Originally Posted by
cyccommute
WD-40 is a lubricant. It contains 25% of the same (or similar) oil that is found in all oil based bicycle lubricants. That oil is in about the same ratio of oil to solvent as well. It’s not going to melt your chain if you use it as a chain lube but, because it is a spray, it is easy to get it everywhere. Bicyclists generally don’t use spray lubricants for that singular reason.
I think WD-40 (original) may be formulated a bit different now. Back in the day, it was *prohibited* for use on aircraft linkage spherical rods ends (Heim joints) as over time it would dry to a varnish and the joints would stick or jam. WD-40 was originally developed as a Water Displacer, and perhaps the original formula had an intentional varnish to stay behind to help keep out water and/or corrosion resistance. Currently, it doesn't seem too bad as a chain lube if you have nothing else, it doesn't seem to get sticky over time. That said, chain lubes with "anti-wear additives" have been shown to reduce chain wear. You know what has that? Plain old motor oil (which I used to deride as too pedestrian for a serious biker). Recent tests have shown melted wax to be superior; I used wax for 15 years on my road bike because it was cleaner, went to oils thinking it was better lube, but I was wrong. I'm going back to wax with my next new chain and cassette.