Originally Posted by
Woodwind314
Could you clarify what you mean by the lower loop? Anything lower than the sprocket (as the 'returning' part of the chain that does not carry any pedaling load), or do you differentiate between the 'loops' the chain makes around the 2 RD jockey wheels?
I use the term lower loop to mean the entire length of chain between the chainring and cassette on the lower or returning side. Returning loop is probably more precise, but upper and lower is easier for most people.
Originally Posted by
Woodwind314
I do have a basic understanding of tribology, although it is slightly rusted. (Pun intended). However, I fail to find specifics on bicycle chains, which differ considerably from motorcycle chains. So if it's not too much trouble, I'd like to repeat my question: Would a good bicycle chain, new, grit free have any metal-to-metal contact in its bearings under load? (thinking hill climbing out of the saddle).
If not, where does the black stuff come from, that on a new chain develops within less than a 100 miles, and which very clearly comes from the inside? I had always taken that to be metal abrasion remnants...
Thanks for your patience.
Bike chains are a bit unique because they operate at very high loads compared to their size. The nearest comparable application in terms of loading (relative) may be fork lift chains, but they don't move nearly as much.
If we succeeded in reaching the ideal of zero metal-to-metal contact on mechanical devices there'd be zero wear but life isn't ideal, and narrow bike chains are far from ideal, hence the fairly high rates of wear. Even if you ran chains in clean room conditions they'd still turn black with wear by product made up of metal dust.
While the goal of chain lube is zero wear, the best we can hope for is a good fight in what will always be a losing battle.