Our last Tech Talk of 2015 provided 5 tips for Winterizing Your Ride, which, unless you live in the southern hemisphere should come in pretty handy about now. Even here in recently drought-plagued Northern California, we’re getting a lot of rain and cold already in 2016.
In the introduction to that article, I wrote, “It’s easy for water to get inside frames, and it’s a common cause of rusting on steel frames (there are no such worries with aluminum, titanium or carbon frames).”
Aluminum corrodes, too
To which Holland, Michigan, roadie Kerry Irons took exception and replied, “In your article you twice note that aluminum won’t rust. While this is technically correct (rust = iron oxide) the follow-on implication that we don’t need to worry about protecting aluminum frames is not correct. Aluminum (especially when exposed with no anodizing or paint) will easily corrode, and that corrosion is enhanced by the same things that make steel rust faster.
“Of course you know what happens to aluminum spoke nipples that haven’t been properly lubed during a build. The white powder that we see on exposed aluminum is aluminum oxide, and I can attest from personal experience that aluminum frames certainly docorrode and need the same kinds of protection that steel does.”
I asked Kerry if he would like to share his experiences with aluminum corrosion to help other RBR readers, and he agreed. So this week, I’m turning over Tech Talk to him.
Winter commuting in Michigan
First, a little background. Kerry explained that his experience with aluminum frames was with a Cannondale H-400 hybrid, which he used for year-round commuting in Midland, Michigan, where the average winter temperature at the time was 29 degrees Fahrenheit (about -2C) with 50 inches (127cm) of snowfall. And where the road department salts the road to melt the snow.
Kerry says, “Aluminum is a self-protective metal, and as long as things don’t get too acidic or alkaline then the small scratches that a bike frame would see are not a problem for a typical road rider. This is true whether a bike is anodized, painted, or clear-coated.
“But if you ride on salted roads, then the resulting salt slush will greatly reduce the protection offered by the thin layer of aluminum oxide. There also can be problems when other metals are in contact with the aluminum – steel bolts can set up a galvanic cell with the aluminum becoming the sacrificial metal. If you’re not familiar with this concept, it is the basis of zinc coating of steel (galvanized steel) in which the zinc serves as the sacrificial anode. Underground pipelines are protected in the same way with a chunk of zinc connected to the steel pipe; the zinc corrodes and the pipe stays whole. It’s called anodic protection.”
A “high-salt diet takes its toll”
“My Cannondale developed a fairly large area (a few square inches) of paint delamination, and under that paint bubble is the telltale white powder of aluminum oxide. Salt from the road got through a nick in the paint or along the bolt holes that hold the rear rack just above where the wishbone seatstays join. The paint bubble runs 3-4 inches from about an inch from the seat cluster along the center section of the wishbone, and then about an inch down each of the seatstays from the wishbone junction.
“There are much smaller areas of paint bubbling where the bottom bracket cups contact the frame and where the cantilever brakes contact the bosses on the seatstays. Steel BB cups and steel bolts holding on the brakes combined with the “high salt diet” of winter commuting in a snowy area have taken their toll.
“Other areas of the frame that likely have paint nicks (down tube, chainstays) do not have this corrosion so it may well be the combination of salt and steel bolts that caused this extensive corrosion.
“This was a commuter bike that was maintained to ‘commuter standards,’ which meant making sure that the braking and shifting were up to snuff and that the chain was properly lubed, but a clean frame did not result from the regular maintenance procedures. It probably saw 25,000 total miles over a decade of year-round commuting.”
The worse your riding conditions, the more chances of corrosion
“In sum, perhaps you are right that corrosion is not a worry for most aluminum road frames, as they will probably not be exposed to the salt of winter commuting riding in some areas like Michigan. But, if I lived in a coastal area with frequent rides along the seashore, I would be more worried. I’ve seen aluminum spoke nipples badly corroded in those conditions so I can only assume aluminum frames would be subject to the same.
“I put nearly 60,000 miles on a steel road frame (spring, summer, fall, but no salt) over 10 years and despite a few paint nicks it never showed a trace of rust because it was properly prepared, primed, and painted by the builder. It just speaks to being aware of the corrosion possibilities and watching your frame if it is steel or aluminum. For the past 18 road seasons, I’ve been on titanium. :)”
Thanks for sharing your tips,Kerry. You’re right that salt from the ocean attacks steel and aluminum, too. I’ve also seen extensive corrosion on bicycles and components on bikes ridden indoors a lot on trainers. It’s caused by riders sweating on their bikes and parts and rarely or never cleaning it off.
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