Let start off by saying that I really hope this does not come as a surprise to any readers… but it’s not only OK to wash a bicycle / tandem with soapy water and then protect it with a good wax: it’s essential to long-term frame (and component) care.
What brought this to mind was the discovery of some pretty good oxidation on the underside of a frame I was working with below the 2nd bottom bracket shell, most still hidden under the paint but with a few spots where the paint has chipped-off. On the bright side, oxidation hardens aluminum so it’s mostly a cosmetic issue not a place where the structural integrity of the frame will ever become an issue.
While I’m not sure how often the frame was washed, the evidence would suggest salts were allowed to remain on the frame long enough to work their way through the paint via nicks or pores in the finish.
Wiping down a frame just doesn’t cut it since it won’t loosen and allow you to rinse away the salts from sweat and sports drinks that find their way onto our frames during long hot rides. In fact, wiping down without washing with soap and water can actually force contaminants into the finish. Applying wax over those contaminants protects the contaminants.
For anyone who has come to believe that washing bikes is a bad thing, washing gets a bad rap because a novice with a pressurized stream of water in their hands can wreak havoc on any one of the many bearings that you’ll find on a bicycle, i.e., in the headsets, bottom brackets, wheel hubs, rear derailleurs, shifters, and brakes. While some people may think that “sealed bearings” implies sealed against water the truth of the matter is that cartridge bearings have dust seals that are not water-tight, just incidentally somewhat resistant to water penetration. However, not resistant to water penetration from a pressurized stream or when immersed in water.
So, how do you prevent damaging bearings while washing a bike? Simple; never direct a solid stream of pressurized water at a bike! And, that goes double for using pressure washers: those suckers have no place being anywhere near bicycles. Instead, just use a dust pan brush and a clear bucket of fresh water or an open hose end to pre-rinse before washing. I use a Gilmour metal shut-off valve on the end of our hoses (AS1MFF) to control water flow since it can be cracked-open to create a light spray or opened to create a steady flow of water for rinsing… but not a straight stream of high-pressure water.
After rinsing, use a big old bucket of nice soapy water and some soft brushes or sponges to lather everything up and then hit the bike with a nice flow of water to rinse away all of the soap and dirt/contaminants. After washing and drying follow-up with a good coat of wax to seal the paint and the surface of the frame below any chips. The crank arms, seat posts, handlebars, etc. will also all benefit from this cleaning process, as will the internals of your shifter / brake levers. There’s just nothing bad that can come from a good frame washing, and dont’ forget to make sure the underbelly / boom tube and eccentrics are all washed and rinsed. You really don’t want to end up in a position like the one I found myself in when working on a friends bike and staring at an ugly patch of oxidized aluminum while pulling bottom brackets.
Beyond that, you get into drive train cleaning and lubrication which is a different subject all together.