Chain line with new 8/9sp cogs
 

Hi was wondering on these new 8/9/10 sp rear cogs how much chain line issues and are there cogs not expected to be used from the big or small chain rings?

Dave

Kinda muddled question here. Chain line issues are more related to SS IGH bikes. Derailer bikes rely on unclean chainlines to work.

The basics is that the bike as a mechanical thing will perform best when the chain runs as straight as possible, and that you as a biological engine runs best at a certain cadence.
Somewhere between these two is the golden compromise, where neither you or the bike is hurting very much.
Running on the small chainwheel and the smallest sprocket or the biggest chainwheel and the biggest sprocket is called cross chaining and is generally frowned upon, particularly if you're running a triple front.
Exactly where cross chaining is beginning to hurt is an open question, some will avoid only the last sprocket at either end of the cassette, some will avoid the two last sprockets at either end of the cassette. Some will say that using all sprockets from the middle of a tripple is OK, other will recommend avoiding the last sprockets at either end even from that position, and so on.

As (hard) cross chaining usually is pontless in terms of the gearing it gives(which usually can be had at other, mechanically less stressful combinations of chainwheel/sprocket as well), there's no need to go there anyhow.
So:
1) avoid the extremes which aren't doing anything for you anyhow.
2) pick a cadence that keeps your heart and knees happy.
3) then spend a little effort on which combo which'll give the straightest chainline for that cadence.

Ok let me put it another way, if you bought a new bike with 10sp rear cog setup and where advised not to cross chain, in fact the derailuers setup wouldn't allow it, would you feel cheated or feel the setup was a compromise? Or being bike savvy you (in general) expect some gear combinations not to work due to excessive chain angles.

Not really talking a mechnical /cadence issue here, more of a perception.

Every single gear combo works whether it's Shimano 9 or 10, or campy 10 or 11. You can shift into those gears, and you can ride those gears. Extreme chain angles increase wear which you obviously know already.

No. Pretty much the same as a car/motor cycle/boat salesman telling me not get the tach into the red. It'll run there, but it will wear faster.

Not exactly cheated, but I'd see it as as sign of the bike having been shoddily assembled. Common assembly practise is to cut the chain to a length that will allow cross-chaining, at least structurally. Cut it too short and cross-chaining goes from inadvisable to impossible.

Well, one man's compromise can be another man's ideal. Suppose I ride mostly on the plains, then I get a sudden urge to head for the hills for a ride or two. I can get a wide-range cassette on easily enough, but I might not be quite as eager to swap out my short-cage RD. Running a full length chain might get me in trouble with too much chain slack, but running a slightly shorter chain is only an issue if I miss where I'm at in the gears.

As (hard) cross chaining usually is pontless in terms of the gearing it gives(which usually can be had at other, mechanically less stressful combinations of chainwheel/sprocket as well), there's no need to go there anyhow. Having a chain long enough to allow big/big is an insurance against blowing your RD through operator error, but doesn't influence performance otherwise. Could easily be seen as "the best" option in some circumstances.

If it's a bike in stock configuration I expect all the gear combinations to go in, but I'm aware that some of them are borderline functional and may not run clean, or creak and rattle more than usual.