Wowbagger's is an interesting comment. From benign to most severe I'd rank chain service conditions in the following order
- IGH with large sprockets, good chainline and low static tension (noticeable sag in the lower chain run) inside chaincase
- as above but without chaincase
- as above but with spring-loaded tensioner
- as above but with smaller rear sprocket and/or smaller chainring
- bushingless chain on derailleur system using large sprockets and low-angle chainlines (think 2x5 systems)
- bushingless chain on derailleur systems using small sprockets and high-angle chainlines (think 1x11, 1x12 etc, or running badly cross chained e.g. on a 2x11 system)
Somewhere in the middle you can put a fixed gear or singlespeed with a high static tension; this knocks chains out faster than otherwise because dynamic chain tensions (when you go over a bump) rapidly increase in a way that can theoretically result in an infinite chain tension.
Chain lubes work by creating a lubricant film that inhibits metal to metal contact in the bushings/half bushings and/or by mitigating the consequences of that contact. So for the former, a high film strength is required and for the latter some clever chemistry (solid lubricants, EP additives etc) are desirable. Note that the latter type of additives can also help the chain cope with other particles (dirt, wear debris etc) that are floating around in the lube too. It isn't clear how all chain lubes work, or if certain lubes are really better suited to some applications than others.
The other line of defence that chains have against wear (once the lube film is breached) is super hard bushing materials. Very narrow chains don't work at all unless they have hard bushings; the half-bushings are each only about 1mm wide in a modern chain, because the inner side plates are pierced during manufacture, which leaves a large entry radius on each side plate and a comparatively short parallel sided half-bushing.
Cross-chaining buggers the chain up twice over; it makes metal to metal contact in the half-bushings almost inevitable and it also causes more wear between the side plates, thus loading the lube up with wear debris that grinds the chain to atoms even if the chain stays relatively free of road dirt.
In theory it ought to be possible to make a much more wear resistant 1/8" chain (for IGH/SS use) provided it has full (large area) bushings and a high film strength lube is used. However chains made this way are either dirt cheap with soft bushings ( e.g. KMC B1) or fantastically expensive, with bushings of unknown quality. In practice this means that -presumably because of economies of scale- a 3/32" bushingless chain of high quality (eg KMC X1) is most likely to have the longest (cost effective) wear life in such applications.
Using cheap chains which last about pro-rata less long is OK but has both risks and benefits; a benefit is that you may not ever feel the need to clean a chain before it goes in the bin. A major downside is that the rate of wear can become quite high, quite quickly, and this can 'catch you out' and leave you with a set of (expensive) sprockets that won't accept a new chain any more. If you use chains that are only going to last 1/3rd the mileage, there are x3 chances of being caught out this way.
cheers
