Bicycles and Aluminum Corrosion Again

SpaceShuttleYes, this relates to today’s Esoteric Observation on Bicycles and Cycling – Image from Space.com

I never meant for this to become Killa’s Esoteric Observations on Aluminum Corrosion blog, but here we are. In a recent post I wrote about a corroded stem face plate on a friend’s bike. Another episode of aluminum corrosion was brought to my attention recently in a pretty spectacular manner.

The rider in front of me (Let’s call him RocketMan) suddenly lost control and fell on straight level ground. He might have hit a bump or something, or not. Read on. I and another rider swerved around him but the third rider back (We’ll call him Mario) T-boned RocketMan, broke a few of RocketMan’s ribs, destroyed his (Mario’s) classic steel Masi frame, launched over the bars, and fractured a vertebra upon touchdown (but that’s another story.)

Pardon a brief diversion to the topic of bicycle wheel engineering. Mario reported to me that despite absorbing enough force to buckle his frame tubes, his front wheel remains absolutely true!

 

Back to aluminum corrosion. This is not an article about the crash, but rather about the cause. The primary cause of this crash was, in my opinion, a corroded handlebar.

The bicycle of RocketMan ended up in my garage because, well, I’m the guy’s mechanic. Both drops (Drops are the lower curved ends of road bicycle handlebars) of his aluminum handlebars were broken. The right drop was completely broken off, the left was still attached by about a quarter of the circumference of the aluminum tube.

Aluminum bars usually bend. They don’t usually break. And RocketMan fell on his left side, so how did he break the right drop? I only had to un-wrap his handlebar tape to see that corrosion had eaten through most of the metal just above the brake levers – exactly where sweat drips off your hands and collects under the tape.

What I think happened to cause this crash is that RocketMan hit a small bump while riding on the drops, or corrosion simply reached a critical level. I think his right drop broke off first, causing him to lose control and fall. The left drop, I think, broke on impact with the ground.

The evidence suggests crevice corrosion just like the stem face plate I wrote about previously. Here the interface between tape and handlebar creates the crevice, and sweat is the electrolyte. That white stuff is not salt, It’s aluminum hydroxide. And there was a lot of it under the tape!

I’ve seen plenty of corroded handlebars over the years. I’ve seen scary-corroded bars that I thought would crumple like paper that I couldn’t bend or break. These were the worst I’ve ever seen. A metallurgical analysis of the remaining metal would be very interesting, for a certain definition of interesting.

Some riders will go without changing tape for five years. (Oh, you’re supposed to change it?) RocketMan’s bars had been taped up and ridden for about 15 months, not unusually long, but most of it in very sweat-inducing Texas heat and humidity. How much do you sweat? How often do you look under the tape on your bars?

Let’s take a few lessons from this failure:

  • Inspection, inspection, inspection. Look under your tape every six months or so, especially if you ride in hot humid climates. It’s relatively easy to un-tape back to the levers and re-wrap.
  • Or just go ahead and change tape more frequently. It’s pretty cheap, and everyone knows that new tape makes you faster. This is a result of the well-known “New Stuff Principle”.
  • Change your handlebars if they’re corroded.
  • I’ve never been a fan of carbon fiber handlebars (because they tend to break on impact rather than bend) but at least they don’t suffer from this insidious failure mode. It’s something to consider if aluminum bars don’t last for you.

By the way, RocketMan is a retired space shuttle astronaut. In one of those cosmic coincidences of life the aluminum oxidation process that caused his crash is the same chemical reaction that powered his Space Shuttle solid rocket boosters.

4 thoughts on “Bicycles and Aluminum Corrosion Again”

  1. Great observation, as always. And a fun text to read too. 🙂

    Never seen anything similar. The adonization/pain wasn’t enough to prevent corrosion, or does it have to be damaged to start the process?

  2. Steve Heller E-mailed me the following comment with some good precautions on carbon handlebar use and care:
    Comment on the handle bars, totally agree on aluminum hazards. Carbon fiber handle bars as designed, if not knock offs (buyer beware), also have significant user errors associated with them leading to crashes, yes with the poor preventative maintenance regarding tapping metal bars, and no corrosion inspection, yikes! Consideration regarding carbon fiber bars if not used correctly are a worst hazard if something is clamped to tight on them, this caused stress fractures to occur which can propagate unaware to the user and cause a catastrophic failure. The frequency for inspecting carbon fiber bars, should be frequent, if anything has been added to the bar as clamped, e.g. lights, aerobars, speedometer, etc.. especially if over the handle bar tap. Again food for thought, I am speaking from experience as I ruined a $300 dollar handle by clamping aerobars to a carbon fiber handlebar. I noticed the hairline fracture propagation and removed the bike from service until the bars were replaced.

  3. The brake lever perches/mounts weren’t steel, or some other metal other than aluminum, were they? Because if they were, galvanic corrosion could also be a contributing culprit. We deal with it all the time in the motorcycle world, especially Harley Davidson in that they tend to use untreated aluminum case covers, and steel case bolts to hold them in place. The classic “white powder” is usually the result when pulling said bolts. In many cases, dissimilar metals being in contact with one another will cause the headache we know as corrosion. Nice article on spoked rims by the way. I’ve used it in my discussions many times as reference when inevitably some other biker (and I mean, motorcyclist) claims spoked rims are ALWAYS inferior to cast mags, usually pointing at my ride.

    1. Hi Condor! Thanks for commenting. Actually the bands that fix the brake levers to the bars are ferrous. I discounted galvanic action because the corrosion is scattered about under the tape, not concentrated at the point of contact between band and bar. But as you point out, it certainly could also be a contributing culprit. Yes, spoked wheels are amazing, aren’t they? I’m making this up as I go along, but I think spoked wheels clearly outshine cast wheels in strength to weight ratio. I’m not so sure about fatigue resistance. It may be that where weight is the over-riding factor (bicycles) and fatigue cycles are relatively low, go with spokes. Do spokes ever break on motorcycle wheels? Killa

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