has the least amount of time to occur. Dry by hand then put it in the sun to try to get water out of the crevices ASAP.
  4. Especially if you live near the coast, keep the bike from experiencing temperature and humidity cycles as much as possible. Outside is the worst because you get condensation and temperature swings every day. Being under a deck has very little impact on reducing that. Being in an enclosed garage is much better. Being in a climate controlled space is best.
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  • Your solution is to tell someone to change the entire frame & fork too get a better headset? Priorities may differ between people, but that is about as backwards an order as I have ever seen.

I’m overly cynical. I think that that modern bikes and components are designed and manufactured to a price point and a certain design life. If you choose to own a modern bike you accept the additional cost of disposable bearings.

I have never seen a IH bearing failure that was the frame as the root cause. It was damage caused by poor use and/or bike maintenance.

You sound very sure, how did you measure the roundness, size and parallelism of the bearing seats in those frames to eliminate that as a root cause of failure?

Drop in bearings are ideal when they fail prematurely due to bad design.

Seat of the pants and N=1## over 10+ years of weekends at my shop. Failures with clear signs of corrosion and/or intrusion from water/mud in the cases I have seen. I don’t doubt HS failures from poor frames happen, but it seems far less common in my neck of the world vs user inflicted damage.

For reference, I live in a state with low relative humidity most of the year and far away from any common corrosion sources (salt). The road bike HS failures I have seen are from bikes subjected to “roubaix” style races in terribly wet and muddy conditions. Same holds for gravel and MTB where mud is the clear cause seen and felt during inspection. All that parallels BB in most cases with a double replacement in those cases. But BB only is still more common due to location and exposure.

Can I ask question your own certainty here? Theoretical best/worst case design ideology here or some level of practical experience?

My shop literally sells and services millions of dollars of bikes every year. HS failures are well down on the list of frequent issues compared to drivetrain (including BB issues which I see as a far larger problem in tandem with you), brakes and other non-HS stuff. It’s not even a drop in the bucket of problems and repairs we see.

Not much to add, except that it’s always worth adjusting some angles* after washing a bike.

*moving the bike around, basically. I’ve seen bikes after washing that will sit there looking all dry and innocent, then when I tip them onto the back wheel to move them/hang them half a litre of water will pour out of the seat stays! Similarly, move a bike from leaning on the non drive side to the other side of the room and suddenly there’s a puddle that’s come out of the BB.

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I think a significant contributing factor is my close proximity to the Ocean and the occasional Monsoonal downpour I get caught in whilst out riding. I suspect that water got in when I stored my bike.

I’ll be more diligent at keeping it inside, my mech said he’s going to make sure it’s sealed better when he replaces everything.

Thanks all for your comments.

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