Originally Posted by
Woodwind314
Hm, I just checked on my road bike (campy chorus 8 speed), and if there is any difference in distance between sprocket and jockey wheel, it becomes smaller with smaller sprockets.
Bikes do vary, and I should have added "usually" in the statement. But the point remains that as side flexibility increases the ability of the jockey wheel to push the chain over as you shift.
Originally Posted by
Woodwind314
Wouldn't cross chaining introduce a sideload on the lower jockey? Of course this would be much smaller than the sideloads on the upper jocked during shifts, but the lower jockey would run with it's (low) sideload for as long as it's out of the perfect chainline, no?
Yes, though load may be too strong a term because there's close to zero tension in the lower loop. Also cross chaining is a matter of degree. On a 2x9 road bike, the larger chainring lines up between the 3rd and 4th sprockets, so high gear riding also represents a decent amount of deflection.
Rather than look at cross chaining as a black and white issue, I prefer to think of in shades of gray, there are aligned sprocket pairs, then others that are mis-aligned by varying amounts. I'm not at all sure that riding fully cross-chained for a short while is any worse than riding in high for a longer while.
Originally Posted by
Woodwind314
As you seem knowledgeable about chains: I have often wondered if any lubricant could prevent metal-to-metal contact between pin and sleeve in the chain under load. It seems to me that the load bearing surface is just too small and the form of the gap between pin and sleeve would promote lubricant displacement under load.
The express purpose of any lubricant is to prevent metal to metal contact. When that happens the lubricant has failed. You can hear it in a bike chain as sort of a chirping sound - the same as a squeaky hinge but at a different pitch.
The ability of a lube to prevent metal/metal contact depends on it's film strength, and the pressure pressing the two parts together. Thinking in bike chain terms, a lube that's perfectly OK spinning along at a moderate pace in the flats, may be inadequate for the higher chain tension when pounding up steep hills. The lubes ability to replenish itself in the working area is also a key factor, as it's constantly being forced away from the point of contact.
Originally Posted by
Woodwind314
Do you have hard facts on that? Specifically, at which chain load metal-to-metal contact occurs (if it does at all) even with a perfectly lubed, grit-free chain?
There is a ton of literature on the subject. Search using key words like "lubrication science" or "bearing lubrication" or "plain bearing lubrication" You'll have enough reading to keep you busy for a couple of years.